[SCzEngrgGroup]

Now that I have a working ATC, I want to automate as many operations as possible. That means, in part, ditching my auto-reversing tapping heads (one Chinese, one Procunier, and one Tapmatic), and switching to tension/compression heads. The easy answer would be to buy several, but at ~$175 each, thats a major investment. They're simple devices, so I figured: Why not make my own! Here is my design:



The tap is held in an ER20 collet chuck that will be made by sacrificing one of my many non-AT-friendly Chinese TTS-knockoff ER20 chucks. The top "cap" is made from 1.5" 303 SS round, with the 3/4" shank pressed-in. The outer housing is 1.5" x 1/16" wall 4140 tube, pressed into the top cap. The lower cap, at least initially, will be 6061, to make it easier to broach the 1/2" hex hole for the output shaft. The shaft allows the ER20 chuck to move up and down ~+/-3.8", while springs (not shown) between the housing end caps and the washers in the center of the hex shaft provide the tension/compression feature. the top of the hex shaft is turned down to 1/2" round, and rides in a bushing in the top cap, to better center the hex shaft, and provide lateral support. The whole thing costs about $10-20 in materials, and is dead-simple to make.

Here is the first part - the shank, top cap, and housing, made in about 90 minutes this AM.



Once the prototype is done, I should be able to knock out 3-4 more in an afternoon, and each of my most-commonly used taps can then be permanently mounted in their own tapping heads!

Regards,
Ray L.

[SCzEngrgGroup]

And here it is nearly complete, missing only the internal springs and snap ring, which I'll pick up when I go to town tomorrow:



I think it's going to work like a charm and was a total no-brainer to make - requires almost no precision at all.

Regards,
Ray L.

[UniqueMachining]

Ray

Looking forward to the final product. Sure could use half a dozen.

Do you see producing these for sale or perhaps publishing the plans.

John

[daniellyall]

well that something you could make for pocket money ray

[SCzEngrgGroup]

Ray

Looking forward to the final product. Sure could use half a dozen.

Do you see producing these for sale or perhaps publishing the plans.

John

Not a chance. You can buy one from Tormach for about $165, IIRC. Shars also has them sometimes. Make your own - it's not hard....

Regards,
Ray L.

[engnerdan]

Instead of doing a hex that needs to be broached you could do a round with flat sides.

Like this
Attachment 284162
Attachment 284164

These are another option if you don't have scrap tool holders laying around. All you have to do is press on a flange for the tool changer.
New C3 4 ER16 75L Floating Tapping Screw Collet Holder CNC Turning Toolholder | eBay

Or these from shars
3/4" ER20 Floating Tap Holder - Tool Holders - Toolholding & Workholding - Products

-Dan

[SCzEngrgGroup]

Dan,

That would work, but it's a lot more machining. I have the hex broach, and the hex bar, so fabrication is a breeze, with very little metal removal to be done, and no mill work - just simple hand lathe work. I'm finding the ONLY critical part to be machining in the proper sequence so the hex shaft ends up perfectly co-linear to the TTS shank (not hard, and even the prototype came out almost perfect in this respect), and getting the ER20 chuck pressed on perfectly co-linear (hard, and the prototype needs a little "fettling" to get this right).

The Shars ones are nice (a friend has one), but often out of stock, and would have to be modified to be ATC-friendly. The shank is hollow (there's a spring in side it), so modification would be required to shorten it down to TTS size.

I also really like the ideal of having some compliance in the system, to eliminate stress on the tap in case the head is off-tram, the chuck has runout, the hole is slightly off-center or crooked, etc. Seems like cheap insurance, easy enough to do, and makes the machining less critical.

Regards,
Ray L.

[MRM RCModels]

Hey Ray. I'm really interested in this. The tension compression head will work for the torus pro? Anything special required to make it work?

[SCzEngrgGroup]

Hey Ray. I'm really interested in this. The tension compression head will work for the torus pro? Anything special required to make it work?

A T/C head can be used on almost any machine. Operation is simple - pick your RPM (typically 300-1000 RPM), and feed down at a feedrate of RPM/Pitch. When you cut threads to the desired depth, stop, then reverse the spindle, and feed back out until the tap clears the hole.

Unfortunately, I have not had time to finish even my first head yet....

Regards,
Ray L.

[Superman]

I use a similar T/C holder from VERTEX
- like Ray's design, it uses a key to drive it instead of a hex

uses standard ER16 collets, great if you commonise your tool holding range with milling cutters
- allows clamping up to 10mm (0.4") diameters......T/C range is about 6mm extension Vs 2mm compression
- should program feeds to be about 95% , so that head extends slightly as you tap. ( when reversing it comes back to it's starting pos - minus any machine discrepancies ie spindle stop & reversal, while not feeding )

VERTEX-MILLING-GRINDING-TOOLING-CNC-LATHE-GRINDER
You can purchase items separately ( without collets ) ( guessing it was about $100.00 )
- be careful when ordering, can have larger nut ( STD ) or the smaller castle nut ( needs a special spanner )

VERTEX-MILLING-GRINDING-TOOLING-CNC-LATHE-GRINDER....3rd pic on RH side shows a 1/4 sectional view

Tormach shows it for $136.00 --- link

IMO...you couldn't make a tool for that sort of price ( labour @$50/hr ....6hrs = $300..... minimum ), plus it is off-the-shelf replaceable

[adel314]

Ray, firstly thanks for the design. I am building one at the moment, however I am wondering what ~+/-3.8" means. Is it + 3/8 and -3/8 travel?

thanks

Alex

Quote...
. The top "cap" is made from 1.5" 303 SS round, with the 3/4" shank pressed-in. The outer housing is 1.5" x 1/16" wall 4140 tube, pressed into the top cap. The lower cap, at least initially, will be 6061, to make it easier to broach the 1/2" hex hole for the output shaft. The shaft allows the ER20 chuck to move up and down ~+/-3.8", while springs (not shown) between the housing end caps and the washers in the center of the hex shaft provide the tension/compression feature.

[SCzEngrgGroup]

Ray, firstly thanks for the design. I am building one at the moment, however I am wondering what ~+/-3.8" means. Is it + 3/8 and -3/8 travel?

Yes, it was designed to have 3/8" travel in either direction, which is probably a lot more than needed.

Regards,
Ray L.

[adel314]

Yes, it was designed to have 3/8" travel in either direction, which is probably a lot more than needed.

Ray L.

Thanks. That is good to know. I have a spare Tormach TTS 16mm holder which I was thinking of boring out to form the upper part of the housing but I wasn't sure if was long enough so if I can achieve less travel the washers and springs will likely fit inside it.

Alex

[SCzEngrgGroup]

FYI - If you don't have a hex broach (and I'm sure very few people do....), the way commercial tapping heads work is the shaft is round, with semi-circular cros--section pockets down opposite sides. The lower housing has bores on opposite sides, having the same diameter as those pockets. The shaft is inserted into the housing, ball bearings dropped into the holes, so they sit in the pockets in the shaft, then set-screws put in behind the ball bearings to prevent them form moving away from the shaft. I suspect you'd want to make the shaft from a hardenable steel, to prevent the ball bearings from denting the pockets, making the shaft more difficult to move up and down. But, this construction is probably much easier for most people to manage. I used the hex shaft and hex broach only because I already had them, so it was easier for me.

Regards,
Ray L.

[adel314]

I do like the idea of a hex shaft so my plan to mill the hex slot on my CNC mill. I did this once before for a bush on my TTS Air Cylinder. The only difficulty I am having at the moment is to get Solidworks and HSMWorks to play together so I can mill the hex profile onto the 18mm straight shank of the ER16 collet holder. I will then turn that down and shorten it so that it will fit into the 16mm TTS holder.

Thanks

Alex

[adel314]

btw, Ray - it looks like you just used screws to fix the washers to the hex rod - is that the case?

Thanks

Alex

[SCzEngrgGroup]

btw, Ray - it looks like you just used screws to fix the washers to the hex rod - is that the case?

Thanks

Alex

No. There is a snap ring on the shank, and the washer are either side of the snap ring.

Regards,
Ray L.

[adel314]

Well, first step in the process is complete. I have successfully milled the 6 facets onto the ER16 12mm arbour. I discovered after doing this that it is possible to purchase the collets holders without the arbour. So if anyone else out there is thinking of making one of these it might be easier to buy the separate collet holder and then turn a length of hex stainless steel rod to fit the collet holder.

The next stage will be to turn if down to fit within the 10mm TTS cutter holder and add the ring grove for the circlip.



Alex

Collet Holder Link.
ER16 Chuck Motor Shaft Collet Spindle Extension ROD Hole 8mm FOR CNC Milling | eBay

[adel314]

Making progress. I just need to add the circlip and the springs and it should be ready to test.
Attachment 323372Attachment 323374

[adel314]

The completed version - not test yet as I need to do some additional work on my mill. The end cap is held in place by two 5mm grub screws that have pits milled into the housing of the main collar. I am hoping that these will provide enough holding force to match the largest tap I will encounter.


Attachment 323450