Craftsman Benchtop Sander

[dillonf]

I have an old craftsman benchtop sander (6"x48" belt & 9" disc) that I use for woodworking. Could I use this to sand the faces of thundereggs and geodes? I would like to take them down to 220 on this machine then finish them off on an 8" All U Need. The coarse grinding on the All U Need is real slow and inefficient.

If I used the craftsman would I need a special type or disc or belt? I was thinking about trying to use some generic aluminum oxide discs and belts.

(Safety wise I purchased a 3M respirator, and I plan on doing it outside with a wet/dry vac attached.)

[JR8675309]

Dec 28, 2022 18:22:40 GMT -5 dillonf said:

I have an old craftsman benchtop sander (6"x48" belt & 9" disc) that I use for woodworking. Could I use this to sand the faces of thundereggs and geodes? I would like to take them down to 220 on this machine then finish them off on an 8" All U Need. The coarse grinding on the All U Need is real slow and inefficient.

If I used the craftsman would I need a special type or disc or belt? I was thinking about trying to use some generic aluminum oxide discs and belts.

(Safety wise I purchased a 3M respirator, and I plan on doing it outside with a wet/dry vac attached.)

Should be able to, I plan to w my bench sander. I've polished Teggs with an orbital sander w AlOx. I just dipped the egg in water and sanded, rinse and repeat. Indeed, proper precautions necessary. Hope that helps!

[dillonf]

Thanks JR8675309 I'm gonna try it out next week and see how it goes.

[liveoak]

I use an inexpensive 1" X 30" woodworking belt sander for some troublesome cabs with Silicon Carbide belts.

I use a sponge at the bottom of the belt travel to keep it all moist, and use it outdoors.

The thing with your large combo machine - it's cast iron, so water will make it rust &

that's a much more expensive machine than my 1" X 30" belt is.

The other advantage of the 1 X 30 is you can get lots of grits cheaply as they sell them for knife makers on Amazon.

Red Label I've found is a good brand.

Patty

[dillonf]

So I gave it a go, and it didn't really work out all that well. I bought some new aluminum oxide belts and thought I'd try some dry sanding. I have seen numerous videos of this with the Richardson's rock ranch high-speed dry sander. I tried sanding 2 different thundereggs - one Priday egg and one fallen tree egg.

Mistake 1 - I used some nice looking eggs   I have quite a few that aren't that great and I should have tested the method out with them first! 

Mistake 2 the dry sanding caused some burning and glazing on the fallen tree egg I tried to sand. Additionally it was way too aggressive (80 grit Al Ox) the fine layered opal deposits in the egg chipped. See below:

The egg on the bottom is the half I tried sanding notice the burn marks and the chipping on the Opal layers.



For comparison look at this one I have taken to 220 on the All-U-Need



You do see some darkening of the green/grey bands in the egg, but there is no burning/glazing.


On the Priday egg I also saw some burning, and the calcedony chipped and peeled back in layers - this has never happened with the All-U-Need and I have polished about 6 Priday eggs (12 halves) now. Additionally I had some chipping on the edge of the egg which I have occasionally seen on the All-U-Need, but seemed more common with the benchtop sander.



So my take away - dry sanding on the benchtop sander is no good. For reference the machine is 2400 FPM on the Belt (6" x 48") and 3100 RPM on the disc (9"). I ran the eggs on both and the burning happened on both the belt and the disc. I didn't try it wet, but based on liveoak comments above using water with this machine is likely a bad idea. 

[stefan]

Your biggest issue I think is heat build up (burning and glazing). That will cause the rock to chip and fracture. The good news is that could be removed with a wet sand on the flat lap. Yes it is very tiresome, but all is not lost. I did a thunder egg half by hand once (SiC grit and water and a window pane) Took forever (several weeks working about 15 to 30 minutes at a stretch) so yea I get how long it takes!