3 jaw or 4 jaw chuck

[J-G]

I just rely on common sense when I don't know what I'm doing.

By far the best policy. If it 'feels' right it usually is.

 

[Inspector]

As long as you learned what common sense was a long time ago and built on it. Some people's common sense is closer to nonsense but it make sense to them. Often a frightning thing to be around.

Pete

 

[Sandyn]

I sat on the decision for a while, but got a 4 jaw self centering chuck. I opted for the 125mm. My goodness!! what a monster compared to my old 100mm Pratt Burnerd.

I tried some out of round steel bar and it gripped it without any problem. The chuck is pretty good quality. I assume it is Chinese . No country of origin on the box or unit, but it carries the same number as the Sanou K12-125

My old Pratt chuck was a bit worn. I took it to bits and cleaned it out and examined the jaws. I found they were worn along the gripping face. I tried grinding them (nothing to lose). I re-assembled the chuck and using a circular grinding stone in the tailstock chuck, set the main chuck so it just gripped the grinding stone lightly and ran the stone in and out of the chuck a few times, then closed it down very slightly. It worked amazingly well, but the grinding stone wasn't really good enough to do more. A diamond grinding point would be perfect, but soooo expensive. When I took the chuck to bits,I could see what was causing the old chuck to be a bit sticky when operating. Each of the pinion wheels were worn at the shaft end. Would be easy to put a bush in to take up the wear. The gear surfaces were fine.
Overall really happy with the new chuck.

 

[Rorschach]

Looks good, have fun with it. See if you can get yourself some soft jaws for it, 4 jaws are very versatile with soft jaws as you can use 2 for gripping unusual shape objects.

Also, get yourself a mt2 arbour with myford thread on it, then you can put the chuck in your tailstock and use it as a self centring/cross drill drill jig for stock that is too large to spin in the headstock.

 

[Sandyn]

Looks good, have fun with it. See if you can get yourself some soft jaws for it, 4 jaws are very versatile with soft jaws as you can use 2 for gripping unusual shape objects.

Also, get yourself a mt2 arbour with myford thread on it, then you can put the chuck in your tailstock and use it as a self centring/cross drill drill jig for stock that is too large to spin in the headstock.

Thanks I'll have a look for soft jaws.
can you explain the second part more. I understand the MT2 arbor in the tailstock and fitting the chuck. The drill in another chuck in the headstock.
The centres of the tailstock and headstock are the same height from the bed, So that places a limit on the dimension in that plane, but no limit to size in other directions. I don't get how I can get a cross drill when the centres of the headstock and tailstock are always in line?

 

[Inspector]

The usual way of fixing the jaws is to put a small grinder in the tool post and with it and the lathe running kiss the stone to the jaws and advance it in. Repeat until all jaws are cleaned up. The jaws need to be held in such a fashion as to preload them so the slack is taken up.

Pete

 

[Rorschach]

Thanks I'll have a look for soft jaws.
can you explain the second part more. I understand the MT2 arbor in the tailstock and fitting the chuck. The drill in another chuck in the headstock.
The centres of the tailstock and headstock are the same height from the bed, So that places a limit on the dimension in that plane, but no limit to size in other directions. I don't get how I can get a cross drill when the centres of the headstock and tailstock are always in line?

Maybe this pic will help. The 4 jaw chuck would be used in place of the cross drilling jig. It is also self centring on any stock and holds it secure so much safer than the picture.

 

[Sandyn]

Thanks! This morning when I woke, out of the blue, I thought of a metal bar in the tailstock chuck and understood what you meant. Makes perfect sense now and a great idea.

 

[jonn]

As long as you learned what common sense was a long time ago and built on it. Some people's common sense is closer to nonsense but it make sense to them. Often a frightning thing to be around.

Pete

Read up on agnotology, something much practised in USA, and seemingly coming to UK. As to common sense, it might be common, but often doesn't make much sense.

 

[Rorschach]

Thanks! This morning when I woke, out of the blue, I thought of a metal bar in the tailstock chuck and understood what you meant. Makes perfect sense now and a great idea.

I had a small 4 jaw SC with no backplate that I was struggling to find a use for so I decided to mount it permanently to an MT2 arbour. I use it in the headstock (with drawbar) or in the tailstock pretty much only for cross drilling stock. I also have made a little adaptor that lets me put a MT2 in my drill press table again so I can mount a lathe chuck there for drilling items too awkward to do in the lathe. Very handy.

 

[Sandyn]

Read up on agnotology, something much practised in USA, and seemingly coming to UK. As to common sense, it might be common, but often doesn't make much sense.

Very interesting. I had a conversation some time ago with a flat earther. It was an interesting conversation, but I soon realised the guy was quite insidious His aim was to try and plant seeds of doubt about any argument I put forward. I'm not sure what the aim of these people is?