Old 1/2" chuck

One of the unusual items left to the museum with other tools is this little 1/2" two jaw chuck. It was on a MT1 arbor which I removed to find out which Jacobs taper it had. It looks like it is intended to hold round stock up to 1/2". I took it to bits and cleaned it up a bit to find out whether it is worth getting a J33 x MT2 arbor for it. I fitted it onto a 12mm ground steel bar running 0.0005" tir and it runs about 0.004" tir on the body (the original MT1 arbor may be bent). I initially thought it was for holding taps, but the jaws make more of a hexagon shape.

I have some pictures, but have forgotton to add them to my album before posting this thread.

Edited By old mart on 16/10/2021 20:42:06

An old boring head with a similar symbol popped up in my ebay feed a few hours ago 'Crown' brand

Crown Boring Head Ebay

I have a 100mm 4 jaw independent chuck in a cupboard at the museum, marked Crown, and foreign. You reminded me that this 1/2" chuck has foreign marked next to the MT arbor. The screws are 8-32, replacing the original slotted ones which had seen better days, I had expected 4mm, or 3BA, but the 32 tpi gauge was the best fit and they screw in nicely. The design would work with hexagonal bar stock, but 1/2AF would be too big on the corners.

Edited By old mart on 16/10/2021 21:37:30

..just for interest, that pattern of drill chuck is still made;

Meridyen - Drilling and Cutting

There is another thread about this style of chuck somewhere on the forum, my old Chas Strelinger & Co catalogue from 1895 has several of them in it.

Edit, found the thread and the image I posted at the time

Edited By JasonB on 17/10/2021 07:03:32

I have a ½" Crown one of these myself, but rarely use it as the arbor is both well dinged and slightly bent.
I've not tried removing it thus far, as I wasn't sure if it was taper or threaded.
Did you work out what taper arbor suits yours?

Bill

Thanks, Jason, that thread is very interesting. As for the taper of the arbor, With the chuck dismantled, I could get a reasonable measurement of the end of the arbor and compare it with the outer end. Having some very heavy metal blocks and a suitable thick walled tube, it was easy to break the taper with a large punch and a club hammer. I have measured the taper and it is close to J33,

J33 0.624" x 0.5604" x 1" length.

Arbor 0.624" x 0.581" x 0.903 length.

Edited By old mart on 17/10/2021 18:48:53

I used to have one and the jaws where 90deg vees to take square stock.

An update on fitting a MT2 arbor with a JT33 end. I bought one from Myford LTD, a good price and fast delivery. It was a failure. I had runout of about 0.020" tir. After removing the arbor, there were witness marks at the large end of the taper and I could feel the mismatch. That meant that JT33 had too steep an angle. After some investigation, the only candidate left would be the B16 which is based on the MT2 angle, and has a large end of 0.6195"

The JT33 angle per side is 1.80422 degrees.

The B16 angle per side is 1.43055 degrees.

I'm not sure about the B18
I've just received a different make of chuck but along the same lines so I've been having a play.
I've tried measuring the included angle of the tapers of the Crown arbor, the new unknown make, and an MT2 arbor as a sanity check as we know what that's supposed to measure.
For the included angle I was trying to use some parallels and one of those little digital inclinometer cubes, but over a short taper, hard to get repeatable readings.

I also set up the three tapers in the lathe and used a pair of dial gauges to measure the single sided taper over ½" and doubled it up to give the single sided taper per inch, doubled it again to give the actual taper per inch and times 12 to give taper per foot.

Again a bit tricky as the MT1 Crown arbor is bent, which is why I wanted to replace it with a new MT2 one.
I rotated the arbour, measure max and min deviation from concentric, set the arbour half way and measure the taper from there ( and again at 180° ) . This means that the arbor was sloping slightly up or down, but I was measuring at 90° to the slope, so over ½" hopefully not a major error.

The readings I got;

MT2 0.050"/inch or 0.600"/foot (which more or less tallies with what's expected from the tables)
Crown 0.040"/inch or 0.480"/foot
Unknown 0.060"/inch or 0.720"/foot

The Crown arbor was about 0.630" at the wide end and about 0.598" at the narrow end

A truncated (at the wide end) Brown & Sharp No7 is a possibility as they are 0.5010"/foot
Wide end 0.7201", Narrow end 0.600"
The small end is about spot on, and the taper is about right.

J33 is 0.624 - 0.5605 = 0.0635"/inch or 0.762"/foot so not that.

Jarno are 0.600"/foot taper, so not suitable

B16 is the small end of an MT2 , so again 0.600"/foot and not suitable

It looks like my unknown chuck might have a J33 arbor, particularly as the existing one looked to be home made, and wasn't a very tight fit, into what was a rusty hole.

I think I'll end up starting from scratch, and making one for each chuck on the lathe

I couldn't find anything suitable in Machinery's Handbook, and the tapers I've mentioned above came from Wiki
https://en.wikipedia.org/wiki/Machine_taper

Bill

Edited By peak4 on 22/10/2021 21:54:38

.

I doubt if this is much practical help, Bill but …

Machinery’s Handbook [30th Edition] gives the critical No7 taper values to five decimals :

.50147 and .60000

MichaelG.

.

[ disturbed night … hoping to get back to sleep now ]

Thanks Michael; badly worded on my part. I'd already looked through my copies, and couldn't find any other tapers in there which might fit the bill, though I'd used 11th & 20th, rather than the later pdfs that are now available.

Hope it wasn't me that kept you awake.

Bill

.

Not at all, Bill

… I didn’t see your post until about 04:15

MichaelG.

If the B16 arbor does not work, I will put it aside as a spare like the JT33 one. I may well simply Use the jaws to clamp onto a true running 1/2" steel bar as in the first post and bore the taper parallel to shrink in a MT2 soft ended arbor. This is purely an exercise, as I cannot really think that it can match a standard drill chuck. Trying to measure these type of angles which run to seconds of arc with a digital angle finder which only resolves 6 minutes is futile.

Looking at the series of Morse tapers, I find it difficult to understand the mindset of the person who failed to make them all the same angle.

Old Mart, from the measured tapers above, the ones done with a pair of clocks, not and angle gauge, I think the B16 is wrong; not only that, but the thin end of an MT2 up the spout wobbles around.
I've just made a new arbor this afternoon, to fit the Crown chuck, using a ground bar and clocks to set the taper angle on the top slide.
I made an initial taper on the blunt end of an MT2 arbor I've had in stock for years.
A check with blue, and adjustment, to get a good match, finished to size, and fitted the chuck.

With the MT2 still directly in the lathe spindle, and the chuck mounted on the new taper, runout at the face of the chuck on a ½" ground bar is about 3 thou total with about 8 thou at 2" distant.

Not as good as a nice new Jacobs or Albrecht, but fine for some jobs.

Bill