# Making a lathe chuck back plate, first timer



## great white (Jan 10, 2019)

My Atlas TH42 has it's original 4 jaw chuck. It has "Atlas" stamped right in the face. 

It's a good old soldier and it works, but it's sloppy and takes a fair amount of fiddling to get it dialed in. On the plus side, I've gotten pretty proficient/quick at mounting stock in a 4 jaw chuck! 

The key slots in the body seem worn/sloppy, which makes tightening and adjusting an extra hassle. The jaws will often not have a square grip on the work piece either. To the point where you can look in to the jaws and actually see they don't have full contact along their length on the work piece.  

I suppose I could try "refreshing" the old chuck, but I'm pretty sure it's close to the end of it's useful life with the way the jaws move inside the chuck body slots. Again, they're not completely horrible, but you can feel the slop when you grab them and I can't see how I would be able to compensate for material that has been worn away over the last 60-70 years of use.

I've got a "new" 4 jaw chuck I picked up a long time ago, before I even bought the Atlas. If I recall, it's an "ebay special". IE: No name. It's roughly the same size as the orginal Atals chuck with a body that measures 6.25 across it's face (The Atlas is 6.00). But it has one advantage over the atlas chuck: it's not worn. 

So I'm looking to cut a back plate for it and try it out. This is something I've never attempted before, but you gotta start somewhere!

Getting a pre-machined plate would be prohibitively expensive where I live. Even just the shipping would be crazy. I'd love to be able to, but it's just not in my budget. I'm also looking to start learning thread cutting. 

Getting a chunk of cast is also not an easy option here, it's just not something that's readily available. A chunk of steel the right diameter is possible, but not cheap either. Tariffs and whatnot have driven the price of metal crazy here lately......that's all I'll say about that.



By the same token, having a local shop make me one (even if just a raw plate with threaded center hole) would also be crazy expensive.

So I'm left with making my own plate and with something I can source locally.

First hurdle is the internal threads. Boring to size I can do, but I've never cut threads. Let alone internal ones. It seems reasonably easy from the videos and manuals I've seen, set the gear train to the right combo and run 'er in and out. But I'm not as naive to believe it is going to be that easy. I'm thinking I need to practice a bit before trying to cut the plate. I do use collets in the Atlas, but I don't have a nose guard for the threads. Perhaps I should practice by making a thread guard before moving to cutting the plate? That wouldn't be too expensive, it's something I need anyways and would be the exact threads I need to cut in the plate. Seems to make sense to start there.....

The cast iron plate is another issue. As mentioned, it's not easy to find here and crazy expensive to ship something in. I do have a couple of older cast iron weight sets and a couple plates measure out to about the right size. I know weight set cast iron plates can be a crap shoot as to what is in them, but I don't have a lot of options here. 

Carbide tooling is what I will be using and I have lots of inserts available. If it cuts reasonably well without killing a carbide insert, I should be able to carry on making the back plate and have a decent finished product, right?

Which brings me to the method of cutting the plate on the Atlas. I'm not sure the current chuck will be big enough to hold the cast iron weight. There's enough swing over the bed, I'm just not sure I can get an adequate grip on the raw plate. Both because of the rounded outside edge of the plate and the amount the jaws would likely have to be out of the chuck body. At least not well enough to bore it and cut the internal threads. So what are my options to mount the plate (or a chunk of steel) for at least getting the center hole bored and threaded? Once it's to that point, the rest gets easier because it's at least on the spindle and I can make the diameter/chuck registers.Once it's mounted on the spindle, I'm back in my wheel house for machining procedures.

So, any advice here?


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## BtoVin83 (Jan 10, 2019)

You probably need a piece at least 1 1/2 inches thick, do you have a weight set that thick?


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## pdentrem (Jan 10, 2019)

I have a back plate for an Atlas sitting. Here is a topic I started awhile back. Hope it helps you out. 

I would chuck it up and cut the front to form the collar area then flip it around and clamp on that new collar, if you are concerned about the holding strength and then bore and thread the spindle hole. Have to go back to work. Later

https://www.hobby-machinist.com/thr...ed-spindle-backing-plates-for-my-lathe.19802/


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## Latinrascalrg1 (Jan 10, 2019)

I don't know much about what you asked but i can recommend using pvc pipe to practice on.  It's cheap and easy to work with which is perfect for getting the feel of what and how to work the machine then when cutting the real deal you can go by mostly muscle memory giving you the ability to concentrate more on how the cut is going vs worring about if you are doing it correctly! 

Although my first thread job was a male thread (I know sorta different animal)  it really did go very easy which I contribute to spending a small amount of time practicing on some pvc.


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## mikey (Jan 10, 2019)

You could order one already threaded to fit your spindle and take it from there: https://littlemachineshop.com/products/product_view.php?ProductID=1792


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## mattthemuppet2 (Jan 10, 2019)

I made a backplate for my 4" 4 jaw from a piece of 1" plate I found at the scrap yard. Cut it roughly round with an angle grinder and hacksaw, then turned down enough of the diameter so I could turn it around and do the rest. Then drilled, bored and threaded the hole for my spindle - you can either take the chuck and plate off the spindle, turn it round and test (=tedious) or you can make a copy of the spindle nose and use that as a Go-gauge (=more work, less time). As soon as you have the hole done and back of the plate machined to dimensions, you mount the backplate on the spindle, face it flat and cut the chuck register.

It's pretty straight forward, even to do it from plate, just takes a while. Backplate has been doing its job of holding the chuck on the lathe for 3 or 4 years without complaint


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## middle.road (Jan 11, 2019)

Also hit up YouTube for back plate videos. There are a bunch of good ones there.


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## GrayTech (Jan 11, 2019)

Can you just cut a new register on the old backplate and reposition the holes? 

Sent from my H3123 using Tapatalk


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## great white (Jan 18, 2019)

Latinrascalrg1 said:


> I don't know much about what you asked but i can recommend using pvc pipe to practice on.  It's cheap and easy to work with which is perfect for getting the feel of what and how to work the machine then when cutting the real deal you can go by mostly muscle memory giving you the ability to concentrate more on how the cut is going vs worring about if you are doing it correctly!
> 
> Although my first thread job was a male thread (I know sorta different animal)  it really did go very easy which I contribute to spending a small amount of time practicing on some pvc.




I like that PVC idea! I've got lots of scraps lying around I could use...


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## great white (Jan 18, 2019)

GrayTech said:


> Can you just cut a new register on the old backplate and reposition the holes?
> 
> Sent from my H3123 using Tapatalk



Nope, too small. The atlas chuck has a very small back plate for some reason. It's a 6" chuck, with what looks like a 3" register.....


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## Chris Hamel (Jan 24, 2019)

I made a backplate for my 9 inch sb lathe out of aluminum.  I first made a 1 1/2   8 nipple.  This was really helpful because when I  cut threads I like to advance my tool until I get a good fit instead of trying to calculate how deep to cut.


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## P. Waller (Jan 26, 2019)

great white said:


> ]By the same token, having a local shop make me one (even if just a raw plate with threaded center hole) would also be crazy expensive.


What exactly do you consider "crazy expensive"?

$150.00 for material.
3 hours machining time @$125.00 per hour.
$525.00 for something that you can not buy on ebay or anywhere else.

One will quickly run out of money doing such work in the USA at Asian import prices.
I am curious, at what price would you actually buy this part.
As little as possible is not an answer.


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## great white (Jan 26, 2019)

P. Waller said:


> What exactly do you consider "crazy expensive"?
> 
> $150.00 for material.
> 3 hours machining time @$125.00 per hour.
> ...



comment like that demands on one possible answe:

As little as possible.

And I’m glad I don’t live where you live if it’s $150 for a 6” diameter chunk of cast iron...


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## Chris Hamel (Jan 27, 2019)

If I am not mistaken, your Atlas has the same type spindle as my 9 inch South Bend.  It is an 1 1/2 x 8 thread.  All you need to do is search ebay for 1 1/2  8 back plate.  No matter which one you get you will have to do the final machining.  You mount the back plate on your lathe spindle and machine it to fit your chuck.  They do this to minimize the run out.  I have done several for my South Bend.  Take your time and you won't have a problem.  I did make one back plate out of aluminum which has worked out fine, but the cost for one from ebay isn't that much.  Here is a possible solution.

https://www.ebay.com/itm/6-Fully-Ma...h=item46104c7d0e:g:wJsAAOxy2E1SDQtH:rk:2:pf:0


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