DIY Tension/Compression Tapping Head

Some of you may recall about two years ago I designed a tension/compression tapping head, and built one prototype. The prototype was mostly ok, but had a runout problem, due to the way I made one of the parts on my crappy lathe. I ran out of time, and haven't gotten back to it until now. A few days ago, I made some design changes, and updated the prototype, resolving the problem. I am now in the process of making 6 more, so I can have all of my commonly used taps permanently mounted in ATC-friendly TC heads.

Here is a Fusion360 rendering of what it looks like:

http://www.cnczone.com/forums/attach...d=364392&stc=1

And the on-line viewer for the design: A360

And the Fusion360 design file is below, in case anyone wants to make their own. Just remove the .zip extension, and import into Fusion.

I sacrified some cheap Chinese knock-off TTS ER20 chucks to make these. I first cut then in half, at the top of the ATC groove, then bored precision 0.495" holes in the center of the two halves. The 303 stainless "top cap" of the tapping head presses into the hole in the TTS shank, and has the remainder of the ATC groove machined into it. This cap has a 0.500" dia. x 0.500" high boss on top, making it a VERY tight press fit into the hole in the TTS shank. The ER20 chuck is attached in exactly the same manner to the 303 stainless 1/2" Hex shaft that provides the required sliding motion. The "housing" is just a short section of 1.5" thin-wall tube, and houses a set of springs that provide the tension and compression force, with +/-1/4" of travel from the rest position.

I should have all 6 heads up and running in a few days, once the springs show up...

Regards,
Ray L.

How did you design the springs and what was the source?

The springs are P/N 9657K285 from McMaster-Carr. Six per head, they go on the three screws, one on either side of the "Spring Disc". I didn't put them in the model because I couldn't figure out how to get them positioned properly.

Regards,
Ray L.

How is the female hex made? Is it broached?

Yes, I have a 1/2" Hex broach I use on both the PDB and ATC. If you don't have a broach, you can instead use a round shaft, and mill semi-circular slots using a ball-nose endmill, then drill radial holes in the end cap, for ball-bearings backed by set-screws, with the balls riding in those slots. Or just cut a keyway, and use a long square key.

One tip: Whatever you do, make it a slightly "loose" fit, so the ER20 has a bit of radial float, so you don't stress the tap if the hole is not perfectly centered under the spindle.

Regards,
Ray L.

Below is what is inside one commercial T/C head. A nice design, but a lot more difficult to machine, and would really require hardening some parts.

Attachment 364488

Attachment 364490

Attachment 364492

Attachment 364494

Attachment 364496

Regards,
Ray L.

Awesome!! Thank you Ray!!

Making good progress. between "Honey-Do's" and other interruptions. I hope to finish the six TC heads perhaps tomorrow. At least the worst is over - I've got the housing assemblies all done, just need to make the (simple) bottom caps and shafts. The ER-20s are already machined to accept the shafts, so that whole job should not take very long.

Attachment 364584

Attachment 364586

Attachment 364588

Regards,
Ray L.

Woo Hoo! I've got all six new TC heads, plus the original prototype, all ready to go, except for the springs, which should arrive by about noon tomorrow!

Regards,
Ray L.

Success! I now have 7 T/C tapping heads - six new, compact ones, and the original prototype from a year or two back. They work perfectly!

Attachment 364728

Regards,
Ray L.

Video of tapping a hole or it didn't happen. :nono:

Video, drilling and tapping 6 1/4-20 holes in some 1/4" 6061 scrap:

https://youtu.be/csLaKGFvvaY

Regards,
Ray L.

Quote:

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Originally Posted by SCzEngrgGroup

The springs are P/N 9657K285 from McMaster-Carr. Six per head, they go on the three screws, one on either side of the "Spring Disc". I didn't put them in the model because I couldn't figure out how to get them positioned properly.

Regards,
Ray L.

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The commercial T/C head that you picture uses only two springs. What is the advantage of using 6?

Quote:

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Originally Posted by SCzEngrgGroup

Video, drilling and tapping 6 1/4-20 holes in some 1/4" 6061 scrap:

https://youtu.be/csLaKGFvvaY

Regards,
Ray L.

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Ray, are you tapping on a torus pro or the pulsar? I wasn’t aware that the torus pro could reverse its spindle. I bought the demo machine John had for sale.
Dave Z


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