Aussie Lapidary Forum
LAPIDARY => Gemstone Faceting => Topic started by: MakkyBrown on July 30, 2021, 08:55:52 PM
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I went shopping today and purchased some pewter. Got a bit over 1.75kg for the grand total of $12.30 which is not bad considering the tin spot price is getting close to $50aus/kg and would be a good bit more to buy locally.
I have two trpes. Four piece are from reputable Asian manufacturers and would be 97% tin, 1.5% antimony, 1.5% copper. They are newer and slightly less tarnished than the other two pieces. The other two pieces are made in Melbourne and say super fine lead free pewter, they would be older than the Asain pewter. I am not sure of their tin content but they are not that tarnish compare to some other pewter I looked at today so I suspect the tin content is still quite high.
The plan is to melt it all and put a 3-5mm layer onto some old copper laps I have and don't use. :) Hopefully I have enough for 3 laps.
CheersMB
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They are great for polishing Makky! One of our members melted down pewter some years ago and produced some pure, all pewter 6 inch laps. They are thick enough for re facing if they spoon and work really well as polishing laps, I use one with white cerium oxide and it works really well on quartz. I have another with 50,000 diamond for harder stones. I do have a spare, which I haven't used yet.
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That's the plan Bucket, I need an oxide lap so I'll be making one hopefully later today using the 97% tin pewter. I wanted to try a darkside but they are out of stock at aussiesapphire so I'll go tin. Just ran a cut over my copper laps to clean them up, gee 600grit on copper is a bugger to machine ::)
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Hope you have a good cutter and grinder to resharpen your tooling
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I kept pulling the carbine tip and sharpening on my cabbing machine. I made two laps, first one looks better, might melt the second one again. Will machine tomorrow and have a look.
MB
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Since you know a bit about molds MB, what would you recommend for coating a copper concave cutter mandrel with some metal I'm going to cut off an old BATT lap.
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Here is one done. Probably the flatest lap I own. Made up a large backer plate to bolt the laps to. Gee my 3 jaw chuck is good, face run out on the 6inch lap face and backer plate only about 0.0024mm. It hardly moves the needle on the gauge. Lap is about 11mm thick , should be lots of tin thickness for machining in the future.Bit of a pain machining the backs as I can only hold 125mm on my lathe.
MB
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I am not really a mold expert. I was going to use steel to make mine, but that is down the to do list quite a bit.If your mandrels are of copper and close to size you might just get away with tinning them. Perhaps tin them on a rotisserie to build an even thickness then machine flat in the lathe or grind flat/round on your faceting machine
MB
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Had a bit of a laugh when I read you're not a mold expert, the guy from the club that mad them found an old saucepan that was just over 6 inches in diameter and poured the molten pweter into that, then milled it to the correct size, he used to do them while he was at the club!
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I think I've taken the process to the next level bucket ;) . Mold = hose clamp(conveniently 12.7mm wide) around the copper lap and pour in the pewter. Probably easier in one piece. Now to find some more pewter to make an 8inch or maybe 9inch split lap.
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That worked really well! Looks to be well-bonded to the copper base. I haven't tried cerium on tin for polishing quartz, will be interested to hear about the results.
Now Makky, if you can just come up with a way of also doing sintered bronze diamond disks in your workshop...
RC
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Rough Creations, for the Cerium and Tin for Quartz, head to your office/art supply place and pick up a sheet of tracing film. It's not paper but a sort of plastic film, very tough stuff, impossible to tear.
Cut disks.
To get it to stick to your master lap a small drop of sewing machine oil on the lap will stick it down. To use the oxide polish mix a very thin mixture in a dropper bottle and just drop the occasional drop on as you go.
These are good and cheap and if you get any contamination throw it out and fit a new disk. One sheet will make dozens of disposable polishing disks.
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Rough Creations, for the Cerium and Tin for Quartz, head to your office/art supply place and pick up a sheet of tracing film. It's not paper but a sort of plastic film, very tough stuff, impossible to tear.
Cut disks.
To get it to stick to your master lap a small drop of sewing machine oil on the lap will stick it down. To use the oxide polish mix a very thin mixture in a dropper bottle and just drop the occasional drop on as you go.
These are good and cheap and if you get any contamination throw it out and fit a new disk. One sheet will make dozens of disposable polishing disks.
Thanks, that's a great idea for disposable laps. I do regularly polish quartz successfully with a Darkside lap and cerium, it's just that I have never tried cerium on tin, guess I have never needed to as the plastic composite Darkside lap does the trick. I do have a Battlap that I could try one day with cerium oxide, just out of interest, but I have reserved it for use with diamond.
RC
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Not having a lot of luck trying to plate the copper mandrels. Tried putting the mandrel shaft in a pistol drill, setting the speed to a good balance between gravity and centrifugal force.
Worked well, didn’t take much heat to get the mandrel hot enough to be able to melt a stick of batt metal on it and let it cool as it rotated. Looked good, but on the lathe patches of copper were showing through.
Electroplating won’t be any good, as the plating is measured in microns. So, thinking of making an aluminium mold, with the mandrel in the middle. Heat it all up and drop chips of batt metal into it, then turn on the lathe.
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You could mold a cylinder, drill a hole in it and stick brass 1/4 rod in the center of it. Or make mold that has a hole for the center to be held in position. Maybe steel mold and paint with heat resistant paint. I'll be interested in how you go as I'll be doing the same one day.
MB
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When I get this sorted will start a new thread on making mandrels.
Haven’t done any concave cutting since thinking of making a mod to the pushrod that drives the back-and-forth motion of the mandrel. Not going to do very well with my concave entry in this year’s OZ guild comp because of the ruts in the polish. The only way they can be created is at the end of the stroke, so will have the pushrod doing a random stroke.
Still working on ideas about the mold for coating the copper mandrel, one idea is coating the inside of it with alfoil.
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Just tried to make an 8inch, made an aluminum backer. Tin to aluminum adhesion = 0 :P ::) The copper was good. Might be the grade of aluminum or something. So now to find a 200mm saucepan with sharp corners and give that a go. Knowing my luck it will get stuck in the saucepan :) It is going to be a bit weighty about 3kg being all pewter.
MB
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MB, novel use of a hose clamp, I've seen them used for a lot of things, but this is a first. RC, I've used the white cerium oxide on pewter laps most of my time and can say that quartz comes up a treat. Not as good for harder stuff though. I have a darkside as well which does work well, but unfortunately it's got something in it which is causing fine scratches so haven't cleaned it properly yet, it may need refacing.
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I have a darkside as well which does work well, but unfortunately it's got something in it which is causing fine scratches so haven't cleaned it properly yet, it may need refacing.
I occasionally place a clean sheet of 1000 or 1200 wet and dry paper back-side down on a piece of glass if this happens. Lay the Darkside polishing surface on the dampened sandpaper and do some small circular orbits. Any quartz shards or similar are quickly removed, and you can wipe the disk with a clean rag, rinse and continue polishing.
That said, I am enticed to try pewter/tin with cerium just the same.
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Hey RC, what sort of cerium are you using and where did you buy it. I only have the pink stuff and it has some how got coarse crystals in it.
MB
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Frank, Clarry Trevena uses a lump of aluminium with 1/2 inch holes drilled into it and smaller holes drilled in the bottom to hold the shaft around which he is pouring the pewter.
He stands the shafts in the holes and the pours the pewter into the mould and extracts them by twisting the shanks with a peace of multi grips.
His pewter is a specific aluminium alloy bearing metal from a machinists handbook. From memory there are 3 reveries that give different hardness bearings. He uses soft or medium. He made Bob. Boddington a hard one, I am not sure how successful it was. He has the local
Metal supplier make 5kg mixes at a time for him.
PS, he then machines down 3 at a time so they are within 0.01mm diameter of each other as a matched set.
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Makky you could try Aussie Sapphire, the last lot of white cerium I bought was from Shell-Lap in Adelaide and they not longer exist. I think they got rid of a lot of their stuff to Gemcuts in Ballina NSW. If you get really stuck let me know, I may have some to spare as I use very small amounts. I mix it into a milky like liquid and now that the pewter is charged, I only use 3-4 drops usually per stone, depending on the size. Charging was just by use of the lap, started using a reasonable amount of cerium and polishing a bit on the dry side. Now if the lap starts to dry out, I just give it a very light spray of water, just enough to dampen the lap, not wet it, as if you use to much water, it'll wash the cerium off.
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Hey RC, what sort of cerium are you using and where did you buy it. I only have the pink stuff and it has some how got coarse crystals in it.
MB
Yeah, Bucket is on the money with his technique. Seems like cerium is something to be very careful buying and not try to save money by using Ali Express etc. Aussie Sapphire sells the 2 micron white stuff which I use religiously on my smoky. I have used other cerium and I have certainly experienced the occasional 'foreigner' in the powder giving me scratches and heartache. I reckon the Cerium Battstiks would be another option. I have a Zirconium oxide Battstik from AS which is also good on quartz, but seems to be a *lot* slower than cerium oxide.
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Hey Bucket the pot($5 tip shop alloy saucepan) worked great. Thought it was stuck but gave it a few FIRM, last resort, bangs on the bench and out it popped. Much to my amazement ;D . I have split this one for 3k/100k, 195mm diameter, 11.8mm thick and roughly 40mm wide bands.RC order some cerium from AussiesSapphire, also noticed today Ruby Vale is selling the Chinese resin laps we purchased for $200 each.
MB
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Thanks for the info Gordon. Can remember seeing cast aluminium moulds years ago for those who want to make their own fishing sinkers, they were made in two halves.
So, looking at making an aluminium mould out of 25x25 bar which I have plenty of. Cutting it in half length ways, milling the surfaces, join together, then bore it 12.5mm. Bore a 10mm diameter copper bar right through for the shaft to protrude, so I can support it at both ends.
Heat it all up and pour the batt metal in the gap and then turn it to 12mm diameter, should work ok.
Lap looks good MB.
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The new 8inch lap weighs 2.7kg = at least a dozen tankards and goblets. I've pretty much cleaned out all the op shops of cheap pewter in local Hobart area. Going to be awhile before I can make a couple more.
MB
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These laps are becoming addicting. I have made two 8inch ones so far and I am not really wanting to use 6inch polishing laps again. Need to make more. :) Oh and they are polishing perfectly.
The only problem making the 8 inch ones is uneven cooling causing pitting indenting in the center, requiring a few mm to be machine off. But the end result is great. Tested on quartz, sapphire and spinel so far. Faultless polish.They are a lot harder than tin laps.
MB
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I much prefer the 8" laps too. Have you tried cerium oxide with them on quartz?
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Tried it on one of the 6inch ones, works well. But preferring my 8inch 100k and split 3k/100k atm. Need to make a few more 8inch laps :)
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Glad to hear they're working for you Makky, the 8" split sounds like a good thing except for the weight! A bit more lower tech than what you're normally doing though! The three I have are all 6" and quite frankly, for polishing, I wouldn't use anything else.
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Just trying 1200 diamond on a pewter 6inch for fine cutting sapphire, producing a very nice pitting free finish and no deeper scratches or orange peel. :) I think I prefer it to my sintered 800.
MB
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Got this pewter pitcher today, stopped at the local tip shop while passing by. See how it is nice and shiny, and not tarnished. That is due to the high tin content. It is made in Singapore and would be 97% tin. I think this is the best pewter for laps, and perhaps avoid the older pewter that has higher % copper and really old pewter that has lead in it. Paid $8 and it weighs roughly 1.1kg.I think I'm going to put pewter on all my copper laps, in the unlikely event I need a copper lap I can just flip one over and use the back.
Straight tin vs pewter 97%, the pewter is better. Behaves like a pure tin lap but is heaps harder and doesn't round the facet edges as much.
I am thinking of making a triple spit lap 1200/3000/100k for sapphire only. ;D
MB
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Very nice pitcher MB, would have thought you would have kept it to put your XXXX in and make everyone think your posh.
Pewter is probably what BATT laps are made of, as you can buy ingots of the stuff. I use four BATT laps, one 3k, 14k (which I don’t use much), girdle polish 60k and 60k. I have the 60k girdle polish separate because of the 3k contamination I’ve had in the past imbedded in the rough side of the stone.
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Pewter is probably what BATT laps are made of, as you can buy ingots of the stuff.
As per the information provided by Gearloose:
Comparative Hardness of Lap Alloys Hardness (Brinell)
Pure Tin 5.3
63:37 Tin/Lead solder 14
95/5 14
Britannia Pewter 22.5
Sn die cast YC135A 29
BATT™ 32.5
Commercial Rolled Zinc 43
The BA5T alloy is a bit harder again compared to BATT but is quite a bit more expensive.
Cheers Leah
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Thanks Leah, I was trying to post that exact table last night but it glitched :)
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Very nice pitcher MB, would have thought you would have kept it to put your XXXX in and make everyone think your posh.
Pewter is probably what BATT laps are made of, as you can buy ingots of the stuff. I use four BATT laps, one 3k, 14k (which I don’t use much), girdle polish 60k and 60k. I have the 60k girdle polish separate because of the 3k contamination I’ve had in the past imbedded in the rough side of the stone.
Fortunately the pitcher has a small dent or two so I don't too feel guilty melting it, some pieces I have left on op shop shelves as I figure they'll find a better home than me melting them. The pewter laps might be slightly softer than a BATT lap but far closer to a BATT than a straight tin lap.
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For those chemists out there, I scanned my Battlap with a Hand-held XRF unit I had lying around.
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It has only 52% Tin (Sn), 12% Potassium (K), 10.5% Calcium (Ca), no Lead (Pb) or Zinc (Zn) of note, very little Antimony (Sb) 0.8%, a little Bismuth (Bi) 1.5%, Sulphur (S) 1.5%.
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(https://aussielapidaryforum.com/forum/gallery/9/medium_112303-250821092251-97221152.jpeg) (https://aussielapidaryforum.com/forum/index.php?action=gallery;sa=view;id=9723)
It also seems to have Thorium 2.7% (Th), lol. Didn't detect any Copper (Cu) of note, either.
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The balance (Bal), about 20%, is element(s) the unit can't measure, in this case it is probably Magnesium (Mg) or possibly Aluminium (Al).
Mag-Thor... Google that one, guys.
RC (nervously looking for his geiger counter).
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Far to much time (and technology) on your hands, RC!
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Far to much time (and technology) on your hands, RC!
Yeah, you're right, I should be working, any distraction is better!
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Very interesting RC. Looks to be a casting pewter alloy with some other things. Your going to have to do a SG test on it, to see if it is high Mg. I think I'll stick to my pewter laps without extra additives.2.7%Th is a lot, do XRF machine false positive ?
MB
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Could contain calcium silicide powder, seems readily available.
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2.7%Th is a lot, do XRF machine false positive ?
MB
Well, false positives are possible, if it was a rock that I came across in the field I would be sending it off to the lab for a proper determination. The hand-held XRF units are mainly suited to screening of samples, as they only test a very small area each reading. In a rock with many minerals, you have to be aware that many readings must be taken in different spots, it is even more preferable to crush/grind the sample to make it homogeneous. I do remember a few years ago getting repeated high-tungsten readings in some drill core with the XRF, in areas where sphalerite crystals were also present. The high tungsten values were not reproduced in the lab results.
RC