Thumb screw

[Phil PParticipant @philp]

You could always turn off the plain un-knurled part of the head by a few thou, then make the hole in the knob to be a press fit size for the remaining knurled part of the head.

However I defy anyone to defeat some Loctite retainer such as 601 etc, by finger and thumb force alone. That is what I would use.

Phil P

[JasonBModerator @jasonb]

If you think it will unscrew with Loctite then add a grub screw in from the side, even grind a flat on the screw head for it to bear on.

[MacolmParticipant @macolm]

I have made quite a few such thumbscrews using aluminium for the outer. I just use a tight press fit, ensuring there is a smooth lead radius on the cap screw. The aluminium will easilly expand if the fit is over tight, though a smear of WD40 or thin oil is a good idea to prevent seizing. The design in the first post, with the hex retained, is sensible, but none of mine so far has come slack. If necessary, step the bore so that the cap screw knurling will grip.

[John HinkleyParticipant @johnhinkley26699]

Posted by Vic on 22/09/2023 17:50:36:

Posted by John Hinkley on 22/09/2023 10:05:34:

Surely there's no need to go overboard on this? Just how much torque is a thumbscrew expected to apply? I would have thought that there was sufficient grip between the knurled part and the socket bolt by the application of Loctite or similar or press fit or even heat/freeze fit. But then, I've been wrong before and will, no doubt , be again.

Like Martin Kyte, above, I'd make it in one piece and then broach the socket afterwards if integrity is an issue.

John

I don’t, and I suspect many others don’t have the tools to broach hex sockets.

As a point of interest though can you show us the tools you use for this. I doubt I can justify buying half a dozen different size broaches but it’s still of interest.

Hello, Vic,

I'm afraid that I included the rotary broaching tool and all its other accessories in with the sale of my lathe a few weeks ago when I disposed of all the machines in my workshop. However, there is an album which gives a bit of information on its construction here should you want to view it. The design was based on the principles outlined by Mike Cox on his web site, though I altered it to suit the materials I had to hand in the scrap box. For example, I used a redundant revolving centre for the rotary broach part and selected various odd bits of assorted mild and silver steel for the rest. It was designed to accept 8mm diameter broaches which are available purchase commercially but I chose to make my own ('cos I'm a cheapskate). I also made a video of the broach which is here on YouTube. should you feel inclined to watch. The video was made after the broach was constructed so doesn't show much of the actual machining but I do try to explain the method.

John

[Nigel Graham 2Participant @nigelgraham2]

Hemingway Kits list a rotary broaching attachment kit, but I don't know its capacity (without studying the catalogue).

I've not bought one, though have built a couple of their other projects, and they come with instructions as well as drawings. The photographs with mine suggest they make the prototypes on a Myford or similarly-sized lathe, so within most model-engineers' workshop capacities.

[VicParticipant @vic]

Posted by Michael Gilligan on 22/09/2023 17:53:56:

Posted by Vic on 22/09/2023 17:46:06:

[…]

Unless the knob is well secured to the cap screw it will come undone on the first use. […]
.

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Good grief !!

I thought that was what the ‘Retainer’ grades of Loctite * were specifically designed to prevent.

MichaelG.

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*[similar products are available from other suppliers]

Do you have a link please Michael. It’s not something I’ve needed very often. The stuff I have is very old.

[Michael GilliganParticipant @michaelgilligan61133]

Certainly, Vic : Here’s 638 but you will find 601 elsewhere on the site.

**LINK**

https://www.henkel-adhesives.com/bg/en/product/retaining-compounds/loctite_6380.html

638 is a little stronger, and 601 is more fluid

MichaelG.

[Author]

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