Getting the right ‘feel’ on a captive adjuster nut

[Kealan O’CarrollParticipant @kealanocarroll32466]

[Kealan O’CarrollParticipant @kealanocarroll32466]

Hi all,

I'm not sure if this is the right place to post this question or not; feel free to move the thread

I'm planning on making an adjustable carriage stop with a dial indicator, similar to the one shown here;

Except for the hard stop at the bottom, I'd like to make it adjustable and use a captive nut like as per the below. I'll probably knurl it but leave the engraving off as the DTI can handle the measurement side of it.

My question is about the detail of the captive nut; I'd like to get a nice feel on the nut as you can imagine. I think a micrometer type feel would probably be too light, but a normal 6H/6h fit of a nut on a bolt would be too sloppy; does anyone have any tips on achieving a nice feel here? I thought about using an O-ring but I'm afraid that might feel rubbery (!!) and have too much stiction.

Any steer in the right direction would be appreciated

[Tim StevensParticipant @timstevens64731]

A rolled thread will be nicer than a cut one, and a ground thread better still. And there should be nothing squashy about an O ring if you fit it in the 'slack' side of the adjustment. Then the actual tightening will be metal to metal. And of course, you will make the faces really square to the thread, so that no tilting can spoil the feel.

Tim

[HopperParticipant @hopper]

If you tap the hole first then finish the male thread carefully with a split die, you should be able to adjust the die in small increments to cut the thread to the size that feels best to you when you screw the nut on. You could also perhaps make the thread a bit tight and get final fit and finish by lapping the two parts together with fine lapping paste.

[Jeff DaymanParticipant @jeffdayman43397]

One traditional way to get a good fit would be to make the slot a little undersize and file or surface grind until the dial wheel will just barely fit, with a bit of grease on it, something like .0002" of clearance. The dial would be hardened, traditionally in industry.

If you want to make the slot a little big and use some kind of take-up for the slop, a rubber o-ring could be used but a greased wave washer of hardened spring steel will likely feel smoother and will last a very long time with the same feel, unlike an o-ring. Links below to some examples.

https://www.amazon.com/wave-washers-wave-springs/b?node=16410981

[John HaineParticipant @johnhaine32865]

+1 for an O ring on the lbs of the screw.

[egaParticipant @ega]

Kealan O'Carroll:

Your photos show two notably well-made items and have prompted me to add a dial gauge to my own simple hard stop. I am aware of the danger of over-clamping the stem of the gauge and wonder how the one in your photo is retained; it looks as though it might just be a pinch screw?

Incidentally, am I right in thinking that the block in the first photo slides on and is clamped to both the lathe bed and the stop rod?

[Chris TriceParticipant @christrice43267]

Posted by John Haine on 26/10/2018 13:59:50:

+1 for an O ring on the lbs of the screw.

+2. O ring all the way.

[Neil WyattModerator @neilwyatt]

Use a second serial tap

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