# What is a Self-locking Stub Arbor?



## Chips O'Toole (Jan 31, 2020)

I found out a guy named Duclos made his own air spindle and wrote it up in Home Shop Machinist magazine, so I bought a back issue and looked at it. It looks like a surprisingly simple project, which suggests there are things about it I don't understand. The article appears in two issues, and I don't have the second part yet. Maybe that's where the fun starts.

As part of the process, he tells the reader to make a self-locking stub arbor. He gives no details at all, like every hobbyist is born knowing how to do this. I don't even know what a self-locking stub arbor is. I know what an arbor is, and I guess "stub" means it's short, but that's about it.

Can someone tell me what he's talking about? I'll upload a photo of a photo. Sorry about the quality.


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## mmcmdl (Jan 31, 2020)

Not sure how it relates to the air spindle , but there are many types of locking arbors . Think of how a Hardinge lathe chuck adapts to the spindle . Most only lock in one direction so be aware of CW or CCW rotation .


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## Chips O'Toole (Jan 31, 2020)

Unfortunately, I do not know how a Hardinge chuck works.


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## JimDawson (Jan 31, 2020)

Never seen or heard of that before, but it looks like a sprag clutch.  I normally make stub arbors that are either threaded OD or ID as needed to secure the part.  These are normally built as a temporary, single use, work holding device.


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## mmcmdl (Jan 31, 2020)

OK , how about counterbore sets . It has one arbor and all of the different size c bores lock at 1/4 turn . Usually a pin with an angled cam which locks them on . Removed easily with channel locks , pliers etc .


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## jmkasunich (Jan 31, 2020)

Chips O'Toole said:


> I found out a guy named Duclos made his own air spindle and wrote it up in Home Shop Machinist magazine, so I bought a back issue and looked at it. It looks like a surprisingly simple project, which suggests there are things about it I don't understand. The article appears in two issues, and I don't have the second part yet. Maybe that's where the fun starts.
> 
> As part of the process, he tells the reader to make a self-locking stub arbor. He gives no details at all, like every hobbyist is born knowing how to do this. I don't even know what a self-locking stub arbor is. I know what an arbor is, and I guess "stub" means it's short, but that's about it.
> 
> ...


From the photo, I'm guessing that then the cutter (not shown) tries to rotate on the arbor, that little pin rolls with it until it wedges between the ID of the cutter and the flat on the shaft.


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## Cadillac (Jan 31, 2020)

jmkasunich said:


> From the photo, I'm guessing that then the cutter (not shown) tries to rotate on the arbor, that little pin rolls with it until it wedges between the ID of the cutter and the flat on the shaft.



That would do absolutely nothing. Assuming the cutter has a round hole for mounting to the arbor with the above situation the cutter would still spin. If the cutter had a keyway and the pin fit the keyway the cutter would have some movement until it rolled to the edges of the flat on that arbor. Guess will have to wait for vol.2 of the author to find out.


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## mmcmdl (Jan 31, 2020)

Fun At Home Shop Projects ........commenly Known As " G " Or Government Jobs
					

Cheap mans boring head . Not a Criterion nor Walhopter but will get you thru non-critical jobs .  Bore or drill a piece of stock in one end true to OD . Turn part around and turn an OD that is offset for your shank . Make another piece that fits your bore with an offset boring bar hole . You...




					www.hobby-machinist.com
				




The boring head uses a cam type self locking mechanism .


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## Chips O'Toole (Feb 1, 2020)

The arbor is for stock, not a cutter.


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## Chips O'Toole (Feb 2, 2020)

It looks like no one here knows what "stub arbor" means in the context of the article, which confirms my suspicion that the reference was not adequately explained. The author of the article tossed it in there as if any machinist would know what he meant, but it appears that he was expecting a little too much.

Now I have to ask myself...do I care enough about this to venture over to Practical Machinist and deal with the flame masters?


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## T Bredehoft (Feb 2, 2020)

I'm gonna take a guess at this.....

Its' for second operation on a production part. The part has a concentric bore which would be a very nice fit on the stub arbor. 

The operator installs the stub arbor concentric in the lathe, with the loose pin in place. The operator then slides the work over the arbor and turns on the lathe. The pin wedges itself into the corner between the arbor and the work, spinning the work. The work is completed, the lathe stops and the operator twists the work top toward them, loosening the pin. They remove the work from the lathe, dig the pin out of the chips and repeat the    procedure on the next piece. 

And Bob's your uncle.


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## Chips O'Toole (Feb 2, 2020)

That's what I thought when I saw it, but why would the pin lodge itself instead of rolling?


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## BGHansen (Feb 2, 2020)

Chips O'Toole said:


> I found out a guy named Duclos made his own air spindle and wrote it up in Home Shop Machinist magazine, so I bought a back issue and looked at it. It looks like a surprisingly simple project, which suggests there are things about it I don't understand. The article appears in two issues, and I don't have the second part yet. Maybe that's where the fun starts.
> 
> As part of the process, he tells the reader to make a self-locking stub arbor. He gives no details at all, like every hobbyist is born knowing how to do this. I don't even know what a self-locking stub arbor is. I know what an arbor is, and I guess "stub" means it's short, but that's about it.
> 
> ...


Which issue are you missing?  I have every issue starting from the first one in 1982 (or whatever year they started publication).  Might be able to help you out with part 2 . . .

Bruce


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## jmkasunich (Feb 2, 2020)

Chips O'Toole said:


> That's what I thought when I saw it, but why would the pin lodge itself instead of rolling?


Same reason morse tapers don't fall out.  If the size of the pin and the size of the flat on the arbor are chosen properly, the angle between the flat and the point on the workpiece ID where the pin touches is very shallow and self-locking.


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## Chips O'Toole (Feb 2, 2020)

BGHansen said:


> Which issue are you missing?  I have every issue starting from the first one in 1982 (or whatever year they started publication).  Might be able to help you out with part 2 . . .
> 
> Bruce



Thanks, but I decided to spring for both issues. It's entertaining to look at these old magazines. It's surprising how little machine prices have gone up. It looks like lathes were more expensive in real money than they are today.


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## Chips O'Toole (Feb 2, 2020)

jmkasunich said:


> Same reason morse tapers don't fall out.  If the size of the pin and the size of the flat on the arbor are chosen properly, the angle between the flat and the point on the workpiece ID where the pin touches is very shallow and self-locking.



This is the kind of information I was looking for. Now to get specifics. Maybe I can find something in Machinery's Handbook.


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