Mini - lathe

[nobleswood]

After thinking this over I'm going to work on the idea that the mounting holes in the faceplate are the problem and make some adjustments there.

[Mike Tashjian]

Easy to think the machine has to be perfect to make perfect parts but that is not true for a minute.  You just have to know how to make your parts with the machine you have.  Every machine in every shop I ever worked on had some issue that you had to work around because nobody was going to fix it.  Learning the proper sequences and running a machine within it's limits will let you make very good parts.  It takes time to learn and skill sets will be learned as you go.  Be patient and make parts, it will get easier as you go. 

[John A]

Once you get it set it should hold until it gets crashed. The tooling will cost at least as much as the lathe. It’s a great pass time, the hours fly by so getting the time to use it gets difficult. There are two things a lathe can do, one is replicate itself and the other is hurt the operator badly.  Watch out for “machine hypnosis “ and make some cool stuff. I have a pile of stuff that I wasn’t happy with,  sometimes I can make something the first try, some times it takes a couple or more and I’m glad I don’t have to earn a living that way!

[pehayes]

After thinking this over I'm going to work on the idea that the mounting holes in the faceplate are the problem and make some adjustments there.

So, you have no register dome on the spindle to force or maintain concentricity.  Here's an idea.
Find a plate of 1/2" metal.
Drill the three mounting holes but make them small enough to thread internally.
Mount this dummy plate up against the spindle and use short bolts from the back side which will hold the plate in position and mark that as your standard, or re-mount position for every usage.
I saw on the video that the chuck DOES have a recessed back to allow for attachment to a register dome.
Now, turn 1/8" or so from the front of this dummy plate so that you create a register dome for a snug fit with this chuck recess.
Drill 3 new holes in the dummy plate and recess the back side of those holes to the dimension of allen head bolt heads.
Unmount the plate from the spindle and mount it to the back of the chuck using these recessed allen bolts.
Now remount the plate to the spindle and with luck you will have something very close to concentric.
You might then consider a gentle grind to the jaws to approach precision.

This is delicate work for a beginner, but a good learning project.  You might need help from someone with a mill or another lathe to ensure that your bolt holes are in a precise "bolt circle" layout.
Starting with 1/2" or 3/4" aluminum plate would be easier to work with and might serve you a long time.  Once your skillset develops you might do it again in steel for better durability.

I have made backing plates like this numerous times in order to adapt other, odd chucks and fixtures to several different sized lathes.  You're trying to make something like this:



The accuracy is still dependent upon using the bolt holes of the spindle face and that may vary slightly every time  you remove and reinstall the chuck.  With practice, you will learn to remont and restress the bolts always in the same direction so you can at least be accurately repetitive if not accurately concentric.

Patrick Hayes
Fremont CA

[pehayes]

What is the size of the pass-through hole in this chuck?
Could you mount a collet in the spindle, then a precision rod in that collet, then install the chuck by first clamping it to this mounted rod before bolting?
In this way, you would get the jaws very close to concentric before bolting down the chuck.
Of course, there has to be enough room for  you to now remove the precision centering rod and the collet that was holding it.
Might be something you'd have to make.  Perhaps sacrificing some other purpose built tool with the proper taper.  Start by measuring the ID of your pass through hole in the chuck.

Patrick Hayes
Fremont CA

[nobleswood]

Thanks! I like the backing plate idea, rather than throwing money at a new chuck & hoping. 

[pehayes]

This guy did a lot of work.  Should be helpful guidance for you.

http://www.bazmonaut.com/machines/hobbymat-prazi-md65-lathe/fitting-new-chucks/

Patrick Hayes
Fremont CA

[nobleswood]

Bazmonaut. I've been reading his posts they have helped especially as he's working with the same lathe.

Anyway, success !

Pulled the chuck, checked the mounting studs for nicks & kissed them with a fine Nicholson file. Remounted & managed to get TIR to 0.005". Good enough for me.

Thanks for the advice, pointers & ' no need to be paranoid' guidance.
 'Hello my name is Tim & I'm a Perfectionist' 

[Chuck in Indiana]

Good enough for me.

You can do better, grasshopper..

[PeteS]

I had a machine shop instructor in college who said ".001?, why you could drive a truck through it!".
You want to aim for perfection.

Pete

[Chuck in Indiana]

I know nothing about that little lathe except it has a good reputation. I'd bet money (Not Guzzi content)    that the spindle is on the money. If not, you will have to make it so. (New spindle bearings, etc.) *Assuming* that it is, there is no reason that you can't get it to run true.
In general, 3 jaw chucks aren't terribly accurate, but there are some tricks you can learn. Just the same, (it has a good reputation, again) unless FedX really did a number on it.. you should be able to get it running better than .005.

[nobleswood]

Obi - Chuck,

I am interested in the ways to set up the chuck to be more precise. 

From what I could measure the faceplate & the spindle had just under 0.002" TIR. Which is the specification in the sales brochure.

[Lumpy Idle]

Go on YouTube and subscribe to training videos by  Joe Pieczynski.  He diagrams and speaks in a common way and has a sophisticated, commercial shop.

Patrick Hayes
Fremont CA

yes, piescynski is a machinist's machinist.  there are a number of really good online machinists and you will find them easily once you start poking and prodding for machinists on the utoob. i would highly recommend Blondihacks for small machining/lathe tips. quinn dunke is excellent and knows her way around machining and especially the small home lathe that she uses. do not miss blondihacks.