We recently had a question about milling fine patterns in 92% copper, 8% nickel coin. The user would like to mill through to the other side of the coin and create a pattern with finely detailed edges.
Yes, this definitely can be done. You generally are able to mill at a
max of 1Xs the diameter of the tool. So it is a trade-off between the diameter
you will need for the finer details of your design and the number of passes you
will need to make to go through the material. The micro end mills are available
with lengths of cut that are 1.5Xs and 3Xs the diameter. The type of mill you
use would depend on the diameter you choose and what operation. The more flute
the better your finish will be and the more cutting action per rotation of the
tool you will get, however if the material is mostly copper, that may clog the
flutes and require a 2 flute for the roughing portion of the operation.
Ideally, if you can find a diameter that will allow you to do the whole pattern
without a tool change, that would be nice, however you may have better results
doing it in two steps. Maybe use a larger 2-flute tool to allow a complete cut-through
to the other side, and then rough out the bulk of the pattern. Then you could
follow-up with a smaller diameter 4 flute tool that will allow you to finish
the detail. If you do the whole thing with a very small tool, it may take
awhile. You want to keep the tool/flutes as short as possible to improve
rigidity, however you need some room for chip evacuation. As with everything in
the milling process, it is a trade-off between a few different variables.
As far as the speeds and feeds, we have all of that information
available at the links below. An easy way to do it is to plug the values from
the chart into the online calculator. One variable you won't know is the
limitations of the spindle speed of the machine you decide to purchase. Which
brings me to my next point.
We don't really have a recommendation for a particular machine, but I
know there is a huge range of options out there. I believe you will want to run
these smaller tools run at higher RPMs, so that might be a factor. If you plug the
variables from the speed and feed chart into the calculator, that will fill in
a spindle speed you could use as a reference. One of the brands that has been
around for awhile for smaller work like this is Sherline. http://www.sherline.com/
Please see the point-by-point answers per your list below. Also, here is
the link to the speed and feed chart and calculator. Just let me know how else
we can help you move forward with your project.
Thank you for
Speeds & Feeds: http://www.kodiakcuttingtools.com/CarbideEndMillSpeedsAndFeeds.asp
Online Milling Speed & Feed Calculator: