PDA

View Full Version : Need Help with Delrin



mdred68
06-17-2010, 01:01 AM
I have to make a few parts for my brother out of delrin and i don't any expierance machining it. What is a good end mill to use? Are helicoils installed the same way that they are in aluminum? I have to tap several 2-56 holes and i would rather do it with a machine rather than by hand, what type of tap to use,what kind of speeds and feeds to use,and should i use tap magic or some other kind of lubricant? Thanks for the help.

JRouche
06-17-2010, 01:49 AM
I have to make a few parts for my brother out of delrin and i don't any expierance machining it. What is a good end mill to use? Are helicoils installed the same way that they are in aluminum? I have to tap several 2-56 holes and i would rather do it with a machine rather than by hand, what type of tap to use,what kind of speeds and feeds to use,and should i use tap magic or some other kind of lubricant? Thanks for the help.

This project sounds interesting!! 2-56 threads in delrin. So yer gonna helicoil the holes? I didnt know they went that small? I thought 4-40 was the smallest.

I havent done much work with delrin, just a lil. Depends on the hardness of it. I have seen some that is gummy soft and others that are pretty darn hard, like acetel.

For an endmill I would use one that you would use with aluminum. Two flute to remove the chip load. Im thinking a four flute will hold the chip load in the pocket too long and melt. Ok, maybe not melt but get warm and sticky and load up.

Fast removal of the chip load to keep it from packing up.

I havent milled any delrin but have turned it. It likes a really sharp bit.

If it were me Id grab on of my new OSG carbide endmills that are razor sharp and go to it.

But really? A 2-56 thread? I wanna see the project. I would drill an undersized sized hole and insert my own fully threaded insert and glue it in. JR

Walter
06-17-2010, 02:16 AM
I second the new sharp 2 flute end mill route. One of the problems I've had with milling plastics in general is holding them, so be cautious of the cuts you take as (at least for me) mine have tried to lift from the vise. If you go to purchase new end mills for this don't go high helix. Do try air stream cooling, especially if you have to work deep. I've also run carbide insert facemills with tpg inserts and had no problems.

I can't speak to tapping, but at 2-56 helicoil is out. Are these gonna be through or blind? Tapping this stuff is really gonna be easier with a gun or spiral tap as your not likely to get chips no matter what you use, mostly strings. Have you thought about using a forming tap? eliminates the chip situation and would give you stronger threads. For lubrication I think I'd most likely go with a dish soap/water mix.

macona
06-17-2010, 04:05 AM
I was thinking form tap as well but I think the plastic will not hold shape and you will get a real tight screw fit.

John Stevenson
06-17-2010, 04:07 AM
I machine a fair bit of plastics and use ordinary single flute carbide router cutters.
I find them better than end mills as they have more room to get rid of the chips and it's reworking the chips that cause a lot of the burning.
An air blast helps as well.

Can't help with the threading as I don't go that small but perhaps just a drilled hole and self tapping screws ?

Liger Zero
06-17-2010, 05:12 AM
I havent done much work with delrin, just a lil. Depends on the hardness of it. I have seen some that is gummy soft and others that are pretty darn hard, like acetel.



Delrin is acetel. Delrin is the trade name for a type of acetel. Just like Dodge is the name of a certain type of car/truck.

You can find small brass inserts with the threads you need. Google injection mold threaded inserts. Normally these would be placed in the mold and the plastic would flow around them.

In this case look for "heat stakeable inserts" or "Sonic Weld inserts"

What you do is drill the hole undersize then heat the insert with some type of heater and press it into the part. Plastic flows, insert sinks in, material shrinks and cools around the part.


As always, when thermally working Delrin and related POM materials have plenty of airflow to carry away the fumes and clean your machine up as Delrin can be mildly corrosive under the right conditions. (yes I know someone will be along to say otherwise, I'm going on the data I have and my own practical experience.)

mdred68
06-17-2010, 06:35 AM
The helicoils i need to use are 8-32 the 2-56 holes are only tapped. Thanks for the input everyone.

strokersix
06-17-2010, 07:10 AM
Attach your shop vac hose close to the cutter and suck the chips out of the cut. Works great and keeps chips from spraying all over the shop.

MotorradMike
06-17-2010, 08:06 AM
The helicoils i need to use are 8-32 the 2-56 holes are only tapped. Thanks for the input everyone.

Tapping #2-56 in Delrin will be difficult unless you drill oversize. The thread is already tiny so if it's going to require some holding power I'd recommend the heli-coil route.
The tap required for the Heli-coils is a lot bigger than #2-56.

I put these little buggers in Al fairly regularly and have found this helps.
a) make sure you tap the hole vertical.
b) make a tool to hold the insertion tool vertical, don't depend on the Heli-coil to go in without cross-threading.

Ken_Shea
06-17-2010, 08:09 AM
E-Z lock makes press fit insertable inserts, from 0-80 and up if you decide to go that route.
http://www.ezlok.com/Home/index.html

A.K. Boomer
06-17-2010, 09:10 AM
Very sharp 2-3-or 4 flute adjust speeds and feeds accordingly to the flute #

HSS or Carbide will work fine as long as its razor sharp.

Iv installed quite a few heli-coils in both UHMW and Delrin --- good way to go and will surprise you at how much strength is there once done right, I would not melt anything into it.

Evan
06-17-2010, 09:21 AM
Power tapping Delrin is an almost certain way to lose a tap melted in a block of plastic. I do plenty of work with plastics including Delrin and Acetal. Hand tapping is the only way to go, especially with small sizes. The smaller a tap is the greater the surface area is in relation to the volume of the tap. That means it will heat up far faster than a larger tap. You absolutely cannot get away with power tapping with something smaller than about 1/4 and I wouldn't try it with anything below 1/2". With a 2-56 tap you will be able to overheat it even by hand tapping if you turn it too quickly.

A.K. Boomer
06-17-2010, 09:29 AM
You may be right for the small stuff, We do use a power tap for say 1/4 20
so that means the heli-coil tap is actually much bigger, You can definitely tell its a little "sticky" but never had a prob. at that size, like milling - the tapping tool should be brand spanking new or one set aside just for plastic, regular cutting fluid is what we've used.

What iv noticed is you have to keep the tap moving (although very slow)
it seems if you stop and then have to re-start it settles into the plastic and takes allot of effort to crack it loose again, the procruiner (sp?) tapping head goes all the way in and with a flick of the quill handle immediately goes into reverse without delay --- very helpful.

knudsen
06-17-2010, 09:33 AM
I've done it, it's not bad, just keep the tap perpendicular. It's been 10 years since I did it, but as I recall, for some reason, starting with a bottoming tap works best. I think a starting tap just acts like a drill. Play around on some scrap. Be sure to back off every 1/2 turn until you feel the teeth hit the burr, and if it feels stiff at all, back it out some and brush off the swarf. If you are buying hte tap, it will probably be a three flute anyway, but I think that would be best for chip clearance. Delrin is fun to machine. Dream material. Anything works on it, but of course, sharp tools with much chip clearance is best. If you are buying tooling for the job, look at MSC. I think I saw end mills specifically for plastic cutting. Otherwise, a stinky new 2 flute uncoated HSS. HSS will last forever if you mark it "plastic only" and don't cut any metal with it. You can cut as fast as you like, until melting point. Compressed air works great as a coolant, and blows the chips onto someone else's machine to clean up :D

A.K. Boomer
06-17-2010, 09:42 AM
Delrin is fun to machine.



Certain aspects of machining delrin can be "fun" I guess ---- but if you really have to remove some material it sucks more than anything else unless you wear a really good charcoal filtering mask,,, Delrin gives off gases that are extremely toxic - will give you an instant headache and screw with your entire day...

RKW
06-17-2010, 10:04 AM
Delrin/Acetel machines nicely using two flute end mills. Plenty of thread inserts available with 2-56 threads and you can always make your own.

You might also consider thread forming screws for plastic as they work really well and do not require tapping at all.

John Stevenson
06-17-2010, 02:35 PM
Power tapping Delrin is an almost certain way to lose a tap melted in a block of plastic. I do plenty of work with plastics including Delrin and Acetal. Hand tapping is the only way to go, especially with small sizes. The smaller a tap is the greater the surface area is in relation to the volume of the tap. That means it will heat up far faster than a larger tap. You absolutely cannot get away with power tapping with something smaller than about 1/4 and I wouldn't try it with anything below 1/2". With a 2-56 tap you will be able to overheat it even by hand tapping if you turn it too quickly.

Sorry disagree, I regularly do 4mm, 5mm and 6mm with my air tapper in Delrin.

machinistchest
06-17-2010, 03:35 PM
I cut delrin all the time. It`s a walk in the park, the stuff cuts like butter . I keep a new set of endmills just for cutting plastic (sharp) and the taps just the same. Water will keep the tap cool if using a tapping head. It can`t be cut fast enough to generate any heat to melt or become toxic. If your cutting tool is dull, sharpen it!!!

Have at it! it`s nice to work with....MC

Evan
06-17-2010, 04:03 PM
It can`t be cut fast enough to generate any heat to melt or become toxic. If your cutting tool is dull, sharpen it!!!


Sure it can. It releases formaldehyde when it is near the melting point. Milling and turning aren't the same as tapping. If you run a tap in fast it will melt the material almost instantly regardless of how good the tap is. I use the highest quality taps available from Dormer and Yamaha and that makes no difference.

Liger Zero
06-17-2010, 05:08 PM
I gotta back Evan up on this one: Delrin and Sons emit gas when heated. I mold the stuff, had to build a vent system consisting of sheetmetal hoods and dryer-hose to suck the fumes out of my shop.

John Stevenson
06-17-2010, 06:10 PM
Liger,
I don't disagree with what you and Evan say about giving off gas.
However Evan states you can't power tap under 1/4" but I do it weekly on many holes.
Never had one strip or melt as yet.

Liger Zero
06-17-2010, 06:21 PM
I suspect the Delrin fumes are the source of your jokes.

:D

knudsen
06-17-2010, 06:28 PM
Certain aspects of machining delrin can be "fun" I guess ---- but if you really have to remove some material it sucks more than anything else unless you wear a really good charcoal filtering mask,,, Delrin gives off gases that are extremely toxic - will give you an instant headache and screw with your entire day...

Uhhhh, sure:


CONDITIONS TO AVOID: HEATING ABOVE 230 C./ 446 F.- FORMS
FORMALDEHYDE.


Over the span of almost 20 years, myself, 3 different machinists and several engineers worked with it regularly with no headaches, except from management. I did much less than the others, but my shop was attached to theirs with no walls. If you get it that hot, you deserve a headache :p

http://www.alro.com/DATAPdfs/Plasticmsds_Pdf/MSDS_Delrin.pdf

If you guys are passing around the crack pipe, you skipped me :D

oldbikerdude37
06-17-2010, 07:07 PM
Sure it can. It releases formaldehyde when it is near the melting point. Milling and turning aren't the same as tapping. If you run a tap in fast it will melt the material almost instantly regardless of how good the tap is. I use the highest quality taps available from Dormer and Yamaha and that makes no difference.

You tapping at 20,000 rpm?

Even if he tapped that tiny hole at 4,000 RPM I dont belive it would melt

Evan
06-17-2010, 07:42 PM
You tapping at 20,000 rpm?

Even if he tapped that tiny hole at 4,000 RPM I dont belive it would melt

Try it and report your success, or lack thereof. Cube/square ratio means that the surface area which generates the friction is much larger per unit volume on a small tap than on a large tap. A small tap is much easer to overheat in plastics. If you want to actually see what happens try it in Lexan.

John, if you are using Acetals that have combined lubricants then tapping isn't an issue. Even black Acetal taps better than native white since black contains carbon black which acts as a lubricant.

John Stevenson
06-17-2010, 07:48 PM
Yes it is black, never though about that.
I have shed loads of white, I'll give it a try first opportunity I get.
Might be a few days though, still bogged down with motors.

oldbikerdude37
06-17-2010, 07:56 PM
[QUOTE=Evan]Try it and report your success, or lack thereof. Cube/square ratio means that the surface area which generates the friction is much larger per unit volume on a small tap than on a large tap. A small tap is much easer to overheat in plastics. If you want to actually see what happens try it in Lexan.
[QUOTE]

Its your fairy tale so its up to you to prove it, make a video if you are so smart and YOU prove it.

you made the claim you do it.

Tony Ennis
06-17-2010, 09:45 PM
make a video if you are so smart and YOU prove it.

Haha, he is that smart.

Liger Zero
06-17-2010, 10:13 PM
Lets cool down folks.

All I'm doing is warning about the possible danger, that's all. Ultimately it is up to the OP on how to proceed. Just laying the facts out based on MY experiences with the substance.

A.K. Boomer
06-17-2010, 10:21 PM
Uhhhh, sure:




Over the span of almost 20 years, myself, 3 different machinists and several engineers worked with it regularly with no headaches, except from management. I did much less than the others, but my shop was attached to theirs with no walls. If you get it that hot, you deserve a headache :p

http://www.alro.com/DATAPdfs/Plasticmsds_Pdf/MSDS_Delrin.pdf

If you guys are passing around the crack pipe, you skipped me :D


You guys must have burnt out noses (crack pipe:confused: )

I smell the stuff all the time im cutting it, and im not burning it or melting it - milling or lathe but the lathe gets extreme - 6" piece - turning @ moderate speed and medium feed @ .050 doc with ultra sharp HSS, If it don't about knock you out then your about dead anyways --- I have way better things to do than make things up, and were talking almost instant headaches -- and I don't get headaches (except with delrin and MSG) and its not just me.

You can wear a mask - but that wont help your eyes from burning...

Herm Williams
06-17-2010, 10:37 PM
I use black or white often. I have best luck using 1/2 shaft carbide zero rake router bits. I generly hold ths speed to about 1k that keeps the swarf from flying all over the shop.
re

Evan
06-18-2010, 12:34 AM
Its your fairy tale so its up to you to prove it, make a video if you are so smart and YOU prove it.


It isn't a claim. It is my experience working with Delrin and Acetal. I use a lot of plastics and have tapped plenty of acetal and have quickly discovered that power tapping isn't a good idea. I normally power tap just about everything I can but certain plastics are the exception. Acetal is one of them.

I am not going to make a video of melting a good tap into a piece of acetal. The taps I buy cost between 13 and 30 dollars apiece and I am not going to waste one.

Machining acetal is a different story. If you want to see a video of CNC machining acetal using my dual purpose 4th axis indexer/lathe then see here:

http://ixian.ca/gallery/albums/videos/4_axis_twist_lo.wmv

JRouche
06-18-2010, 02:29 AM
Wow! Alot of good points. When Im cutting material I try my best to cut it and not burn it off. Doesnt matter if Im cutting metal, plastic or wood.

I can tell if Im burning the material off and not cutting it. Easy to see with wood. The wood will show signs of being burnt. Say with a router bit. The bit is dull and burning through the wood. I still get a cut, but the edge is scorched. Time for a new router bit or sharpen the shaper bits.

Metal is pretty close to seeing where the cutter is dull. It will show signs on the material. And the shavings. The material will be heated up and the shavings will be more "chunky", not sharp and uniformed in size. More of a ripping and burning then a cutting. And you will see some discoloration of the material and a higher feed pressure. Not to mention the overall look of the turned piece. Might be rough, or might be burnished looking. Like it was rubbed and not cut.

And in an extreme case of a dull cutter there will be sparks and melted metal peeling off. And Im not talking about high speed turning of tool steel with a nice ceramic or CBN bit, thats common. Thats just the intense heat of the shavings making that light show, they are still cut shavings, not burnt off shavings. Nuther topic about turning HSS.

So with plastics the very last thing you want is heat. I dont care what the make up of the plastic is. Delrin (acetate), Poly this or that, or some of the simpler plastics. Many of them are heat sensitive. And most of them dont cut like steel.

They dont have the heat conductivity that steel has. Its alot lower. You place some heat to the plastic at the cutting edge and it wont conduct it further into the part. The heat will stay right there at the cutting edge and smear the cut. Thats why a really sharp bit is needed. Razor sharp for plastic. Thats why you see carbide used for many plastics. It will hold its razor sharp edge with a higher temp than HSS will.

Because the heat isnt being drawn off at the cutting edge, the heat is held at the edge. Pretty high heat too. You wouldnt think so, its just plastic. But yeah, the heat soaked edge gets pretty high. And Im not even talking about some of the plastics that are infused with some really abrasive stuff like glass. Carbide is used for the abrasives also.

Plastic and heat. Very sharp bit, one that is for plastic only. It will die on steel. But cut plastic like butter. And I wouldnt take a cutter that has been used on steel to cut plastic. Its been dulled already... JR

Liger Zero
06-18-2010, 05:22 AM
Delrin (acetate)


Acetyl not acetate! Two TOTALLY different materials, trust me on this.

Its not a case of "Meh same difference" that'd be like saying stainless steel and aluminum are the same thing because both are shiny.

Evan
06-18-2010, 05:46 AM
There is also the issue that Delrin and generic Acetal are not the same product. Delrin is Acetal Homopolymer and acetal such a Quadrant Acetron is Acetal copolymer. If the product is actually branded Delrin then it is acetal homopolymer. If it isn't branded Delrin then it is acetal coploymer.

The two plastics are not always interchangeable as they have different properties. They have slightly different melting temperatures, different strength, different impact resistance and different chemical resistance.

Delrin is about 10 to 15 percent stronger, has a slightly higher melting temperature but tends to have core porosity on large extrusions and has very poor resistance to acids including acids in foods such as acetic acid.

Acetal copolymer has a slightly lower strength, impact resistance and melting temp but has good resistance to acids.

Both give off formaldehyde gas when heated during machining. Both will chip break when machined fast enough but it may be difficult to hold the part securely enough to cause this to happen.

Both will trap a tap or drill if tapped or drilled too aggressively. For best results when drilling large holes in acetals use a spade wood working bit with the cutting edge modified to almost zero rake. Don't try to drill a hole to nearly the right size and then open it slightly more. That will guarantee melting and trapping of the bit.

Liger Zero
06-18-2010, 04:00 PM
Despite being a plastic expert I still get the homo- and co- polymer thing mixed up from time to time.

Moral of the story: Consult a material property chart before deciding. :)