herb
spending too much on rocks
Member since November 2011
Posts: 469
|
Post by herb on Oct 8, 2016 11:25:56 GMT -5
Hi all,
I have a 16 inch rotary flat lap that I am trying to get used to using. I wanted to get some kind of felt or similar pad to use for the finer grit stages (800 - 1000) to hold the grit better than just the flat metal plate could. I've heard of people using things like outdoor carpeting but the only outdoor carpeting I've ever seen looks pretty course to use with fine polishing grits.
A couple of months ago, I saw somewhere online a magnetic backed felt pad for around $60 which seemed like it would be just what I am looking for, but I apparently didn't bookmark the site and now I can't find it anymore!
As an experiment, I tried some felt from a craft store that I stuck down to the metal pad with some temporary spray adhesive, but the felt was too soft and the geodes that I was trying to polish tore up the felt pretty quickly.
If anyone has ideas or sources for either home made solutions or commercially available solutions, I'd love to hear about them!
Thanks, Herb
|
|
|
Post by woodman on Oct 8, 2016 14:40:03 GMT -5
I use a rotary flat lap with 180 grit silicon carbide grit and water, grit stay on pretty good, it is a balance of not enough water to too much. you want it to make a nice slurry. Then I sand on a high speed bull wheel 100 grit, 200 grit and 400 grit. then polish on a rotary flat polisher using cerium oxide polish. there are not goood short cuts. good luck
|
|
herb
spending too much on rocks
Member since November 2011
Posts: 469
|
Post by herb on Oct 8, 2016 18:24:19 GMT -5
The reason I wanted to try some kind of pad for the higher grits is that I am not seeing much difference in the look of the geodes after 200 grit. At the 400 grit stage, I see areas that look shinier, but the whole geode never gets to that level. I've even marked the areas that look duller with a sharpie marker and ran them through again, and have had the area that I marked look shinier even with the sharpie marks still somewhat visible! Maybe I am not using enough grit? I've never seen any info on how much grit per minute to use is desirable. The lap plate has a uniform gray color from the grit on it, so I don't know if it really is a matter of not enough grit?
I have a dry grinder that Richardson's Ranch sells, but have not used it much. I am not crazy about the idea of that much rock dust in the air even with wearing a mask. Plus, the few times I tried it, I tended to grind long enough to get the geode too hot and ended up with surface cracks.
|
|
|
Post by woodman on Oct 8, 2016 20:36:47 GMT -5
It helps to preheat items that will check or crack under the heat. a good particle mask will get the rock dust if the mask fit as it should. I have never used a Richardsons high speed sander. I like the bull wheel sander. a light touch when sanding is good. don't get in a rush. Pratice on junk material. Friends of mine flat lap with 120 grit and then go to the sander.
|
|
|
Post by Rockoonz on Oct 8, 2016 21:23:08 GMT -5
When I have used high speed sanders I always have at least 3 pieces so I can rotate through them with each grit and set them down to cool as soon as they get warm. The biggest cause of poor polish on flats is missing spots or not sanding/grinding enough on the early stages. That's been my experience anyway.
|
|
|
Post by paulshiroma on Oct 8, 2016 21:36:37 GMT -5
i've got some large pieces of what look like outdoor carpet that came with my lap for the higher stages (1000 AO and above). Mine, however, is one of those vibe laps so the process is slightly different.
|
|
|
Post by tims on Oct 14, 2016 16:19:55 GMT -5
Have you tried leather? I just hand polish but use a 1x1 piece of leather with one side that's very smooth and the other more suede; the suede side seems to hold the polish better. Would be cheap to try and durable.
|
|
scottyh
starting to spend too much on rocks
Member since November 2007
Posts: 181
|
Post by scottyh on Oct 25, 2016 0:11:59 GMT -5
You don't need felt to make the polishing pad,
On my flat lap I make my own polishing pads by gluing woolen carpet (any type will do) to a magnetic backer. From your description of the patchy finish it sounds like the face isn't completely flat. I would suggest spending much more time on the coarse grind (80 grit)in order to make sure the face is really flat.
Cheers Scott
|
|
rxscram
has rocks in the head
Member since August 2011
Posts: 513
|
Post by rxscram on Oct 25, 2016 10:54:51 GMT -5
|
|
herb
spending too much on rocks
Member since November 2011
Posts: 469
|
Post by herb on Oct 29, 2016 16:05:31 GMT -5
Sorry for disappearing everyone! I forgot to check for more replies to my post!
paulshiroma: I'll have to check out the carpet option. I've never looked that carefully at outdoor carpet, but I wonder if the pile will be too high for the higher grits?
tims: I've actually thought about trying to hand polish with leather! I was worried how many hours it would take to polish a geode that way! I guess I should give it a try and see.
scottyh: glueing woolen carpet to a backer is basically what I was thinking about with the felt. I guess I have to hit my local carpet store to see what my options are for outdoor or woolen carpet. Anyone know where I can get a magnetic backer for a 16 inch lap plate? Regarding spending more time on the course grind, the geodes certainly look flat when I am done with them, but maybe I am rushing things. But at the 400 grit stage the area that looks shinier keeps moving around on the geode faces which I don't think would happen if it is an issue of not being flat enough from the courser grit. I notice that when the lap is running, the plate has a slight wobble up and down as it spins. Hard to measure the amount but maybe 2mm of travel. I was worried that maybe the lap is bent but laying a framing level across it in all different directions I don't detect any issues. It could be that the arbor shaft the plate is attached to is not perfectly plumb and that is what I am seeing.
rxscram: Pricey indeed! That would probably be the best option but it is not in the budget right now!
|
|