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Vibralap information or experience or advice wanted

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Marra Mamba:
Hi members
I have had built a 3 x 39 inch Vibralaps, grinding is fine I have a great pre-polish and they walk around the table nicely but on the carpet polishing table they do not walk but spin on the spot. I have tried different types of carpets, leveled the tables, different types of and amounts of powder, adjusted the chain lengths. I am still getting a brilliant polish but it takes time and from previous experience they should walk. They walk on the grinding table because water stops them from gripping but on the carpet polishing table the carpet seems to grip a bit.The last machine I had was a 27 inch Diamond Pacific which I never thought to check the size of the offset before I sold it some time ago. I have put a 6 mm offset on the shaft and am wondering does anybody out there know what I need to increase the offset to to achieve that effect? Sorry for the long winded post but have spent a couple of months on this during lock down and am out of ideas  any suggestions would be appreciated. MM

pito:
Hi  I built my 24 inch dia flat lap 15 years ago with a 2.5mm offset on the shaft. So with nothing on the lap, if I put a very small amount of grit on the lap and run it  the grains of grit run around in an approximate diameter of 5mm. The machine works fine with the rocks moving both when grinding and polishing. From what you said you have an offset of 6mm on the shaft, so in your case the grits, if you did my test, would make a diameter of 12mm- which seems too much to vibration to me.
pito

Marra Mamba:
Hi Pito
Thanks for your reply I will try it this afternoon and see what the grit pattern looks like and let you know any particular size grit? I will try 80 as it will be most visible
A friend of mine made 48 inch laps and told me 6 mm but it was a long time ago he might have it wrong next time he does maintenance on it he is going to measure the offset and let me  know so keep on tinkering I get a mirror finish on most stone but frustrating they won’t walk it means I need to watch it not what I need when I have many other things to do thank you again I will try that
MM

Marra Mamba:
Hi Pito
I have tried that a bit hard to tell as the grit did spread quite quickly another question if you don’t mind was your counter weight opposite you offset? I am mucking around with that,  it certainly improves the action if not directly opposite the offset, they spin faster Been polishing for 30 years every now and then you get a machine that won’t play nice polishing is very much smoke and mirrors again thanks MM

pito:
Hi, some time ago I took off the counter balance but it was opposite the throw. Can't remember why I took it off.  Just thinking about your application - I used a 25mm drive shaft and with the 2.5mm offset could get a 20mm short stub to hold a flat flange 20mm bearing to bolt to the plate. If you have a 25mm drive shaft with your offset you would end up with a 12 to 13 mm short stub for your bearing to attach to your plate - I think it is a bit small for your size plate diameter. I think you must have a much larger drive shaft - in any case you can measure the throw by rotating the drive shaft by hand  and measure the movement of the plate from a fixed point for 1 complete rev of the drive shaft. I do occasionally have problems with large rocks where the mass of the rock is a fair distance from the plate - they tend to just want to rotate or bounce around- but no problems when the weight of the material I am polishing is low eg slabs even 2" to 4" no problem provided the surface dimensions of the slab are bigger than height ie the lower the centre of gravity the better. Interestingly enough I don't have any problems in the grinding stage with ones that give problems in the polishing stage. I use lead weights on slabs and only use 80 grit which breaks down nicely and then go direct to polishing using dry alum oxide.
pito

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