Bringing a bell mouthed chuck back into service

My 4 jaw chuck that gets used on the rotary table was not holding properly - it was bell mouthed, so only holding the stock on 4 points, rather than 4 lines.
I've never really liked the commonly put forward fix, so this is a different way of addressing the same problem

[@christianmoser2579]

How is it possible that you only have 2k subs? Those videos are much more akin to someone like bigclive than what the metrics say... Please continue the good work, and have a nice one :)

[@occasionalmachinist]

Don't know. I like to think my subscribers are a better quality subscriber, worth say 100 times any ordinary subscriber😁

[@joemcgarry1106]

Nice job. I reworked chuck jaws the same way. I too found it beneficial to taper the jaws causing them to hit a slightly harder in the front. I ground them in my sine vise, rather than a dedicated fixture. If your mill has wear as mine does too you can always finish the fixture in your surface grinder. I never liked grinding jaws in a running chuck either for the reasons you state.

[@occasionalmachinist]

I guess a similar result. I did think about using a vice but with a fixture like this it eliminated setting up each jaw individually, so I thought more repeatable.
As the mill is 60 years old, I would guess there is some wear in there. I included those methods for getting square and parallel surfaces because of that - I was sure that otherwise there would be people grousing because their mill is old and worn, so would not be able to get things as precise as I could...

[@joemcgarry1106]

@@occasionalmachinist Yes, valid points. A lot of home shop people don't have a surface grinder to finish a fixture. Your method, and explanation were spot on, as usual. I spent 40 years in a tool room. I don't miss working, but I do miss working with others. Cheers

[@hilltopmachineworks2131]

Interesting approach to a common problem with chuck jaws.

[@occasionalmachinist]

It seems to work. I suspect it is similar to what chuck manufacturers would do, although perhaps with more sophisiticated jigs/ fixtures

[@graedonmunro1793]

good idea all round.

[@RB-yq7qv]

very nice job.

[@occasionalmachinist]

Thanks.

[@Warped65er]

Thx for the vid.

[@alanremington8500]

Good idea !!

[@paulrayner4514]

good idea, I assume all the jaws are exactly the same dimensions

[@occasionalmachinist]

Yes. The 3 jaw chuck was different, but I made up new plates (used the same fixture) and that worked just the same

[@brianmckenzie1739]

Interesting to see your reasoning - but way, way too many steps - and a couple I'd find fault with (i.e. milling the inside face of your little square piece - but after squaring up the outside; and the remaining procedure making use of such a thin strap across the mill table).
Why didn't you clamp the jaws directly to your angleplate, aligned to remove say 0.05mm off the jaw inner end with the surface grinder - and make any subsequent adjustments from there. Using feeler gauges seems very imprecise . . . .
Not wanting to be negative - but I don't think this video is enhancing your channel, which I otherwise enjoy.

[@occasionalmachinist]

The inside of the fixture was milled square to the squared surface (or parallel to the base if you like) as I wanted to be able to use the fixture for measurement/ checking as well. I edit these videos down by a fair bit, so the shots of me using it like that were probably not included. Not sure what you mean by 'thin strap'. The strap I used for a stop is about 8mm thick and bolted down on both ends - it was not moving. The Al strip could have been thicker, but did the job. Those steps were included to show how you could get a square surface (or a flat surface) from a mill, as I thought at the time that if I did not show those steps I would get comments saying I did not show how I insured that my datums were square or parallel. I can't recall if I mentioned it, but normally off the mill using parallels surfaces are typically parallel to say 0.1mm. Using that method those surfaces were within 0.02mm.
The reason for not clamping directly to an angle plate was simply repeatability. Using a fixture like this is much more likely to result in the same amount being taken off each jaw. If I clamped straight to the plate, I would have had to set up 4 times, so 4 opportunities for something to be not quite the same. Not so important for independent chuck jaws, but for self centring jaws, that introduces error.
Feeler gauges are a well established way of measuring. In this particular application I would have liked smaller steps in thickness, but tool makers the world over check small gaps with them all the time. When I worked in the auto industry, they were often used as no-go devices on checking fixtures too. Based on the final check with test bar, not being able to get a 0.05mm feeler in there means a gap of less than 2 thou. Maybe not perfect, but that's the sort of clearance for a hole/ shaft fit that typically gives a nice sliding fit (negligible side to side movement), so certainly an improvement on what was there, and took a chuck from something that should not have been used to something fit for purpose.