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Author Topic: Speed for cast acrylic  (Read 6713 times)

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Speed for cast acrylic
« on: September 11, 2010, 02:35:16 PM »
HI I am new to CNC so some of the terms are a bit strange to me.
Whats speeds am I supposed to use for cutting cast acrylic sheets. I am using 1/8 inch 12x16 sheet and I want to cut some gears out of this material I am using a CNC table that uses a dremel tool to cut with and I have a dremel bit that is numbered 111 and 113  it looks like and end mill bit I used to use about 20 years ago but it is about 1mm in diameter with cutting edges that run vertically from the tip to end of the cutting surface is about 1/4 inch this is all for the 111 the 113 is slight larger in diameter. I need something this small due to the fact that I will be making like I said gears with many teeth and not lot of circumference an example is 41 teeth and 1 1/2 inch diameter gear. I have experimented with the default setting and it seems to melt the acrylic I tried making .04167 depth cuts, 1/3 of the material, in my test. The cut material comes off in little molten globules, the finished cut seems to look OK all I tested so far was a circle but the edges looked, again, melted. I would prefer a simple dry edge cut powdery if that is possbile. I know there is the bit speed which is one of 10 settings on the dremel tool. and then there is the table speed. I was using the  fasted bit speed but the default mach 3 table speed which seemed a bit slow.

Also what do you think it will be for 1/8 to 1/4 balsa and plywood (for RC PLANES)
Jeff

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Re: Speed for cast acrylic
« Reply #1 on: September 11, 2010, 07:59:28 PM »
Afraid I only work with metals so cant be of help but hopefully some of the router guys will be able to give you some pointers.
Welcome to the forum though :)

Hood

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Re: Speed for cast acrylic
« Reply #2 on: September 11, 2010, 08:02:29 PM »
Just did a quick google and this came up, it may help
http://www.plasticsmag.com/ta.asp?aid=2332

Hood
Re: Speed for cast acrylic
« Reply #3 on: September 13, 2010, 08:46:01 PM »
when turning cast acrylic 18mm rod, i keep the revs down to around 600rpm and use fabreze as a coolant. So i would imagine take it easy is the order of the day.
Re: Speed for cast acrylic
« Reply #4 on: September 15, 2010, 05:12:09 AM »
Hey Jeff,

Check the following links:

http://www.onsrud.com/xdoc/FeedSpeeds

http://www.onsrud.com/xdoc/ChipHardPlastic

http://www.onsrud.com/xdoc/ChipSoftPlastic

These numbers are obviously for their bits, but it still may help. Honestly, I don't know if acrylic falls into the hard or soft plastic category, so hopefully someone else will speak up. You may also want to look into getting bits designed for cutting acrylic. Onsrud and Precise Bits are two I know of.

If you're seeing melting, then you need to either slow your rpm's or increase your feed rate. On my machine I set up a small test where I cut a straight line at the desired depth a few inches long. Check the results and then adjust your settings as needed and test again. I think you need to be prepared to waste a little material to determine the most optimal settings for your machine (that is unless someone here can give you numbers from their experience). I've also broken a couple small bits in testing!  :(  Stings, but I consider it the cost of learning.

Once you've dialed in your settings a little, try cutting a few circles and see how they come out. That should tell you real quick how those settings will work. If your settings aren't right, the machine could lose steps and your cuts/parts will not be accurate. If that happens, then back off the feed rate some.

All that applies for any material really, so with your balsa and plywood, run the same tests to determine the best settings for your machine. And make notes for each bit you test in case your ever need to reconfigure your machine or you lose your config somehow.

I'm no expert myself and all this is from my own experience in learning how to cut materials on my machine, so don't take this a gospel, but I hope that helps!  :)

Dave