Grinder nonsense...

Chris Lyons

Chris Lyons

Joined
Feb 22, 2017
Messages
89
I am hoping someone who knows more than I do (which should probably be most of you) can help me figure out wth is wrong with this thing...

So I have an OBM grinder (not the best I know) and I am having issues with tracking solid.
When I apply pressure to the belt, it wanders off to the left and if I push too hard I can stop it. It is the 1.5-2hp motor (running on 110v). I am running it on a VFD. It does this regardless of speed being used.

At first I thought it was low pressure from the 25 lb gas piston, so I ordered a 40lb from Mc Master, and although that one is a bit longer, it still works... It does not walk the belt as much, but I noticed that the sound is now much louder, and my platen and wheels get pretty hot during use. I am not sure if there is too much pressure being applied, but in searching on the forum for this issue... some guys are running 60 lb springs with no issues, so IDK. I am concerned that it might wear out my motor or wheels prematurely if there is too much pressure.

It also has a fair bit of belt wobble, making it difficult to grind plunge lines and get clean bevels.

I checked the alignment of the drive wheel to the other wheels, and it seems pretty lined up.

It may be worth mentioning that I have had to replaced the idler wheel (or tracking wheel) in the first year that I've owned it. The crown wore out of it and it was not tracking anymore.

I'm not sure what I need to do to get this thing to run true. Thanks for any insight.
 
Well, I'm not an expert, but you should only have one wheel that has a crown.

If, like me, you bought a crowned drive wheel and a crowned tracking wheel they're gonna fight and not work real well.

I eventually used a file to remove the crown from my drive wheel, but it still isn't that great, I just need to buy a new one.

Anyway, one crowned wheel, lots of pressure on your spring. Make sure you pull your tool arm out enough that your gas spring is at least half compressed.
 
A.McPherson said:
Well, I'm not an expert, but you should only have one wheel that has a crown.

If, like me, you bought a crowned drive wheel and a crowned tracking wheel they're gonna fight and not work real well.

I eventually used a file to remove the crown from my drive wheel, but it still isn't that great, I just need to buy a new one.

Anyway, one crowned wheel, lots of pressure on your spring. Make sure you pull your tool arm out enough that your gas spring is at least half compressed.
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Clarifying question, did you buy an OBM grinder that came with a crowned drive wheel? I'll have to go look and see if my drive wheel is crowned. I have also been considering getting a larger drive wheel.. mine is 4". Been looking at others like a 5 or 6", as to my understanding they will move the belt faster
 
What's the platen made of that you're using?
I've used an OBM for about 4 years and noticed that the basic platen wore out pretty quick and had grooves, but I wasn't concerned because I always planned to JBweld a pyroceramic glass to it, and I figured the grooves were a good thing. I haven't had the problems you're describing, except with random belts.
 
"It also has a fair bit of belt wobble, making it difficult to grind plunge lines and get clean bevels."

The OBM is a shitty design.

That's Wheel alignment

Chris Lyons said:
When I apply pressure to the belt, it wanders off to the left and if I push too hard I can stop it.

I noticed that the sound is now much louder, and my platen and wheels get pretty hot during use.

Some guys are running 60 lb springs with no issues

I am concerned that it might wear out my motor or wheels prematurely if there is too much pressure.

It also has a fair bit of belt wobble, making it difficult to grind plunge lines and get clean bevels.

I checked the alignment of the drive wheel to the other wheels, and it seems pretty lined up.

I have had to replace the idler wheel (or tracking wheel) in the first year that I've owned it. The crown wore out of it and it was not tracking anymore.
Click to expand...

Heat, being able to stop the belt and worn out wheels all point to insufficient belt tension.

The belt is slipping and wearing out the wheel with the back of the belt.

Pull down on the arm and pull out the toolbar.

The belt should be guitar string tight. You should be able to get a good twang when you pluck it.
 
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Thanks for the replies guys, I'm going to put the 40 lb piston back on and see if I cant get the wheels better aligned somehow, check the bearings, and see if there is crown in the drive wheel. At least now I have a starting point!
 
12345678910 said:
The belt is slipping and wearing out the wheel with the back of the belt.
Click to expand...
Note, the OP said the crown on tracking wheel wore out, slipping belt wouldn't cause that crown to wear, only the crown on the drive wheel would be affected by slipping belt.
Chris Lyons said:
if I push too hard I can stop it
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You are saying you can stop the belt? Not the motor? Stopping belt causing it to slip on the drive wheel is lack of tension for sure. Lack of tension will also cause tracking problems.
Chris Lyons said:
my platen and wheels get pretty hot during use
Click to expand...
How far out is the platen from the platen wheels? The belt should just "kiss" the platen during use. Be sure to check the bearings in the wheels if they are also getting hot. The wheels shouldn't be getting "hot", perhaps warm, but not hot. With the belt removed all wheels should turn freely by hand. Spin them and they should "coast" to a stop.
 
If you were to put a ruler across your flat platen wheels, how far is your platen sticking out? Is your platen glass or mild steel?

I think you're stacking up problems. Low tension + high drag = belt slip and wobble.
 
kuraki said:
If you were to put a ruler across your flat platen wheels, how far is your platen sticking out? Is your platen glass or mild steel?

I think you're stacking up problems. Low tension + high drag = belt slip and wobble.
Click to expand...

You're right. I made some adjustments. I changed out the gas piston from the 25 lb to a 40, solved a bunch of problems right there. I backed the platen (mild steel) to only about a 1/16" past the wheels. I also checked the wheels and they were too tight when assembled so not spinning freely. I backed them out like 1/32 of a turn and now they coast to a stop instead of only one or two revolutions they were getting previously. These changes made a big difference in performance. I think I am also going to pick up an uncrowned drive wheel, as there is some crown to it. While I'm at it I'll probably change it from a 4" to a 5".

Thanks for all the insight fellas!
 
kuraki said:
If you were to put a ruler across your flat platen wheels, how far is your platen sticking out? Is your platen glass or mild steel?

I think you're stacking up problems. Low tension + high drag = belt slip and wobble.
Click to expand...
John it is good to see you on the forum You have been kind of quiet. Have a great New Year
 
Simple fix I used on mine was to put a bead of 3/4" wide tape 1/8" thick around in the center of the tracking wheel
Gauged the belt tension by having the tracking wheel move down around a 1/4 - 3/8" when pulling the platen forward and tensioning belts.
 
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