Lathe chuck key material advice needed

[StevoParticipant @stevo]

Hello all…

Ive got a small 4 jaw chuck, which looks like it has a 3/16 square hole for the adjustment of each jaw.

I want to make a chuck key, (YES – I know I could buy one, but I need to use the lathe to revisit / hone my skills!!).

My question is, what material for the square section – mild steel would be a bit soft, so silver steel or key steel brazed into the end of, say a 9mm mild steel shaft?

Thanks in advance!

[StevoParticipant @stevo]

[John McNamaraParticipant @johnmcnamara74883]

Hi Steve

When I got my first lathe secondhand there was no square key for the 3 jaw chuck, As a temporary key I ground a high tensile cap screw down to fit and Brazed it to a mild steel T handle. I never did get around to making a better one the temp job worked fine for the next 5 or so years until I sold the lathe.

Regards
John

[Gordon WParticipant @gordonw]

Last one I made was from sq. key steel, works OK but does not get a lot of use. Not at all sure of the steel composition but it was sold as key steel.

[LambtonParticipant @lambton]

Steve,

As John suggests make it from a HT cap screw. If you start with a 3/8" or 10mm you will be able to cross drill the top and fit a tommy bar made from untreated silver steel secured in place by Loctite.

The shanks of cap head bolts are very useful for all sorts of jobs. Whilst working for a gunsmith I made lots of firing pins for shotguns using this material and have never had one fail. Get proper Unbrakos if possible. Many imported from the Far East are not so good.

Eric

[BazyleParticipant @bazyle]

The one on my 5 in chuck is a little bigger and made from mild steel. If I used enough force to bend it I would be straining the chuck. The hex on the bigger 4 jaw is smaller so needs a stronger material though and got a bit of allen key soldered into a MS bar.

[Michael GilliganParticipant @michaelgilligan61133]

Steve,

Last time I suggested this, someone panicked on my behalf … but I assure you that with the right choice of old Tap it works a treat.

• Find a surplus HSS Tap, with the appropriate size of square, and
• A suitable length of rod,1/2" or so in diameter, as a handle.
• Drill and tap the handle to the appropriate size, and counterbore to accept the shank of the tap
• Apply some Loctite to the threads and shank of the surplus Tap, and screw it firmly into place
• Decorate to taste, and enjoy.

H&S Warning: Choose a Tap that has a "full body" not a reduced diameter "neck"

… If you haven't got a suitable one in stock, there are plenty at the Car Boot Sales

MichaelG.

Edited By Michael Gilligan on 26/02/2014 13:34:24

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

An Allen key is made of exactly the right material .

Very cheap to buy . Just grind a square on the end and use as is or insert a section into a mild steel T handle .

Grind square on shortleg to use as is and on the long leg to cut off for insertion into handle .

Old Allen keys make all sorts of useful tools :

Other Allen keys of odd sizes by grinding smaller .

Square head keys .

Screw drivers – especially for restricted access .

Drivers for odd screw heads .

Easy outs – grind a square or hex taper and ram into hole .

MikeW

[HughEParticipant @hughe]

Hi Steve

I used a piece of square bar from an old door lock brazed into a piece round bar. Still going strong 20years later with no signs of wear.

[Ian S CParticipant @iansc]

Find a high tensile bolt, metric 8.8, UN six radial dashes on the head. I thought, that's small 3/16", so I measured my Super Adept, and found it's 9/64". Ian S C

[chris stephensParticipant @chrisstephens63393]

Hi Stevo,

Plain old 303 stainless should more than adequate, made one yonks ago and still works fine. Best not to make these things out of anything that tends to be brittle just a bit "tough" and, in the case of stainless, not prone to rust.

chriStephens

[JoParticipant @jo]

It sounds like the same sort of size chuck as I have on my Cowells. So options:

1, Make a really hard key, that way you can apply more pressure to the adjusters, to get the jaws really tight against the work and possibly damage the adjusters or the work.

2, Make the key out of something softer than the adjuster and accept that if you try to over stress the key the end of key might bend.

On my Cowells I opted for the later, 303 stainless. And don't forget to make yourself two as it makes centrering a 4 jaw so much easier .

Jo

[egaParticipant @ega]

Perhaps worth mentioning despite OT, my large four jaw seems very happy with a short extension and tommy bar from a 3/8" sq drive socket set. As someone mentioned, the same approach allows the use of two keys.

[jason udallParticipant @jasonudall57142]

I’m with the “softer than” guys.. ( sounds rude)..
You can make another key ( and infact should)..but the chuck screws are harder to fix..
Its better to take the corners off your key than your adjuster..

Keep the reduced section as short as possible. ..torsion. ..
From the array of materials ( hard and soft) used it seems to not be critical anyway.

But a good fit is the most important…maximises drive ..resists rounding most

Edited By jason udall on 27/02/2014 09:47:36

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

‘ But a good fit is the most important ‘

Just so Jason and true for many fitted together components in engineering .

Tough key and hard chuck screw is a good combination for industrial size chucks .

It’s still a good combination for small chucks – the important thing is to limit leverage of operating handle .

For really small chucks a screwdriver handle works well and is a bit easier to handle that a very small T bar .

MikeW

[Michael GilliganParticipant @michaelgilligan61133]

Burnerd 4" 4-Jaw, with the original screws [tough, but material spec. unknown]

Very hard square key with nicely finished corners [from HSS Tap, as described above]

… Everything fits well, and nothing damaged yet.

There is no need to lean on 6 foot of Gas Pipe just to tighten a small chuck.

MichaelG.

[John McNamaraParticipant @johnmcnamara74883]

Using discarded High speed steel taps worries me a bit, Having broken a few over the years they sometimes fail leaving sharp splinters, a brittle fracture almost like they have shattered with little warning. Not good for your hands if you gash yourself.

Taps are hard but not tough, for this job we want a tough medium hard material that resists bending, while at the same time if it is overloaded it yields bending rather than shattering.

Good quality name brand Allan keys and high tensile machine screws, are unlikely to shatter they are tough.name brand

Regards
john

[Michael GilliganParticipant @michaelgilligan61133]

John,

I respect your opinion

… All I can say is that I am very satisfied with the results of repurposing my old tap.

MichaelG.

[Gordon WParticipant @gordonw]

Good quality Allan keys and other quality tools can shatter, they leave very sharp edges, still got the scars. Just be careful as with everything.

[JoParticipant @jo]

You must be really abusing your tools if it causes them to shatter.

The guy has a diddy little lathe chuck that has a 3/16" square key. A stubby tommy bar of maximum 1 1/2" total length should be more than adequate, preferably the tee of the key should also be soft so that it bends if someone forgets and gets over enthusiastic.

Also check the distance between the key hole and the lathe headstock: you want to be able to rotate both chuck keys without the Tee bar catching on the headstock.

Jo

[Gordon WParticipant @gordonw]

Jo- no abuse at all. The last it happened was with a very expensive socket extension bar, just bought new from a tool supplier. just leant on it to push the socket on, shattered into a 3" long shard which stuck in me. Obviously faulty , supplier gave me a new one after a bit of talking to, think maybe waving the broken remains might have persuaded him.

[Tony Pratt 1Participant @tonypratt1]

From an engineering point of view a HSS tap is about the worst thing I can think of as a chuck key. An extremely brittle key is the last thing you want, a soft or ideally toughened steel is the correct way to go.

Tony

[jason udallParticipant @jasonudall57142]

Ok. For those who have used square from hss tap. .good for you.if it works then its ok..
Lets face it , it serves to drive the tap and seems resilient enough in that application.

For me getting hss designed to cut steel in a position to do just that to the inside of a, less than readily accessible ,component wouldn’t bemy first choice but if it fits well on the flats..chance of broaching a nice round hole is slight..

[Michael GilliganParticipant @michaelgilligan61133]

O.K. chaps, you've told me I'm wrong.

I may put a picture in my albums some time, but I'm not going to try to persuade anyone.

Just for the record … there are no sharp corners or cutting edges anywhere that might contact the socket of the chuck screw. It's probably 20 years since I made it, so I can't remember the details off-hand, but I think it was a 5/16" BSF Tap, with a 1/4" square.

[i.e. more substantial than many lathe tools]

MichaelG.

Edited By Michael Gilligan on 27/02/2014 20:50:23

[jason udallParticipant @jasonudall57142]

Michael..I don’t disbelieve you.
I also believe you chose the square fit carefully. .

I also believe you were prepared to deal with the side effects if it doesn’t go swimmingly.

What I might do myself is one thing
What a cautious suggestion to someone, of maybe less background knowledge, might be different.
We differ. I hope in a friendly way.

[Author]

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