Reccommend me a chuck

[SamI]

You will have better luck if you search on "Sjogren chuck", pronounced show-grin. They have been sold by Hardinge and others.
https://www.roviproducts.com/collet-chucks/sjogren-speed-manual-collet-chucks/

Ah yes, apologies, that was a typo in my original post! I’ve seen those but other than a few popping up on eBay (rarely for the correct spindle) I cant seem to find anywhere that sells them over here. I think after seeing your drawbar chuck though this seems like a much neater idea!

 

[Bob Korves]

I am having one problem with the drawbar collet closer I built. The needle thrust bearings make it smooth and easy to tighten the work in the collet. However, they also have much less static friction, so they tend to let the setup loosen a bit each time the spindle is started, due to the inertia at rest of the hand wheel/drawbar assembly. I also suppose that the opposite happens when I shut down the spindle, but it must be to a lesser degree. I intuitively understood this issue when I when I designed and built the collet closer assembly, and lightened the hand wheel, which also improved the grip of it. At the time, I was more worried about it auto-tightening itself rather than coming loose. As it is now, the hand wheel needs to be tightened after every couple of starts or the drawbar goes loose on the collet. I am considering ideas to improve the situation. My ideas so far are further reducing the rotating mass of the hand wheel and/or perhaps making some sort of connection that would need to be manually released to loosen the drawbar. Well, further thinking while writing this made me realize that such a catch would probably need to related to the collet threads, which seems unlikely. Perhaps there is some option at the left end of the spindle to lock (and release) the hand wheel assembly to the spindle. It works very well like it is, but is annoying to have to keep tightening it. If anybody builds one, consider the issue in advance.

 

[SamI]

I've been having a bit of a think about this over the last few weeks.

My thoughts now are to modify a Grizzly lever operated collet closer but to do this I'll need to either modify or make the 5C business end.

As it happens I have acquired a nice 5" lump of 17/4 PH steel. I am not 100% sure on it's condition however I'm assuming it's in the annealed form. I imagine that if this was aged it would be a good choice but was wondering if anyone with a little more experience could comment. I did think about using a lower grade of steel and fitting a MT to 5C adaptor but I figured that machining the 5C profile into the chuck on the machine would ensure concentricity to the lathes axis.

 

[MrWhoopee]

I've been having a bit of a think about this over the last few weeks.

My thoughts now are to modify a Grizzly lever operated collet closer but to do this I'll need to either modify or make the 5C business end.

As it happens I have acquired a nice 5" lump of 17/4 PH steel. I am not 100% sure on it's condition however I'm assuming it's in the annealed form. I imagine that if this was aged it would be a good choice but was wondering if anyone with a little more experience could comment. I did think about using a lower grade of steel and fitting a MT to 5C adaptor but I figured that machining the 5C profile into the chuck on the machine would ensure concentricity to the lathes axis.

17-4 PH is not that hard in any of its conditions. It has excellent strength, toughness and corrosion resistance, but the hardness will not get above Rc 44 (condition H900). The nose piece for a collet closer needs to be about as hard as the collets, in the range of Rc 58-60 (maybe even higher). Oil hardening or air hardening tool steel would be ideal. Regardless, it will need to be ground after heat treating. Anything less will wear fairly quickly. Fretting and galling may also be problems with 17-4.

 

[MrWhoopee]

I am having one problem with the drawbar collet closer I built. The needle thrust bearings make it smooth and easy to tighten the work in the collet. However, they also have much less static friction, so they tend to let the setup loosen a bit each time the spindle is started, due to the inertia at rest of the hand wheel/drawbar assembly.

Bob,
Things you've probably thought of....
Further reducing the mass of the handwheel (thin the web, drill it out) will help. If you have a VFD, can you reduce the rate of acceleration? If you have a foot-brake, stomp it hard to re-tighten. Replace the needle roller bearing with something with more drag. Add some sort of an adjustable drag that will prevent unintentional loosening but allow intentional loosening. Scrap the handwheel and build a lever type (you need a new project, right?)

Lever type collet closers usually have some sort of positive lock that prevents loosening, but that's not practical with a handwheel.

 

[SamI]

17-4 PH is not that hard in any of its conditions. It has excellent strength, toughness and corrosion resistance, but the hardness will not get above Rc 44 (condition H900). The nose piece for a collet closer needs to be about as hard as the collets, in the range of Rc 58-60 (maybe even higher). Oil hardening or air hardening tool steel would be ideal. Regardless, it will need to be ground after heat treating. Anything less will wear fairly quickly. Fretting and galling may also be problems with 17-4.

Thank you for your advice. I suppose that rules out making one at home then unless I get some sort of an adapter. Now I’m going to have to find something else to do with a whopping great lump of steel! I do have another chunk of miscellaneous steel (I suspect 8630) which may be better suited if I’m going down the adapter route.

Failing that I’ll have to try and find a chuck designed for a drawbar. I’m sure they exist I’ve just not come accross any yet.

And for information, I had considered getting an adaptor straight into the spindle however without modifying the leadscrew covers the carriage won’t get closer enough to the headstock for short work.

Thanks again,

Sam