NWG platen/belt issue, need help/thoughts

REK Knives

REK Knives

Well-Known Member
Hey guys. I have been having an issue w/ my belt sitting off one side of the platen by something like 1/32" or something. What I mean is that it is not touching the platen, not that it's not tracking properly. It's not much but it's enough to throw my grinds/edges off a little bit.

I have done everything I can think of... replaced platen w/ new fireplace glass. Then I replaced the wheel directly above it (3" contact wheel) because I found out that was not true. I have tried adjusting the platen in different angles w/ no success. Any ideas? I am at a loss... (yes it's flexing in where I push my finger, it's only on the right side of the platen, when you are facing it grinding, that I am having this issue, the left side is fine)

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Grind a couple of U shaped shims with a taper and slide them in behind the platen then tighten the bolts. OR...fold some HT foil or any foil for that matter and put it on the backside of the platen bolts, then tighten the bolts. Both these will kick the platen forward on the right side. It wouldn't hurt anything to pull the top of the platen out till it touches the belt evenly.


Rudy
 
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Rudy Joly said:
Grind a couple of U shaped shims with a taper and slide them in behind the platen then tighten the bolts. OR...fold some HT foil or any foil for that matter and put it on the backside of the platen bolts, then tighten the bolts. Both these will kick the platen forward on the right side. It wouldn't hurt anything to pull the top of the platen out till it touches the belt evenly.


Rudy
Click to expand...

Thanks for the input Rudy... I did that a little, and I even tried it to the extreme but it did not fix it. I almost wonder if it is not something to do w/ the belt, it seems worse w/ the Cubitron II (984F) belts after I have used them for about 2-3 minutes. New belts don't seem to do that as much really.
 
I had the same issue. All I can say is shim it shim it again and about the 1000th try you will get it just right.
 
Most of the problem is that angle iron isn't a true 90 degree angle. I've always made my own platens, some out of aluminum but mostly steel. If you really look, most have a radius on each leg and sometimes a slight angle. You have to tweak something on each one, draw filing, grinding or mill. If you're tool chalanged, go simple and see if you can tweak the platen mount where the bolts go in. Even a washer ground on a taper can help. Once you identify the problem, its just a matter of time before your brain goes to work.


Rudy
 
Well I've got glass on it to make it flat, I even lapped the glass! But I have tried shimming it a little and then a lot... even when the right side was tweaked out so much it was pushing the belt out 1/4" on that side I was still having the issues. Really weird. I need to just buy a new grinder I guess =( I've got two things I am going to try though.
 
It sounds like the angle iron you used to mount platen is out of square and possibly has some twist.

Have you put a machinist square on it across several planes and angles?

It's just a piece of angle iron. I've never seen one that was square. Depending on how far out it is, you could make it square or go find another piece that is close for just a few bucks.


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Sure sounds like that the platen is not sitting square, so you can put it out as far as you want and all it does is it makes contact with the one side. By the way adding the glass won't correct this problem but making a new platen probably will.
Frank
 
it could also be a wheel out of square. if the wheel mount threads were tapped crooked or a spacer is not true it could cause the belt to lean like that.
 
Thanks for the help guys... I do not think anything is out of square, at least not that I can tell... I have checked everything w/ a straight edge to make sure all the wheels are lined up front to back, and a level to make sure everything is lined up vertically. There has to be something I am missing though.

I have tried shimming and preventing any "twisting" of the platen, I also made a new platen, and I think I may have the first issue fixed... However, now I am running into a new problem where both sides of the belt are bowing out toward me. I have had this problem on and off over the past several months. It seems to do it with all different belts which makes me think there is something w/ my belt sander not lined up or tension or something. Look what it's doing.

The first one is a flexible long thin knife, After this I thought that I may have inadvertently pushed on the ends and induced this issue. So then I grabbed a super thick knife and its still doing it. Thoughts?

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I would guess the angle iron is not square and would shim or grind it to get it that way.
The top wheel could also not be square with the rest of the wheels. This will cause the belt to hunt back and forth.
 
set the platen proud of the wheels, lay a straight edge across the platen face and check with a feeler gauge at each end of both wheels. if you have already done this or something similar you may also need more belt tension.(edit) just went back and looked at your original post again and realized they are contact wheels. your wheel(s) could be dished. lay a straight edge across the length of each wheel also.
 
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I don't know if you fixed your problem or not but looking at the picture it looks like you have a washer behind the angle iron on the bottom. Can't really tell about the top bolt, to much shadow.
 
First thing to check when the belt acts weird on the platen is proper tension. The platen should be really proud above the wheels and the belt should be in high tension.
From the picture looks like the bottom wheel it's way out of square to the arm, is it just picture's distortion?
Is the weels holding plate of enough gauge to be stiff and not bending under the belt's tension?
 
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