Method of joining for chuck key?

Thanks Mick B1,

Yes all good & valid points, though the chucks I 'need' them for are drill chucks that will mostly be used in the tailstock.

Regarding wear, is SAE 660 bronze more difficult to turn than CZ121 brass? And is it generally a harder material, ie likely to dent less????

Chris.

Yes you can, but only in small sizes and with non standard tapers I suspect - clockmakers use them to hold clocks together.

eBay Brass Taper Pins

Regarding wear, is SAE 660 bronze more difficult to turn than CZ121 brass? And is it generally a harder material, ie likely to dent less????

It all depends what you want to dent with it

Edited By Nick Clarke 3 on 28/05/2020 15:25:45

Ah yes I had seen and wondered what clock makers tapered pins were, I think they use them to secure the pillars to the plates like an engineer might use a cotter pin, only more refined!

I don't really know it - it's a leaded bronze that's said to be free-machining and resistant to wear. I've machined a fair amount of phosphor bronze PB102, and that's much tougher than CZ121, with a continuous chip and darker, more coppery colour. You need more clearance for tapping and good lubrication.

The X-ray suggestion was tounge in cheek. No metal will completely stop X-rays so thicker or denser metal just needs more exposure. But you rapidly get into unrealistic times. Dental X-ray generators are at least 70 kVp and the thickness of brass that will reduce the intensity of 70kVp by a half is only 0.01mm. 10 half value thicknesses is normally considered to reduce it to negligble levels so yes a dental machine is unlikely to do the trick but it depends obn the sensitivity of the sensor. Older dental X-ray units were lower energy 50-60kVp which on the face of it seems safer, but it isn't. The lower energy means longer exposure and the dermis absorbs more energy at the lower kVp. (its actually a spread of energy and on dental machines a aluminium disk is used to filter out the lower end of the spectrum.

Robert G8RPI.

Thanks Mick, Ok I will stick with brass, good to know phosphor bronze PB102 is the darker of the two bronzes though, and bronze being a fair bit more costly too.

Chris.

Has anyone suggested it being shrink fitted?

Thank you, no, how would that be achieved then?

Cheers

Chris.

Turn the hole to be smaller than the part it's to be mated with, at a ratio of about 1 thou per inch. Heat the female part with a gas torch (doesn't have to be red hot). Press together quickly! If the male part heats up before its fully driven home, game over!. The resulting fit is stronger that a press fit.

This is the way I'd do it.

Thanks for the explanation Rob, Ive learnt a lot from this thread.

Yes Garry I like it, so for me its a toss up between cross pin or thread & rivet the end.

Do you think it likely the peened end would show when finished an irregular circle due to the thread?

Cheers

Chris.

If the male part heats up before its fully driven home, game over!.

Not true where the coefficient of expansion of the outer is sufficiently greater than the inner, particularly where tapers are concerned.

Carbide cutters are fixed in position, with some systems, by shrink fitting - and easily removed after heating the holder sufficiently, at the end of the cutter’s life.

This method will prevent an irregular shaped circle.

Thanks Garry, yes that covers all bases for me. When you drew that did you made a side on drawing first?

Steel for the shaft?

GLR offer EN1A, EN8, EN24T & EN1A.

The square section that's to fit the chuck is to be 1/4". So the shaft maybe 3/8"-1/2" dia.

I have an Amolco Mill.

I'd rather not have to harden it, so reading up on it EN8 would be what i'm inclined to go for, but I really don't have enough experience to have a strong opinion, so any input most welcome!?

Regarding Loctite 270. Does this go off as quickly as the stuff bought in the local post office etc?

Cheers

Hi Chris,

Yes, I did a side-on drawing first.

I've made an extra key for my individual 4-jaw chuck (2 keys make it so much easier to centre work) and didn't bother to harden it. I've never seen anything to suggest that I made a mistake, though I'm sure many will say I'm wrong.

Thanks Gary, wish I had those drawing skills, if you had posted the side on image I'd have used it scaled as my pattern! (-:

Oh yes that's a thought Ive read about using two keys on a 4 jaw, Oh and presuming that's at least 4" dia that's way more torque than on my little drill chucks, so that's great to know,

Cheers

Chris.

Hi Chris,

Is this what you wanted?

(-: Yes! thanks so much!

Chris.

I think cross-pinning is better than threading and much better than shrink fitting.

There could be considerable torque on the joint, tightening and releasing the chuck. With shrink fitting you're dependent on interference friction, and with threading a tight releasing could throw much of the stress onto the peened countersink.

Still, if you get a problem it should be easy enough to cross pin it afterwards.

I hadn’t contributed to this because I thought the big question was ‘how were the original parts secured?’

Now that we’re onto ‘how do I build something similar?’ the answer seems obvious :

Loctite 638 or similar

... and yes, I am confident that [properly used] it would take the torque.

MichaelG.