Plexiglass machining

[bogusmill]

I am about to make a box from cellcast acrylic plexiglass for a customer, that needs to be polished for visibility. Does anyone know what kinds of speeds and feeds I would have the best luck with? Is it like aluminum, steel, titanium? Also what about precautions for fumes, what about cutting fluids? Any suggestions to this would be very helpfull!

[Jim Whipple]

I've cut some plexiglass in the past (3d stuff) adn with .25 ball, 2 flute carbide, 75 ipm and 6000 rpm worked well for me. I use valcool VNT 935

HTH

Jim

[ERIC14779]

have fun!!!!!!

 

If you have to end up with a opticaly clear end product....

 

Use a Cold air Gun to keep the heat out of the cut (if you are not going to use a coolant that the plastic supplier suggests)

use close stepovers to get the part surface as close to final shape as possible.

 

And be ready to do a lot of hand polishing.

[questech]

Bogusmill,

Would it be possible for a bit more detail on the part geometry.

In general hss cutters are quite a bit sharper. They will cut with the least amount of heat and result in a lot better surface finish. You will want to use high quality cutters to avoid the horizontal lines. On small parts and cutters -max rpm 10 or 12k 100 ipm .125 cutter and so on. For facing try to use an old fashioned fly cutter setting the leading flute .005 lower than the others. Double back tape works well.

 

Care for a fish?

[Jack Mitchell]

Bogusmill,

 

If this application is 2D or a basic profile, then by all means use the fastest spindle speed you have. – If a ¼” Slotdrill then suggest .005/rev using flood coolant – the machined edge will require a very light rub at most.

 

If this application is as stated, do not approach & retract at a corner, lexan, and other polycarbonates should be treated as we would a carbon electrode. (Always install a radius at every corner otherwise a chipping will occur). (Arc in & arc off at the midpoint of a line if at all possible and always climb mill).

 

Often a customer will allow the addition of tooling holes if you ask for permission,

 

If this application is facing or surfacing you will indeed have a task before you; the problem with polishing such materials is the inconsistency of heat & abrasion – even a moment of greater heat will cause optical distortion. – you would actually fair better trying to wax a black car in direct sunlight

 

Also try this approach – machine a mold cavity, heat the lexan, then vacuum to the desired shape.

 

One place that I worked at did tremendous amount of lexan shielding for IBM, they heat formed the lexan to incredible tolerances and shapes – all was for operator viewing while testing and manufacturing a variety of electronic components.

 

Regards, Jack

[Jack Mitchell]

One other note:

 

Often you can profile a piece of softwood which can be used as a form tool so to speak.

 

Application: Make a lexan windshield that wraps at the corners - like on your car.

 

Machine the profile in wood, place the lexan upon it, heat very carefully with a propane torch, maintain a very consistant flame & flame distance, timing is everything - once you catch they hang of it, the lexan will simply lay down upon your profile.

 

You could also make the mating piece of wood to trap the lexan between both pieces - until the part cools & sets.

 

Hope this helps, please let us know.

 

Regards, Jack

[McRae]

Propane Jack??

 

Use an Oxy Hydrogen torch. Using a carbon based flame on an organic compound can only mean Black marks. With the combustion of Hydrogen, the by product is water. And by the way, this will improve any surface that you have cut and make it transparent again. I don't know how elegant or dimensionally stable the result will be but try it.

 

Jack's vacuforming ideas are great, I think I will make some toys for my son this christmas that way...

 

[ 10-21-2002, 08:50 AM: Message edited by: Andrew McRae ]

[PBpaul]

Be careful of the terms "Lexan" and "Plexiglas"- Lexan is a brand name of polycarbonate. We make templates from it on a regular basis with a 1/16" diameter carbide cutter without a problem. Plexiglas, on the other hand, is a brand name of cast acrylic and we have never been able to get a decent template from it. It melts, glues itself back together, breaks bits, gives us a lot of grief. As Dave Barry says, "I'm not making this up."

Paul

[bogusmill]

The cuts I need to make are V shaped notches, with 45 degree walls and a small radius in the bottom, .500 deep in .825 thick mat'l. The material is not Lexan, just Plexiglass, Acrylite GP to be exact. I have a HAAS VF-4, 7500 rpm and use Stuart water based coolant, supposedly similar to Cimcool.

 

[ 10-21-2002, 09:34 AM: Message edited by: bogusmill ]

[MACHINEMASTERG]

we cut plastics her and as far as polishing the stuff try baby powder and water works good!!

[Roger Peterson]

Vapor polish????? I used this on some acrylic parts many years ago. I don't remember the cost but the result was excellent.

 

good luck

[chris m]

quote:

---

Avaition Research

---

Is that anything like Aviation Research?

 

Andrew you have too much free freakin' time

 

C

[McRae]

Chris,

 

I live my life to the fullest and most productive that I can. By using Cafeene to regulate awake times, I figure that by only sleeping 5 hours per night rather than the Standard 8-1/2 hours that at the end of the week I will have gained a day!

 

This way I can honestly say that I work 8 days a week...

 

Remember, there is time enough to rest when you are dead!

[bogusmill]

Yes, Just like Aviation!

 

Does anyone know if this stuff taps well? If so, what taping fluid?

 

[ 10-22-2002, 12:34 PM: Message edited by: bogusmill ]

[Jim Whipple]

I tap a lot of it...6/32 and 8/32 500ish rpm

Jim

[McRae]

I would consider some threadmilling for this application. Any trouble with Creeping after machining?? UHMW will creep for at least 3 days after removing ruffing passes, best to let this sit for a while and then remachine to finish dimensions.

[PBpaul]

To clarify a point about what I said about Plexiglas (acrylic) not machining worth a hoot, vs Lexan (polycarbonate) which does machine ok.....As long as the as the acrylic is cast acrylic, I understand that it'll machine OK, too.

[bogusmill]

It is cast and it is machining just fine. It is the extruded mat'l that has problems. Going to try flame polishing and am trying to find out more about vapor polish.

[Jack Mitchell]

bogusmill,

 

Please sign off with a real name (First name only, if you prefer) - for we all have one of them.

 

And please tell us how you make out with your result.

 

We are all learning as well.

 

Regards, Jack