Milling Advice

[VicParticipant @vic]

I agree with Pete. I get a great finish with a fly cutter.

[JasonBModerator @jasonb]

Actually Dave you can bring a blinted milling cutter back to life by roughly grinding a 45deg chamfer on each corner particularly if it has just been used for shallow facing cuts. This is not painful to the pocket and can simply be done on a basic bench grinder or with acoarse diamond slip.

I suspect what has also helped with Andrews finish is flood coolant to clear the swarf so none getting cought under the cutter and swirled around. A constant power feed also helps give a uniform finish.

The only downside to flycutting (and face mills) is that you want your tram reasonably good to avoid a concave surface

[Robert Atkinson 2Participant @robertatkinson2]

I found this thread interesting as I'm just doing a job that needs a flat surface with a good finish. It is similar to Andrew's application a heatsink for high power semiconductors. This is a aluminium heatsink and as usual with these it is near pure so soft and sticky. It's also used so I have to re-surface it and plug a couple of holes. The original finish was obviously made with a fly cutter. I did consider that approach but my mill is a small high speed model (SX1LP). so not Ideal. I decided to try a 90 degree (two insert) 25mm indexible end / side mill from ARC
https://www.arceurotrade.co.uk/Catalogue/Cutting-Tools/Indexable-Carbide-End-Mills/90-Indexable-Carbide-End-Mills
with APKT 1604 PDFR polished inserts. This has the added advantage that the semiconductor (MOSFET in SOT227B package) will just fit in the width of a single cut.
Had a go today. Using it dry with vacuum chip extraction, 2100 RPM and light cuts. Finsh is pretty good (not up to Andrews standard). It's clearly a milled surface but no roughness detectable by a fingernail .A check with some blue, a flat and one of the devices shows it is flatter than the MOSFET. The critical area of the MOSFET is in good contact with just finger pressure dispite not being perfectly flat. I'll sort out some photos. The holes that needed plugging were tapped M3 so I put plated brass screws in with Loctite 601 retainer. Left it for an hour and just machined the heads off.

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