Cutting Delrin

[Hwingo]

Good Day!

I am in the process of choosing the proper cutter for fabricating a spur gear from Delrin. Historically, my experience has been poor when milling Nylon, Teflon, Polycarbonate, Plexiglas, etc. I am reasonably certain much of my problems have revolved around my choice of cutter, spindle speed, and feed rate. So, I am "coming to the well" in search of wisdom and knowledge. I am considering buying a cutter from Harvey Tool as they have cutters specifically designed for cutting 'plastics". Boy, "plastics" include many types doesn't it? So:

1. What cutter is the best choice for cutting a spur gear from Delrin?
2. What is the appropriate spindle speed?
3. What is a suggested feed rate?

Any or all information would be greatly appreciated.

Thanks,
Harold 

[ArtF]

Hi Harrold:

    Im not a great user of plastics, I use lase on acrlic, but generall in any plastic a bit like an onsrud with its helical upward pull
is what Id use. Around 20KRPM ( whatever my highest is..), and a speed fast enough not to melt. We're I cutting it , Id play witha small
piece of delrin, trying a feed around 400mm/min and a low pass, like 4mm or so, but thats me..

:)
Art

[Hwingo]

Thanks Art. I appreciate your reply.

Harold

[ArtF]

Harold:

  Np, you will find settings vary widely , and its because each person tends to have their own cutting style.
The largest mistake though, is almost always cutting too slow. Is intuitive to cut slowly though things, its
human to assume slow and steady will be most accurate and easiest on the cutter, but  in most cases, you want
much faster than youd think intuitively.
  I once had an onsrud rep show me proof on a machine, that when the chips heat up, you have it right. So I
often feel the chips flying off, if I can feel them as hot, or at least warm, it means the heat isnt building in the cut
to melt or deface the work, its in the chips and flying away.


Art

[bosr]

I take heavy cuts in Delrin with a spindle RPM of 3000 at 60 inches per minute.

For me at least, the chips fly out nice and crisp (no melting) leaving a perfectly smooth finish.

Randy

[Hwingo]

Good Morning Guys,

Thanks for the additional info.

Randy, your information was really helpful because it gives me a point of reference. My CNC mill doesn't spin much faster than 3740 RPMs so letting me know that you cut Delrin with a spindle speed of 3000 @ 60 ipm helps me greatly. I was about to attempt a feed rate of 8 to 10 ipm.

Do you use a standard carbide cutter or one similar to those used for aluminum?

Harold

[bosr]

I generally use a sharp 2 flute high speed steel end mill.  2 flutes allow the chips plenty of room to evacuate.  Carbide has produced mixed results for me (usually poor). 

[Hwingo]

I generally use a sharp 2 flute high speed steel end mill.  2 flutes allow the chips plenty of room to evacuate.  Carbide has produced mixed results for me (usually poor). 

Thanks Randy.

Harold

[David Morrow]

Here is some technical info from Onsrud that may help.
http://www.onsrud.com/plusdocs/Doc/index.html?model.code=TECH027

http://www.plasticrouting.com/

And another:
http://www.plasticsmachining.com/magazine/archivesniser.html

A short quote from the above link :

" Tool Selection
Once capability has been determined in terms of properly maintained machinery and rigidity of part to be machined, tool selection becomes paramount. Router tools for plastic cutting are application and material specific. In almost all cases, one cutting tool cannot be utilized across a variety of plastic material.

Generally speaking, plastic can be categorized as either hard or soft plastic. Soft plastic will curl a chip and hard plastic tends to produce a splintered wedge, which is actually broken off in the machining process. The use of ?O? flute tools in straight and spiral configuration with high rake angles and low clearance will aid in eliminating the knife marks associated with soft plastic. Hard plastic is best routed with double edge ?V? flutes, spiral ?O? flutes with hard plastic geometry, or two and three edge finishers. These tools along with the proper chipload produce a crater free finish. Cratering in hard plastic occurs when the shear strength of the material is exceeded in the routing process. "


I have cut some big chunks of nylon like material on my Sherline CNC. Here is a pic of a small hydraulic press that I designed and made. That white thing in the center is a piece of 1" plastic and it cut like butter. But, I'll be damned if I can recall what I used. Most likely a 1/4" garden variety end mill as it would likely be the smallest end mill with enough flute length that I had.

[ArtF]

Wow, what a nice press. How much push can you get on that thing?

Art

[David Morrow]

Wow, what a nice press. How much push can you get on that thing?

Art

The label on the jack says 12 tons. The steel is 3/8" and I designed it so that there are no welds on the vertical pieces lessening the chance that a bad weld might give out at the wrong time ( is there ever a good time ? ). My brother has a plasma cutter and powder coating oven in his home workshop so this was a simple job for him. The white plastic is there to act as a guide but, if I did it all over again, I would use 4 - 1" steel rods to better capture the platen. I did machine a piece under the platen to capture the top of the jack so it won't slip. This pic was also taken before I installed the springs to lower the platen after the pressing is done.

[ArtF]

Very nice Job, Very Clever design. Kudo's..

Art

[Hwingo]

Hey Guys,

I just noticed that several posts have been submitted and I was not aware of these posts. For some reason, I am not getting notifications that someone has answered my threads. I am not ignoring you. Please bear with me until I can get this sorted out.

Thanks,

Harold

[Viljo]

Bit late to the party, but 2 very useful tools for any milling or turning machinist for feeds and speeds are FSWizard (online version is free!) and GWizard Calculator.

Both have tons of materials and you can tune them as needed for your machine, finish etc.

[ArtF]

Agreed, I use both as references.. Great product, and very well supported..

Art