Help on key for 4-jaw chuck needed

Finally got round to fitting the 4-jaw chuck that came with my Bantam only to find that I did not have a chuck key.

Measured the square socket on the jaws at 7.6mm AF - roughly 19/64" - is this some special Colchester size? Or have I got some sort of mongrel chuck? The chuck has D1-3 taper lock pins that I ended up making as the price new was excessive

I can make a chuck key but would prefer an off-the-shelf as homemade will not be strong enough.

Trevor

Trevor,

I have made several chuck keys over the years always from large high tensile bolts. M16s are ideal for smallish keys.
I have also made arbors for 1"bore lit saws from M24 bolts reducing the shank to 16mm threading it 20tpi to suit my Clarkson chuck, turning the hexagon off the head then turning a suitable spigot to take the slit saw.

A chuck key needs to be tough resisting torque just like a high tensile bolt. Made directly from such a bolt no heat treatment is necessary. Don't use silver steel as it is not suitable for this application. ( I am sure many of you will tell me they have successfully used silver steel for chuck keys but I have always found it to be a greatly over-rated material for many applications).

Just measured my two Bisons

3-jaw 9.5mm hole, 9.0mm key

4-jaw 7.2mm hole, 6.7mm key

So about a 7mm or 9/32 square end should do you.

Lambton,

With you on Silver Steel, it is soft un-treated and brittle when hardened. Like the idea of making from high tensile bolts, the metal is sufficiently tough but not brittle.

The lack of replies leads me to the conclusion that I will be knocking one up tonight.....

Trevor

Edited By Trevor Wright on 29/12/2014 09:22:17

Jason,

Cannot find a 7mm or 9/32" at the usual suppliers.....will have a more detailed look at lunch break....thanks.

trevor

Bison list 7mm as spares, you could always grind down the next size up from a cheaper source. Or try somewhere like Home & workshop or G&M Tools

**LINK**

Thanks Jason,

emails sent to both contacts.

Trevor

The square rod in most door locks is about the right size 5/16" or 7 , 8mm. Ive made a few keys and all still working.

Typical, found one from cromwell tools, IND4905910K, out of stock.....

Gordon, could turn a diameter and press fit to a T bar.......need a 4 jaw for that though......

Trevor

Just how many replies do you expect in 45 minutes on a Monday morning? On a normal day I would have spent most of that on the M25 traffic jam but as it is a holiday I had barely got up and lit the fire by that time. Only just got awake enough to log in

The key for my Boxford 3 jaw is just mild steel but maybe Colchester owners are a tougher breed.....

I just drilled a bit of rod in the end , filed the corners off the square and hammered it in. Weld up and cross drill for tommy bar. I f no welding gear soft solder down the hole will hold it. I'm trying to type this in a woolly hat and padded jacket but my fingers are going. Back to welding, at least keeps the fingers warm.

It all depends on the correct heat treatment.

Russell.

Gordon, was not having a go at you, just trying to be ironic, seems some cannot see it.......

When a post has over 50 views and only one reply it kind of confirmed what I was already thinking, hence the comment. Jasons post was there when I submitted.

trevor

I made a second chuck key for mine out of a bit of odd stock I had lying around, and it's been fine. it might be just me but I find two chuck keys essential for setting and making fine adjustments, loosening and tightening opposite jaws at the same time.

Bob..

I find it hard to believe that a home-made key will not be strong enough. My British made chucks all have keys made from a soft material, most likely mild steel. The only one with a hard key is Chinese. If a mild steel one isn't strong enough I would suggest that you are over-tightening the chuck.

As far as silver steel is concerned, it has about twice the yield strength of mild steel in its soft, supplied state. 8.8 HT fasteners are only slightly better:

Yield strengths:

• Mild steel 250 MPa
• Silver steel 480 to 690 MPa
• 8.8 HT 640 MPa

Russell

I did not for a minute think you were having a go, don't care if you do. As others have said mild steel is good enough. I made two small keys,one short and one longer. Made from black bar with brass knurled knobs on. These are invaluable for setting the 4 jaw before final tightening with the big key.

I made a mild steel (EN 3B) key for a 5" chuck 30 years ago. I'm certainly not strong enough to twist it but then I never use a long tube on it to do so. Colin

When making your key make sure it is long enough for the Tommy bar to clear the dial gauge used in setting the work in the chuck. I made mine too short and it is a constant source of irritation, I must make a longer one!😢

By the use of D1-3 it indicates the machine is probably a Chipmaster or a Bantam. Just a point to watch, the camlock holes are almost the same size square as the 4 jaw chuck holes. Don't get the spanners/keys mixed up, you will finish up splitting the corners of the square holes. A correct fitting spanner/Key is essential.

The chucks that came with my lathe use 10 mm keys, and when I change jaws, or move them over a long distance I use the speed wrench from my 3/8" drive socket set (Just if anyone is interested).

Ian S C