Knife Grinder Build advice

[Dweed144]

Hello All.
New to the forum.

I've just built a 2x72 grinder and I am having some issues that I thought your collective expertise could help resolve.

I am using a 170N gas strut, which I think could be too much tension.

When running the belt in normal operation the tracking wheel is canted over at quite an angle to get the belt to run central on the platen.
In reverse it comes straight off, no matter how I adjust the tracking.

I have experimented with moving the tracking wheel position on the shaft (in and out) and it doesn't have any significant effect. What seems to make a bit of difference is the height of the tracking arm, the higher it is the more angle is required on the tracking wheel. That said I only have 40mm of adjustment on the arm, and I imagine the force exerted by the strut changes over that distance too.

I can't work out what element of the geometry is skewing it. Or whether it is the pulleys which are the problem. I bought the pulleys from an ebay seller in poland who manufactures them. They were quite cheap. From eyeballing it it could be that the tracking wheel is not quite evenly crowned.

Thanks in advance for any tips!

 

[Natlek]

That grinder looks nice . Did you check alignment of other three wheels ?

 

[Natlek]

Tracking wheel should align with other wheels in this direction , too ..

 

[Dweed144]

Thanks.
Yes the wheels are all aligned. The jockey wheels sit evenly about 1mm further out than the drive wheel but they are a little wider.
Everything seems in plane..

 

[Natlek]

They must be aligned in both direction............. check it again .I don t see anything else what can cause this .If aligned is perfect , tracking wheel should sits almost aligned with other wheels ...That angle is too much

 

[Natlek]

When I say aligned I mean this .IF all wheels are on ONE plate ALL of them should have 90 degree angle to plate measured on every point around the wheels .

 

[Stacy E. Apelt - Bladesmith]

Take the belt off and grab the tracking wheel from the end. Try and wiggle it. If it moves either the bearing or the plastic core is not right.

With the belt off, spin the tracking wheel. If it wobbles, the hole in the plastic core is not plumb.

Check the drive wheel the same way.

What Natlex was saying is, Imagine a line going through each bearing axle and the motor drive shaft. These imaginary lines should all be parallel in all ways. In the one photo it looks like the drive wheel is canted downward a lot. Perhaps the tracking hinge setup isn't correct.

 

[Josh Rider]

Could be that your tracking arm needs to be more parallel to the tool arm. On mine I moved the air shock further to the left and bolted it to the side of the grinder so the tracking axle was more in line.

 

[jll346]

Hope you figure it out. Beautiful looking grinder

 

[NC Biker]

Josh is right, your tracking arm needs to be parallel to the bottom of the belt, which would be close to horizontal. This will give you the best tracking and as others have said you have to have the center line of all the wheels on the same line.

 

[Ken H>]

You might also check your tracking wheel - and perhaps adjust it some by shimming the front or rear bracket a bit. Here's the tracking adjust I have, you can see how I can "twist" the tracking wheel to move belt to center of wheels. With the proper adjustment it runs in forward or reverse with only a small moving of belt when switching directions.

edit: Hmmmm, that image is larger than planned.

 

[Drew Riley]

170N =~38lbs.

That’s really not too much at all, though I doubt the spring force is your problem, from how your describe the issue.

Make sure that with your tracking wheel in a horizontal position, that the center line of all of your wheels are in the same plane.

With your tracking arm compressed all the way down, put a belt on and pull your tool arm out as far (and tight) as it will go, before releasing your tracking arm. Lock the tool arm in place, then let your tracking arm do it’s thing. See if that helps.

 

[Tin.Man]

Shorter gas shock to get your tracking assembly parallel to the bench surface will fix it.

 

[mike-E]

If you look at your tracking wheel from above, standing on the motor side, it(your tracking wheel) is twisted to the right. You will either have to cut those welds off the hinge or make another arm. This is probably the most important junction on the whole grinder. You should consider using bolts instead of welds there.

 

[kuraki]

What Tin.Man and Josh are saying and where the twist mike-E spotted may be coming from:

Fixing the tracking on a KMG

 

[jll346]

When I had a few KMG grinders. They worked best when the arm was close to parallel with the body.

 

[Dweed144]

Thank you everyone for your instructive comments.

I had designed the arm so that the pivot was running parallel. I checked and it is roughly so, as you can see in the attached photos (it actually can drop beyond by a fractional amount.
The original photos were not at full running tension.

The problem exists still when the pivot is parallel, however it is worse at raised angles.

The axle mount is a bolt on assembly onto the arm, so I could adjust for skew if I increased the clearance for the bolts. It could be a touch skewed at present, but if it is, it's only very slight.

The drive wheel has a little wobble in its rotation (will check the runout on the motor shaft to see if it is the motor or the pulley), but the shaft is running at 90 degrees to the bench. As are all the other pulley shafts (save the tracking pulley of course).

 

[Ken H>]

Good looking bracket for the tracking adjustment/wheel. If you loosen the two allen screws will the bracket twist any at all? While the wheel looks square, just twisting the bracket a VERY small amount can change tracking a good bit. Also, while the motor just has to be square because of the way the mount is part of the total grinder, you might try putting a shim under front or rear of motor to "cant" the motor a tad.

Is there any flex at all in that tension arm? Can you move it left to right with just hand pressure? You don't want ANY flex.

Your grinder build looks too good (solid & rigid) not to work good once everything is lined up.

 

[Natlek]

Wheels and belt are only moving part , so tracking problem must be there.....And only problem which affect tracking can be geometry , right ?
Judging by the pictures , to me looks like tracking wheel is not aligned with other wheels .........
I mean on this ................ view from above . In that direction tracking wheel must be aligned with other wheels.....if it is not aligned it already has an influence on tracking ....

 

[Gilbert M]

Nice build. I wonder if you try some wide flat washers(make it tight enough to not move on it's own) instead of the bushings you have for your tracking arm pivot. Then set your arm and tracking wheel were they should be and run the grinder slow and push or pull the tracking arm right or left to see if you can get it to track correctly .