Machining nickel silver for main frames

[Terry Bendall]

I am trying to profile mill some loco main frames using 0.018 inch half hard sheet and a new 6 mm dia cutter. The speed is fairly fast and a fairly slow feed. This seems to raise a large burr that peels back as I advance the cutter to the line. Has any one any idea how to avoid the problem or can direct me to a source of information that may help.

Thanks very much

Terry Bendall

[John Bateson]

Terry,
In your post you say "some mainframes". Not to distract you from your machine tools but if there are several sets then have you considered chemical milling or etching. I think you can now get an A4 sized page for around £100 - and of course you can sell on any extras. Am doing something similar for a project I am working on.
MRJ 190 is very helpful in this respect.
John

[Russ Elliott]

We had a natter about this at CLAG - the feeling was that the effect you describe was a characteristic of milling/machining nickel-silver. Using a smaller diameter cutter might alleviate the situation a little, but we reckoned you will just have to put up with cleaning off the inevitable burring, and that of course will probably ruin any axlecentre accuracy strategy based on relying on the cutter alone. How much chatter are you getting?

[Terry Bendall]

Thanks for your response Russ and apologies for not responding earlier. Having tried today with a smaller cutter and slower speed the finish was better but not perfect. There was some chatter on the first attempt which was cured to some extend by using double sided tape under the metal as well as the clamping screws. I think that you are right in saying that the process may not be viable for absolute accuracy.

Terry

[Countryman]

Sorry, only just got round to seeing this one! Terry and I have discussed this off-line but others may be interested in my findings. The successful milling of Nickel-Silver depends upon good clamping of the material, cutter size, feed speed and run-out of the milling spindle. I did a test cut on a sheet of 0.022” half hard NS using a 1/16” 2 flute end mill. It cut very well and I can discern no burr whatsoever. I have attached pictures of the result. Spindle speed was about 2800 rpm. If you need to use a larger diameter cutter I would suggest that a solid carbide end mill will give the best results.

Cheers,

Brian

NS1.JPG

NS2.JPG