Author Topic: Chuck backstop for Sherline, per GH Thomas design  (Read 2178 times)

Offline gerritv

  • Full Member
  • ****
  • Posts: 797
  • St Catharines, ON
Chuck backstop for Sherline, per GH Thomas design
« on: December 02, 2024, 06:59:29 PM »
I am making a lot of small nuts and need to set them one by one in the 3 jaw, precisely located. A back stop was needed so I adapted GH Thomas' design from Model Engineers Workshop Manual.

No drawings, it was 'made to fit' in both the materials at hand and the lathe itself.
The tips are replaceable, depending on the thread size of the nut. Another adapter will get made if I need to back stop larger parts.

the only modification to the Sherline was to grind away the first (inner) tooth on the jaws of the 3 jaw chuck. This particular one already had some damage to the jaws so didn't risk much in doing so.

Works a treat, esp. in conjunction with the Lever Cross Slide.

gerrit
Don't confuse activity with progress

Offline AVTUR

  • Full Member
  • ****
  • Posts: 291
  • West of England
Re: Chuck backstop for Sherline, per GH Thomas design
« Reply #1 on: December 02, 2024, 08:19:41 PM »
Lever cross slide? I guess it is obvious but I know nothing about the Sherline lathe.

I doubt if one could be fitted to a Cowells.

AVTUR
There is no such thing as a stupid question.

Offline Dave Otto

  • Full Member
  • *****
  • Posts: 4919
  • Boise, Idaho USA
    • Photo Bucket
Re: Chuck backstop for Sherline, per GH Thomas design
« Reply #2 on: December 02, 2024, 08:24:37 PM »
I'm confused, are we looking at two different stops or do these two assemblies work together? It appears that the upper one has a taper on it, does that match the spindle taper?
I don't have the book. :)

Thanks
Dave

Offline gerritv

  • Full Member
  • ****
  • Posts: 797
  • St Catharines, ON
Re: Chuck backstop for Sherline, per GH Thomas design
« Reply #3 on: December 02, 2024, 08:28:08 PM »
This thread shows the lever cross slide on a Sherline lathe. No reason why the design can't be adapted to a Cowells.
https://www.modelenginemaker.com/index.php/topic,12088.0.html

Gerrit
Don't confuse activity with progress

Offline gerritv

  • Full Member
  • ****
  • Posts: 797
  • St Catharines, ON
Re: Chuck backstop for Sherline, per GH Thomas design
« Reply #4 on: December 02, 2024, 08:31:48 PM »
I'm confused, are we looking at two different stops or do these two assemblies work together? It appears that the upper one has a taper on it, does that match the spindle taper?
I don't have the book. :)

Thanks
Dave

The taper portion fits into the spindle and is locked in place. (MT1 taper), the threaded rod slides into that, using the 2 nuts on the end you can set the depth. The RH tip insert is, in my case, for M3 threads in a hex nut blank.The step on that insert lets you set the nut square, tighten the chuck, withdraw the threaded rod to inside of taper and then machine the end of the nut as well as tap it.

gerrit
Don't confuse activity with progress

Offline Dave Otto

  • Full Member
  • *****
  • Posts: 4919
  • Boise, Idaho USA
    • Photo Bucket
Re: Chuck backstop for Sherline, per GH Thomas design
« Reply #5 on: December 02, 2024, 08:56:47 PM »
So after you slide the threaded rod out from the rear? Does the insert stop piece stay in place? Also, is the threaded rod just held in place by hand when inserting the nut? What is the purpose of the keyway?

Thanks again,
Dave

Offline gerritv

  • Full Member
  • ****
  • Posts: 797
  • St Catharines, ON
Re: Chuck backstop for Sherline, per GH Thomas design
« Reply #6 on: December 02, 2024, 09:05:06 PM »
The threaded rod has a 'blob' on the end that holds the M3 stop piece, it retracts into the MT1 taper. the threaded rod et al stays in place during work.

Not totally sure of purpose of the keyway, I included it as it is in his design. Easier to do now than do it later when it might actually be needed.

This section view should explain things better than I can :-) I didn't model the threaded rod.

Gerrit

Don't confuse activity with progress

Offline Dave Otto

  • Full Member
  • *****
  • Posts: 4919
  • Boise, Idaho USA
    • Photo Bucket
Re: Chuck backstop for Sherline, per GH Thomas design
« Reply #7 on: December 02, 2024, 09:18:04 PM »
What is the purpose of the part on right?

Dave

Offline gerritv

  • Full Member
  • ****
  • Posts: 797
  • St Catharines, ON
Re: Chuck backstop for Sherline, per GH Thomas design
« Reply #8 on: December 02, 2024, 09:25:05 PM »
I will take some photos of it in operation, all will be revealed. (I've been switching between Dutch and Canadian all weekend so likely not the clearest descriptions at the moment.)

gerrit
Don't confuse activity with progress

Offline Dave Otto

  • Full Member
  • *****
  • Posts: 4919
  • Boise, Idaho USA
    • Photo Bucket
Re: Chuck backstop for Sherline, per GH Thomas design
« Reply #9 on: December 02, 2024, 09:27:40 PM »
Thanks I appreciate it.

Dave

Offline gerritv

  • Full Member
  • ****
  • Posts: 797
  • St Catharines, ON
Re: Chuck backstop for Sherline, per GH Thomas design
« Reply #10 on: December 03, 2024, 06:56:48 PM »
Here are 2 screenshots from the book. I think that is ok considering fair-use paradigms.

First one shows the components, he provides limited dimensions expecting you to adapt it to your lathe.
Second one shows the back stop in use. I haven't made item 11 yet, it is meant to be used for facing or thinning nuts by threading them onto extension and then pulling it back against the guide (rh blob) that is held in the 3 jaw chuck as shown in F and G. B-E are for making the nut body and ejecting it.

Item 10 is designed so the middle section is just smaller than the across-flats measurement, the tip is a close fit in the tap drilled nut.

This book has quite a lot of useful items described, jigs, fixtures, methods and tools are well covered.

Gerrit
Don't confuse activity with progress

Offline crueby

  • Full Member
  • *****
  • Posts: 20246
  • Rochester NY
Re: Chuck backstop for Sherline, per GH Thomas design
« Reply #11 on: December 03, 2024, 07:00:57 PM »
Neat device!

To avoid having to remove the little bit on the back of the jaw like you described in your other post, I wonder if it could be modified to be an expanding arbor style, gripping at the far left end of the headstock bore?   :thinking:

Offline gerritv

  • Full Member
  • ****
  • Posts: 797
  • St Catharines, ON
Re: Chuck backstop for Sherline, per GH Thomas design
« Reply #12 on: December 03, 2024, 07:15:42 PM »
Yes, that would work but I think having a guide near chuck is a worthwhile feature, the diameters are quite small when you get below M3 nuts. The droop might make it irritating to feed through the chuck jaws.

gerrit
Don't confuse activity with progress

Offline crueby

  • Full Member
  • *****
  • Posts: 20246
  • Rochester NY
Re: Chuck backstop for Sherline, per GH Thomas design
« Reply #13 on: December 03, 2024, 08:00:32 PM »
Yes, that would work but I think having a guide near chuck is a worthwhile feature, the diameters are quite small when you get below M3 nuts. The droop might make it irritating to feed through the chuck jaws.

gerrit
What if the guide was a close it most of the way through the headstock, just went narrow at the chuck end?

Offline Dave Otto

  • Full Member
  • *****
  • Posts: 4919
  • Boise, Idaho USA
    • Photo Bucket
Re: Chuck backstop for Sherline, per GH Thomas design
« Reply #14 on: December 03, 2024, 08:14:23 PM »
Yes, that would work but I think having a guide near chuck is a worthwhile feature, the diameters are quite small when you get below M3 nuts. The droop might make it irritating to feed through the chuck jaws.

gerrit
What if the guide was a close it most of the way through the headstock, just went narrow at the chuck end?

That is kind of what I did for my Weiler lathe. Just using a piece of 3/8" all thread and have a split bushing with a shoulder that locks it into the spindle at the left end, there is a jam nut that locks the all thread to the split bushing. Then there is a piece that threads onto the all thread which is a close slip fit in the spindle bore for the right end, but you need to keep it left of the #5 Morse taper. This works pretty good for a lot if things but as Gerrit has pointed out it lacks rigidity and precision for fussy small work. I use it mostly when longer parts need to be cut or faced to length. 

Dave

 

SimplePortal 2.3.5 © 2008-2012, SimplePortal