Square Stevenson's block from Arc?

I cut a replacement chuck key square on a Boxford shaper before I got a milling machine, using a set square of the table against the first cut flat to set up for the next one. Repeated until all four flats completed. Shaft was sat on a parallel in the vice. Calculated the depth of cut from the O/D, measured progress on the first flat & zeroed the tool slide at the finished size & cut the remaining 3 flats to the same setting – finished square was a nice snug fit in the chuck jaw recesses.

Might not be absolutely dead-on square, but the chuck doesn't complain & I'm still using the key with no noticable difference in fit after several years.

Nigel B.

The easiest way is to fit a chuck to the rotary table. It centres jobs like your chuck key on the table's axis, making it straightforward to cut the four faces of the square with a milling machine. Might be possible to attach your lathe's chuck, but chucks for rotary tables usually have four bolts passing through the chuck's body so they can be undone from the front. The bolts engage with T-nuts in the rotary table's slots. If you haven't got a suitable chuck, welcome to the wonderful world of model engineering, in which there's always some new accessory wanted!

Rotary tables shine when other than right angles are needed, otherwise not essential because other methods produce right angles. I made my chuck keys by gripping the shaft in an vice on the milling table with the end sticking out enough to receive the end of the milling cutter. After the first flat was cut, I turned the shaft 90 degrees in the vice and used a set-square against the face to get it exactly* vertical. Then cut the second and other faces in the same way.

If you don't have a machine vice, the shaft can be clamped directly to the milling table. It's a little more bother adjusting it compared with a vice.

*exactly needs some qualification. A casually used set-square will get close enough to 90 degrees for most purposes, but on this job the short face length and fiddling with the shaft in the vice limits accuracy. The vice problem is much reduced if it already has a V-slot jaw, or V blocks are used, to keep the shaft horizontal. Good news, chuck keys don't need to be anything like accurately square! I wouldn't risk it, but I'm sure our more accomplished brethren could eyeball a good enough square end on a chuck key, not just with a milling machine, but by hand filing it in a bench vice.

Work-holding, especially of odd shapes, is a skill in it's own right.

Dave

Turn down the end of the bar to the required diagonal dimension, minus a few tens of thou. Then file the flats. Since the starting diameter is slightly smaller than theoretically correct, a small chamfer should be left on each corner. Keeping the chamfers the same size, and parallel, will ensure that the flats are just that, flat and parallel to the opposite face. Shouldn't take more than a few minutes.

Andrew

Filing rollers that you fitted to the lathe toolpost while holding the job in the lathe chuck so you could file down to a set level and nice and straight used to be a popular home workshop item but seem to have gone out of fashion these days, maybe due to the availability of cheap milling cutters and even milling machines for the home shop.

I have clamped the work direct to the milling machine table using the tee slot. Use a sqaure when rotating to the next face.

if you're going to file it in the lathe, then you could use the jaws of a four-jaw chuck to provide the indexing.

But a chuck doesn't need much precision of either the square or concentricity to the stock, so mark out and file in the vice. Or mill to the lines by eye. It's not worth lots of setup time for such a simple job.

Never had one move yet (Famous last words!) ranging from 1" diameter in the 3-jaw down to 1/8" diameter set to run dead true in the four jaw. Both chucks ancient Myford fittings. Ditto on my even more ancient Drummond. I think if we were taking deep cuts at high feeds in industry, it would be a different matter. But the lathe and vertical slide are so comparatively flexible that you have to take shallow cuts at fine feed anyway so I have never had a problem with the legendary cutter being pulled out. Mind you, I do have a firm hand with the chuck key.

1" Cutter on 1" steel plate. Luvly.

Edited By Hopper on 13/06/2022 12:27:17

Like it, fiendish!

The diagonal is is square root of twice the flat and 'a few tenths' is about 0.01mm.

So, for an 8mm square,

diagonal = sqrt( 2 * 8 * 8 ) or 11.31mm

So the shaft would be turned to 11.30mm or a little less

Or for Imperial Fanboys, a 3/8" square,

diagonal = sqrt( 2 * 3/8 * 3/8)

diagonal = sqrt( 18/64 )

diagonal = sqrt( 9/32 )

diagonal = sqrt(9) / sqrt(32)

sadly, because I don't know how to calculate sqrt(32) as a fraction,

diagonal = 3 / 5.66 = 0.53", less a few tenths, say 0.5295 inches.

Dave

If your chuck key is not too long, clamp it in your mill vice vertically. Then using the X/Y cut the square. No need for the rotary table.

Of course if you really want to be adventurous you could forge it.

(. . . yes I know, you actually wanted a real one).

regards Martin

Edited By Martin Kyte on 13/06/2022 16:20:20