a simple but quick tip for tapping delrin.

Cue Crazy

Cue Crazy

AzB Silver Member
Silver Member
Some people will know this, and some may would figure It out quickly same as I did, but while I had It on the brain I thought I would pass It along in case It's ever of use to anyone, and can save them some time.

I finished up a cue yesterday, and today I needed to make a set of Delrin caps for It before I delivery the cue This evening. Well I forgot one important step that I usually do when making these caps. Although Delrin makes for very smooth threads, due to the nature of the material Tapping the stuff does not always remove the same amount of material, as for example wood or phenolic. Being a softer material, when You use the same size bore as you would use with other materials the fit tends to be much tighter. Normally I will bore a slightly larger ID to account for this, but I got in a rush this morning, and forgot that step. after all was said and done, and My caps were to size with the profile I desired, I had a shaft cap that was fine, but the handle cap was way too tight for My taste. I mounted the tap in My tail stock, kept chasing the threads over and over, and that would loosen up the fit a hair, but I noticed that no material was being removed, and what was actually happening was that the tapping was only warming the material, slightly expanding It temporarily, and giving the illusion that It was working. It would screw onto the handle easier, but as the material cooled down, It would get tight again, so after several times of doing this and seeing no difference, I finally decided to stick the cap in the freezer for a few minutes, And try tapping again to see if that helped Me get a bite on It. This time when I backed the tap out I saw some very fine shavings, and It worked like I had hoped. End result The cap now screws on the handle with a perfect fit.

Like I mentioned It's just a simple fix for a simple problem, but I didn't have to risk a re-bore on the ID, or tearing the clean threads up, and It was a quick, easy, yet effective solution.

Greg
 
Thanks for sharing your experience. We can all learn new tricks from each other.
 
Great tip.
Freezing also makes rubber machinable. Useful for rubber bumpers, etc.
 
I was dealing with this same issue last night. I'll have to give it a try tonight, thanks!
 
Well, I hope It's of use to someone. I'm not sure if It will work for everyone in every situation, but It was just enough for what I needed, and saved me some time and possibly material. I'm not sure if It was the shrinking or the cold actually hardening the material that helped, but It did the trick for me. The cue was delivered last night and the customer was very happy, so the end result was I have a load off My mind, and all is good. Of coarse I'm still backed up on other fronts, and working on catching up, but It's mostly simple repair work, and I should be able to get caught up by tomorrow night. Maybe tonight If I ride the morning hours out like I usually do.

Greg
 
Phenolic is another material that I have had problems like that.
Wonder if freezing it will work?
Got to try that next time.

Thanks Greg and some green for you.
 
WilleeCue said:
Phenolic is another material that I have had problems like that.
Wonder if freezing it will work?
Got to try that next time.

Thanks Greg and some green for you.
Click to expand...


Hope It's of some use. You could try It, and see if It helps.

The thought of moisture from the freezer had crossed My mind, but since Delrin is supposed to displace moisture I figured why not give It a shot. I did not have to leave It in the freezer for long, maybe 5-10 minutes was all, and who knows, leaving It in there longer may have helped remove more material. It worked perfect the first time for me, so I did not need to try leaving It in any longer.

I've used phenolic for inserts in the past, but I can't remember if I had the same problem for sure. It seems like they worked out alright the first time. I was tapping the phenolic for a 5/16 pin though, and may have used a larger ID to begin with, I know the fit was good, just don't know what I used to get there at the time. When I make up threaded phenolic ferrules though, I slightly under cut the tenon, so that the thread Dia goes on smoothly, and does not tear the threads out that I'm trying to make, and I don't under cut the ID of the ferrule It's-elf. The result is they still screw on just right, snug enough to have no slop, so It's possible that if I didn't undercut that tenon I would have the same problem, and would get an overly tight fit.

This Delrin was 3/8-10 as that is what I have been using in My cues for a few years now. I am not sure if the tap size would change the results from putting It in the freezer or not. The shavings I got from It on the last try were very minimal, but It was just the right amount. The cap went from Me having to grip It with My palm to screw It on the handle the last few turns, to being able to spin It on most of the way with one, and tighten the last turns with 2 fingers. That's pretty much the same results I try to achieve with the way the shaft's fit. I like them to fit so that the shaft does not move if you try to bounce It while only partially threaded on the pin, but not too tight, and then I like to feel It snug up just a hair more on the last 2 turns. Obviously that was not as important to me on the caps, It just happened to turn out that way.

Greg
 
Heating or cooling of materials can have lots of reasons for doing this. When threading,depending on the temp change and length of thread, it can give you a progressive shorter or longer thread engagement.
Some precision made parts are shrunk onto mandrels for final machining,then heated to be released.
There are shrink holders for precision milling ,holding carbide cutters in steel holders.
We used an induction coil to heat the holder to place or remove the cutters.
Dry ice is always a good form of cold when you don't live in Alaska.
 
carguy said:
Great tip.
Freezing also makes rubber machinable. Useful for rubber bumpers, etc.
Click to expand...

I have a rubber bumper that nees turned downed - This was a timely and helpful post!!!

THANKS very much!

Gary
 
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