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Fit & Finish Fit and Finish = the difference in "good art" and "fine art." Join in, as we discuss the fine art of finish and embellishment.

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  #1  
Old 03-26-2012, 02:41 PM
Ed Tipton Ed Tipton is offline
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Question on grinding

Whenever I grind blades using my trusty Grizz, I get this really bad "bounce" whenever I try grinding on the platen. The original platen had the standard Grizzley teflon coating affixed to the platen, and it started to scrub off some of the coating onto the back of the belts. When that problem developed, I peeled off the teflon coating from the platen, and epoxied a 10" x 2" quarter inch thick piece of plate glass to the platen thinking that such a smooth surface would run perfectly smooth. WRONG!! The glass is still perfectly smooth, and there is no "coating" or anything adhering to the back of the belts, but whenever I try grinding on the platen, it jumps and bumps around like there are bumps of material under the belt....but there is nothing there but smooth glass and smooth belts.
I don't understand where the "bumps" are coming from, but it's impossible to get a good grind using the platen. I am able to use the contact wheel without a problem, but I don't like the idea of possibly damageing the contact wheel.
I have read where Ed Caffrey uses cork as a backer for his belts, and I'm wondering if using cork or a material with some "give" to it might cure the problem....since the platen with the glass is a surface without any "give" to it.
I use both Al/Ox belts and also ceramic belts. The problem persists with both belt types and with all grits.....although it is less bothersome with the coarser grits.
Anyone else out there had a similar problem....and how did you fix it?
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  #2  
Old 03-26-2012, 07:01 PM
Recurve Recurve is offline
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Do you have enough bevel on the top side of the glass to keep the splice of the belts from catching as they rotate? Just a thought. - Jim -




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  #3  
Old 03-27-2012, 09:17 PM
Ed Tipton Ed Tipton is offline
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Recurve....Actually, there is no bevel at all. The grinder is adjusted so that whenever no grinding is being done, the belt does not touch the glass but barely misses coming into contact with it. However, the problem I am having does not seem to be cyclic or rhythmic. I dont believe it is being caused by the belt splice. It seems to be far too constant....as though there were something on either the belt or the glass...but both are clean.
It's really quite puzzling as to what is causing the problem. The machine runs smoothly without any roughness or anything to suggest a bad bearing or problem with the machine itself.
Prior to having this problem on this belt grinder, I had a similar problem with a disc grinder where I had glued the sanding disc directly onto a back-up plate using disc adhesive....but again....there was nothing but metal under the disc.
I'm thinking that using cork or some material such as a rubber "pad" may quiet it down, but I just don't understand why it is as rough as it is when both the glass platen and the belt are smooth and clean. Whenever the belt runs freely without grinding, it runs smoothly even if I adjust the machine to where the belt is in contact with the platen. Also, the grit side of the belt feels completely normal....but it acts as though there are small clumps of material either on the belt itself or the platen. There is nothing unusual at all whenever I am using slack belt grinding...only when I use the platen.
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Old 03-31-2012, 11:10 PM
JCPollard JCPollard is offline
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I've wrapped thin corrugated cardboard around the platen to help with belt slap. I would also check your platen isn't flexing from the drag of the belt when pressures applied . Good luck I'm sure you'll find the solution.

James
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  #5  
Old 03-31-2012, 11:36 PM
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AUBE AUBE is offline
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Are the belts you use butt spliced or overlapped? This is the spot where they attach the two ends of the belt together. A small rise or dip in the height of the belt will cause the bumping.

Other than that I don't know what the problem is. The only other thing I can think of is if you have your belt tension far too low and the belt is slipping, then catching, on the drive wheel over and over.

I used a Griz with a plate glass platen for a few years with no problems. Also I kept enough tension on the belt where it sits flat on the platen at all times.

Where are you getting your belts from?
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  #6  
Old 05-11-2013, 07:22 PM
watersmark watersmark is offline
 
Join Date: Feb 2012
Location: Michigan
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i have a home made unit and used a thick piece of leather from a drive belt used on a john deere to drive a remote tool its heavy i used contact adhesive to put it on with and put outside , shiny side against belt it gives just enough so no bounce been using 3 years this way
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  #7  
Old 05-15-2013, 07:48 AM
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Ed Caffrey Ed Caffrey is offline
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Quote:
I have read where Ed Caffrey uses cork as a backer for his belts
Let me clarify! I DO NOT use cork for backing on my belt grinders.... ONLY on the disc grinders! (cork on a belt sander is asking to get hurt!) DO NOT DO IT!

There are 2 things that cause that "belt thump"....

1. As has already been mentioned....the top and bottom edges of a glass platen face need to be radiused.....

2. The most likely cause is belt joints...not all belt joints are created equal, and you'll find the "belt bump" will be the worst on the cheaper, lighter weight backing belts (the worst are the micron/mylar belts, and to a lesser degree the J-weight belts.

Finally, this is might not sit well with some, but it also has to do with the quality of grinder....I've worked on a fair number of grizzly machines, and they, along with most other two wheel designed machines exhibit the "belt bump" more so then other designs.

I experience it too, on my machines, but more often then not when it's the worst, I take notice of the belt joint, and find the belt joint(s) is the main factor.


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  #8  
Old 05-25-2013, 09:32 PM
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Gary Mulkey Gary Mulkey is offline
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Another thing that you must do on a Grizzly is to run the belt as tight as possible. The tension spring on the top wheel won't apply enough tension. Tighten the belt enough to compress the spring as much as possible.

I'm not sure if this is your problem but could contribute to it.

Gary


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