Tag: wheelchair

Post 2003: TiLite Aero fork bearing replacement, Part 3: Replacing the bearings.

Recap:  This is a series of posts about replacing the fork bearings on a TiLite Aero wheel chair.

In the first post, I removed the forks from the chair.  What should have taken about five minutes actually took several hours, owing to a bearing that was rusted solid onto the fork axle.

In the second post, I worked through all the details on bearings.  As long as you know the size of the steel sealed bearings that you need, you can pick them up for around $1 each on Amazon.

This third post is about driving the old bearings out of the fork, and pounding the new bearings into the fork, using only these tools and materials:

  • snap-ring (c-clip) pliers
  • hammer
  • screwdriver
  • improvised bearing drift:  13/16″ spark plug socket (YMMV)
  • a smear of grease.
  • a surface to pound on.
  • a soft vise to hold the forks as needed (I used a Workmate bench).

The snap-ring pliers are not optional, unless you’ve got a whole lot more dexterity than I do.  There is one c-clip in each fork, whose purpose is to ensure that the bearings do not slide down from the weight of chair and user.  That c-clip is difficult to get in or out without c-clip pliers.

Also, be warned that driving the bearings in with a hammer and “drift” is not for the faint of heart.  You end up hammering pretty hard.  About as hard as you might when pounding a nail into a 2×4.  You have to do that, to get the bearing to seat all the way at the bottom of the hole it fits into.

If the very idea of hammering that hard on an expensive wheelchair part makes you squeamish, then you’ve got good sense.  This is nobody’s idea of a good time.  But once you’ve started this, either you drive that bearing all the way home or you buy/make a bearing press that can finish off what you started.

If I had to do this multiple times, I’d shop for a bearing puller (to take the old ones out) and a bearing press (to push the new ones in) before I started the repair.  There are also kits specifically marketed for common wheelbearing sizes (e.g., a kit for pulling and pressing in R8 bearings).

But you can do it with just the crude tools listed above.  That’s how I did it, for this one-off repair.  That’s really the point of this post.

Get the old bearings out using screwdriver and hammer.

The basic idea is simple.  You’re going to push the top bearing out of the top of the fork.  (As shown above, you’d be pushing it from below, so that it moves toward the camera.)  Then remove the c-clip, using c-clip pliers.  Then push the bottom bearing out of that same opening.

In other words, the top bearing comes out first, then you remove the c-clip, then the bottom bearing comes out.  And all of that comes out of the top hole in the fork.

To achieve this you:

  1. Flip the fork over (from what is shown above), and hold it in some fashion.  I used a workbench as a soft-sided vise. If you are careful, you can simply rest the flat top of the fork on a couple of cutting boards, or chunks of wood, but you must leave the full width of the hole unobstructed so that the bearing can come out.
  2. Insert a flat-bladed screwdriver through the bottom of the fork (the side away from you, in the view above).
  3. Catch the corner of the blade of the screwdriver on the inner bearing race of the top bearing.  (The one nearest the hole that these must come out of).
  4. Give the screwdriver a sharp tap.
  5. Move the screwdriver so that it catches the opposite side of the inner bearing race of the same bearing.
  6. Give the screwdriver a sharp tap.
  7. Move the screwdriver blade back to where you started.
  8. Repeat 2 – 6 until the bearing falls out of the top of the fork.

You keep moving the screwdriver from side to side, as you tap these bearings out, to try to ensure that the bearing stays level within the fork — perpendicular to the axis of the hole in which the bearings sit.  The last thing you want is to get the bearing wedged kitty-corner in that hole.

What makes this hard is that these are interference-fit bearings in a metal casing.  The hole they fit in — in the fork — is just slightly smaller than the diameter of the bearing.  So, while the bearing is friction-fit to the housing, there’s a lot of friction involved.

Which means, in no uncertain terms, you are going to have to tap these vigorously to get them to move.  And yet, not so hard that you break them.

How much force?  Take a look at this fellow, around 30 seconds into the video to get an idea of what a “tap” is likely to be, for driving a steel bearing out of a metal bearing housing:

He doesn’t bother to move the screwdriver from side-to-side for that particular bearing.  But you will want to do that here, particularly for the second bearing, which has to travel quite a ways before it is free.

A better view:  This next video provides an excellent view of what you’re trying to do with the end of the screwdriver, at around 1:10 into the video.  (Though, this particular bearing came out quite easily.)

Too easy:  Here’s yet a third example of this technique, around 30 seconds into this video, where the bearings are driven out of a plastic wheel.  You’ll have to hit harder than this to drive them out of the titanium fork.

I hope that gives an adequate feel for the process.  Catch the edge of the back side of the inner bearing race with a screwdriver.  Tap with as much vigor as necessary to move the bearing.  Move the screwdriver from side-to-side on the bearing to help keep it aligned within the bore.  Keep tapping until the bearing drops out.

Remove the c-clip. And do the same thing to the other bearing.

Clean up, grease up, test the fork axle.

Clean any gunk out of the inside of the fork.  It is particularly important to make sure there is absolutely nothing stuck in the “corner” of the bottom of the hole.

Why is that important?  Above you see the c-clip groove, inside the fork.  The first bearing you put in must be driven completely below that groove.  Then you place the c-clip in that groove.  Then you drive the second bearing into the rest of the space.   If the first bearing doesn’t sit absolutely flat on the bottom of the hole, you won’t be able to get the c-clip in.  And that, in turn, prevents you from correctly re-assembling the fork.

Wipe any gunk off the c-clip at this point, as well.  Just for good luck.

Coat the inside of the fork with a layer of thin grease.  I think lithium grease is what is what is typically recommended.  Some say that this helps prevent the bearing from seizing in the fork, so that you can get it out next time.  I say it helps lube the bearing going into the fork, because you’re going to need all the help you can get to drive the bearing all the way into the fork.

So spray a little grease in, move it around, then swab it out with a paper towel.  You want just the thinnest possible layer of grease.

Test to see if the new bearing will slide over the fork axle.  You’ll note that I barely bothered to clean up the axle.  In particular, I don’t want a nice shiny raw metal surface on that axle, because that just invites corrosion.  Leave it alone if you can.  The only thing that matters is that the new bearing can be slid over it.  Assuming it does, slide the new bearing off, and apply a thin layer of grease over the fork axle.  Wipe off any excess with a paper towel.

A brief calculation on freezing the bearing and heating the fork.

I’ve driven bearings like this many times.  It’s always a stressful process.  I’ve learned to take every advantage I can, if I’m unsure that I can drive the bearing into its housing properly.

Common advice for this next step is to put the bearings in the freezer to cool them, and take a heat gun to the bearing case (the fork, in this case) to heat it.  The idea is the take advantage of the coefficient of thermal expansion of metals, and give you a little extra room as you are driving the bearing.

Based on this reference, and my calculation, taking a 1 1/8″ diameter bearing from 70F down to 0F, while heating the titanium housing an equal amount, should increase the clearance for the bearing by almost a thousandth of an inch.

Believe it or not, it is well worth doing that, given that these are more-or-less zero clearance bearings.

If you are unsure of your ability to drive this bearing into this housing, go ahead and take the time to freeze the bearing, and use a hair dryer or heat gun to heat up the fork.

If nothing else, it’ll give you the courage to bang all that much harder at the next step.

BUT THIS COMES WITH A WARNING: WORK FAST.  The coefficient of expansion of steels is higher than that of most titanium alloys.  The upshot is that if you heat both the titanium fork and the steel bearing, the steel bearing will expand more than the titanium hole.  The bearing will actually get tighter, not looser, in that hole.  So if you’re going to try this freeze/heat trick, you need to get the bearing seated before it warms up to the temperature of the titanium fork. 

As a compromise, you could just freeze the bearing, and leave the fork alone.  That will help some, and there’s no harm done if the bearing warms up to room temperature during this process.

Bearing abuse, or using a drift to install the new bearings.

Normally, at this stage, you’d say “installation is the reverse of removal”, and leave it at that.

But in this case, that’s wrong.

To be clear, what you just did to remove the bearing — pounding on the center bearing race — ruins the bearing. At least, if you beat on it hard enough it will.  All the force of your hammer blows was transmitted through the “innards” of the bearing, in order to get the outer race to slide along the bore in the fork.

You are NOT going to do that when driving the new bearings back into the fork.  Instead, you are going to drive the new bearings by beating on the outer bearing race only.  Never on the inner bearing race.  That way, the force of your blow is transferred through the steel race directly to the side of the hole.  And you are not counting on the “innards” of the bearing to transfer the force of your blows to the outer race.

Clear enough?  These bearings come out one way, but they go in in a different way.  Beat on the outside race ONLY as you put them back in, because you don’t want to break your brand new bearing.

This is where you need to find a drift for your bearing.  A drift is some sort of sturdy hollow metal cylinder that’s just a fraction of a hair smaller in outer diameter than your bearing.  The idea is that as you beat the bearing down into the fork, using the drift, it only beats on the outer bearing race, and does not press on any of the “innards” of the bearing.  You can buy sets of drifts in graduated sizes on Amazon.  But, typically, you’ll use a socket, out of socket set.

Beating the first bearing flush.

Here are the issues.

First, you’re beating a metal bearing into a metal bearing housing — the fork. That’s going to take quite a bit of force.  And the further you beat it into the fork, the harder you have to hit it to move it.  So, you start off with taps, and you end up with hammer blows.

Second, until you have the bearing flush with the opening, it’s critical to keep the bearing level — going in evenly all around.  Stop every so often and eyeball the bearing.  If it’s high on one side, tap that side down, and then carry on.  So, center the bearing on the opening, nice and level, and start with gentle taps — on the outer race only.  (If you have a brass-faced hammer, this would be a good use for it.  I used a steel carpenter’s hammer.)

Eventually, you’ll get the bearing driven flush.  That’s when you need to center the drift on top of the bearing, and start pounding it home.  No more tap-tap-tap.  At this step, it’s bang-bang-bang.  You must drive this all the way to the bottom of the hole or you won’t be able to re-assemble the fork correctly.

Once you have the first bearing driven home, use your c-clip pliers (and fingers, and screwdrivers) to get the c-clip firmly seated in the groove.  There are no style points here — however you can get the clip to seat in the groove, that’s fine.  Note that once the clip is correctly in the groove, almost all the clip is hidden.

Finally, drive the second bearing in flush with the surface of the fork.  Same process as the start of the first bearing, being sure to tap-bang only on the outer bearing race.

Pat your self on the back if the result looks like this.  The outer race is flush all around.   And nothing is obviously broken.

.

You’re done

Slide the fork onto the fork axle, put on the washer and retaining lock nut.  Tighten the lock nut just enough to keep the fork from rattling.

And you’re done.

If all this pounding on expensive metal parts is off-putting, consider using bearing puller/press designed for this size of bearing.  For sure, if I did this routinely, that’s what I would do.

An end-note on cheap bearings

I’ve watched a lot of YouTube videos on this topic, and I’ve seen a lot of people do things to sealed bearings that they really shouldn’t.  Take the seals off and grease them.  Change just one of a pair of bearings, because only one was thoroughly worn out.  Pop a bearing out of its fitting and put it back in the same fitting.  I have also seen my wheelchair-using friend hesitate to change bearings, or wait until the bearings are obviously worn.

All of this arises, I think, from the notion that these bearings are somehow precious.  If a set of bearings for your caster wheels is $40, you might think about taking some non-recommended steps to try to prolong their life.

And that, in turn, derives from the ludicrous prices charged for these commodity bearings by DME suppliers.

Hence the importance of the just-prior post.

You can easily buy commodity steel sealed bearings, in sizes to fit wheelchair fittings, for around $1 each.  Sealed bearings are designed to be disposable.  They are not designed to be serviced.  And at $1 each, it’s no hardship to treat them as the disposables that they are.

I hope this series of posts has been helpful.

Post 2001: TiLite Aero fork bearing replacement, Part 1: Rust never sleeps.

 

This is Part 1 of a series of posts about replacing the fork bearings on a TiLite Aero wheelchair.

In this post, I only describe the “teardown” part of the process.   That is, getting the forks off the chair.  The removal and replacement of the bearings is for Part 2.

If you didn’t realize this repair might involve a complicated “teardown” step, and you were thinking of doing this repair yourself, then this post has done its job.

On this particular chair I ran into a worst-case scenario: The steel fork bearings had rusted solidly to the steel axles that they spin around.  This stops you from removing the forks from the chair, which you need to do, in order to get to the fork bearings.  Your choices are a) replace a few hundred dollars of wheelchair hardware, or b) break the bearings free from the steel axle that the bearing races are rusted to.

This step took several rounds of heating the axles with a propane torch, spraying with lube, then pounding and prying until the rusted-on bearings broke loose.

Edit:  You can see an alternative way to beat on the axle in this reference.   There, the user removed the fork axle from its fitting first (i.e., took the fork axle off the wheelchair, fork and all), then beat the axle out of the fork.  That’s arguably a smarter approach than what I did.  At the minimum, it shows that I’m not the only one have the problem of fork bearings that rusted solidly to the axle they sit on.

Other than spending a couple of hours doing that, the repair went smoothly.

The only practical takeaway is that before you buy new bearings, bearing puller, bearing press, and so on — first try to remove your forks from the wheelchair.

If they come off readily — once you have removed any retaining hardware —  move on to the next post, where I talk about options for replacement bearings, in some detail.

But if the forks don’t come off, even with a bit of lubricant and some gentle persuasion, then ponder just how hard you are willing to hammer on a wheelchair.

My lesson is that, even thought this repair eventually succeeded, I got lucky.  With those fork bearing races rusted to the axle, it could just as easily have ended up with an unusable wheelchair, and a few hundred dollars plus a wait for replacement forks and fork axle assemblies.

N.B., I don’t use a wheelchair.  I did this repair for a friend who does.  I’m writing it up for benefit of anyone thinking about doing a similar wheelchair repair themselves. Continue reading Post 2001: TiLite Aero fork bearing replacement, Part 1: Rust never sleeps.

Post #1914: Pneumatic tires for wheelchair use, no good solution to the problem of flat tires.

 

This is a brief followup to the just prior post, on the use of non-pneumatic (e.g., solid rubber) tires on wheelchairs.

I’m trying to work out what I should recommend if asked to replace more wheelchair tires.  Traditional tires with air-filled inner tubes are much easier from the standpoint of the installer.  The question is dealing with the drawbacks of those from the wheelchair user’s perspective.

The only way to guarantee that a wheelchair tire won’t go flat is to use a non-pneumatic tire.  That includes solid rubber tires, and solid rubber inserts taking the place of an inner tube inside regular tires.

What I discovered in this post is that many anti-flat products available for bicyclists will not work for most wheelchairs, owing to the wheelchair’s use of narrow, high-pressure tires.

When all is said and done, between the past post and this post, I think I now have a fairly firm set of recommendations.

If you cannot tolerate a flat tire on-the-go, then opt for solid rubber tires (and not solid inserts in regular bike tires).  But mount them using the $35 steel bolt-to-the-workbench device sold specifically for mounting such tires on wheelchair rims.  Mounting them with simple hand tools is just too hard and too iffy.

If you can tolerate the occasional flat, the best option seems to be puncture-resistant tires and tubes.  All the rest of the anti-flat products available for bicycle use — chemical sealants, anti-puncture tire liners, tire “wipers, and the like — either won’t work with typical wheelchair tires, or are not available off-the-shelf in the right size or configuration for that use.

Background

Solid rubber tires and solid rubber tire inserts definitely will not go flat.  There’s no air in them in the first place.

But those tires have some drawbacks.  Per the just-prior post, both of those non-pneumatic options are difficult to install using ordinary hand tools.  In addition, solid inserts are difficult to purchase as they must match the tire fairly exactly.

Both types of non-pneumatic tires offer a harsher ride and higher rolling resistance than high-pressure pneumatic (air-filled) tires.  And there are relatively few options available in the correct size for typical wheelchair rims.

By contrast, traditional pneumatic bike tires (tire plus inner tube) are easier to purchase and install, but they have two big drawbacks.  They require frequent, routine re-inflation to maintain the correct pressure.  Otherwise they go soft, and that raises rolling resistance.  And they can go flat, unexpectedly, while you are out-and-about.

The latter is not just a problem for the high rolling resistance you get with a flat.  It’s all too easy to roll a flat bike tire right off the rim, or to damage both the rim and the tire if you keep going on a flat tire.

This post is my research into minimizing the hassle from both of those drawbacks:  routine periodic inflation, and flat tires.

Caveat 1:  In the particular case I’m looking at, my options are  24″ x 1″ or 24″ x 1-3/8″ tires.  This puts a lot of limits on the types of bike-tire solutions that can be adopted for wheelchair use.  You might have other options available if your rims can accept wider tires.

Caveat 2:  My only qualification for writing about this topic is that I’ve changed a lot of bike tires in my life.  And I happen to be friends with someone who uses a manual wheelchair.

Routine inflation:  An electric air pump can solve this problem.

Source:  https://www.homedepot.com/p/Husky-120-Volt-Inflator-H120N/325096203

Best guess, $20 and a trip to Home Depot gives an adequate way to maintain tire air pressure up to 100 PSI.

I don’t think it’s worth belaboring this.  All pneumatic bike tires lose air over time.  It’s not a leak, per se.  It’s that air diffuses through the rubber.  (The same thing happens to rubber balloons and car tires, just much faster and much slower, respectively).  The higher the tire pressure, and the thinner the tire/inner tube, the faster the tire goes soft.  There’s no way to stop it that I have ever heard of.

This means that pneumatic tires have to be topped up on a routine basis.  And in the modern world, the obvious solution for routine tire inflation is an electric air pump.

A standard full-sized manual bike tire pump doesn’t do the average wheelchair user much good for routine use.  Not only are they designed to be used while standing up, they are designed to be fast, that is, to move a lot of air with each stroke.  They do that by using a piston with a relatively large surface area.  But wheelchair users often prefer high-pressure (e.g., 140 PSI) tires, for the low rolling resistance such tires provide.  Even if a full-sized manual pump can achieve pressures like that, it takes a lot of force, owing to the large piston area.

The typical manual mini-bike-pump — the kind you take with you on a bike ride — is both slow and awkward to use.  They are slow because they have tiny little pistons, suitable for pumping tires to high pressures using only your arm muscles.  And they are awkward because they either clamp directly to the valve stem, or have just a short attaching hose, either of which essentially dictates exactly where the pump must be held, relative to the tire.  In essence, those pumps are made for emergency on-the-road use.  You can use them for routine tire maintenance, but I sure don’t.   

Compressed C02 cartridge pumps are expensive for use in keeping tires routinely inflated.  The poorly-designed ones appear hard to use, based on Amazon comments.  But even for the well-designed ones, depending on the pump and the tire, you’d be spending $1.50 and tossing away a metal C02 cartridge every time you topped off your tires.  Plus, based on what I read, C02-filled tires deflate more rapidly than air-filled tires, owing to something-something-something about the ability of C02 to diffuse through butyl rubber.  You’d turn your routine tire maintenance into a $100-a-year habit, for no particular reason.

The efficient solution is an electric tire pump. 

These days, you have your choice of 120 volt plug-in, 12 volt plug in, and rechargeable battery-operated pumps.  You only have to check a few things:

  • How loud are they?
  • Can they do high pressures?
  • How awkward are they to use?
  • How long will they last in routine use?
  • Is the battery replaceable?

And, of course, how much do they cost?  Because, near as I can tell from reading Amazon comments, the cheaper pumps tend to fail several of the checks outlined above.

I have no specific recommendation to make, other than the Home Depot offering shown above.  All I can suggest is (e.g.) reading the comments on pumps offered on Amazon.  In particular, a lot of cheaper battery-operated pumps cannot produce high pressures despite what the Amazon listing might say.  When in doubt, get one that plugs into the wall.

Avoiding flats:  Nothing is bulletproof

If you absolutely, positively must not have a flat tire, the only real option is solid, non-pneumatic tires.  In this section, I’m shooting for two things:

  1. A tire and tube setup that minimizes the risk of catastrophic flats.
  2. A simple, no-maintenance pump that can be kept on the wheelchair for emergency use as needed.

The pump is easy.  Any C02-cartridge inflator that fits comfortably in the hand should be adequate, as would a standard bicycle mini-pump with the addition of an extension hose.  Either would be small enough to be stored long-term on the wheelchair itself.

But finding a combination to minimize the chance of a wheelchair flat is hard, owing in part to the small size and high pressure of the typical wheelchair pneumatic tire.  Puncture sealants (e.g., Slime (r)) do not appear to work at high pressure.  Puncture proof tire liners do not appear to be available in the narrow widths required for wheelchair tires.  The only options that work for typical wheelchair rims combine relatively expensive “puncture-resistant” tires with relatively expensive “thorn-resistant” inner tubes.  Even with that, neither of those is likely to stand up to an ill-placed tack, nail, or screw.

So the bottom line is that there is no good anti-flat solution for pneumatic wheelchair tires. The best you can hope for is that any puncture is small enough that you can inflate the tire, on the go, enough to get you someplace where you can swap out the wheel.

Tire and tube setup.

An important restriction is that the only tires that I know will fit the rims I’ve been working with are 24″ x 1″, and 24″ x 1-3/8″ tires, designed for use with inner tubes.  These are narrow by bicycle standards, and that limits choices quite a bit.

Puncture-resistant tire liner:  No off-the-shelf option in this size. 

Source:  Amazon.com

These are (typically) just a tough piece of flexible plastic, designed to turn aside (e.g.) thorns.  Note what the original Mr. Tuffy tire liners don’t say:  Nails, tacks, screws, staples, and similar.  Given that I’ve had nails go right through the tread of a steel-belted radial car tire, I’m pretty sure a piece of plastic isn’t going to stop them in a bike tire.

But it’s moot anyway.  Near as I can tell, all the ones made for bicycles are too large for 1-3/8″ tires, and are certainly too large for 1″ tires.  For the Mr. Tuffy brand, 24″ wheel sizing starts at 1.95″ and goes up from there.

At best, I could cut them down and use them.  But I’d have to sand down the edges to be sure that the tire liners themselves didn’t cut the tube.

Tire sealants:  Dubious in higher-pressure tires.

Slime (r) does not make ready-made self-sealing inner tubes sized for a 1-3/8 tire.  That said, the original Slime (r) sealant was sold in bottles, to be squeezed into a bike inner tube after removing the valve core.  So it’s easy enough to make self-sealing 1″ or 1-3/8″ tubes from standard tubes and a bottle of Slime (r).  By reputation, this will stop (or greatly slow) leaks from small punctures for about two years.  After which, I think you have to remove and replace the old tubes.

So that’s an option.  Based on what I read on the internet, Slime works, somewhat.  Won’t stop a rip or tear in the tire.  May not seal fully.  But gives you enough sealant to get home on a tire with a small puncture.

This seemingly-knowledgeable user provides a major caveat:

Tire pressures above 45 psi are less effective at sealing, and above 60 psi, don’t expect any effectiveness at all.

Oddly, Slime (r) itself does not mention this limitation.  But now that I Google Slime (r) and tire pressure, I see warnings in multiple locations that Slime (r) and similar sealants will not work well in high-pressure tube tires.  I’m not entirely sure how accurate that is, but until proven otherwise, that’s a caveat for tires in the 100 to 140 PSI range.

FWIW, a competing product in this segment — Flat Out — specifically says “fat tire bikes” (reference).  The implication there is that this sealant would not work in (e.g.) road bikes with high-pressure tires.

Beyond that, Slime has a reputation for sometimes causing problems such as blocked valve stems.  All things considered, Slime (r) may be reasonable for low-pressure (“fat”) bike tires, but whether or not it will work well and without issues for thin, high-pressure wheelchair tires is an open question.

A final issue is the use of Slime (r) in mounted tires that might be stored, unused, for a considerable length of time.  Rumor has it that Slime (r) can “pile up” in the low section of the tire.  If you’re getting close to the point where the Slime loses its ability to flow, you may end up picking up a replacement wheelchair tire only to find that the low section of the tire (as stored) is now solidified Slime.

Puncture-resistant tire:  Expensive and somewhat effective.

As with tire liners, these aren’t a bulletproof solution.  It’s puncture-resistant, not puncture proof.  Near as I can tell, the only puncture-resistant tire marketed in the 24″ x 1-3/8″ size in the U.S. is marketed as a wheelchair tire.  Hence it costs two or three times as much as a regular tire.

Puncture-resistant tube:  Expensive, effectiveness unknown.

There are a handful of “thorn-resistant” (that is, extra-thick) inner tubes marketed in the 24″ x 1-3/8″ size.  These appear to cost about two to four times as much as a regular inner tube.  As with puncture-resistant tires, these are unlikely to stop a tack, nail, or screw.  Whether they provide any additional resistance to punctures from man-made objects, I don’t know.

Run flat tire:  No option in this size.

There are now foam inserts for bike tires that provide some degree of run-flat capability.  These are oriented toward tubeless tires typically used by (e.g.) bike racers.  Near as I can tell, there is no run-flat tire option available for something as small as 24″ x 1-3/8.

Tire wipers:  Maybe, but requires D-I-Y mounting.

A final offering for minimizing punctures goes by various names, but probably “tire wipers” is sufficiently descriptive.  These are typically wires that ride lightly on the tire, and knock off any solid debris that has stuck to the tire, including tacks, nails, and thorns.  The idea is that it typically takes several tire revolutions for such debris to penetrate the tire, and if you can knock it away, it won’t puncture the tire.  These typically mount (e.g.) the same place as the brake calipers on a bike, which means that you’d have to device a custom mounting for use in a wheelchair.

Emergency pump:  C02 inflator or Standard bike mini-pump plus long adapter hose.

Based on what I read on the internet, plenty of wheelchair users adopt standard bike mini-pumps for tire inflation.  These pumps are capable of reaching the (e.g.) 140 PSI required for high-pressure tires, but tend to be slow to inflate a tire, because of that.

The main drawback that I see, for on-the-go use, is that most of these pumps require direct attachment to the valve stem. That means that the user would have to hold the pump to the side, stabilize it on the wheel, and pump up the tire in that awkward position.

I think it’s far easier just to add a two-foot air hose, readily available from Amazon.  That would allow a person seated in a wheelchair to inflate the wheel by holding the pump comfortably in the lap, rather than leaning over to manipulate a pump directly attached to a valve stem.

But by far the most obvious solution is a C02 inflator.  These are compact enough to be held in one hand, and so should be readily usable by a seated wheelchair user to inflate a low tire on-the-go.  A single small (16 gram) C02 cartridge should be adequate to bring a 24″ x 1-3/8 tire up to a reasonable working pressure.

A battery-operated rechargeable tire pump is a distant runner-up.  Most of these are relatively bulky.  Many of the less expensive ones cannot generate high pressures.  And even with that, the batteries would slowly self-discharge, meaning that the user would have to remember to charge the pump periodically.  That’s just begging to find that the battery is dead, just when you need it the most.

Conclusion

For pneumatic wheelchair tires, periodic maintenance of tire pressure isn’t much of an issue.  Reliable plug-in electric inflator pumps capable of 100 PSI are readily available.  These can be had with reasonably long air hoses, allowing the user considerable leeway in hooking the pump up to the valve stem.  All that is required is remembering to use it on a regular basis.

The big problem is flat tires while out-and-about.  There, many of the off-the-shelf solutions available to bicyclists — in-tire sealants, puncture-resistant liners, run-flat tires, and “tire wipers” — are not available (off-the-shelf) for narrow, high-pressure pneumatic tires typically used on wheelchairs.

That only leaves puncture-resistant tires and tubes.  Those may slow down the rate at which flats occur, but neither of those will stop sharp metal objects such as tacks, nails, or screws.

I guess my bottom line is this.  If you can tolerate the occasional flat tire, then go with high-end “puncture resistant” tires and tubes.  Forget Slime (r), tire liners, tire wipers, and similar makeshift solutions.  If not, I’d go with solid-rubber tires (not inserts), along with the steel bench-mounted tool used to install those tires safely on wheel rims.

Post #927: Wheelchair floor-to-chair aid, V3

The brief for this task:  Create a floor-to-chair aid for wheelchair users.  It must be able to be made at home, using only simple hand tools and readily available materials.

The end result is shown directly below.

Above:  Floor-to-chair aid, folded and covered.  For scale, the push-up bars sitting on top are 6″ tall.

Above:  Rear view, folded.  Lower stairs sit atop upper stairs when folded.  The boxes nearest the camera flip away from the camera when put into use.

Above:  Rear view, unfolded.  Lower stairs have been flipped off the top, away from camera, revealing hardboard stair tops.  Push-up bars are on top.

Above:  Front view, folded.  Blue cloth connects the lower and upper sections of the staircase.

Above:  Front view, unfolded.  Lower stairs have been flipped off the top, toward the camera, revealing hardboard stair tops.  The blue cloth keeps the upper and lower stairs connected. Continue reading Post #927: Wheelchair floor-to-chair aid, V3

Post #917: Floor-to-chair aid, user focus

This is the final set of refinements for my floor-to-chair aid staircase.  I’ll build a new set of stairs incorporating all the changes when the materials arrive later this week.

The upshot of this posting is that the only configuration you can build out of readily-available parts is a staircase with four 4.5″ steps.  And that it might be a good idea to carpet those steps.

As planned, the entire setup, including carpet and pushup bars, should cost about $55, and should take just over three hours to build.  The footprint of the stairs will now be 48″ x 32″

Details follow.

Continue reading Post #917: Floor-to-chair aid, user focus

Post #913: A D-I-Y floor-to-chair aid for paraplegic wheelchair users

This post is now superseded by Post #927.  Ignore the post below, and look at #927 for the final plans for this device.

This design works, but it’s really a proof-of-concept.   I’m now looking for easier ways to build it.  As I figure out improvements, I’ll post them separately, and link to them here.

For example, today (12/12/2020) I tested whether or not the lower cartons need to be reinforced.  They don’t.  The empty cartons themselves are sufficient.  That alone shows that there are faster, cheaper ways to build these steps.

See Post #914 for proposed modifications and a somewhat easier way to do this.  I’ll post a revised set of directions when I rebuild this tomorrow.

Post #917 now gives the final changes.  As it turns out, the only set that’s feasible to build and use, using off-the-shelf materials, is set with 4.5″ riser height and four steps.  I’ll document building that set when the materials arrive later this week.

Original post follows.

 

This post is a set of instructions for creating a broad, shallow, portable staircase.  The idea is that a paraplegic wheelchair user could use this staircase,  along with a set of pushup bars, to move from floor to chair level or vice-versa.

That’s a picture of my wife sitting on the finished steps, left.  It’s meant to illustrate how sturdy these steps feel, as she is perfectly comfortable sitting on them.

This is a followup to Post #886: A floor-to-chair/chair-to-floor aid for wheelchair users.  If you want the background on why I’m doing this, and what this is for, read that post. Continue reading Post #913: A D-I-Y floor-to-chair aid for paraplegic wheelchair users

Post #887: Volkssteppe, working toward simple D-I-Y plans for a floor-to-chair aid for wheelchair users.

Warning:  This is just the background.  I don’t get around to making these until the next post on this topic, which will occur after I’ve gathered the needed materials.  To see the wood DIY version of these, look at the just-prior Post #886. 

Edit 2/24/2024:  The actual construction is shown in Post #927.  To see that properly-configured cardboard is more than strong enough for this use, see Post #891. 

My last post presented plans for a practical way to allow wheelchair users to transition easily from from floor to chair and vice-versa.  The key insight — from a wheelchair-using friend — was that all you need is a broad, shallow set of steps, and a couple of “push up bar” handles (like these, say).  Portable handles vastly simplify the construction, relative to a device with built-in hand-holds or railings.

My friend reports that this combination of stairs-plus-portable-handles has increased her mobility.  Which, apparently, is high praise indeed.

For many people, constructing that set of stairs may not be possible.  While the carpentry wasn’t complicated, it required space and tools adequate for cutting up a full sheet of plywood.  The final result was nice, but what good does that do you if you can’t obtain one?

Today’s post goes in the opposite direction:  Volkssteppe.  The people’s stairs.  I’m going to work out how to create the same functionality using tools and materials that almost anyone can easily obtain and use.  It may not look as nice or last as long.  But it will work just as well as the original.

In this post, I use this as an opportunity to present some systematic analysis of this particular construction problem at hand.   I’m not actually going to produce a working set of stairs using this new approach until the next post on this topic.  The reason is that I need time to gather the materials and work out exactly what I’m going to do.

Corrugated Cardboard

After looking over the options, the obvious choice of material for this project is corrugated cardboard.

When I say “cardboard furniture”, I’m guessing that many people immediately dismiss the concept.  They’re thinking in terms of a cardboard box with a tablecloth spread over it, or some sort of spindly little table.

You might be thinking that cardboard can’t possibly be strong enough for this use, right?  If so, think again.

Virtually everything you own, short of an automobile, was packed, protected, and shipped in corrugated.  Heck, not only do we ship almost everything in corrugated boxes, Ikea is now shipping those boxes on corrugated cardboard pallets.   (That idea isn’t even original — corrugated pallets have been in use for more than two decades.)

Source:  Green Label Packaging.

My point is that if manufacturers routinely make cardboard pallets capable of supporting a ton or more, you can probably make a small set of cardboard stairs capable of supporting 300 pounds.

If you still don’t get it, just Google “corrugated cardboard furniture” and look at the examples.

Source:  Google images.

Or maybe watch this guy jumping up and down on his cardboard chair, at 3:50 into this YouTube video:

So, with a bit of planning, there’s no doubt that the average person can build a set of cardboard stairs strong enough to support an adult.

Now let me briefly list the advantages of corrugated cardboard, relative to almost any other alternative.

  • Available everywhere.
  • Cheap, typically free.
  • Easily worked with knife or shears.
  • Easily joined with common wood glue or carton-sealing tape.
  • Relatively lightweight if used well.

Too many choices for method of construction.

For these stairs, I am sticking to the basic footprint and form outlined in my just-prior post.

  • Each step will be 12″ x 30″, to accommodate both the user and the handles.
  • The top step will be 18″ above the ground.
  • A four-step staircase will be 4 feet long, with 4.5″ risers.
  • A three-step staircase will be 3 feet long, with 6″ risers.

I am also sticking to the “carcass and skin” approach of the prior model.  That is, I’m going to build an ugly, functional structure (the carcass), then add a nicer-looking surface on top of that (the skin).  This lets me be as crude as I want to make the functional parts of the structure as strong as needed.  In this case, the “skin” will be large sheets of blank cardboard, covering up the internal details of the construction.

Beyond that, there are any number of ways to build a completely functional set of steps.  There are simply too many choices. 

And there is surprisingly little systematic guidance on the engineering of cardboard structures.  For a material that is everywhere, and used for packing just about everything, I could find no systematic engineering guidelines for using it in construction.  No rules-of-thumb as to how much weight a piece of corrugated cardboard would support.  And so on.

And after examining a few boxes, I think that part of the reason is that corrugated comes in a wide range of thicknesses and weights.  There is no one standard corrugated cardboard to use as a reference.  Hence, there’s little standard guidance on using it.

That said, I’m basing everything below on a medium-sized carton from Amazon, which turned out to have walls that were 1/8″ thick, and weigh in at just about 1.6 ounces per square foot of cardboard.  Or, conveniently enough, one pound for every ten square feet.

A nosology of cardboard furniture construction

Even if I can’t find a good engineering guide, I can at least try to categorize the various techniques used to make strong cardboard furniture.

1  Simple stacked sheets.  

Source:  Homedit.com

With this method, you build a solid block of cardboard, in the desired shape, by stacking up cardboard sheets cut to shape.   For strength, the sheets would be vertical, with the corrugations (channels) running vertically.

This approach clearly could generate a set of stairs strong enough to support a person.  If in doubt, review the YouTube video cited above.

The main problem with simple stacked sheets, for this project, is the sheer amount and weight of cardboard required.  Assuming zero waste, and not accounting for the weight of any glue used, for the shallow 4-step stairs described above, if I simply made a solid set of steps, it would require:

  • 720 square feet of cardboard.
  • Equal to about 45 “medium” moving cartons.
  • Weighing about 72 pounds.

Glue could easily add another 13 pounds, even if used sparingly. 

Calculation:  Titebond is a commonly-used high-quality wood glue and would be suitable for this purpose.  Titebond says that, for wood applications, the maximum spread rate for their glue is 250 square feet per gallon.  At that rate, if you thoroughly glued this together, you’d end up using (720/250 =) almost three gallons of glue.  Titebond (same source) weighs 9 lbs/gallon, half of which is solids, so that would add maybe (3*9*0.5=) 13 pounds.

The total weight of the stairs could easily approach 100 pounds.   And, once you figure in the wastage, would easily require gathering more than 1000 square feet of cardboard, or the equivalent of 60 to 70 “medium” moving cartons.  There would also be a considerable amount of waste left over, after cutting out the required shapes.

In short, if used as a brute-force approach, it would simply be too much.  Too much material, too much weight, too much glue.

That said, one obvious alternative is to make the structure hollow.  Laminate up a series of broad “U”s.  Each broad “U”, upside-down, would be a step.  They would be laminated from strips cut from cardboard.  Would that work?

If I make each step 4.5″ thick (from tread surface to underside of tread surface), that would still use abut 450 square feet of cardboard, amounting to maybe 27 “medium” moving boxes, and weighing in at over 50 pounds.

So that’s better, and results in less waste.  But it’s still not what what I would call a sterling candidate.  The only way to reduce it further would be to make the step cross-section thinner than 4.5″.  That would certainly require experimenting to see how thin I could make it and still have it be sturdy enough to sit on.

Tentatively, I’m going to dismiss this one.  I see almost no modern commercial cardboard furniture made this way, and I think that’s probably sending a signal that this is not very practical.

2 Strength from geometry:  Folded beams and triangulated surfaces.

Source:  Time, inc.

This approach typically gets billed as “origami-like”.  That’s because, at first glance, the strength of the furniture derives from the carefully folded cardboard.

At root, this is about creating horizontal load-bearing elements that act like structural beams.  That is, single pieces of cardboard folded so that you would have to stretch or rip the cardboard along the bottom edge of the beam, in order to make the beam deflect downwards.  These constructed horizontal beams are then married to inherently strong vertical members such a thick cardboard, or thick cardboard folded into geometrically stable shapes such as triangles.

That said, the one thing I notice about most of these is that they are NOT made of recycled cardboard and NOT made out of standard 1/8″ thick carton cardboard.  Instead, all or nearly all of these origami-like pieces seem purpose-built of virgin materials, and most seem to use corrugated that is substantially thicker and stronger than what you find in garden-variety cartons.

Upon reflection, I think that goes hand-in-hand with this approach.  My guess is that if you start piecing together materials and using a variety of thin, waste cardboard, you compromise the structural integrity.

I judge that this approach, by and large, isn’t going to be practical for a set of instructions focused on using whatever-is-available scrap cardboard.  This is great for commercial product or piece of artwork, but it looks inherently risky when translated to a set of D-I-Y instructions using scrap materials.

3 Structural grid (or grid-plus-envelope) method.

The hallmark of this method is criss-crossed strips of cardboard, oriented vertically.  This comes in two varieties that look similar, but work in completely different ways.

source:  Planet Paper

The first variety is more-or-less an air-filled version of the stacked sheet method.  This translates a load vertically, to the floor, via vertical sheets of cardboard.  You can tell these by the presence of closely-spaced cardboard strips held in a vertical orientation, as in the seat portion of the chair pictured above.  Mechanically, this is really not very different from the solid stacked sheets, it just uses less cardboard, and uses the criss-cross pattern to keep the sheets in the proper orientation.

If you were then to place a sheet of cardboard over the seat of this chair, you’d have “structural grid plus envelope”, per this website.  You still have a structural grid of vertical cardboard sheets transmitting load to the ground.  they are just hidden beneath a cardboard envelope.

 

Source:  Dezeen.com, office design by Paul Coudamy

But the second variety of structural grid is a classic beam.  These elements take a downward stress, and carry that stress horizontally over to some load-bearing element.  In effect, these are horizontal elements built just like a hollow-core door:  Continuous skins on top and bottom, glued tightly to a central (mostly air-filled) core that holds those skins a fixed distance apart.

In the picture above, the horizontal bookshelves are just slabs of very thick corrugated cardboard.  The wide spacing between the top and bottom paper layers gives them enough strength to hold up the weight of the books.

So these elements work like an I-beam.  In order to flex this downward, you have to compress the top skin, stretch or break the bottom skin, or both.  The significant distance between top and bottom skins — maintained by the core — makes it quite difficult to do either.  And hence, you get reasonable load-bearing capability with relatively light weight.

I doubt that I could make a properly functioning beam of this sort from scrap cardboard.  The problem is that the two skins need to be held rigidly apart.  I doubt that I could cut scrap cardboard accurately enough to create that tight, non-moving bond between upper and lower skin.

But at this point, it seems pretty clear that the first type of structural-grid-plus-envelope — cross-crossed strips of vertically-oriented cardboard — is the most promising technique so far.  All I want to do is translate the force of someone sitting on these steps, down to the ground.  It looks like I could do that, with used cardboard, with a structural grid approach.  So that’s where I’m headed.

Post #886: A floor-to-chair/chair-to-floor aid for wheelchair users. (Picture added 11/16/2020)

This post is completely irrelevant for most readers.  If it doesn’t apply to you, just move along.  I’m posting this for a very specific target audience who would not otherwise be reading this blog.

This post is a brief description of a how to build a sturdy, cheap, relatively light-weight system to allow paraplegic wheelchair users to go from floor to chair and vice-versa, within their homes. In a nutshell, this is a set of broad, shallow, lightweight carpeted steps, coupled with a pair of standard “pushup bar” padded handles to allow the paraplegic user to mount those steps.

Making this set of steps requires power tools and a place to use them.  But the design is simple enough that any halfway competent D-I-Y carpenter can make them.

Edit:  That’s the steps and one push-bar, pictured above.  I didn’t take pictures as I made this set of steps.  So this amounts to a materials list, some crude drawings, and a set of written instructions.  And, I hope, one picture of the final product, which I will include when I can. Continue reading Post #886: A floor-to-chair/chair-to-floor aid for wheelchair users. (Picture added 11/16/2020)