Acrylic!!!

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HPGreyling
Posts: 123
Joined: Sat Nov 15, 2014 11:37 am
Location: South Africa

Acrylic!!!

Post by HPGreyling » Fri Dec 05, 2014 6:13 pm

Just thought I got the hang of cnc. Then tried to get a dust shoe cut from acrylic.

Well I tried all the speeds and feeds on the wiki and forum. Some worked relatively ok. Other speeds made my So2 run in its own direction, melt the shavings and got in everywhere.

Ive dismantled my machine now 3 times just cutting 1 piece as the shavings/ cuttings got into the delrin wheels and caused the machine to stutter as these shavings created difficult to remove obstacles in the smallest part of the V.

Decided to do the dust shoe on the scroll saw as I just about had it with acrylic.

WillAdams
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Re: Acrylic!!!

Post by WillAdams » Fri Dec 05, 2014 6:18 pm

Sorry to hear about your difficulties, but glad you had a fall-back option.

Did you keep notes on this?

- what sort of acrylic --- source?
- which endmill and feed / speed combinations were successful?

The wiki isn't going to get better unless people share information.
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HPGreyling
Posts: 123
Joined: Sat Nov 15, 2014 11:37 am
Location: South Africa

Re: Acrylic!!!

Post by HPGreyling » Fri Dec 05, 2014 7:31 pm

I used the 1/8 2 straight flutes for the cuts at different speeds on the quiet spindle.( Still waiting for ordered assortment of bits,) The best speed seemed to be maximum for extruded acrylic and the feed rate 400mm/ min and plunge rate 100 mm/ min. If you have tricky corners slow down your feed to around 380, seemed to me as if the bit then creates the leastamount of bulges in the corners. Step down I tried 1mm but the spindle gets bogged down. (Wanted to cut 6mm )Changed to .8mm with better results. The edges a were smooth.

To note if the shavings land in the cutting groove remove them asap as they harden and trap the bit when it comes around again leading to your bit either going astray or the bit biting deeper than expected.

Good luck with this tricky material

Damin69
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Re: Acrylic!!!

Post by Damin69 » Fri Dec 05, 2014 9:57 pm

Yes acrylic I found flies everywhere. Need to vacuum it as it is cutting very messy.
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LouisV
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Re: Acrylic!!!

Post by LouisV » Fri Dec 05, 2014 10:01 pm

HPGreyling wrote: extruded acrylic
That's the problem. Extruded acrylic is not easy to machine. Stick to cast acrylic, it machines beautifully and is much more forgiving. I'm sorry you had so much trouble, I hope your future cnc projects go better. :)

Caesar S
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Location: Seattle, WA

Re: Acrylic!!!

Post by Caesar S » Sat Dec 06, 2014 2:08 am

Without a dust shoe, well cut a dust shoe first :-) portion the cuts into several small jobs (e.g. a small circle, then a larger circle, vs. both at the same time). This allows you to pause, vacuum chips from rails. While cutting continuously vacuum the chips.

But before even cutting acrylic. Test out the cuts on soft wood first (plywood works fine for me). Once the design works then use the plywood dust shoe to cut the acrylic dust shoe :-)

For info, for Acrylic and Polycarbonate (which is tougher) I use 30,000 rpm, feedrate of 1500 mm / min, plunge rate of 800 mm / min.

My spindle is a 600W router. I have yet to mount my 600W DC spindle, maybe when I finally put my control box together.

HPGreyling
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Location: South Africa

Re: Acrylic!!!

Post by HPGreyling » Sat Dec 06, 2014 5:03 am

Ive done, all you guys are suggesting here. Ive got 2 plywood dust shoes. Its just I cannot see where I cut when putting them on.

I always break my job up i to smaller subtasks. Easier to restart when so ething goes wrong. Istoodby the job and vacuumedbut still smaller pieces seemed to go unnoticed on AWOL and stick to my wheels.

If only extruded is available ......then you get extruded and frustrated

Hopdfully today I will have a dust shoe cut....... on my scroll saw!

HPGreyling
Posts: 123
Joined: Sat Nov 15, 2014 11:37 am
Location: South Africa

Re: Acrylic!!!

Post by HPGreyling » Sat Dec 06, 2014 12:54 pm

OK, finally got it right.

To do before cutting Acrylic:

Cover/ shield your makerslides as best as possible as the biggest issue came from acrylic shavings sticking to the rails and thereby ensures that the gantry will get stuck. I used paper to cover until I can get the proper covers.

Secondly : vacuum as close as possible in the cut directly behind the bit. As the shavings that stay in the cut wil harden and deflect the bit the next time it comes around.

My settings for the larger cuts that gave the best results were: Feed 400mm/min, Plunge 100mm/min. For smaller cuts or more complex cuts I found that if I bring the feedrate down just a tad to 380mm/min and plung rate to 75mm/ min gave the best results.

After the cutting I just sand down any roughness that might occur and polish the piece simply over an open gas flame.

Caesar S
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Re: Acrylic!!!

Post by Caesar S » Sun Dec 07, 2014 5:32 am

FYI Inventables where you buy the ShapeOko also sells material ...

HPGreyling
Posts: 123
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Location: South Africa

Re: Acrylic!!!

Post by HPGreyling » Sun Dec 07, 2014 5:57 am

Ceasar you didnt have a look where I am. South Africa.

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