Centering Chuck

[shadowdog500]

Hello,

I just bought my first lathe last week, and this is my first post here.

I bought a Mini Lathe from Cummings.

Out of curiosity I took the chuck off to measure the run out in the spindle using the procedure described in mini-lathe.com.

I can happily report that the run out smaller than my dial indicator can detect because the needle on my dial indicator did not move at all.

When reinstalling the chuck I checked it with the dial indicator and noticed that the chuck can be shifted off center, and that the total movement was a little over 0.002". I centered the chuck the best I could but it is currently offset and the total movement when checking it with a dial indicator is slightly less than 0.001".

Is there a trick to centering the chuck with the spindle when reinstalling it?

I was thinking about using a hose clamp to align the chuck with the spindle before I tighten the three nuts that hold the chuck on. I am sure that there is a proper way to do this and I thought I would ask here before I try my centering via hose clamp solution.

In addition is there a good book or two that someone could recommend on the proper procedures to properly set up and run a lathe.

Thanks,

Chris

[pastera]

Don't worry about the outside of the chuck being perfect. If you have some known good round stock (drill rod, ground stock) check the chuck runout with that. The three jaw self centering will have more than ±0.001 runout in the scroll so it may not matter.

You could try to get an exchange or simply live with it and use the movement as a "set-true" chuck - chuck your stock and then move the chuck to get it centered.

If you really need to center stock really close, get a 4 jaw independant and you can center as accurate as you like.

Take a look at www.mini-lathe.com for full tear down and cleanup instructions.

Aaron

[aminear]

You shouldn't be able to move the chuck around on the rabbet fit. It should be a tight fit, some a little tighter than others but tight.

[ZipSnipe]

Chris I had and still have the same problem but worse as mine is about .003 out. Does your chuck have a back plate? If so loosen the backplate(make sure the backplate is tightened on the spindle) from the chuck. Then just snug the bolts on the chuck to the backplate and have the most precise round rod( a good sized non chinese endmill will work) you can get chucked into the chuck. Put you indicator on the rod, turn your chuck by hand and indicate the rod in by lightly tapping the chuck and tightening the bolts as you go. Mine is outta wack and because where I work we have a very precise lathe I just haven't gotten around to fix it. Good luck and like someone else said .001 is not too bad.

[Paulo E.]

Like Pastera said...... Dont worry somuch about the outside of the chuck
.001 is not bad at all considering is probably a cheap ass chuck anyways.
What does matter to you is the runout of the stock you will be turning.
Check the jaw runout with a pin gage. 1 inch dia if possible to give you
nice surface to indicate on.

As for the books the only thing I can recomend is to see the books being
used by your local trade school. That should be a good start to teach you
the basics from the ground up.

Good luck Bud..

[Alan Haisley]

Another thing about 3 jaw self centering scroll chucks: The runout on a piece of held round stock will often be different for different diameters of material.

This means that if you center the chuck for a 1" diameter round it will probably not be centered for a 1/4" round.

You will also find that the centering doesn't repeat. If you center a piece and then remove it it will probably not rechuck centered.

The cure is as Aaron suggests: get a 4 independent jaw chuck for the lathe and use that when precision is needed.

Alan

[chaterlea25]

Hi,
Have a look at this article, If you are starting from scratch with lathes this is very good info.
http://www.americanmachinetools.com/...se_a_lathe.htm

Regards
John

[shadowdog500]

Thanks for the responses.

I used suggestions from your responses as well as from several PMs I recieved and continued to play with it until I got the chuck to within half a thousands. This took just under 10 minutes to do. I could take more time to try to get it perfect. but I would want to get a good drill rod instead of the chinnees drill bit that I was using and would have to alter or fine tune my centering method because i feel it would take all day to get it dead on. Now that I read that "dead on" for a 1/2 inch rod does not necissarily mean dead on for another diameter rod makes me wonder if I do need a four jaw chuck.

I will keep what I have and try to learn all that I can before I start buying extras.

John, Thanks for the excellent link.

I video taped the chuck centering operation. The video is ten minutes long. If any of you want to spend ten minutes wathcing the video, I would really appreciate any comments or suggestions on anything you see.

Here is the link to the video
http://www.youtube.com/watch?v=Hi_s0iQkRFA

Thanks,

Chris

[neilw20]

After putting something in the 3 jaw chuck, and nipping up it up, but not really tight, with the dial indicator, keep turning to each to each key hole and tighten slightly. Rotate to next and repeat, and repeat...
The scroll will have some clearance, and very often, you can get it spot on using this method. Give it a try. Works for me.
You can also lap the jaws by putting a piece of mild steel in the tailstock, tightening the three jaw gently at first, add some grinding paste the start the spindle. The diameter in the jaws should the size of job you chuck mostly.
Run for a bit. Stop add more paste, run again. It works really well.
It is very inportant to use MILD STEEL so that the paste embeds itself in the surface.
I have achieved 1 thou at a foot with a chuck in good condition.

[pastera]

You really only need a four jaw for two reasons

1 - you need to intentionally offset a part
2 - You are not going to turn all surfaces concentric (stock is finished size or second op)

Having two chucks is very nice if they are tight fitting because you can
remove them with work installed and not loose centering.

If the loose fitting chuck really bothers you, make a chuck adapter that fits tightly on the spindle and chuck. You will loose half an inch of space but will get a repeatable fit.

Aaron

Originally Posted by shadowdog500 Thanks for the responses. I used suggestions from your responses as well as from several PMs I recieved and continued to play with it until I got the chuck to within half a thousands. This took just under 10 minutes to do. I could take more time to try to get it perfect. but I would want to get a good drill rod instead of the chinnees drill bit that I was using and would have to alter or fine tune my centering method because i feel it would take all day to get it dead on. Now that I read that "dead on" for a 1/2 inch rod does not necissarily mean dead on for another diameter rod makes me wonder if I do need a four jaw chuck. I will keep what I have and try to learn all that I can before I start buying extras. John, Thanks for the excellent link. I video taped the chuck centering operation. The video is ten minutes long. If any of you want to spend ten minutes wathcing the video, I would really appreciate any comments or suggestions on anything you see. Here is the link to the video http://www.youtube.com/watch?v=Hi_s0iQkRFA Thanks, Chris

[bluej_x]

nice you tube video but i would have hit the chuck on top with a light weight plastic face hammer when the indicator showed the high spot.

[shadowdog500]

Thanks, I will try it with a non marring hammer tonight.
[Update} I tried the hammer trick and it worked great! Thanks!

Last night I started making a device that slides over the chuck that has four adjustment screws that ride on the spindle at the 12,3,6, and 9 oclock positions. Using this hopefully I can center the chuck using the same process used in a four jaw chuck. I made a proof of concept prototype out of PVC pipe and a hose clamp and I was able to center the chuck in a minute or so but the pvc was flexing allot.

I know it is overkill but It is a good project to get some hands on practice with. Working the inside with the boring bar was interesting. I had to lean over to look in to see where the bit was touching. I almost wanted to mount a magnetic base mirror on the base of the compound to see what was going on.

Chris