Machining Nylon 6

I have a hot job to machine some Nylon 6 parts. I tried cutting it dry with an 1/8" 2fl carbide EM.
I'm getting a bit of a burr on the .157" holes.
The tolerance on the holes is +- .002" so, interpolation is Faster than a tool change, and better able to adjust to the size.

Any thoughts on using coolant or air blast on these?

Thanks!

Pete

Use flood coolent.

Use flood, or an air chiller.
That will decrease the burrs.
You might want to use a single flute HIGH POLISH endmill, like waht is used on a cnc router.
Best of luck.
Doug.

flood coolant, and be careful when you're drilling to make sure the cut plastic is clearing away from the drill, or else it will clog up and melt/burn a ring at the top of your hole, and believe me, it sucks hardcore. Razor blades work good for deburring the part after.

How about using a .159" drill? It always seemed that this type of stuff wants to drill a bit smaller than the drill. You might consider undersizing the OD of the drill a short distance behind the cutting end, to reduce rubbing and heat.

Doesn't nylon absorb moisture? I'm not sure about the flood coolant.

Yes,
coolant is needed to cool the nylon down to prevent melting and clogging the flutes, also I got better results with sharp HSS tools rather then cab. And a sharp Swiss army knife is always handy to deburr.

If you have to machine 6/6 nylon, to fine tolerances, my heart goes out to you.Using water based coolants on nylon will shoot your tolerances to hell. All non-blended nylon will absorb water...big time. My one boss likes nylon, because it is cheap. He can't understand why the stuff grows and shrinks. When nylon sits around, it has the same relative humidity as the surrounding air. When it is wet and hot, it decays and balls up. Sometimes I just put the stuff in the fridge to get it ready for the final pass. Baking the stuff will make it shrink as the water goes away. I use 99 precent isopropyl alcohol, if I am forced to use a coolant. I also use it sparingly. A touch of bacon grease will make drilled nylon holes look slick and keep the stuff from melting on you. Cold air blast is a godsend.

We color nylon parts by using water based dye and dropping the finished nylon in the hot water dye. When the water evaporates, the nylon is dyed to the core. It will then return, within reason, to it's former tolerances, after drying.

I suggest the least amount of cutter flutes possible with the greatest rake and clearance. I have always had very good results with high speed polished tools. I personally have created material settings on my milling software just for plastics. I keep the RPMs low and the feed rates high. Nylon is one of those materials that will not stand for light cuts. It will just move and not cut. Hole sizes are as much a function of feed rate, as drill size. The faster the cut, the less likely the darn stuff will just move aside. I generally push the drill feedrates until the chips look like sticks with little zig zags.

With nylon; using carbide and negative rake tools is an exercise in herding cats. Call Arthur R. Warner and get some of their high speed inserts. Generous positive rake and slower speeds will make you a happy camper.

I suggest a little Wild Turkey or Makers mark be calculated into the quote. After working with nylon, a good stiff drink is always in order.

+1 on having a couple of shots when trying to make this stuff to tight tolerances.

Charlie, did you get conned into machining the "door seal retainers" for exec. jets too????

I can hear the grief in your post, and it reminds me of the above job.

God! what a nightmare. Nylon 6/6 18" long, 12" wide, 3/8" at its thickest, and .05" at it thinist. (most of the part was thin!)

Again, 3t3d remember the "air chiller"
a MUST for Nylon.

best of luck,
Doug.

I had to turn down the RPMs and increase the feed to get nice sharp edges. The nylon wants to melt and leave a burr otherwise. This worked very well for me with no coolant.
Bill

More,more, more...I am soaking it all in. My thanks to those of you who have replied with useful information. I have had some trouble with teflon, nylon and polyethelene in the past and some of the ideas you have mentioned are good ones. Tell me more about some of your "fun with plastics jobs", that is if Pete doesnt mind me steping in on his post.

I have found that rinsing teflon parts with Isopropal alcohol seems to help remove some fine hairs I still have a lot of trouble keeping the burs down. Most of this machining has been done with a .060 or .030 dia endmill. I have seen advertisements from other shops that advertise deburing up to 50 times magnification. I cant imagine how you do that.

Charles

Sorry if this aint an option, but have you ever tried contacting the customer to see if Acetol (Delrin) can be used as a substitute? Because, the difference is an entire world of machinability. Acetol, is actually fun to machine. Just enough stiffness to break chips and stay stable, yet soft enough to machine the way plastic should. (sounds like a commercial).

This may be too late, but in a former life
I machined a *lot* of nylon 6,6 and the key
to getting good cutting properties was to
heat-treat the items beforehand in a furnace.

This would drive off all the water and make
them cut reasonably well.

Use the highest sfpm you can get, and use
the sharpest, high postive rake tooling
available.

Jim

Subsituting material isn't an option. I am 3'rd down on the chain of contractors, the material was already bought, the engineers involved don't take as kindly to suggestion as they might. Other customers are better tuned to changes.
I machine many hundreds of punds of Delrin at a time. It realy is nice stuff to work on, except if you push too hard, too much rpm and feedrate it outgasses something unfriendly, and will give you a whopper of a sore throat. Of course that is from leaning into an enclosed machining center that is producing a few hundred punds of chips in very short time, so it does get concentrated in there.

I got the nylon prototypes done, they were in a hurry, then they were called out of town, so the approval for the remainder of the production was delayed...
We will run the production starting Monday morning now. Sunday I will try to get a better part by taking some of the suggestions.

Thanks for all the great suggestions so far!
Holding the +- .002" has not been a problem yet, surprisingly... However, once it leaves the shop, and gets dry or moist it is anybodys guess what will happen to it.... Turns out the holes with the tolerance are only clearance holes for plastic push in rivets!. (shakes head and mumbles)

I sure don't have any problem with this post drifting off to other plastics. The more discussion the better.

I've worked with teflon before. Now there is a plastic to work with! Surprisingly dense, and $$$.
Makes nice looking parts.

One part I had to make for an electronics company was out of Delrin, I had to hold +- .0002" on a part about 2" square. Delrin worked Ok for that...
Other jobs with acetal and the material had a lot of stress built in to it. Shaving off one face to get it to thickness on a 7" X 9" X .75" part and it would curl like a potato chip.. I didn't specify stress releived material. My mistake.
The curl was about .007" of curve over the part.

Worked on Durapol for electronic wave soldering once.. That stuff is pretty abrasive, the shop that sent it to me used carbide burrs instead of cutters to cut it.

Pete

(edit, I spelled Potato as if I were Dan Quail)

[ 07-17-2005, 02:03 AM: Message edited by: 3t3d ]

Dave K,
Do you mean Acetron GP? While both Acetron and Delrin are acetals, there is a world of difference. Delrin has a lot of air space in it and it is a bit brittle. Acetron GP is a true homopolymer and it is not plagued by the microscopic air bubbles of Delrin. I just love Acetron GP. It machines like butter and gives a finish as fine as frog hair. Delrin is used, by me, for things needing a bit more rigidity. Acetron is good for making something to whip Godzilla's butt. Delrin can sometimes shatter.

If the customer is a real cheapskate, why not use filled Nylon? It is not hygroscopic and it machines a thousand times better. For really cheapo plastic, use HDPE (High Density Polyethelene) and enjoy. The stuff machines like wax and absorbs absolutely nothing. It is used for cutting boards in kitchens and you can use the chips as filler in baby food. It is totally inert. I use it where we once used wood. It is super cheap and replaces wood. A 48 by 96 by one inch sheet is $169.00 for the virgin HDPE. We just went through 150 sheets of HDPE and I felt like laying back and having a cigarette after that job.

Dave K,
Do you mean Acetron GP?

Click to expand...

Gee, I never heard of that. But no, I meant Acetol. Acetol is the actual material of Delrin. Delrin and Acetol are really the exact same thing. Delrin is just a name brand.

im trying to fallow along...
really , i am...

3t3d,
Lordy; currently it sucks to be you. I wish you the best of luck, and dry weather.

Dave K,
Honestly I never heard of Acetol. It may be a brand name of a company I never heard of. I have found most acetals are just like Delrin, except Dupont didn't make them. Acetron GP is chemically the same, except they found out how to make it uniform. Somehow the formaldahyde bubbles do not form in the extrusion process. I am going to bug the GE materials plastic engineer on Monday. I just love calling him at 5:00 and asking a question.

I just love calling him at 5:00 and asking a question.

Click to expand...

I'll bet that just makes his day. Actually, Acetol, and Acetron GP could turn out to be the same thing. When I cut Acetol, I get that "sharp" stinging odor also. I'm told that smell is the acid that's added to the material. Let me know what you find out. You peaked my curiosity.