Steel body lathe chucks

Ok, probably a daft question & a daft idea but....before i start something i can't finish....

Are steel bodied lathe chucks generally hardened or not?

I know chuck JAWS generally are, but what about the body?

Reason i ask is i have a nice used UK made chuck with ALMOST correct PCD to fit mini lathe spindle. must be <1mm in it.

Just need to enlarge mounting holes a little.

Thought i'd better ask before wrecking a perfectly good old chuck trying to drill the holes out..

Thanks.

I don't know, but try taking the edge of a file to an out of sight part of it. A file will obviously cut unhardened steel and be fairly obviously reluctant to cut hardened.

Dave

I think some of them are spheroidal graphite cast iron, so should be no problem to modify.

I don't think steel body chucks are actually hardened but the one I had something to do with was made from pretty obdurate stuff.

Clive

Iv'e never met a hardened lathe chuck in 50 plus years of using them, as per SOD a file will confirm or not it's state of hardness.

Tony

I believe there are standard cast iron, SG (ductile cast iron, sometimes called semi steel) and steel chuck bodies. As already mentioned, the file test will tell if it can be drilled.

I drilled a dowel hole in my qc toolpost with a cobalt drill.

That doesn’t rotate at high speed! I would think all-steel chucks are likely only required for (larger) high speed installations.

A lot of the low cost Chinese chucks seem to be steel bodies. I haven't seen a hardened one yet. Must be cheaper or easier for them to use steel than the traditional cast iron. Cast iron would have the advantages of damping vibration better and resisting distortion under compression better and a better bearing surface where the jaws slide but steel seems to work ok for hobby purposes.

Edited By Hopper on 22/11/2022 09:08:23

On the unimat 3 jaw for example some of it is hardened and some of it is easy to drill so it's really something that varies with the producer

Times change! For most of the 19th century, cast-iron was cheap and steel expensive. Neither material was made to a specification, so what you got depended on geography and the skill of the producer. Geography mattered because ore contained impurities that altered the qualities of the metal. At first no-one knew what the impurities were or how they effected alloys, or how to manage them. Cast-iron isn't fussy for many applications: all that's necessary is that it melt and pour without serious flaws. Steel is much more difficult because small quantities of elements like Sulphur, Phosphorous, Nitrogen, Manganese, Nickel and Vandadium alter steel's properties radically. A tiny amount of sulphur makes steel easier to machine, but very slightly more weakens. embrittles, and makes it impossible to harden.

In the good old days it was cheaper and easier to make chucks out of cast-iron; castings are simple to machine and the metal absorbs a useful amount of vibration. Unfortunately cast-iron being weak in tension makes them likely to burst. Big chucks, anything above about 5", must be spun within their rating, and it's unwise to spin small ancient cast-iron chucks at high-speed on a modern lathe. Bursting chucks were quite common in industry before WW2, but I've never heard of it happening in a home workshop. However, an ancient chuck made for a treadle-lathe, might be dangerous at 3000rpm.

Gradually during the early 20th century, steel became the preferred metal for 'quality' chucks. Although steel was more expensive, and harder to machine, and more prone to ring, the resulting chuck could be run at much higher speeds. As ever higher cutting speeds are essential in cut-throat manufacturing, steel chucks have tended to supplant cast-iron.

Interestingly, improvements in steel manufacture mean steel today is about 40% cheaper than cast-iron. Part of that is modern cast-iron being tightly specified, but the situation is confused by many small foundries melting whatever comes to hand to make non-critical items like street furniture. Scrap cast-iron can be anything between aero-space and horrible carp!

It's not as simple as 'steel being suitable for hobby purposes', though I suspect there's a cross-over point where the advantage switches between cast-iron and steel. The deadening property of cast-iron helps reduce vibration, a feature worth having on smallish machines that don't run at high speed. But today, that means making the chuck from a high-end cast-iron and testing it carefully at speed, pushing the price up. Steel doesn't have a bursting problem and although machining is a little more expensive, the metal is cheaper. It might also be more economic for a bog standard chuck maker to rationalise production by making steel only, because steel chucks are 'OK' for most purposes.

Dave

That is the part that matters in today's world.

The other thing that has changed is machining time and costs have been slashed with CNC and carbide tooling. Once upon a long time ago, cast iron was used to provide the basic shape with minimal machining needed to finish it off. Chuck castings would have had the core hollow to speed up machining the hole up the middle and the cavity for the scroll plate etc to sit in. Today it is quicker and cheaper to just machine it from a solid piece of steel.

Edited By Hopper on 22/11/2022 11:26:25

Thanks for all the replies & especially the file tip.

Sounds like i should be good to go, i'll use the file test just to be sure.

A friend has just taken delivery of a new small lathe.

The 3 jaw chuck and jaws were unidentified.

A diamond needle file allowed the chuck body and then jaws to be marked so that they would be replaced in the correct place. The alternative set of jaws were fitted, to confirm that they met on centre before being marked to match their locations in the chuck.

Howard