Author Topic: Question about an old post on fitting chucks.  (Read 1184 times)

Offline LakeHouseMetals

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Question about an old post on fitting chucks.
« on: November 22, 2022, 01:32:53 AM »
Hello,
New user to this forum, and to machining, more or less.
A few years ago, when I was still working for a living, and had income, I was gathering equipment for what was to become my hobby in retirement.  One of the machines I found was a 1941 South Bend 9C that appears to have been in very good condition even before someone spruced it up with new paint, etc.  Anyway, from reading, lurking on sites like MEM, etc, it seemed clear that sooner or later I would need a four jaw chuck.  I actually found a place online that was selling brand new Atlas 6" four jaw chucks sporting the 1.5" 8TPI specs used on my SB.  When it came in, I was excited, but then pretty disappointed to find it would not thread all the way onto my spindle!  I set it aside and continued to use the 3 jaw that came with the machine.  But now I want to turn a shaft with an offset pin on it and I think I really need the four jaw.
So, Google led me to Steamer's post about fitting a chuck to the spindle.  I did not know that was 'a thing', I thought my new chuck would 'just fit'.  But hey, now there is hope!

I have a question on the process that was used.  Early on, Steamer stated "but first we need a plug gage in the form of a dummy spindle"...

Why is that?  I would have guessed I could just chuck a straight bar into the 3 jaw, turn the four jaw around and clamp down on that bar, indicate on the inner bore and true things up until the new chuck was running 'true and concentric'?, and then open the bore to fit my spindle.
I don't see what the dummy spindle does.

Thanks for any help anyone can provide.

R. G. Sheehan

Online vtsteam

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Re: Question about an old post on fitting chucks.
« Reply #1 on: November 22, 2022, 02:57:08 AM »
If the 4 jaws were perfect and the bar turned first before mounting it, yes. But perfection of jaw alignment is not something I found  in my own new 4 jaw chuck. Just because jaws on a 4 jaw can be adjusted in position doesn't mean they grip perpendicular to the reference plane of a register in every location they are moved to. Maybe you can do it that way, maybe not, depending on your personal requirements and the reality of the accuracy of your chuck. Also, the dummy spindle lets you check the accuracy of your bore and facing

But also, not being there, I can't  actually see why your chuck won't seat, there could be a couple of reasons, and maybe easier solutions. For instance, turning a spacer.
« Last Edit: November 22, 2022, 03:10:43 AM by vtsteam »

Offline steam guy willy

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Re: Question about an old post on fitting chucks.
« Reply #2 on: November 22, 2022, 03:05:15 AM »
To get a really good fit it is advisable to make a plug gauge first to fit the recess in the back of the four jaw chuck after removing the back plate that came with it. It may need several "goes" to get a nice fit with the new mandrill .  You will possible need to remove quite a few faces of the gage to achieve this" fit" but when it is done you can turn down the new backplate you have acquired just the once to keep as much metal on the backplate by using the gauge . this will be quite a tedious turning operation but you will not have to acquire another  backplate if you take to much off it ...

Hope this helps

Willy

Offline Jasonb

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Re: Question about an old post on fitting chucks.
« Reply #3 on: November 22, 2022, 06:59:26 AM »
"and then open the bore to fit my spindle."

If you don't have a bore micrometer etc how will you accurately measure the hole you are boring in the chuck?

Steamer used the gauge he previously turned to size the hole until the gauge just fitted rather than go by measurement that may not be perfectly accurate for example just using digital calliperes

Online Jo

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Re: Question about an old post on fitting chucks.
« Reply #4 on: November 22, 2022, 08:15:02 AM »
I am not sure if the others have answered your question: "Why do you need a plug gauge". When you need something to fit exactly we use a plug gauge: this is something that is spot on the right size, shape etc as what the new piece must fit and we use it to check if any more needs to be turned off (or if we have gone too far  :Doh: ).

When it comes to fitting a back plate you have to first make the backplate fit the nose of the lathe. It is a bit tricky making something to fit the nose of the same lathe that you are using to turn the item to turn said item on - the chuck is mounted on the lathe nose and you don't want to take the work out of the chuck to check if the backplate fits on the lathe nose as it won't go back on the same  :ShakeHead:.

So you start by turning up an exact copy of the lathe nose (the plug gauge) so you can use that to check you have turned the back plate to the correct size.  If the plug gauge fits the backplate you know when you take it out of the chuck it is going to fit the nose of the lathe  ;)


I have a plug gauge I made for copying my Hardinge's nose taper  :)

Jo
« Last Edit: November 22, 2022, 08:33:42 AM by Jo »
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Offline Chipswitheverything

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Re: Question about an old post on fitting chucks.
« Reply #5 on: November 22, 2022, 09:04:27 AM »
Just a thought about the plug gauge that is a replica of the lathe's spindle nose:  if it is made on a "parent" shank of reasonable length and diameter, then it could be useful later for adapting as a mandrel for transferring the lathe chucks over to a dividing head or indexing fixture.  Particularly if the stock from which it is formed has centres initially put in accurately at both ends, to facilitate future turning operations to size the shank to fit a dividing head bore or taper in due course.   Might make the job of doing the plug gauge a more attractive one if it seems to offer that extra purpose....  Dave

Offline john mills

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Re: Question about an old post on fitting chucks.
« Reply #6 on: November 22, 2022, 09:05:40 AM »
the plug gauge can be made and checked against another backing plate which fits the lathe whiteout moving the one you are using to make the plug gauge.
can you see what is stoping the new chuck from screwing home?
is it a backing plate chuck or some are direct fitting  the chuck is machined too fit the spindle.the chucks i have are direct mounting .
i would not touch the flate face that was machined when the chuck was made that fits again the flange if it is not damaged assuming it was
correct .if the thread fits would not re cut it .what is the part which needs adjusting to make it fit.
john

Online vtsteam

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Re: Question about an old post on fitting chucks.
« Reply #7 on: November 22, 2022, 02:49:48 PM »
I think the why question for a plug gage has been well answered. I'm just curious R.G. is your chuck itself threaded, or does it have a back plate bolted on that is threaded? I have a 4 jaw for my Craftsman that was unitary, no backplate, and I had a similar problem. Just wanted to clear that up in case the mention of backplates seems confusing to you. The need for a plug gage to check any machining of the register would be the same however.

Offline LakeHouseMetals

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Re: Question about an old post on fitting chucks.
« Reply #8 on: November 22, 2022, 04:41:13 PM »
Okay, you guys have convinced me a plug gage is the best way to go.  So, never having turned threads before, could I just turn the 'registering' part and skip the threads for now?  Don't get me wrong, I like the idea of having that separate spindle clone that I could use in the future, possibly to make something like the faceplate balancing fixture I read about in a Harold Hall book on lathes (I think).  But I would really like to get a four jaw mounted up, so I can try to make that camshaft, so I can put the magnetic chuck back together, so my surface grinder can get into service.  (Is it common for projects to 'chain' together like that?).

Anyway, following is what I have to work with.
1941 South Bend 9C - Spindle register diameter   1.510"
                                                 register depth        ~0.188"  (from the back until the thread starts)
                                                 thread depth          .873"  (including the register depth)

Cushman 5" 3 Jaw (came with lathe), has back plate, threads all the way on, albeit snugly.  Register bore  -  1.531"

Old yard sale Craftsman 6" four jaw, jaw threads in the body are not good so I don't trust it to hold well, has back plate, will not thread all the way on,  Register bore  1.502

Even older? NoName 6" four jaw, spindle threads are pretty rough so afraid to get it anywhere near my lathe, has back plate.  This is a very 'slim' chuck with small jaws.  Seems to need something like a 9/32 hex to adjust the jaws? Is there such a thing as a four jaw chuck for a -wood- lathe?    Register bore  1.503"

New Atlas (Pratt Bernerd, made in England) 4 (edit - not 6) jaw, will not thread all the way on spindle, NO back plate,  Register bore  1.500"

After making a plug gage (with or without thread), my plan is to 'practice' on the Craftsman.  If I can I will separate the back plate, mount it backwards on the SB, and try to open the bore to fit the gage.  I might do that again with the old NoName before finally getting to the new chuck.

Thanks for all the information.
R. G. Sheehan





Offline mklotz

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Re: Question about an old post on fitting chucks.
« Reply #9 on: November 22, 2022, 05:25:18 PM »
When I was starting out, I decided to make a collet chuck for my lathe.  Since I needed to turn internal threads to fit the threaded spindle on my lathe, I needed to make a plug gauge.

After I made it and used it to manufacture the collet chuck, I wondered if it could be of any other use.  Its first use was to manufacture a spindle thread protector of aluminum.  I put this on the spindle threads when I'm doing something on the lathe that involves removal of whatever chuck is on the spindle.  I'm pretty careful about dropping tools but accidents happen and I don't want to replace a spindle.

The plug gauge reached its pinnacle when I got a rotary table.  I bored the gauge out and mounted it on a short arbor that matched the hole in the rotary table, thus allowing me to mount any of my lathe chucks on the table and have them automatically centered.  Keep this in mind when you make your plug gauge.  Before removing it from the chuck on which it was turned, drill and bore a hole through it.  This will allow you to easily center it later to bore for an arbor or whatever, should you find another use for it.
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Offline GWRdriver

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Re: Question about an old post on fitting chucks.
« Reply #10 on: November 22, 2022, 08:24:05 PM »
I am not sure if the others have answered your question: [snip]
Neither am I, but if so I have an option to consider.

I have a 1950s-vintage South Bend 4-jaw chuck in VGC, as originally supplied with a new lathe.  FWIW the register ID on this chuck is 1.5300" and I'll have to say I was surprised by this.  If I were doing this job (matching a 1.510" spindle register) I'd aim for 1.515" ID.  As a comparison I measured a Super-7 spindle register which is 1.2500".  I them measured a new factory face plate and a standard P-B OEM 3-jaw chuck which is 1.2515".  As you can see your register clearance mileage may vary!

I have a number of chucks threaded for 1-8 (based upon an Atlas spindle standard of 1.500") and all of them are 1.505"-1.508" ID, and the 1.505" actually makes for a snug fit.  Given your tooling here's how I would do this job.

I would start with the Plug Gauge.  Chuck up a piece of bar and turn a very shallow and very short taper over it's length, such that the measured diameter of 1.515" occurs roughly in the middle of the tapered section.  Mark the point exactly where 1.515" occurs.   If you have the means of accurately taking the inside measurement of the chuck register you can dispense with the plug gauge.

Mount the sturdiest 3-jaw you have on the lathe and chuck a length of bar, of the largest diameter you have, very snugly.  Making a truing cut along the bar for a length equal to the depth of your 4-jaw jaws + " or so.  You now have a true running stub mandrel.

Reverse the 4-jaw (face toward the headstock) and mount it on the stub mandrel.with its own jaws.  Using the jaw screws adjust the register recess to run dead true.  Before doing anything else check the runout of the chuck body, face and rim.  There's very little can be done about that if it's out (wobbly) but at least you'll know, and you'll also know your jaws are running parallel to the lathe axis.

Assuming you've checked both the spindle and the chuck threads for fouling, on account of shoulder depths, you can now proceed to bore the register using the plug to stop at 1.515".

I've made most of my own back plates (including a couple of D1-3's) and this has worked pretty well for me in a few instances.  It's not the only way . . . but it's A way.

Best of luck,
Harry

Online steamer

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Re: Question about an old post on fitting chucks.
« Reply #11 on: November 23, 2022, 12:35:11 PM »
A plug gage is a smart approach.   Sorry for the late reply,  been busy

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Online steamer

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Re: Question about an old post on fitting chucks.
« Reply #12 on: November 23, 2022, 12:41:12 PM »
Is the post you referenced in my rebuild thread ?

https://www.modelenginemaker.com/index.php/topic,369.0.html

Dave
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Offline Mcgyver

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Re: Question about an old post on fitting chucks.
« Reply #13 on: November 23, 2022, 06:10:59 PM »
Here's some shots and commentary on how I did a couple of them earlier this year. 

https://www.metallum.shop/lathe-threaded-back-plate/
« Last Edit: November 23, 2022, 06:33:57 PM by Mcgyver »

Offline LakeHouseMetals

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Re: Question about an old post on fitting chucks.
« Reply #14 on: November 28, 2022, 04:21:24 PM »
Dave/Steamer,

Following is the post I was originally referring to:

https://www.modelenginemaker.com/index.php/topic,2189.msg35127.html#msg35127

-rgs