2 years, 8 months ago-
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This MD&R 30 lap came in a lot. I can’t find information online about it. Does anybody knows it’s composition? It seems harder than plain tin. I was wondering about the lead content and the safety of using one.
Thanks.A fellow member on Gemology Online board wished to have this message relayed to you. Evidently he is not a usfg member and can’t post.
“According to MDR’s “the Book of Gem Cuts (vol. 2), the #30 is type metal, usually composed of tin, lead, and antimony.”I have this volume as well and a old MDR catalog that lists the different laps and in the volume 2 #30 is only listed as “Type” nothing else I see. Strange but true.
But in a catalog it is listed as #30 TYPEMETAL with the following description: aluminum backed, precision machined. An excellent lap for Garnet, Topaz and Zircon using Linde A. A good lap for Tourmaline. Hardness 2.0, shipping wt.2lbs.Also just for further info the #28 is “TIN/TYPEMETAL” which I assume it is a mix of metals and they state as a hardness of 1.8 which I also assume that would mean more lead content giving a slightly lower hardness than the #30.
But then #26 “TIN/LEAD” they state is 50%-50% and a hardness of 2.0.
It appears they had their own hardness scale for the metals, but they did not disclose all the details of the metals.
Maybe possible the gentleman on the GO board knows something more about the MDR laps in the comment “usually composed of tin, lead, and antimony”.
Anyway hope that helps some.Evidently he is not a usfg member and can’t post.
Please tell your friend that he doesn’t need to be a USFG member to participate in the forums. He does have to register on the website. You have to be logged in to reply to or originate posts.
The “friend” is here now! Lost a computer 4 1/2 years ago and didn’t get back until now (other than lurking)
And Al, I still did re-join USFG. Y’all deserve my support.
Thanks you Gregory and your friend for your reply. Old good leaded pewter, it makes sense. This helps a lot. I will avoid using it.
In a way, using your old typemetal lap is a good way to keep it out of the land fill. Just don’t lick it, and especially don’t feed it to children 😉
if it is not contaminated with any coarse grit other than having been used with lindy A i would try it with 50,000 diamond powder at very slow speed it might work great. i just ordered a 6″ cast pure tin disc from a seller of tin on ebay. really rough so i machined one side and bonded it to a master lap then machined the other side true flat. i don’t know the hardness but with my polishing method it works great. i demo’ed it to jeff theesfeld USFG historian and he liked it. the tin cost me $24 and master lap $10 and 30 minutes to do so, $34 for a great working TIN lap. i will say the #30 is a bit harder. the first mistake everyone does is to score the laps. they are machined flat so have very fine grooving great for holding the polishing agent. scoring creates channels to waste the polishing agent and also build up cutting materials and since most run their laps fast these cutting can dry, be pushed back up and cause scratching. having worked at crystalite back in the 70’s i know how to make and machine polishing laps and made the plated laps. gemmakerma@cs.com
Gemmakermz hi. It seems it had an alumina layer crust build on top. I cleaned it but it is giving me trouble with 50,000 diamond so I may turn it to a pre polish one until it meets a lathe. Tin works great so far. Can I ask how you bonded the tin disc on to the master lap.Thanks for the valuable info.
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