Poor cut quality

[DMW]

Hi,

I recently picked up a Bungard CCD/2 milling machine, so I am hoping for some professional quality isolation milling.

It came with some unbranded (Just in a unmarked plastic container) 0.2mm 30-degree V-bits, these bits are a delight and cut beautifully at 750mm/min, 60K RPM, they cut a little wide, the total width ends up being about 0.45mm (about double for some reason?)

Now I really want to cut at ~0.2mm width. So I have bought some 0.1mm 30-degree and 10-degree bits, so far I have bought 3 different inexpensive sets of bits. Each time the cut is really really bad, they tend to cut at around ~0.3mm with a really unacceptable finish. Under the microscope the bits dont look any different (to me) from the 0.2mm bits I mentioned above.
I have tried cutting at different speeds, RPM and cut-depth (120mm/min, 450mm/min and 600mm/min, and spindle speeds 30K (minimum) and 60K (maximum) without much improvement.

I have just tried some 0.2mm Chinese 30-degree bits I bought, so in theory the same as the unbranded ones which came with the machine, but again the cut was really bad, so I am guessing its down to the quality of my bits? (Though some had some good reviews on Amazon).

I once read about using cutting oil, I have also just tried to place a small amount of machine oil on the copper area to be milled with no effect.


Can anyone please recommend a supplier of good quality engraving bits for PCB isolation routing (10 to 30-degree) I can get in the UK?

I have attached some pictures of what my cuts have looked like, as you can see all the Chinese stuff is just very wrong!

Many thanks in advance,
Dom

[m_c]

Speeds and feeds are critical to good cuts, especially in copper.

Run the figures through a speeds and feeds calculator to see what you should theoretically be running at (https://fswizard.com/# is good), but you may need to deviate from those somewhat.
A big problem is that you're machining copper, which can be very "gummy" to work with. It doesn't always cut cleanly, and it likes to stick to the cutter.
Speeds and feeds are critical so that you're continually cutting, and not rubbing, but you also have to ensure chips are not sticking to the cutter (a touch of WD40 will work well), and chips are being cleared (just enough air flow to ensure chips are getting blown away from the cutting area is enough).


That's the fundamentals. There is at least one other semi-regular on here who works on such a small scale, so they may be along soon with some tips.

[magicniner]

It's worth reading up on engraving tool geometry as wrong-uns look good if you don't know where to look, this is a fair description -

http://www.pilotltd.net/engraving.htm

- Nick

[DMW]

Hi Thanks for the information, unfortunately i couldn't get any sensible numbers out of pilotltd I dont think its quite the right tool for the job.

Im going to try the Mega Electronics tool £10 each and if not there is a Bantum 0.003" engraving bit on Digikey for £30 each.

I tried these:
https://www.eternaltools.com/carbide-engraving-bits
30 degree 0.1mm, but again very poor cut quality.

Regards
Dom

[Doddy]

Have you not considered straight-shanked end mills?, something like

https://www.shop-apt.co.uk/micro-diameter-end-mills-2-flute-altins-coated-ultra-fine-grain-carbide-60hrc/micro-carbide-end-mill-for-general-use-0-3mm-diameter-2-flute-altins-coated-60hrc.html

These are what I've had the best success with in the past.

[Dave_stoke]

Have a look at Louis belet tools, primarily for watch making, they are fairly expensive but all their tools are polished and the smoother the cutting edge the nicer the finish.
Rainford engineering supply them. They also supply cheaper tools that perform very well too. But I would definitely take a look at Louis belet. Around £48 for a 2mm bit but IMHO you're buying pure quality.

I can't afford any yet but as soon as I can I will definitely be investing.

[Dave_stoke]

Hi Thanks for the information, unfortunately i couldn't get any sensible numbers out of pilotltd I dont think its quite the right tool for the job.

Im going to try the Mega Electronics tool £10 each and if not there is a Bantum 0.003" engraving bit on Digikey for £30 each.

I tried these:
https://www.eternaltools.com/carbide-engraving-bits
30 degree 0.1mm, but again very poor cut quality.

Regards
DomThese are what I have, I'm cutting brass and they die as soon as they touch. Probably me having no experience. But I put a new edge on with diamond disks, I'll be trying again tomorrow with my newly sharpened bits, I have also made sure the edges are bright by finishing on arkansas stone. The best graver finish is one with polished edges. So fingers crossed I edged them right.

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