Turning smaller diameter delrin?

[conceptmachinin]

Hello,

This is my first post good to be here. Thanks for the help in advance!

I need to machine small diameter delrin. It needs to be 2.25 long and at .34 diameter plus or minus .002, then it has a shoulder with a head and chamfer with a combined length of about 2.625. What type of sharp tool could I use. Can someone send me a link to something they would use to turn it? I would like to have a indexable tool bit with a very small nose radius and a good sharp edge. If thats not possible, maybe a brazed tool. Any suggestions? Ideally this is probably a screw machine part, but I'm stuck with it. I'm more diverse with mills, and actually could make this part on a mill, but unfortunately I need to make about 30 of them, and it wouldn't be efficient.




Thanks!


Jimmy

[gunsmither]

I machine a lot of Delrin, and I use a "Knife" style tool of high speed steel. This style tool has a long cutting edge and sharp point. It works great for Delrin, in my experience; leaves a smooth finish, and cuts like butter. Older lathe books show pictures of this style tool.

I have also used small insert tooling with good results, but the Knife tool seems best for my items. You may have to build some sort of back support to keep the Delrin from springing away in order to keep your tolerances, or perhaps a roughing and then a finish cut.

Good luck with your project! Joe

[Mcgyver]

regular knife tool like you'd use for mild steel. is it the length/dia that is concerning, ie amount of overhang? rather than worry about steadies and backstops, just do it in one cut. This is a handy approach when you have to make very small dia longish parts, I made some 1/16 dia pins 1/2" long in steel this weekend doing this in one pass from 3/8 stock - because of the deflection, there was no creeping up on the final OD, one big cut and that's it. super slow hand feed, very sharp tool and you can get a very fine finish on the cut

[conceptmachinin]

Thanks for the replies.

Yes, that is what I planned on doing. Using 1"stock and cutting in one pass. What I am asking is, where can I find a really sharp, shearing tool and insert, or a sharp brazed knife bit? I need a 1" shank and it needs to be a short angle diamond, so I can get in there between the tailstock and the part. Small to no radius would probably work best. This is going to be cut on a CNC lathe.

I've made extremely small diameters on the mill before. Its easy that way, but I need to run production on these parts. (100 pcs a year) and don't really want to take forever to machine them on a mill.


Thanks for your help in directing me to some specialty tooling


Jimmy

[RotarySMP]

Since tool wear is not going to be an issue, why not just grind the tool out of a HSS blank? You can get 1" blanks (but will spend a month on the grinder) or just braze a normal 3/8 or so blank to a 1" key steel. Be a lot cheaper than inserts for this job.

[DareBee]

Exactly

Grind the tool from an HSS blank - only I would use a .25 x 1 or a .375 x 1 rectangular blank.
HSS is by far the best for cutting plastics.

[gunsmither]

Search for "Carbide insert tools" or something like that on the web. You should get all kinds of info about them.

Or perhaps just grind a 3/8" square high speed bit, and machine an aluminum 1" holder to fit in your 1" tool holder. Good luck with your project! Joe

[conceptmachinin]

Thanks for the replies! I don't have a full service machine shop... no grinding capabilities. I will try to find something on the web. I've been searching already, but don't see anything. I wouldn't imagine that there aren't any specialty bits out there for plastics turning.

Jimmy

[Mcgyver]

Jimmy as an old fashioned diy homeshop machinist, I see a certain irony in having a cnc lathe that takes 1" tooling but not being able to get into production for want of a $100 bench grinder. were i in your shoes, buy the bench grinder or take the blank to a local machine shop and ask them to grind it - be prepared though for some heavy duty ribbing. If you were local I'd do it for you, its a few minutes at most and not even tease you that much

[Geof]

Originally Posted by RotarySMP Since tool wear is not going to be an issue, why not just grind the tool out of a HSS blank? ....

When machining natural Delrin, that is White, tool wear is not much of an issue.

When machining Black Delrin tool wear with HSS tools can be a serious issue. We machine both natural and black Delrin and HSS tool life on black is about 1/50th of the tool life on white. It would not be surprising if a single HSS tool showed noticeable wear with increased material deflection in fewer than 30 parts.

[conceptmachinin]

What I will probably do is just machine one out of steel. Should work okay, but then again I can try a high shear insert. I got a few weeks to get them done. Got other stuff to keep me busy right now.

Thanks for the info GEOF

[widgitmaster]

Many years ago Brown&Sharp mad a lathe tool holder for turning long slender diameters, it was called a "Box Tool". It had two bearing rollers, and one small square tool bit with a micro adjuster like a boring head. This tool was in effect a combination of a follower rest and a tool holder combination!

It was used on the older turret lathes which did not have a tial center to support the end of the stock. Try looking through an old Brown&Sharp catalog to find a picture of one, as they were really easy to make, and were the perfect tool for the task you want to do!

I hope this helps!

Eric