MT3 Chuck Mount (Baby Bison in the wild)

So I put a collar on the baby Bison:
1693062712253.png

This is mounted on a 6" D1-3 back plate sourced from Grizzly. Unfortunately it showed .003" runout! After some inspection I realized there was some slop in the factory taper :mad:.
I measured about .002 slop in the taper implying that it was oversize on the radius by .001". Since a D1 taper is 8:1 I needed to take .008 off the flat mounting face. After doing this the taper was tight and actually needs a bump with a mallet to come off. I then re-machined the mounting boss on the front to fit the chuck.
The result is about .0004 of runout! This is repeatable if I remove and reinstall the chuck. Finally! I think I am going to leave the collar since it helps to turn the chuck by hand and I can't see it interfering with anything. It does add to the rotational mass which can be good and bad.
I should also note that this has cured the chatter problems.
 
When it comes to turning the chuck, sometimes it's easiest to slip the headstock into neutral rather than turning the entire gear train.


I'm glad you solved your chatter problem. Seems like the MT mount was acting like one of these:



everbilt-door-stops-13524-64_600.jpg
 
Yes. I'm shocked a 1" shaft could flex like that but I think that was the problem. The baby Bison is now sleeping comfortably knowing that his TIR is good. I hope to get him some new feed soon. Something high in iron.

I need to examine some of my other back plates carefully. I suspect some of them are sloppy as well. But getting these tapers to seat perfectly is a little tricky.
 
rwm said:
Yes. I'm shocked a 1" shaft could flex like that but I think that was the problem. The baby Bison is now sleeping comfortably knowing that his TIR is good. I hope to get him some new feed soon. Something high in iron.

I need to examine some of my other back plates carefully. I suspect some of them are sloppy as well. But getting these tapers to seat perfectly is a little tricky.
Click to expand...
Do you have a pic of that setup?

I have a buck on a 5mt taper, and Im missing the part about where there is a shank between the two.

My taper goes right to the backplate as one piece.
 
That's how mine was set up. By "shank" I was referring to the MT3 shaft. Here is a pic from earlier:
1693181288281.png
I think the diameter of the MT3 "shank" is just not large enough. MT5 would be more solid.
 
rwm said:
That's how mine was set up. By "shank" I was referring to the MT3 shaft. Here is a pic from earlier:
Click to expand...

That baby bison would be a real tasty with a D1-3 (or whatever) on it- but it might take some trickery to pull off.
 
I used this scheme to mount 5" 3 jaw and 4 jaw chucks. Turned the MT taper and drilled 1"+ holes through them. Made the draw bar our of thick wall tubing. The final setup allows me to pass 1 !/8" stock into the headstock spindle. The initial set up worked pretty good, but had a lot of chatter when doing cut off. Checked the Morse taper fit of the chuck mounts to headstock taper. Found only a ring of contact at the outer edge of the taper. Much messing around with Prussian Blue, fine files and sandpaper improved that to full length contact. No more chatter.

I am 80 years old and the stock screw mount 6" and 8" chucks were getting to be a bit much to change. I designed and made the "quick change" system to add some years to my shop life. The new 5" chucks weigh about a third of the old chucks and are more accurate. The system works perfectly. Very quick, easy swaps with no downside while operating the lathe.
Bill
 
It may very well be that I had a bad MT3 fit. Regardless, the D1-3 works great and is almost as quick to install.
 
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