Working with Invar metal

What precautions should be taken when working with invar low expansion
metal. I am told that it is a controlled metal as it is toxic under some
circumstances. Can it safely be machined and ground?
Reply to
Ed Majden
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It doesn't look any more dangerous than many other metals. See
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's/invar.htm Randy
Reply to
R. O'Brian
I have a couple of old books on vacuum tube design and I don't recall seeing any specific warnings on the subject. OTOH, those old guys didn't really worry about that stuff as much as we do.
If it were me, I'd not worry unless I was grinding it. In that case, I'd wear a respirator while grinding and cleaning up.
Reply to
Jim Stewart
Ed,
Everything has an MSDS these days. By these standards, aluminum is much more hazardous.
Invar is just a nickel steel alloy.
Mark
Reply to
MM
Hello Ed:
I'm unsure as to the circumstances under which it might be toxic. My copy of "Amateur Telescope Making" says that "Invar, for example is an alloy of 64% steel and 36% nickel...". The same composition is found at on the web MatLab, with a few minor alloying elements.
Stainless steel is an alloy of iron, nickel, and chromium. Can't see how Invar could be toxic if stainless isn't. If someone is claiming toxicity, you may want to ask for a hard reference.
Regards -- Terry
Reply to
prfesser
Nickel is the new "asbestos".
When you buy stainless TIG rod in California you have to pay an environmental impact fee because of the "hazard" of chromium and nickel.
The only problem I ever had working with Invar was that when machining it on a lathe I could not get a smooth finish on it with a cutting tool. It had to be sanded to smooth it. The stuff vibrates like crazy.
Reply to
Ernie Leimkuhler
I'd be weary of making such a generalization, based only on the components of the material (an organic chemist would have a heart attack).
I do like the idea of asking for a reference, however. I'm sure one could find this info in about 120sec. looking in the yellow pages and then calling a steel supplier.
Regards,
Robin
Reply to
Robin S.
in article snipped-for-privacy@g47g2000cwa.googlegroups.com, snipped-for-privacy@hotmail.com at snipped-for-privacy@hotmail.com wrote on 9/19/05 17:01:
Terry: I didn't think it was toxic either until I ran across this site:
Ed
Reply to
Ed Majden
I tried to get that web page up and failed. Will try again, but I too can't see where Invar would be anywhere near as dangerous as Beryllium. Agree I would not want to ingest any.
On the web site ( just not the right page ) it specifies Invar as a Controled Expansion Metal. I think the Controled goes with the Expansion, not meaning Controled as in tracked hazardous material. I bought a few lbs of Invar Welding rod at Boeing Surplus so Boeing apparently does not see it is especially hazardous.
Dan
Ed Majden wrote:
Reply to
dcaster
Ask over in alt.horology. (watchmaking) Some of those guys work with the stuff daily and would know of any health risks.
Reply to
B.B.
in article snipped-for-privacy@g47g2000cwa.googlegroups.com, snipped-for-privacy@krl.org at snipped-for-privacy@krl.org wrote on 9/20/05 8:26:
If you type Invar in the "search block" on the above site you will go to their product page. There is a Box with an "X" in it. On the left, click on "hazard information" and it explains what these symbols represent. Boy, this stuff is sure expensive! I think I will try something else first. Still have to figure out how to machine an accurate 12 inch radius convex surface for the film pressure plate. I was going to grind it as one would making a lens! Everything has to be precise, as you want it to focus at the same place the standard smaller 35 mm holder does. The distance from the primary mirror and the film holder is kept constant by an invar cage, like the one shown in ATM Book Two/Three. Too bad the focus is not concave, as that would be easy to make with a simple radius bar tool holder. With a convex the pivot point must be in front of the head stock which makes this a more complex task! Ed
Reply to
Ed Majden
Don't grind and inhale your stainless eating utensils either...
Reply to
cs_posting
Thanks I found it. Kind of a standard do not eat this warning. Take a look at Berylium for contrast. Also note that Stainless Steel has the same warning as Invar.
You might want to consider using carbon composite as an alternative. Not sure where you would get some. But it has a very low expansion coef. Slightly negative.
Dan
Reply to
dcaster
Any shop with a CNC lathe can cut the convex side of the disk for you. Just out of curiosity, why does the film holder have to be made from invar? You could make it from a Pyrex blank and grind the curve using standard ATM techniques. Or buy a fused silica PCX lens from Edmund for $50 and avoid 90% of the work.
I'm wondering too if expansion in the film holder has much of an affect on focus. The spacing between the primary and the film holder is certainly critical, and I've seen Schmidt designs with invar rods as spacers. But dimension changes in the film holder due to temperature will be much smaller because the change is proportional to size, and the length of the holder is only a fraction of the length of the spacer rods.
Ed Majden wrote:
Reply to
Tim Killian

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