Lathe Tailstock Tapping Clutch

[mksj]

I was thinking of making some form of tapping and die clutch system for the tailstock in my lathe, where one can adjust the tapping tension so it would release at a given tension. Quite often one is either tapping either under power into a blind hole and when you get to the bottom of the hole it was not fun to have the tap holder flying around or breaking a tap. I already had a sliding tap holder, so I came up with an adjustable tension system that used some bellevue washers as both tension and allow adjustable slippage. The bellevue washers are 1" ID and 2" OD, I also purchased some uxcell T101/904A1 Thrust Tapered Roller Bearings 1.01" Bore 2" O.D. 0.625" Width that is used to prevent the handle hub to spinning the tensioning locking rings. The tapping clutch system slides on a 5/8" rod with a MT3 tailstock end. The handle hub slides on a 1" body which is threaded at the end for the tension locking rings. The tapping body accepts different adjustable taping chucks as well as round die holders, which are locked into the end with a 3/8-24" set screw.

https://www.amazon.com/dp/B07RV1P6CD

I used materials that I had laying around, some 2" steel 1144 rod for the body/locking rings, 2.5" steel 4140 rod for the handle hub and O1 for the tap handles.

Parts and high tech drawing.....


Trust bearing bearing was pressed into to tapping handle hub.


Assembled clutched tap and die holder.


Mounted to tailstock, easy to adjust the tension by holding the front body and twisting the locking rings, the thrust bearing prevents the handle hub from turning the locking rings. I went with two locking rings as an additional safety precaution to prevent the tension from changing once locked together.

 

[RandyM]

It looks beautiful. Nice job. How well does it work?

 

[Just for fun]

Good job Mark, What a great idea, it looks great!

 

[T Bredehoft]

Just curious, what and why is the part that appears to keep the device from rotating?

 

[extropic]

Nice!

Please update this thread with your impressions after some time in service.

Thanks for posting.

 

[mksj]

It works well, I did some tapping 3/8-24 thread in O1 rod today at 150 RPM and it worked as planned. You set the tension by holding the front and back locking rings until there is enough pressure on the bellevue washers that they are not slipping and the drive power is transmitted to the handle hub. It is the friction between the washers that applies the power transmission to the handle section. Nothing fancy, but because they are spring washers and they are stacked, it allows more adjustment range rotational movement of the locking rings when setting the tension. When you reach the bottom of the hole, or if the tap seizes in the hole, the tapping body starts to spin, but the handle hub does not spin providing you are holding it. The tapping mechanism can slide back and for on the 5/8" hollow rod that extends out from the tailstock. The tapping head is interchangeable with different size tap and die holders. Most likely I will use it for 1/4" or larger threads and/or deeper threading.

 

[higgite]

Good job! Very innovative.

Note: For anyone looking for “bellevue” washers and coming up empty handed, look for “Belleville” washers.

Tom

 

[Winegrower]

This is a good looking system...but I believe I prefer the way the Hemingway tailstock die holder works. There is a conical clutch with user control of the transmitted torque. Push the handle toward the part, the harder you push the more the torque. Reverse the lathe, pull the handle and it backs out. I've modified it to hold a tap, with the same concept.

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[rwm]

mksj- Great work and a beautiful execution. Sometimes when tapping I see more resistance on the way out (breaking off the chip.) How do you address that? I guess you would tighten the clutch if you couldn't back out the tap?

 

[mksj]

The tension is pretty easy to set, you can see clutch monetarily slip when tapping in video just before the tap bottoms. Backing out the tap, I usually do not encounter the tension being higher than tapping in. One can easily dial up the torque when backing out if needed. It depends on the type of taps that you use, the material and the lubrication. When I use standard hand taps, I would not normally tap in a single pass, more in and out several times to clear the chips and I use my jog joystick in that case. The exception is larger taps, but then we are talking some serious force required for tapping. I did see the Hemingway tailstock die holder, but I prefer to just set the pressure once for a particular size tap, in particular when I am doing multiple parts. There are many ways to do this, I was looking at something that was simple and minimal cost. It was important on the lathe in that my previous tailstock tap holder, the arms would hit the cross slide if a tap bound up or bottomed out, it was not a good situation if doing any kind of power tapping. Hand tapping was tedious with multiple parts and deep tapping.