New to me Central machinery 8 x 12

Samot

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I picked up a used 8 x 12 Central Machinery lathe.
Tag says 07 model ...
Guy i bought it from said he only made watch or clock parts or something ......
machine is not wore....
it's not scratched or dinged up it just look like it's been sitting in a basement for a long time paint looks like it's new.
Most of the tools are still in the plastic so fella didnt do much with the lil thing....
This is my first mini lathe...
I've been Machining for 20 years....
So the machining aspect is not my issue...
I've got the lathe setup on the table that I made and I'm now going over it with my ol trusty interapid test indicator.....
I put a dowel in the 3 jaw Chuck and I can get about .003 run out which I understand or am I'm hearing this is typical , normal or in tolerance...
I need it better !!!!
so I took the chuck apart today deburred ,cleaned it up, took a stone to it and just made it slick as could be.....
reinstalled and I'm still .oo3 out of round not to mention out about the same horizontal in 4inches or so toward chuck...
I guess the confusing part is when the chuck was off I put the test indicator on the adapter and swung it and I can't get a half thousandth of variance anywhere....
Bearings maybe ?
I've been reading post after post after post and videos on YouTube and all kinds of stuff on this lathe and I figured I would start my own post to get some insight I plan on doing quite a bit of threading with the lathe as soon as I can figure out how to engage the half nut :) and change the change gears I'm use to a big mazak I don't think I've ever changed, change gears before ? :)
:)
Any input would be greatly appreciated
Thank you
 
The .003" runout is the nature of the 3 jaw chuck. The scroll that the jaws follow to loosen and tighten the jaws is not a precision device. It also wears differentially with use, can get damaged in portions of it, and will often give different results with different diameter work. With a different diameter part in the chuck, it might be right on or twice as far out, impossible to guess with confidence. Still, if you chuck up something and turn it, it will be round and without runout where it has been cut. All that is just the nature of the beast.
 
You could always make your chuck a "tap-tru", that way you can dial in the runout whenever you need. But you'll need access to another lathe to do it assuming you have the stock chuck that bolts directly to the spindle. Take 5-10 thou off the register on the chuck so that it's oversized to the boss on the spindle. If you have a bigger chuck with an adapter you wonxt need another lathe, skim the boss on the adapter so it smaller than the register on the chuck. Then when you want to dial in a part, loosen the mounting bolts so that they are just snug, tap the chuck where needed.

I used to have one of these lathes. I had fun with it in the short time I had. I ended up giving it to my lil brother. Here's mine:

http://www.hobby-machinist.com/threads/my-hf-8x14-mini-lathe-mods.11048/
 
Thanks for the response guys.
I guess im trying to wrap my head around how the spindle can be within a half tho but the chuck has runout and taper ?
Again this is the first "mini" lathe ive touched so bare with me here.....
Im also not hip to the terminology and name of all the components of the mini lathe
I have access to another lathe and could chuck up my chuck and turn a couple tho off the mounting area and then dial it in upon install ....
Is that the best option ?
Ive gotta get it better than .003
Ill settle for .001 :)
The Runout is consistent no matter what diameter material is in the chuck...
@darkzero ... i had allready read your post on your 8x12
Nice work and advice ....
Honestly. Im considering the "tap-tru" method .
Like i say the runout is consistent regardles of part size.
I started with an 9in section of a 1in ejector pin now down to a 3/8 dowl i use to use to square up blocks on Blanchard..
Uhg.......
Would one of the after market chucks run truer?
Heck i just thought of putting the other jawz on and indicating az they are still in the wax paper maybe they arent damaged.
Is there a "precision" scroll available?
I just never ran a machine starting out un true...
So its got me spinnin in circles trying to figure out the "cause" .
If the spindle was out id understand...
But its not....
Ill be back :)
 
Try measuring runout at different distances from the chuck with the same work piece in the chuck and see what you get. Something at least 4" long...
 
The proper way to fix this is to regrind the chuck jaws. But if the fit of your chuck on the spindle is loose there's no point in doing this. The tap-tru method is easier & will give you the adjustability whenever you need. On a lathe this size you'll never have to worry about the chuck getting knocked out of true.

If you look at the specs from quality chuck manufacturers, you'll see that the guaranteed runout on plain back scroll chucks is usually .002". For the average inexpensive generic China plain back scroll chucks they don't guarantee better than .003" runout. So what you are getting is normal. Some people have been lucky & have got much better runout but that's just the luck of the draw.
 
I greatly appreciate the responses.
I have used an 8 in ejector pin as well as a 4in 3/8 dowel pin I get the same run out in side the chuck as I do at the end of the part.
Today I need to get into" dad mode" we have a Treehouse to work on :)
Most likely won't be able to mess with the Lathe for a couple days.... Mondayish :)
but I will be back on here as soon as I can....
also while I'm thinking of it , the dial for threading is not turning?
Is there some special way I'm supposed to engage dial for threading?
I just noticed the early this morning ...
Shaft is turning but the gear to the thread dial isn't engaged to the shaft...
Bear with me ,never ran lathe like this one ....
I'm sure it's something simple that I'm overlooking...
of course
 
Does "Shaft is turning" refer to the leadscrew or the shaft in the threading dial?

If it means the leadscrew, then the threading dial needs to be rotated so its gear engages. Normally a bolt on which the threading dial pivots needs to be loosened.

If it means the shaft in the threading dial, then a pin between the shaft and the gear in the threading dial may be broken or a set screw is loose.

This is the threading dial for my Southbend Heavy 10. You can see the set screw on the right of the gear.

Southbend_threading_dial_cleaned_3490.jpg

Picture or two would help us to better understand the situation.
 
the dial for threading is not turning?
Is there some special way I'm supposed to engage dial for threading?

First look behind it at the bottom, check if the gear for the threading dial is meshing with the leadscrew. If not, simply loosen the SHCS on the side of the threading dial block to pivot it to make contact with the leadscrew. I like to pivot mine out the way so it's disengaged when I'm not using it. No sense if having it spin all the time, reduce wear & tear, it doesn't use ball bearings.

Like any gear you don't want it to mesh too tight. If you are unsure of how much to mesh, stick a piece of paper in between, that should be enough gap.

If it is meshing with the leadscrew, then the SHCS that mounts the gear to the shaft of the threading dial is probably loose. There's no key as it really doesn't need one, it's just held on tight by the screw.
 
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