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Help me make my lathe better

Redneck_Sophistication

Redneck_Sophistication

Super User
My old McDougall lathe has an old school thread on chucks. With a floating threaded collar to hold it to the tapered spindle with a key.

The chuck has a lot of run out, and the jaws are worn, not straight.

I’d like to fit a new chuck on, luckily the millwright I bought the machine from had a similar plan and had a plate with the same thread/taper made.

So how can I attach a new chuck accurately and in a way that’s adjustable to be able to true it up?

I think the millwright’s original idea was to use a cam lock base. Is this the only adjustable way? It would also add to the length aswell.
I wouldn’t need it for changing chucks as i have a 4jaw and face plate of a matching thread on type.

Thanks, Dave
IMG_9048.jpeg
IMG_9049.jpeg
 
I'm not really sure what I'm all looking at on that lathe. But I assume the spindle has both a taper and a very large thread with a locking collar. What I'm not clear on is whether or not the backside of the chucks are threaded or have a backplate that is threaded, or just have a taper that is tightened down by a big collar like that on each chuck.

Once we know that, perhaps we can be of more help.
 
Susquatch said:
I'm not really sure what I'm all looking at on that lathe. But I assume the spindle has both a taper and a very large thread with a locking collar. What I'm not clear on is whether or not the backside of the chucks are threaded or have a backplate that is threaded, or just have a taper that is tightened down by a big collar like that on each chuck.

Once we know that, perhaps we can be of more help.
Click to expand...

Here’s a pic of when I was replacing the spindle bearings, the threaded ring is not fixed. Threads onto the chucks to hold it into the taper.
IMG_9137.jpeg


Here is the back of the 4 jaw, and the piece the old owner made. It doesn’t have the relief in the Center but measured the same. Was hoping to be able to mount a new chuck to it somehow
IMG_9138.jpeg


Hope that clarifies it a bit
 
This is definitely a L0 (ell zero) or at most a L1 long taper spindle. That is what I have on my lathe. It is a good system in my opinion. The threaded portion on the chuck may be integral with the chuck or a separate backplate. Of course, the taper needs to be absolutely clean on both parts when mounting the chucks. If there is no runout of the chuck body, then the problem is with the chuck jaws and/or scroll. A properly mounted new chuck should take care of that. If the scroll of the old chuck is ok, the jaws can be ground to correct the runout. The jig is required to properly stabilize and load the jaws before grinding the gripping surfaces.
 
I think the issue is definitely mostly in the jaws.

I checked the chuck body at the rear (only spot that is continuous) and only get 2 thou run out.

But in the jaws is almost 20! Jaws are also uneven, #2 I can jam a .008 feeler in over 1/2 inch!
IMG_9140.jpeg


I am assuming the threaded section is integral, Chuck has screws at the back but only seam I see is where the halves go together. (I think)

IMG_9141.jpeg



Chuck also has three counterbored holes in the face that are unused.
IMG_9142.jpeg




How do I check the condition of the scroll? Disassembly, or chucking differently diameter materials to compare?

Do they still make chucks to fit L0 tapers? I thought these were a long dead way to do things.
 
I think that you'll have to make an adapter to fit a new/used chuck. This Old Tony made one here:
 
Redneck_Sophistication said:
Hope that clarifies it a bit
Click to expand...

Yes, it does. So basically, your chuck and/or backing plate has a male taper and a male threaded collar. The spindle female collar pulls the two tapers together.


Redneck_Sophistication said:
But in the jaws is almost 20! Jaws are also uneven, #2 I can jam a .008 feeler in over 1/2 inch!
Click to expand...

You might be able to fix the Jaws. At the very least, take it apart and have a boo at it. But at the first sign of major problems, I'd set aside for a future date. If it were me, I'd find a suitable new or used chuck that suits the size of the other backplate and machine the other backplate to take it. If I understand what you have, you might even be able to get close to a set-true type attachment. But even if not, you have enough there to get a darn good setup with very low runout.

Then you can use this new chuck to make more backplates to fit bigger or smaller or better chucks - say a better 3jaw sized for the lathe, a 4 jaw, and a collet chuck.

Someday down the road, I MIGHT be inclined to cut the main chuck body off of the chuck you have and use the rest to make another backplate. In the meantime I guess you can use it as is with shims or whatever but using it like that would frustrate the hell out of me so I'd prolly just set it aside for now.
 
Hey @Redneck_Sophistication ,

Looks like the video @David_R8 posted is mostly about making another backplate. At the tail end of the video (23:30) he does cut the new backplate he made to adapt it to his chuck. That's where you need to pickup watching. Of course, eventually you will also want to make more backplate so it won't hurt to watch the whole thing. I confess I hate YouTube so I kept fast forwarding till I found where he started adapting the backplate to the chuck.

BTW - it might be old but it looks to me like a very cool system. At least with that setup, you will have no difficulty operating the lathe in reverse.
 
Redneck_Sophistication said:
The chuck has a lot of run out, and the jaws are worn, not straight.

I’d like to fit a new chuck on, luckily the millwright I bought the machine from had a similar plan and had a plate with the same thread/taper made.

So how can I attach a new chuck accurately and in a way that’s adjustable to be able to true it up?
Click to expand...

Your test with the feeler gauge shows that the chuck is 'bell-mouthed'. On Youtube, Mr. Crispin just posted a video on regrinding his chuck, which was nowhere near as worn as yours. After very careful grinding, he _still_ found that parts where not held perfectly true to the spindle. In fact, he found that he would get different results depending on which of the three spots he used to tighten the jaws. Wear on the internal scroll and the fit of the scroll plate in the chuck body led to small differences in the concentricity of the part held.

As they say, 3-jaw chucks are convenient but not all that true. Even a "set-true" chuck may only be repeatable on exactly one diameter of work piece. Collet chucks are inherently more accurate and repeatable but, of course, come with a different set of other limitations.

Craig
 
@trlvn bell mouth is perfectly what it is. I thought about a self made grinding set up, figured it would be a stop gap measure, so I though getting new(er) chuck would be better in long run

@Susquatch i thought about trying to shim parts true but there no way I’d have the patience for that for too long! Lol
I watched that video from @David_R8 and that is what worries me. He did all that work and it was a loose fit. Certainly a non concern with a 4 jaw at least.

That’s why I was originally thinking cam lock type as I saw a video of them being adjustable.

I know my desires and skills are on different levels! Didn’t want to bolt it all up and be in a worse state.

I just watched another video from “the Yorkshire fab shop” (slow video) doing similar to what I want. Has an L0 or 1 taper made an adapter plate to fit a smaller L0 adapter, then machined to fit the newer 3 jaw.

Even that the adapter is true to the spindle and a tight fit to the back of the chuck, still a bit of run out In the holding.

I guess machining the adapter right on the spindle is best.
 
Redneck_Sophistication said:
I know my desires and skills are on different levels! Didn’t want to bolt it all up and be in a worse state.
Click to expand...

I think @whydontu has it nailed for you. If you can buy back plates for your lathe at accusize, that puts all kinds of 3 and four jaw chucks on your menu with minimal work to fit them up.

I'd say your problems are solved as soon as you buy the parts.

I wouldn't waste another minute on your old chuck. But maybe the two backplates are salvageable.

Btw, a little play in the mating between the backplate and the chuck isn't ideal, but it isn't necessarily a bad thing either as long as you are prepared to be patient as you set it up and lock it down properly. Just call it a poor man's set tru!
 
Ian Moss said:
This is definitely a L0 (ell zero) or at most a L1 long taper spindle.
Click to expand...
looks like L0 or L1 to me too.

I agree tha you shoule buy a new backing plate and decent 3J chuck. When you are really comfortable, then go back and fix the old one.
 
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I just bought two L0 adapter plate from CME and I am happy with them. The taper matched very well, because once the collar was loosen the taper still held very well on its own.

cme-tools.com

8" L0 Semi-finished adapter Plate for LATHE CHUCKS #ADP-08-L0SM-NEW | CME Tools

L0 Semi-finished threaded back plate for 8" lathe chuck. Diameter: 8" Thickness: 7/8" Thread: L0 standard
cme-tools.com cme-tools.com

I had it delivered to my US address, I live an hour from the border. Pick them up and declared it at the border and I was wave through, no duty. I guess he gave me a break because I was on my motorbike. Bonus!

Now I am looking for a reasonably price and quality 3 jaw chuck . I am leaning toward an Accusize 8" 2 piece reversible jaw $462 all in.
 
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@whydontu that plate isn’t even as much as others I came across.

I don’t mind spending the money to get a quality outcome. I hope to have this lathe for good.

@fixerup that’s a great source too! Will they deliver to Canada? I’m not too far from the boarder either, but I’d have to empty the work truck lol. My boss used to have a US PO Box. I’ll have to check with him

Anyone have experience with a chuck from vevor? A lot of their stuff is pretty nice and you can’t beat the price. Add was ok kijiji 10” for 200$! There’s a couple chucks local on marketplace too.

I’ve got a bit more confidence in this now! Thanks guys. Would mild steel be acceptable for an adapter plate? Or better to get 4140 or some other steel?
 
Without claiming to be a metallurgist, I don't think a backing plate needs to be 4140. It's static, does not see any wear in normal operation, not under much load. Lots of them are just good'ol cast iron. The extra effort to machine from 4140 over plain carbon steel probably isn't justified.
 
Redneck_Sophistication said:
I’ve got a bit more confidence in this now! Thanks guys. Would mild steel be acceptable for an adapter plate? Or better to get 4140 or some other steel?
Click to expand...

I'm not sure I understand why you need to make anything. Just buy the backing plate and machine it to fit your new chuck!
 
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