Contact wheel question

K

Ken Kelley

Joined
Mar 6, 2007
Messages
106
I bought a 2" x 6" Sunray caster to see if I can use it as a contact wheel. It has a solid aluminum core and a 70 durometer polyurethane tread. I tried it on my machine and it is very slightly out of round. I need some suggestions as to how I can true this thing up. My initial thought is to mount it on my wood lathe and use either a razor sharp skew chisel or fingernail gouge to trim it up a bit. Maybe coarse sandpaper?

Hopefully, someone has done this sort of thing before and can help me out.

Thanks,

Ken
 
If the contact wheel is the driven wheel you can do it on your grinder with sandpaper mounted on a hard surface like a piece of plywood. Take light cuts.

Otherwise I would suggest a metal lathe taking light cuts.
 
Ken, Here's how I true up wheels on the my KMG.
Split an old belt so it is about 1/2" wide and put it on the KMG. This will expose 75% of the contact wheel face. Using the work rest and a keenly sharperned tool bit, I lightly shave the face of the wheel to remove the highspots. Adjust the tracking to move the belt out of the way when needed. Then follow up with a sanding block to level out the tool marks.

SunRay uses a cast polyurethane which has a pretty low melting temp. I've never had much luck with this type of elastomer because it tends to melt and smear rather than sand away into dust. But you'll probably figure it out. Maybe use a bit of soapy water to "wet" sand the wheel. This might lubricate and cool the rubber enough to make a nice surface finish... I'm just guessing as I've never tried that before.

Of course, use common sense and all the required safety measures.

Good luck and keep us posted.

-Rob
 
Ken

Place the wheel on a shaft long enought to hold on to with both hands, about a foot to 18 inches long. You'll need a stop to keep the wheel from sliding on the shaft. Using a new 320 grit belt and a platen, hold the tire of the wheel against the belt on the platen with the shaft at about a 30 degree angle to the direction of the belt. The belt will keep the tire rotating while eating away the high spots. The closer you hold the shaft to being parallel to the direction the belt is going, the slower it rotates. Don't push hard, you just want to grind off the high points. The rotation speed of the wheel doesn't have to be very fast and is easier to hold steady at slow speeds. You might start of at a fairly slow belt speed if you have variable speed.

Jim A.
 
earlier this year I had to sand some rubber on the lathe that kept trying to melt on me, my solution was to take those air-in-a-can things and turn it upside down and keep spraying the rubber with the foam that comes out. I was able to get a reeeally nice finish that way
 
Thanks for all your suggestions. In one way or another I incorporated bits of all of them to successfully reduce the runout on the wheel to about .002". Not perfect, but a heck of a lot better than it was.

I used Rob's 1/2" belt strip trick and 36 grit on a block to do the rough work. The fine teeth on the flat side of a 4-in-1 rasp took care of the sides of the wheel. Found out that if you get a little bit too frisky with the rasp and use too much pressure the polyurethane tread will melt. Makes a right nasty mess on the tool too & hard to clean off. Works good, but easy does it.

Then I cut a piece of 1/2" dowel and sanded it down til it easily slid into the bearings. Drilled a 1/8" hole about mid-shaft and inserted a 3/4" piece of 1/8" drill rod to serve as a stop. Tried the trick mentioned by Jim and it worked pretty good until the tread heated up. Had a tendency to smear. Sooo...I chucked the wheel in the freezer in the shop fridge for an hour and tried it again. Perfect! The fine grit belt did a great job smoothing the surface. I used a very light touch and put it back in the freezer for a while when it showed signs of getting tacky. After a half dozen repetitions the tread was level and acceptably smooth. It had a tendency to bounce and shudder if I used too much pressure and didn't pay attention to the angle of attack. I found that it worked better if I applied a little braking effect with a finger to slow the rotation speed slightly. It didn't take long to get the feel of the procedure.

I tried some cautious grinding and the bounce is cured. The grind looks pretty good too. I think it will work as long as I don't get too horsey with it and heat it up to the point of melting.

I'll try some more grinding to see if this wheel holds up but I'm certain I will be replacing it with the genuine article within a short time.

K
 
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