Question Newly build SC420V2 keeps killing endmills acrylic

Hi Guys,

I've been breaking my head with my recent start with the SC420 machine. I think that the tuning is pretty good now reaching an accuracy of about 0.04 tot 0.06mm marging in the cutted parts. The only thing that I'm not sure of, is the 2.07mm cut with a 2.00mm endmill.

I'm trying to get some stuff made with 3mm acrylic sheet material, and untill now I killed 5 bits which at random points get stuck in the material and break . I'm using a HF-500 spindle with both single and dual flute endmills and tried 2 different speed settings ; 5mm/s feedrate and the last try yesterday slowing it down to 3mm/s with a cut depth of 0.8mm.

The machine sounds like it's struggling with the side movements in the X-Axis about halfway the length motion whilst cutting. The speed I'm cutting with is 12.000rpm and also tried 14.000rpm. I've installed the suction adapter to clear the path from chips, but maybe there is to much heat build-up? One side of the cutt looks very nice, the other side looks like the cutter is been scraping the material to much and looks like a wobble on the side parts.

Hope that someone can help me out with my search, as said before this is completly new for me as I only have experiance with 3D printing. I would really like to master this craft

All help is much respected!

Hi

I read somewhere on this forum that when milling acrylic to use a slow speed (6000rpm?) and cool with water. Maybe cutting under water would be better still?

Not tried machining plastics myself, so this is only hearsay, but it sounds good common sense.

Peter

Miiling any plastic material like acryl is the hardest thing (with exception of metal...).

The key is down with rpm (5000 - 6000)... down with cut deep, maybe 0,25mm for firts tests and up with feedrate!
The material must be carved. In case of high spindle speed and low feedrate the material will heat up in extrem short time. So in addition use some drops of water + dish liquid.

Good luck!

Thanks for the comments guys! I've also spoke with Rory from stoneycnc by phone a good hour ago and he adviced me to turn up the feedrate speed to around 15-20mm/s and also keep up the spindle speed at 16.000rpm because the HF-Spindle has his torque curve at high rpm's.

Gonna give it a shot tonight and keep you posted on the proces!

Hi,

thanks for feedback! I'm interested in the results. Regarding the feed-rate...yes I think that was the speed range I also used but any rpm > 10.000 were unsuccessfull. We will see...

There is a lot of advice on the internet regarding routing acrylic because it is a popular material to cut. The key is avoid heat build up which melts the material with the risk of it reforming and clogging the bit.

www.plasticsmag.com/routing.asp?fIssue=Jan/Feb-07&aid=4539



www.instructables.com/id/Cutting-Acrylic-With-Your-Industrial-CNC-Router/

I haven't tried it yet but also plan to cut 3 mm acrylic sheet. GWizard feeds and speeds calculator recommended a high spindle speed and low feed rates which is the opposite of internet advice.

Feed and plunge rates in GWizard depend on what quality of cut you select on a slider bar from 100% fine/0% rough to 0% fine/100% rough. At 90% fine/10% aggressive (what I've been using for wood) it recommends a feed rate of around 280 mm/min and a plunge rate of around 140 mm/min for a 3 mm two flute carbide end mill for fine cut. This rises to about 2200 mm/min feed and 1100 mm/min plunge for 10% fine/90% aggressive. These increase only a little with a 6 mm bit.

I would stick with the advice to remove 0.25 mm at a time.

One good tip I picked up was to freeze the acrylic sheet before cutting.

Doug