mirkaba
spending too much on rocks
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Member since August 2006
Posts: 321
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Post by mirkaba on Nov 14, 2007 13:32:13 GMT -5
Help!!! I am having a small problem with my grinder polisher. It is an old Crown 8 inch unit which I have set at 1750 RPM. I have 2 Scott murray Expando drums. The regular sanding belts have always fit loosely so I downsized to the 25 1/8" belts and they are a much better fit. The main problem is flat spots on my cabs. No matter how light my touch I still get little flat spots all over my cabs (with both size belts). So far the only thing that smoothens up the cabs is hitting them with a worn out 400 grit belt after I go through 100, 220 and 400 grit belts. If I hit them with the 600 newer belt the flat spots return. I have read that the drums can be reversed to make the cut less aggressive but have not tried this. Has anyone else dealt with a similar problem? Or do you have any thoughts on this? All input is much appreciated! Thanks.........Bob
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Post by docone31 on Nov 15, 2007 21:18:42 GMT -5
Sand a brick. That makes the belt a little more soft in cabbing.
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Post by johnjsgems on Nov 16, 2007 0:01:28 GMT -5
I think you mean reverse the belt. Reversing the drums would make your belts not stay in place.
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Post by johnjsgems on Nov 16, 2007 0:05:20 GMT -5
Another thought. Any possibility your drum is on backwards? That would explain why the standard belts don't stay in place. It might affect the operation if the undersized belts reduce the flexability as well.
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mirkaba
spending too much on rocks
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Member since August 2006
Posts: 321
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Post by mirkaba on Nov 16, 2007 13:35:27 GMT -5
Hey John.......No the drums are on right. There is a directional arrow on the side. I read on an Expando drum dealers advertisement about reversing the drums for a less aggresive grind. Although not a horrible state of affairs its bothering the cr__ out of me. ![>:(](//storage.proboards.com/forum/images/smiley/angry.png) It just involves an added step. I was shaping some labradorite last night and went from the regular 400 belt to an old 1200 trizact and no problems. I don't care much for the trizact but the 1200 seems to be the only size thats worth a darn.... Thanks.........Bob
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Post by bobby1 on Nov 22, 2007 12:09:24 GMT -5
I aggresively work on an agate scrap to break in new or rigid belts. New belts are stiff and don't flex well enough to give a slight "wrap" around the cab as you are sanding. The ability of the belt and drum to flex and "wrap" around the cab is what eliminates the mini flat spots on the cab. This is ture with grits from 220 down to 600 grit. I also run my machine at about 1500 rpm to give a softer belt/drum effect. I love my well-worn, soft belts. Bob (a cabber going on 50 years of doing it)
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Post by johnjsgems on Nov 23, 2007 11:14:03 GMT -5
I hadn't thought of that but there are dressing sticks for breaking in new belts. Barranca gives one of their 100 grit green dressing sticks with their cab units just for this purpose and Estwing has some really small dressing sticks for this as well. I imagine a teebar diamond dresser would also work.
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mirkaba
spending too much on rocks
![*](//storage.proboards.com/forum/images/stars/star_teal.png)
Member since August 2006
Posts: 321
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Post by mirkaba on Nov 23, 2007 12:49:50 GMT -5
Thanks! That is probably my problem ![:P](//storage.proboards.com/forum/images/smiley/tongue.png) Usually I do 20 or so cabs at a time and I assumed that the bulk grinding would break the belts in. Looking back I realize that I have always had the "flat spot" problem but to a much lesser degree. I will try breaking in a belt with the diamond tbar. Sometimes I think I am just to Scottish for my own good. But for some reason the lortone belts do fit bettet on My Scott wheels. The regular belts have a bunch of play and try to walk off the wheel and cut holes in my splash gaurds and stuff. Anywy I guess I will have to try breaking in both size belts to see what the he!?!?....................Bob
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