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Turning Speeds and Angles for Platinum


#1

Greetings Orchid,

I have started a new venture and would like to know if anyone has
experience with turning Plat. And 18 kt yellow.

I have prepped my tools well with a good finish using the standard
angles prescribed for harder metals but am not getting a good clean
cut particularly on Plat. I know Plat is a much “muddier” metal but I
think I should at least get a clean cut and then I could hand finish.

I’m not sure as to the problem being my cutting angles or my turning
speeds or both.

I was hoping the good people on Orchid might have some experience
with this.

Welcome home to the Good Doctor H.

Gassho
Karl


#2

Hi, Karl. This was asked once before, that I recall, but it was
silver. I’m not hugely experienced, but I do know the answer. I don’t
know about brass, but the other non-ferrous metals need an extreme
angle on the cutting edge. For inserts, look at aluminum cutting
inserts - *CGT. The second letter is the clearance angle, “C” being 7
degrees, which is quite a lot. Where your typical insert has a fairly
subdued edge, these have what looks like a knife sticking up - if you
grind your own just give it a higher clearance angle. Speeds I can’t
comment on in any real way, but I haven’t found any troubles with
typical speeds for the workpiece - it’s that angle that solves it -
and lubricant is highly useful, too. I’d suggest looking at aluminum
cutting inserts - I found them at www.travers.com, but it was a pdf,
which is difficult to link to, and either use them or use them as a
guide for your tool making.

http://www.donivanandmaggiora.com


#3

Platinum may be the most difficult material I have machined. It is
sticky and very difficult to shear a chip away from the surface of
the metal. With steel tools it wants to weld to the cutting edge when
you are cutting and this rapidly ruins the cutting edge and the tool
starts to drag and tear the metal rather than slice it. Carbide is
somewhat better but still not the best answer, you will get better
cutting action and less welding to the tool edge with carbide but it
is not as sharp an edge as steel tools so the surface is still not
wonderful. The best tools for cutting platinum are PCD poly-
crystalline diamond or diamond tipped. They will give a good, bright
cut but cost quite a bit and are easy to damage and still don’t get
great working life on platinum but the cut quality is quite good.

Jim

James Binnion
@James_Binnion
James Binnion Metal Arts


360-756-6550


#4
I have prepped my tools well with a good finish using the standard
angles prescribed for harder metals 

As so often happens, you hit the send button and go off and say,
“Wait a minute…”. What I said in the other post of this was
mostly correct, except for the insert designation is iffy. I have a
good stock of them, and have to refresh my memory whenever I get into
the numbers. For aluminum, the fourth letter is “T”, which is an
extreme rake, which also gives a very sharp edge. The point being
that aluminum tooling has a steep, sharp edge - look at milling
cutters, too, to see it. A good place for all of this is
http://www.carbidedepot.com Both for buying and knowlege. On the
right side is a link to “technical resources”, also application
support. Lot of good stuff there…

http://www.donivanandmaggiora.com


#5

Karl,

Platinum is indeed very ‘sticky’ or gummy - actually the material
sticks to a cutting edge. Machining characteristics of a material
come from it’s physical properties. Pt is dense and is alloyed with
other elements that effect it’s machinability.

Begin by considering the ‘system’ in which you are working. These
are factors that are interrelated.

  1. the material. What alloy are you cutting? Pt/Co - Pt/Ru or Pt/Ir?
    They differ in their machining characteristics.

  2. your machine tool. Is it rigid or loose? Higher HP or lower?
    Higher speed capable or lower? Are you removing large volumes of
    material or not (not is more likely in Pt/Au!!! so look for finishing
    speeds and feeds)

  3. the cutting tool material and geometry. High speed steel cutting
    tools generally don’t work well with platinum. You might find some
    success with a TiN (gold) coated HSS if your machine is low HP and
    you care running at lower speeds / feeds. If you are using carbide
    tools, look for machining recommendations for nickel and high nickel
    alloys like Monel and Inconel. Diamond cutting tools certainly work
    best but are very costly.

  4. the coolant. Use water based or vegetable oil based coolants -
    flood or mist depending upon how fast you are pushing your tools.
    Higher cutting speeds generally call for flood coolant.

These factors when considered together should get you to a solution
with the least amount of experimentation on any material. This
article
contains recommendations that are a good starting point.

http://www.espi-metals.com/tech/machiningnickel&alloys.pdf

I hope this helps.
Paul Finelt, CIRM
http://www.finelt.com


#6
Platinum is indeed very 'sticky' or gummy - actually the material
sticks to a cutting 

Paul’s writing aroused some curiosity in me, so I went snooping
around. This is an interesting article - I’ll past more if I find
them. Doesn’t answer the question, but it’s interesting…
http://www.flowcorp.com/waterjet-resources.cfm?id=329

a bit of stuff

Just a paste, not whole article:

Platinum alloyed with cobalt (Pt/Co) will make a very good
casting alloy. It's wet and capable of filling great detail
during lost-wax process casting. 

Platinum alloyed with ruthenium (Pt/Ru) is a good alloy for use
in machining and lathe operations. 

Platinum alloyed with iridium (Pt/Ir) has great features in
fabricating and all-purpose work. 

Finishing.com had a couple of people asking the same questions,
but no answers.. 

Actually diamond cutting, but discusses tooling, plus this site is
the place to look deeper: http://www.pgi-platinum-tech.com/v11n3.html

And finally, the source:
http://www.johnsonmattheyny.com/technical-manual.php

Hope this helps - just sharing my own learning experience…

http://www.donivanandmaggiora.com


#7
The best tools for cutting platinum are PCD poly- crystalline
diamond or diamond tipped. They will give a good, bright cut but
cost quite a bit and are easy to damage and still don't get great
working life on platinum but the cut quality is quite good. 

Might also check into TiB2 coated tooling, a recent article in CNC
magazine (http://www.haascnc.com/CNCMag/PDF/v11i39.pdf) talks about
the comparison vs diamond like coatings when cutting aluminium, but
might fair well with platinum. Not to sure on the availabiltiy of
this as of yet.

I would also recomend using an oil based lubricant to do your
cutting and run pretty high rpms, taking small cuts.

P@
www.patpruitt.com