Cutting 1/16 inch grooves in acrylic

[keith]

There are a LOT of questions on acrylic and I hesitate asking more, but I've searched all the threads and am still looking for some specifics. I have a customer with a 4x8 sheet of acrylic (I'm not sure if it's cast acrylic or what) and wants to cut 1/16 inch wide grooves 1/16 inch deep and some .225 inches deep. He wants to create a slot track for slot cars, so these grooves will go all along the 4x8 sheet. Questions are:

- Should I use a 1/16 cutter for this?
- I plan on multiple depth cuts but is that the best way?
- What speeds and feeds would you suggest?
- Should I use a mister or some other means to cool the tool?
- I've cut acrylic before when doing lithopanes and occasionally had melting issues. I have one chance at this and I don't want to melt anything, so any suggestions would be appreciated.

Thanks!!!

[steve4460]

I think the thing to do is to keep the RPM down and the feed speed up so you don't generate hight tempretures that melt the plastic If your realy want to this job then I would try to run this at 0.8 ips with a stepdown of 0.0468 at 10000 rpm .With a regular straight router bit that only has one cutting edge on it ,and have one of those cooling blowers hooked up.
The thing is that you don't want the plastic to melt during cutting . To figure this one out may take some trial and error .

keep us posted if you figure it out .
I hope this makes sence to you .

Bot on

[stevem]

I would venture to say that .047” is a bit deep for one pass with a .0625” diameter bit. You might want to start with a cut depth of .020” and a spindle speed of 16,000 to avoid bit breakage.

[cnc_works]

I think that it is critical to know whether it is cast or not. Extruded acrylic melts much easier and can be a real pain to cut.

Donn

[keith]

Thanks everyone. I'm even willing to pause every few minutes to help with the cooling, along with spraying coolant on it with a spray gun. I'll see if I can find out what kind of acrylic it is. Thanks everyone!

[ckurak]

Keith,

I am not sure, but from my experience the cooling needs to be constant. Pausing every few minutes will not prevent the melting. I don't cut this often, but I have followed the router around with a manual air nozzle blowing directly on the surface being cut. This has helped.

Also, the type of bit can make a difference. I use Onsrud's bits that are designed for cutting plastic. The shape of the cutting edge and profile make a difference.

Charles

[don]

Hey Keith,
There is a post thread on Vectrics site about Slot Car Tracks. I've machined a couple for a local group here in town out of PVC and 2 out of MDF. Here is the thread with lots of slot track sites and info there. http://vectric.com/forum/viewtopic.php?t=2690&highlight=track

[keith]

Thanks Don...and thanks everyone for the comments. I ran some quick numbers and he's got a 4x8 sheet of PVC that goes for about $700 on mcmaster carr. Man I'd hate to mess up that piece. I'll be shooting it with either a coolant or cold air. I've had trouble finding a 1/16 cutter meant for acrylic so if anyone has any suggestions I'd appreciate it! Thanks again!

[dewey_dog]

Keith try this: https://www.onsrud.com/oc/pdf/Super_o.pdf

[djmcnutt]

Keith,

I would take Timothy's idea. I went to Onsrud for acrylic questions and had great luck with there suggestions.

[keith]

Thanks everyone. I'll give it a shot!

[harold_weber]

Here is a photo of a corner of an 18 inch square layout template for quilting I did for my wife. The material is Chemcast GP cell cast acrylic. The slots and holes were machined with an Onsrud #63-711 bit (1/8 inch diameter). I was very pleased with the cut quality this bit gave me and the bit is also available as 1/16 inch diameter.

I was not so pleased with the engraved lines which are 0.015 inch deep and were cut with an Onsrud #37-21 engraving bit. The chips tended to fuse together and stick in the grooves. It took about 10 minutes of work with a sharp paring knife to pop the chips out of the grooves. I tried chip loads from 0.007 to 0.010. I'm tempted to try a higher chip load but it now occurs to me that the tip diameter of this engraving bit is only 0.005 inch, so the smallest chip load I tried was still bigger than the tip diameter of the bit............

Are there any thoughts out there on what direction I should move with chip load? The objective is to get some fine scribed lines on the surface, maybe some other bit is going to work better?

I was using spindle speed of 15000 rpm, and can go up to 21,600 rpm.

Understand that cold air blowing on the bit tip may help, so will try that tomorrow as well.


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