Milling: creating a smooth end finish in a slot

**Rob Meades** · 11-11-2016

Newbie question: I purchased a High-Z/S-400T milling machine from CNC Step recently for hobby use. As a test, I'm going to mill a maze into a piece of brass plate. As a prototype step I've cut the same pattern into a piece of perspex. The vertical edges have turned out very well, what I'd also like, though, is to somehow smooth the end of the mill to remove the circular scuffs (see picture below). Can anyone suggest a way of doing that?

Click image for larger version.

Name: maze_in_perspex_1_2.jpg
Views: 358
Size: 130.6 KB
ID: 19589

Cutting parameters were: 2 mm two-flute end-mill, tool speed 3,500 RPM, feed rate 4 mm/second, plunge rate 0.3 mm/second and pass depth 0.3 mm (so 10 passes to make the 3 mm depth above).

Rob

**Ger21** · 11-11-2016

Tram the spindle as good as you can.
Use corner rounded end mills.
Get a more rigid machine.

**Rob Meades** · 12-11-2016

Thanks for the swift response.

Corner rounded end mills sounds good. I'm afraid I need to ask what you meant by "tram the spindle" though...?

That cut was made over a 9 hour period with no return to reference, so I think the registration, which I guess is the derivative of rigidity, is pretty good. Anyway, I'm not forking out more than UKP 5k for a machine!

Rob

**Merlin201314** · 12-11-2016

You need to use a one flute end mill, the 2 flute leave more trace on the end of tool. Especially on perspex. the rigidity has nothing to do with that, the walls are clean, so no vibrations.... 3500 rpm for a 2mm flute and 4mm feed rate is to low, 8000 rpm and up is 🆗

Sended by my tapatalk

**Rob Meades** · 12-11-2016

Ah, good information, this is the kind of thing I will learn by experience I expect. I've been searching on the web for something that will tell me the recommended tool-speed/feed-rate/pass-depth for a given material/tool-diameter/number-of-flutes (all in metric please!). Is there such a thing? I end up doing some part of the calculation manually when it seems trivial to create a proper calculator for it.

**Neale** · 12-11-2016

There are tools like HSMadvisor and G-Wizard, which give you a free trial and then you pay. I think that there might be some free online tools as well, but I haven't used them.