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rlowery
04-15-2010, 10:30 PM
I am new to hollow grinding, this is my first attempt. I am using 8"serrated wheel on a KMG. I started out with a 60 grit belt and all seemed to go well. I changed to a 120 grit and the blade bounces on the wheel. I slowed the grinder down and still have the problem.
I noticed the shaft on my grinder has a little wobble in it, but don't know if this is causing the problem.
Any ideas???

silver_pilate
04-15-2010, 10:37 PM
Is it bouncing on the wheel, or is the belt being "grabby"?

I've found that some brands of belts tend to be grabbier than others, though 120 grit shouldn't be too much of a problem. If it is the belt grabbing the blade, make sure keep the belt dry and wipe off any extra water after each dunk.

If it's just bouncing around on the wheel, it just takes a while to learn the control. Try a more solid grip with elbows tucked against your side, and the knife held in a solid position in front of you. Make the knife an extension of your body so that you have your entire body for support. Then use a secure but gentle touch against the wheel.

Coming from a flat grinding background almost exclusively, I've only hollow ground a couple of blades, and it can definitely be a challenge.

--nathan

rlowery
04-15-2010, 10:42 PM
grabbing would probably describe it best. I will try using a better grip.
Thanks,
Rickey

A.Sharpe
04-15-2010, 10:47 PM
Try a different belt. I have had belts that the seam was not flat this will cause a bounce. Also make sure the belt tension is right. If its too loose the belt will bunch up then pop threw causeing a bounce or hop.

Bruce Barnett
04-15-2010, 11:19 PM
Sounds like the belt join might be causing the problem. Rotate the belt by hand on a small radius wheel till you have the join straddling the wheel. Take a diamond file and get rid of the abrasive at the join so all you have left is the cloth belt. Usually gets rid of the hump/bump which is noticeably worse with finer grits.
Cheers Bruce

Matt Gleash
04-16-2010, 04:22 PM
I usually have problems with belts being "grabby" in the higher grits, like 220 on up...I've learned not to press as hard and they usually work pretty well for me. I did have a 60 grit get grabby last week, almost had a wreck with it, but my glove saved my thumb. Whew! -Matt-

Fross
04-17-2010, 10:05 PM
+1 on the wet belts, this is a mistake I made for quite a few belts, not drying after dunking. This causes a LOT of bouncing especially in the 120 and up grits. I dont have much experience hollow grinding though.

The Tourist
04-18-2010, 10:27 AM
Would this "bouncing" produce what appears to be a small circular divot on the bevel of the knife? (The bevel, not the edge itself.)

rlowery
04-18-2010, 10:31 AM
Thanks for all the help, I am starting over with a new blade today.

Bruce Bump
04-29-2010, 10:38 AM
I am new to hollow grinding, this is my first attempt. I am using 8"serrated wheel on a KMG. I started out with a 60 grit belt and all seemed to go well. I changed to a 120 grit and the blade bounces on the wheel. I slowed the grinder down and still have the problem.
I noticed the shaft on my grinder has a little wobble in it, but don't know if this is causing the problem.
Any ideas???

A smooth wheel would be much better for the finer grits. Serrated wheels are real good for hogging off steel but not so good for finish work. You said the shaft looks to have wobble? That may be half the trouble. Call Rob Frink and see what he thinks.