Anyone had a draw bar problem with Deckel FP2 Imperial S20 Collets.

Hi folk

Earlier this year I replaced a very worn FP2 Deckel draw bar for my vertical head with a new replacement from Franz Singer. (Germany)

Until yesterday I was very happy with it and never had any issues using my 40Int metric collets and other various 40Int S20x2 studded tooling ...

HOWEVER yesterday I needed to use a 40Int 1/2" collet and I could only engage it about 3 turns, sadly nothing like enough to the lock the collet in the taper. I achieved the job by sadly switching to metric.

Today I tried the rest of my imperial collets and only 2 of the eight could be fully screwed in to be of use! (All my imperial collet threads look good with no obvious damage)

Has anyone else had similar issues with draw bars or Imperial v metric collets and new draw bars??

Thanks

John

Hi John,

Jersey John said:

Has anyone else had similar issues with draw bars or Imperial v metric collets and new draw bars??

Click to expand...

The S20x2 "buttress" thread is fussy. I have had two pieces of tooling that did not thread cleanly into the drawbar. Both "hung up" after a turn or two. The other 70 or so items of tooling have not given any problems.

I was able to fix one of the two "bad" threads simply by removing a few hundredths of a mm from the thread OD. I have not yet looked closely at the other one and am planning to bring it to "Uncle Franz" the next time I am in Munich, in the hopes that he has an S20x2 threading die that I can run over it to clean it up.

I suggest you use a micrometer and some thread wires, measure the bad parts, and compare to ones that work OK. This will give you some guidance about what to do next.

Cheers,
Bruce

Guessing this is not your problem, but i will relate it anyway.
Not all collets are created equal!
Bought some 40 taper collets (spares) that were nice in all respects except that the threads at the end were not good....Pitch diameter was shallow and the finish was not so nice....
They were made within "The Pacific Rim" so the cost was commensurate with the thread issue....If your S20's are genuine "Deckel" , well then the above does not apply.

Bruce:
Well you might have a pretty good relationship with Herr Singer, but if i owned a die that cut those threads,don't think i would be using it to chase the heat treated threads on a collet...All the collets i own are reasonably hard at the threads which could easily kill a $100-200.00 tool in a heart beat...
.
Maybe its time to invest in that lathe that cuts metric screw pitches so you can point up those collet threads with a tool that is easily resharpened. Perhaps there are change gears that could be employed
on your Logan to emulate the 2.0 pitch.....(12 3/4 tpi is pretty close)

Cheers Ross

AlfaGTA said:

Guessing this is not your problem, but i will relate it anyway.
Not all collets are created equal!
Bought some 40 taper collets (spares) that were nice in all respects except that the threads at the end were not good....Pitch diameter was shallow and the finish was not so nice....
They were made within "The Pacific Rim" so the cost was commensurate with the thread issue....If your S20's are genuine "Deckel" , well then the above does not apply.

Cheers Ross

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Hi Ross, thanks as always for your input. All my imperial 40INT S20x2 collets are genuine Deckel ones that were supplied with the machine in 1966.

Do you know of a commercial outlet for S20x2 Buttress tip inserts with I believe a 5 degree rake??

John

I had a couple of Schaublin brand collets I picked up as old new stock that were tight as you describe. I mounted one in a collet and set a tool to cut only the 45 degree angle. Did all the cutting in neutral turning the spindle by hand. I happen to have a spare draw bar and use it to test fit those Buttress threads, have done a lot of them holding a 45 degree angle and never had a problem with them. I have to agree with Ross and using a die, not only is that some tough steel but those collets have a key way to add to the mix.
Dan

ballen said:

I have not yet looked closely at the other one and am planning to bring it to "Uncle Franz" the next time I am in Munich, in the hopes that he has an S20x2 threading die that I can run over it to clean it up. Cheers Bruce

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Hi Bruce, thanks for your comments, I'd be interested to hear the outcome!

KR

John

Bruce, I have had the same problem with one offshore collet from Singer, two or three turns and it seizes up. I appreciate the excellent service Singer provides, he keeps my machinery going, so I don't worry about it. However, I don't think they have any incoming QC on Chinese collets, just my opinion, I could be wrong. As per the above comments, the unusable collet thread is too shallow. Using the three-wire method to measure threads, my results show a variance with the thread depth. In this case, the OD was OK which may throw off a casual inspection. To make "lemonade out of a lemon" I look forward to the wishful future when the shop might get a Deckel S1, then it would be a simple matter to grind the thread down to fit. The collet in question was a for square tool, I was lucky enough to get a "real" one a short time later, so the problem has "gone away". As they say, you get what you pay for, however the moral of the story is possibly having some QC on the collets, etc. before selling them.

Hi Ross,

AlfaGTA said:

Well you might have a pretty good relationship with Herr Singer, but if i owned a die that cut those threads,don't think i would be using it to chase the heat treated threads on a collet.

Click to expand...

Good point, I'll check the hardness of the thread.

Maybe its time to invest in that lathe that cuts metric screw pitches so you can point up those collet threads with a tool that is easily resharpened. Perhaps there are change gears that could be employed.

Click to expand...

I do have a 47/37 transponding gear for my Logan that I use to cut metric pitches, so I can try this. But it's not obvious to me how to clamp the (SK40) collet on the lathe, any suggestions?

Cheers,
Bruce

PS: 47/37 = 1.2702 which is pretty close to the correct 127/100 = 1.27 ratio. For a 2mm thread the error amounts to 400nm/thread or about 3 microns on a section with 8 threads.

Well:
If i was going to run these collets, think the most direct would be to cut some soft jaws to match the "40" taper.
Make the jaws so that there is a shoulder at the inside end of the taper ....Would need to cut the taper from small end to large going Z minus....
The shoulder would keep the collet from trying to slide down the taper.

Turn a slug from aluminum that just fits the collet ID in the relaxed condition....then grip the collet in the soft jaws.the slug will keep the collet form collapsing
Cut the thread.

Barring soft jaws, something like this:
Grip a piece of aluminum in the chuck. OD of the stock somewhere close to the OD of the collet at the big end of the taper....

Begin with your largest size collet that needs work. Turn a length , say 3/4" long to the diameter of the relaxed collet bore, make the turned section a slight push fit.

At the shoulder where the turning meets the material, tun a face taper that matches the face of your collet....drill small hole (use hand drill , keep the material chucked) in the face taper about half way out between the OD of the stock and the turning.
Fit small roll pin (1.25mm or so...must be smaller than the width of the slit in the collet)....
Slide the collet on to the turning and engage the pin in one of the slots....push on the opposite end with a live center to force the collet into the face taper....Chase thread....

To run successive sizes , turn the OD of the fixture to fit the next collet size, repeat.

Depending on your tooling, think you could also grip the OD of the collet with a 4-jaw chuck....Most have grooves in the chuck jaws on the grip surface. The intersection between the face taper and the 40 taper
might allow gripping in the chuck directly using the groove to catch that edge....Support the opposite end using a center. Be sure to fit a packing piece into the collet ID before clamping up....

Cheers Ross