Truing contact wheel

J

JoshEarl

Joined
Sep 30, 2007
Messages
197
My home-built KMG clone grinder is running really well now. I was able to salvage an 8" wheel from an old pallet jack, complete with sealed bearings and everything. The rubber seems to be plenty hard for serious grinding.

However, there's a slight unevenness to the rubber on the wheel. My father-in-law, who built it for me, used an antique lathe to trim the rubber a bit and clean it up, but his equipment wasn't quite up to getting a perfect balance.

It seems like there should be a way to true the rubber while the wheel is running on the machine by reaching around back where the belt isn't touching.

Has anyone else done something like this successfully? To clarify, the contact wheel isn't a drive wheel; it turns freely as the belt runs.

Even with the unevenness, it's working pretty well. I'm not expecting a free 8" wheel to be perfect, but a little improvement would be great.

Josh
 
While the wheel was on the lathe, could you tell if the problem was with the rubber...or with the wheel casting that the rubber is molded to?
-Mark
 
I can think of lots of ways to do this. Unfortunately, most of them end up with a trip to the ER.

Obviously, a rigid setup on a lathe with a properly ground cutter is the correct answer.

Short of that, you can sand rubber with sharp coarse sand paper. Perhaps you could reach through with a stick with sandpaper glued to it, rest the stick on something on the other side, then carefully bring the paper to bear on the high spots as it turns. I expect there is a good chance it is gonna go flying, so I'd be afraid to use a real cutter or metal rasp.

No, I've never tried this. But I have ground rubber.
 
polish avenger said:
While the wheel was on the lathe, could you tell if the problem was with the rubber...or with the wheel casting that the rubber is molded to?
-Mark
Click to expand...

I'm pretty sure the problem is the rubber. I didn't get to see it in the lathe, but when I spin the wheel on the tool arm the center seems to spin true but the outer edge has a visible wobble.

Josh
 
Nathan the Machinist said:
I can think of lots of ways to do this. Unfortunately, most of them end up with a trip to the ER.

Obviously, a rigid setup on a lathe with a properly ground cutter is the correct answer.

Short of that, you can sand rubber with sharp coarse sand paper. Perhaps you could reach through with a stick with sandpaper glued to it, rest the stick on something on the other side, then carefully bring the paper to bear on the high spots as it turns. I expect there is a good chance it is gonna go flying, so I'd be afraid to use a real cutter or metal rasp.

No, I've never tried this. But I have ground rubber.
Click to expand...

I hadn't thought of trying to brace both ends of the sanding stick. I can drop the speed of the grinder down pretty low, so I'm not too worried about getting hurt. That said, whatever I try I'll be wearing full protective gear, possibly including Kevlar body armor. :)

Josh
 
Cut a old belt in half so it is only 1" wide. Then fire machine and with the 1" belt centered use a course file on the edge only stick a small amount of file past the tool rest and against the side of the wheel. . Do both sides. I take it the wobble is side to side and not a bump that pushes your work in and out
 
I have used my lathe to true a contact wheel with rubber problems. Nathan is right...setup needs to be rigid and as centered as possible. The cutting tool needs to be freshly sharpened and the speed needs to be fairly high to get a decent finish.
-Mark
 
ib2v4u said:
Cut a old belt in half so it is only 1" wide. Then fire machine and with the 1" belt centered use a course file on the edge only stick a small amount of file past the tool rest and against the side of the wheel. . Do both sides. I take it the wobble is side to side and not a bump that pushes your work in and out
Click to expand...

This is a fantastic suggestion. I actually have some 1" belts so I won't even need to cut one down.

However, the problem is a bump, not a wobble. My bad on that. I think I still could fix it using this suggestion. By tracking the belt side to side I could access the whole surface.

Would a file be likely to tear up the surface of the wheel too much? I'm guessing the rubber is in the 80 durometer range.

Josh
 
Josh: I use a file regularly to true my wheels. The edge of the file will work fine, especially to get the wheel back in round-Lay the file on the workrest. You can see your progress when you shut the machine down-the filed down area has a different appearance than the rest of the wheel.

Once you get the whole wheel dressed, you can wrap sandpaper around the file and clean it up even more. automotive paper is good for this, as it is very sharp.
 
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