Melting Acrylic/Plastic

[Dwayne Dibbley]

I have been trying a 6mm single flute carbide bit @ 21000 RPM 400mm Feed and 2mm depth, but the subject always gets to hot see pic:-

12721

should i try faster feeds? slower spindle ? deeper cut ? or some form of coolant / lube ? to resolve the heat build up.

Thanks

[dazza]

Id say its too fast(rpm)try knocking the spindle speed down by 1000 rpm increments jogging back and fourth on a bit of scrap acrylic.

[Jonathan]

Id say its too fast(rpm)try knocking the spindle speed down by 1000 rpm increments jogging back and fourth on a bit of scrap acrylic.

Agreed - the chipload is too low so you need to decrease the spindle speed and/or increase the feedrate.

[JAZZCNC]

Acrylic as a very narrow chip load range and thats why it melts so easliy. I'd be going for higher feed rate first as 400mm/min is way to slow. Try 18000rpm and 900-1200mm/min then play around with both. Thou i'd be going higher on feed not slower. You'll definatly be wanting to at least double your original 400mm/min. I'd also cut with more DOC start with 50% cutter Diameter but it's not unusual to cut at 100% cutter dia.

The type of acrylic also plays a big part to how it cuts.! Extruded can be a pig to cut and Cast tends to be better.

[Ger21]

I'd go down to about 12,000 rpm and 2000mm/min. I've used similar numbers on acrylic in the past.

[JAZZCNC]

I'd go down to about 12,000 rpm and 2000mm/min. I've used similar numbers on acrylic in the past.

Last Cast acrylic I cut was 10mm thick and I cut it single pass with 8mm spiral upcut cutter at 24000rpm and 1200mm/min and it left a lovely finish but I thought these figures might scare him. . Lol . . . . Funny stuff acrylic and I find the larger the cutter the better finish I get.!!

[Dwayne Dibbley]

lower spindle speed seemed alot better here are some test results @ 9K 700-800 x 2mm ( im increasing slowly :) )

12722

Thanks for the tips

[JAZZCNC]

lower spindle speed seemed alot better here are some test results @ 9K 700-800 x 2mm ( im increasing slowly :) )

12722

Thanks for the tips

Try increasing the DOC and see if that helps often does. Have the tool under engaged is one the most common reasons for poor finish and excess tool wear.

[m.marino]

Jazz is correct on increasing DOC. Also as Jazz posted you really want to work with Cast not extruded. Cutting a lot of acrylic for sign folks and the best I can suggest has for the most part been stated. The only thing I can add is that you want to stay with either two flute or single flute for the best finish. Also doing a finishing pass in the opposite direction will aid greatly in the quality of finish you get (this does include areas where you have not cut all the way through). The only exception to the second pass I have found is when cutting with a V carve bit, than it is one pass and the job is done. -Michael

[Dwayne Dibbley]

Can you easily tell if the acrylic is cast or extruded by looking at it? ( no it does not have a label on it :) )

Thanks

[cropwell]

With a bit of Internet searching……
.
How to tell whether its extruded or cast:
"Burn a piece , extruded burns silently and will drip molten balls , cast burns with a crackly/smokey flame and wont drip. "
.
"Another point worth mentioning is that extruded stinks when it's cut but cast has an almost sweet smell."
.
And on this forum, from John S in Feb 2013
.
"Extruded has white backing on one side and clear on the other.
Cast has clear backing on one side and white on the other."
.
.
Personally, I would only trust John.

[JAZZCNC]

How to tell whether its extruded or cast:
"Burn a piece , extruded burns silently and will drip molten balls , cast burns with a crackly/smokey flame and wont drip. "
.
"Another point worth mentioning is that extruded stinks when it's cut but cast has an almost sweet smell."

Both are true but I'd say the sound is more a Sizzling that crackling sound. The smell is definately sweet smelling.


And on this forum, from John S in Feb 2013
.
"Extruded has white backing on one side and clear on the other.
Cast has clear backing on one side and white on the other."
.
.
Personally, I would only trust John.

You do realise John's favorite pass time was taking the Piss.!!

[cropwell]

You do realise John's favorite pass time was taking the Piss.!!

Who'd a thunk it. - Yes, I realise what the man is about, but I respect his opinion as an engineer.

[m.marino]

Can you easily tell if the acrylic is cast or extruded by looking at it? ( no it does not have a label on it :) )

Thanks

Normally Cast has a white film on it and extruded has a clear film on it. Notice I say normally, I have seen otherwise on more than one occasion. That and ask for cast only when you buy it. Be careful though as some will say it is cast over the phone and you will get extruded. -Michael

[Dwayne Dibbley]

OK I have burnt a piece last night, it was silent burning so could be extruded it also has a clear cover on it so would also point it as extruded.

I have ordered some 12mm cast to see if i get a different result.

Thanks

[m.marino]

Looking at some cut pieces of both here in the shop I noticed that clear cast has no colour to it and extruded has a bluish tint to it as indirect light hits them. Don't know if this is always the case but just noticed it while looking over shoulder at the cut pile of pieces for machining. Michael