Tire Truing Machine Repair

[HO RacePro]

I recently purchased a Professor Motor brand tire truing machine, and it has been getting heavy use. Heavy enough that I've noticed the mounts for the axle bushings have gotten -- to use the correct technical term -- "wallered out". The axle bushings are no longer well contained -- they can vibrate and wobble.



So I designed repair parts for my machine and printed them out. They are designed to be a close fit to the arms that support the axle, and have a small screw which can be hand-tightened to hold them firmly in place. The clip that holds the axle bushing is designed to be a snap-fit which should prevent the bushing from moving.





The axle is no longer directly over the centerline of the abrasive pads, but is still positioned over the abrasive. In the future I might shorten the axle support arms, but I'll wait on that for a bit to see if it is something I really want to do.

By-the-by, in the background of the photo above you can see my "Slideways Shifter" accessory. A rotating cam shifts the abrasive block side-to-side to help achieve a level surface on the tires. I have sold a few of them already and have a few more in stock. Message me if you have an interest.

I decided to check how much run-out I saw with this new setup. The answer to that is -- dang near none. Watch the video.

[BRS Hobbies]

Do you know how the original axle mounts got worn? If the axle is spinning in the axle bushings then how could the outside of the bushings wear the mounts or am I missing something?

[RichD]

If you run the machine in the wrong direction and you have the voltage turned up the axle assembly will tend to jump around and that can damage the bearing carriers.

[Mikeinclover]

I agree with BRS you should not have any wear on that section of the truer. Your axle should be in bushing so there is no wear. I have been using the same unit just mine was zinc coated and I haven't even worn the coating off.
Mike

[HO RacePro]

Yeah, well, now that I think about it the axle bushing mounts should never have experienced wear.

But they have, so a repair became necessary. That's been done.

Since I posted those photos I've made a revision to my repair parts. The rigid half of the bushing clips are now on top rather than underneath. That takes the load off the flexible half. The rigid half will take the load when the tires are in contact with the abrasive. Which is as it should be.
,
That becomes the third version of my repair parts. I almost never stick with the first version of a part I print. I almost always find something that needs to be improved.

And that is the way it is with design. It is rather humbling, but good design is an iterative and exploratory process. You can't be smart all at once.

I was impressed with how little motion was detected on that dial indicator test. The drill-blank axle I used is very, very straight. That looks like a worthwhile test for all my axles.

Always getting smarter. Or at least trying to,

[Model Murdering]

Wow, nice save!

Wallered indeed. Ya might go so far as to say "gnawed". I wish I had a nickel for every time a zinc-like casting pooped the bed on me. Was the machine brand spanken' new?

EB: "I was impressed with how little motion was detected on that dial indicator test."

Yeah, me too. Barely even a wiggle on that needle. Would that everything ran that straight. Did the tires mic out the same?

Bill

[HO RacePro]

Yes and no. Yes, the machine was new. No the tires aren't 'zactly the same size. At least as measured with a calipers. I am going to have to print out a tire gauge. You know, a plastic sheet with all the holes. Only good way I can think of to accurately measure the OD of a tire. If there is any 'give' in the tire a calipers will compress it and give you flaky readings. Have to come up with a good way to make sure the tires end up the same size.

[dungeonracer]

I like 2 things about your design...
1-it gets the tires away from the center of the block. Meaning you can take the block out, swap ends, and have a new sanding area.
2-you can make tiny adjustments to each side. My truer is slightly off, and I have to swap the axle around to get even sized tires.

[Kevan]

Not with that setup he's using you can't as there's a plastic block stuck on one end...other auto recipricators however can.

[HO RacePro]

Kevan is right. That's a downside of my shifter design. Or is it? No reason I couldn't install a cam track on both ends of the block! I'll have to try that.

And dungeonracer, thanks for turning that off-center bug into a feature.

I do the same thing, swapping the axle around to get the tires even. Or try to. i need to print that tire gauge and do some checking to see if that actually works.

[HO RacePro]

Did I say something about design being iterative?

This photo below shows the Mark 3 Repair, on the right, and the Mark 4 Repair, on the left. It also shows the abrasive block with a cam track on both ends.

The reason for the latest redesign is to provide more clearance for the wheel. Adding the second cam track just took a moment with superglue.

It is convenient that printing out new parts is easy and cheap. Well, that was the whole motivation behind rapid prototyping in the first place.

[gsnopoint]

Almost like a design flaw on these types of tire truing gizmos, the axle sits center of the sanding block. Becomes a waste of sanding material. Now, if some smart enterprising lad would design the machine so the axle sits back or forward of the sanding block, one could utilize more of it. Or, as Ed has produced, for those of us already with this sanding gizmo, attachments that push the axle back on the sanding block.
Nice work Ed !! Let me know when you mass produce them.

[HO RacePro]

You might think I'm kidding, but I think the best way to relocate the axle above the sanding block would be to print out several pairs of mounts with different offsets. Yes, you could fit an adjusting screw at the front of each mount, but then you'll want to make sure they are each adjusted the same, otherwise the axle would be skewed versus the block.

I don't think mass production is in the cards, but I'd be happy to print out some parts for folks who have a need for them. Yes, I'll charge for them, but it'd be WAY less than the trouble and cost of replacing the die-cast part.

Smart? Enterprising? C'mon, me? My bank account doesn't think so.