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Author Topic: Sanity Check for DIY cabbing laps  (Read 532 times)

Shifter55

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Sanity Check for DIY cabbing laps
« on: December 23, 2018, 07:53:02 AM »
So I've been thinking making a couple of soft laps that use emery paper to do things like buff tops and round cabochons, but I'ld like to see if anyone has seen other options or has better ideas for what materials to use before I go ahead and do this.

The basic lap design is just going to be a piece of emery paper stuck with PVA glue to some soft rubber foam, in the same vein as some of the wood-backed flat lap machines that you see at clubs.
Currently the biggest concern is the paper not stretching as much as the rubber and glue, which aside from tearing the paper, will also cause problems with needing excessive force to press the surface into a curve when sanding.
My experience with drum sanders has shown that the softer and more elastic the sanding surface, the more even the curve will be on more brittle materials, and will allow for very tall shapes like briolette drops due to only needing a little pressure to give a curve.

Another option for the surface is a coat of abrasive resin just like the Nova Wheels use, but on a large flat surface I can see issues with it being level and achieving a homogeneous sheet with no weak areas.

Has anyone here tried doing this? Or is there a better way to achieve a super round cabochon surface without resorting to commercial grooved laps or taking the years to develop hand coordination for it?

MakkyBrown

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Re: Sanity Check for DIY cabbing laps
« Reply #1 on: December 23, 2018, 09:20:03 AM »
You can buy adhesive backed neoprene rubber circles. I use them to stick sandpaper. Might be able to get it with adhesive both sides.
I've just been polishing curved mirrors with it on my lathe, but holding a small piece of the rubber with sandpaper stuck to it and spinning the mirror.
With rubber/sandpaper on the lap I reckon you'd get a good result holding the dop in your hand and working it on the rubber/sandpaper surface.



   

MakkyBrown

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Re: Sanity Check for DIY cabbing laps
« Reply #2 on: December 23, 2018, 09:35:18 AM »
Think these are what I have.
https://www.aussiesapphire.com.au/soft-rubber-backing-disc-with-psa-back

If you get some rubber sheet or cut up an old wetsuit,  I'd get some spray contact adhesive to stick the rubber to the sandpaper and backer as it stays a bit flexible where as pva sets hard.

Rusted

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Re: Sanity Check for DIY cabbing laps
« Reply #3 on: December 23, 2018, 03:38:00 PM »
The blue foam camping mats are good too, often can be had for $1 or so at the tip recycling yard if you have one.
Shearing supply places have contact glue for shearing comb sanding disks, it doesn't set at all but stays sticky. I have found that the pressure pack contact works just as well and usually gives a more even surface under your wet and dry sheet.
Wet and dry sheets get dull and start to fall apart fairly quickly so be prepared to change them often.
Some of the cheaper wet and dry sheets are fairly pathetic when wet they fall apart rapidly, you might need to shop around for sheets that stand up to being wet.

I originally (1960s 1970s) made my own sanding disks by stretching canvas and a bit of foam over the flat wooden lap, I held it on with a steel band around the outside edge, somewhat cruder but it still works I have seen the canvas just tacked to the back of the disk.
I used glue pot type glue at the time, I think it's called hide glue and used to be used by woodworkers, just sprinkle with whatever grit Silicon carbide you want and it made a very robust sanding disk, it had to be used dry of coarse.
You could possibly do something similar with a 2 pack resin and it would be waterproof as well. Change the Si C for diamond and you would have really good disks.

MakkyBrown

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Re: Sanity Check for DIY cabbing laps
« Reply #4 on: December 23, 2018, 04:58:36 PM »
Those mats would be pretty good, pretty cheap at Anaconda. The mat foam would form to a shape more than neoprene. Might be worth comparing the two.  You can get a non-drying tacky adhesive for carpet tiles that might be similar to the shearing glue.
Worth making sure the glue used does melt the foam. Pretty sure you can by diamond flexible disks, ebay might be worth a look. Remembering now you can buy foam backed diamond pads on ebay aswell, not sure what size or shapes worth a look.

REXL

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Re: Sanity Check for DIY cabbing laps
« Reply #5 on: December 24, 2018, 08:05:28 AM »
The  stuff I use is called 3M feathering adhesive. I got it from Bunnings . It is made specificaly for disk sanding. Holds well and peals off when needed to replace sandpaper. I use wet and dry paper with no problems on foam disks from Aussie Saphire (I think). Been working Opal for years with no problems.

Shifter55

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Re: Sanity Check for DIY cabbing laps
« Reply #6 on: August 01, 2019, 04:26:57 PM »
I've been meaning to get back to this for a while, sadly life has made me busy with other things and I've only just got to build my cabbing laps.
I couldn't get any 3M feathering or contact glue, so I had to settle for UHU gluesticks like you use in school. But the laps work great, much softer than expanding drums.
This orange agate is only polished to 8K right now, but you can see the shine and even curve it has.

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