blackout5783
starting to spend too much on rocks
Member since November 2011
Posts: 248
|
Post by blackout5783 on May 31, 2014 20:05:12 GMT -5
So I've tried a couple ways of sanding and polishing flat surfaces with limited success.
Vibrating lap - total failure, plus I'm apparently not patient enough to deal with one of these
Wet handheld polisher - (like the type to finish stone counter tops) moderate success, but I royally screwed up an obsidian candleholder with this.
So I'm looking at other options. I know I could go the flat lap route like an Ameritool machine. My concern with a flat lap is the size. If there's a center hole, you lose half of the work area. And even without one, isn't it difficult to do anything larger than the lap itself? I'm asking because I would like to be able to do bookend type stuff as well. That would mean at least a 12" lap, and those get pricey fast.
My other thought was a wet belt sander like Covington makes. Has anyone had any experience with one of these? I'm hesitant because I used an expando for cabbing a while ago and really didn't like it. But I was using silicon carbide belts and if I tried the belt sander I would use diamond belts.
If anyone has used either the flat lap or a wet belt sander for big stuff, I'd appreciate any advice you have. Or if anyone uses something else chime in too!
|
|
kradz89
starting to spend too much on rocks
Member since May 2014
Posts: 114
|
Post by kradz89 on May 31, 2014 22:22:10 GMT -5
I don't have any advice, but I am curious too! I don't have the tools to make true cabs right now, so I am starting by working on my cutting and polishing skills by making slabs and little flat pieces (not too successfully, I might add!)
|
|
|
Post by roy on Jun 1, 2014 0:11:52 GMT -5
you wold have to use a flat lap to do big ones in order to polish you would have to have the surface flat or you will have scraches in the center the other way is conture polishing and the other one you gave up on ! i would also say the trying to polish ob shouldnt be the deciding factor i can get that stuff to polish up to good either!
|
|
rykk
spending too much on rocks
Member since September 2011
Posts: 428
|
Post by rykk on Jun 1, 2014 2:45:51 GMT -5
I'm surprised you couldn't get a flat slab with a jiggle pan (vibrating lap). Typically, a vibe lap is the only good way to get a flat slab. Large slabs can be a bit more difficult in the center than small ones. Here's some tips on getting big ones flat:
1) Use 60/90 grit. I've tried 80 grit and it stinks at grinding compared to 60/90. Wastes a LOT of time. Add maybe 3 more tbsp of 60/90 a few hours into the grind and run for at least 15 hours.
2) Make sure to bevel the edges of the slab all the way around. The bigger the slab, the more you may have to bevel. This allows grit to migrate in to the center of the slab better. Maybe pick the slab up every few hours and set it down again to let fresh grit to the middle. Don't know if this last bit really helps but I do it anyhow.
3) Make sure to place adequate weight on top of the slab. A big slab needs a lot of weight - 3-4lbs+ sometimes. Lead ingots like the Lyman mold kinds that bullet casters/reloaders and folks who cast fishing weights are ideal. There's a lot on Ebay.
4) Make sure that the rocks/slabs are circling around the pan at a rate that's not super slow. This assures that the slabs are constantly getting newer grit under them. If they sit too long in one place, the grit under them wears down and can become too fine to make much of a dent in an un-flat or heavily saw marked rock. To get them rotating well, you have to make sure to have plenty of slabs in the pan. A rule of thumb I read somewhere was "fill the pan totally, then remove one or two rocks". At the very beginning, all of the slabs will jitter around chaotically like someone walking on marbles but the rotation should start fairly soon. Sometimes you have to play "traffic cop" and reposition the rocks to get good rotation. There can be some rocks that don't want to play nice and try to go in the opposite direction of the others by spinning the other way. Most times, all you have to do is rotate that rock 180 degrees and set it back in and the merry-go-round begins. Anyhow, hope some of this helps - C-ya, Rick
|
|
|
Post by jakesrocks on Jun 1, 2014 4:42:31 GMT -5
On a vibrating lap, if your slabs are too light they'll bounce around and never get flat. Try adding weight to your slabs. Dop a heavy rock to the center of your slab for extra weight. Heavy fishing sinkers will work too. After hours of searching I found a guy on ebay selling 1/4 & 1/2 pound lead ingots which work perfectly.
If you can find one, the old larger rotating laps work great,and are much faster than a vibrating lap. The drawback is they are hands on. You have to hold the slab and move it around on the lap plate. Some were made without the center hole, and you can use the whole plate.
If the cut off the saw on your slabs is flat to begin with, you can leave the 60/90 grit stage out and go straight to 220 grit. Just grind the little break out nub off the slab. It also helps to grind a very slight bevel around the outer edge of your slab. A flat slab on a flat lap will push the grit away from the slab. The slight bevel will allow grit to get between the slab and lap plate. You don't have to grind very much. Just enough to break the sharp edge of the slab.
|
|
blackout5783
starting to spend too much on rocks
Member since November 2011
Posts: 248
|
Post by blackout5783 on Jun 1, 2014 10:59:04 GMT -5
If you can find one, the old larger rotating laps work great,and are much faster than a vibrating lap. The drawback is they are hands on. You have to hold the slab and move it around on the lap plate. Some were made without the center hole, and you can use the whole plate. I wish I could find one that was big enough for what I wanted to use it for and not have to spend a fortune. A new 12" runs around $1500 from what I've seen, and that doesn't include any pads or laps. A full set essentially doubles the price.
|
|
|
Post by jakesrocks on Jun 1, 2014 11:39:36 GMT -5
Old flat laps show up on ebay from time to time. Usually go for pretty good prices. It's the shipping weight that's the killer. A 20" flat laap without center hole would probable be ideal for what you're doing.
|
|
QuailRiver
fully equipped rock polisher
Member since May 2008
Posts: 1,635
|
Post by QuailRiver on Jun 1, 2014 15:07:48 GMT -5
|
|
rykk
spending too much on rocks
Member since September 2011
Posts: 428
|
Post by rykk on Jun 1, 2014 17:30:10 GMT -5
From what I've read in the past and some experience with a spinning lap, it is very difficult to get the center of a good sized slab to polish with one of those. It's one of the main reasons I bought a vibe lap in the first place. It has to do with the fact that, as you move out from the center, the effective speed of the disk goes up in terms of not rpm but linear inches per second. You can rotate the slab but the the center is always in the middle area of the disk and that's why it's a problem. At least that's what I've read more than once here and have heard on other forums. C-ya, Rick
|
|
blackout5783
starting to spend too much on rocks
Member since November 2011
Posts: 248
|
Post by blackout5783 on Jun 1, 2014 20:33:01 GMT -5
From what I've read in the past and some experience with a spinning lap, it is very difficult to get the center of a good sized slab to polish with one of those. It's one of the main reasons I bought a vibe lap in the first place. It has to do with the fact that, as you move out from the center, the effective speed of the disk goes up in terms of not rpm but linear inches per second. You can rotate the slab but the the center is always in the middle area of the disk and that's why it's a problem. At least that's what I've read more than once here and have heard on other forums. C-ya, Rick I see how that makes sense, but would it matter less if you were using a larger lap and had room to move away from the center? Not that I could afford a 24" or so if I thought a 12" was expensive. Kind of makes me like the look of those wet belt sanders then. All points have the same linear speed.
|
|
Deleted
Deleted Member
Member since January 1970
Posts: 0
|
Post by Deleted on Jun 1, 2014 21:01:19 GMT -5
Wet handheld polisher - (like the type to finish stone counter tops) moderate success, but I royally screwed up an obsidian candleholder with this. Totally screwed up, sounds like "ruined" to me. No way you ruined it. So, I ask, what was screwed up about it? I have experience with that sort of tool. Perhaps I can help. Sounds easy enough to restore that piece in just a few minutes.
|
|
|
Post by Rockoonz on Jun 1, 2014 23:26:00 GMT -5
|
|
rykk
spending too much on rocks
Member since September 2011
Posts: 428
|
Post by rykk on Jun 1, 2014 23:43:07 GMT -5
I'm not sure if the size of the lap disk makes a difference or not. It would depend on how big the slab is, I reckon.
I have a Covington belt sander and haven't have much success with big slabs with it. I'm talking *big* slabs over 5-6 inches in any dimension. The belt is only 3" wide, so there's always a good bit of the slab hanging out when you grind. The sander was given to me used and didn't have a flat piece of metal backing the belt between the two rollers so I made one, myself, for it. I found that having the flat hard against the back of the belt (Yes, I rounded the edge of the metal) made a nasty whacking sound every time the joint in the belt went past. Seemed like a not so good thing, so I moved it away a little. The problem now is that, when you press a slab onto the flat, the two rollers are at a slightly higher level and you end up sanding just the upper and lower edges of the slab. It makes the working part of the belt into sort of a flattened "V". The two rollers are bare metal with no rubber sleeve on them, so there's always a lot of banging on the slab when I try to grind there. It grinds well but I've had more than a few of my best, most prized slabs break in half along unseen fracture lines from all the rattling while trying to bevel the edges. I don't think the Covington is supposed to have any sort of rubber, "expando" type of sleeve on the rollers because I don't see one in their pix. Hopefully, someone reading this knows about belt sanders and will spot if I'm wrong. IMO, most all lapidary grinding equipment is geared towards small to very small workpieces like cabs. Except for slab saws, big polishing heads, and the larger vibratory laps. BTW - I've found that, on very long slabs, it helps to arrange the others in the pan so that the long one has no choice but to rotate sideways around the pan rather than lengthwise. Makes for a shorter distance between the fresh grit and the center of the slab. C-ya, Rick
|
|
|
Post by jakesrocks on Jun 2, 2014 8:10:27 GMT -5
Rick, I found an old Covington belt sander at an estate sale. The previous owner had covered the rollers with pieces of an old bicycle inner tube. I haven't used the sander very much, but the covered rollers seems to work real good.
Lapidary belt sanders are one of those nice to have type tools, but aren't used very much. For the most part they just take up space on the bench.
|
|
rykk
spending too much on rocks
Member since September 2011
Posts: 428
|
Post by rykk on Jun 5, 2014 0:57:04 GMT -5
Yeah, I tried gluing some rubber sheet on the rollers when I first got it. The rubber was good and dense and about 1/8" thick. It flung off pretty quickly. I used contact cement. Might be because the stuff was heavier than an inner tube. And maybe should have let the glue set up more than 24 hours... I hates waitin' fer gloo ta dry! C-ya, Rick
|
|