# Limitation in self centering jaw chuck



## Alberto-sp (Jan 10, 2022)

Hi everyone.  (Sorry my english)

I own a minilathe. It has a 3 Jaw 100mm self centre chuck, and I bought a 4 jaw independent chuck.

The 4 jaw is great, and it cand hold very big parts before the jaws loose the internal screw, but the 3 self centre no. The maximum aperture in the 3 jaw is much smaller than the 4 jaw. but for most of my work, I prefer self centering because is more easy and quick.

So my question is. Is it possible to find, with the same size of chuck, one with self centering jaws but with more aperture? Or the smaller aperture is charasteristic of the self center chucks? I don´t mind 3 or 4 jaws.

Thank you

Best regards


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## Firstram (Jan 10, 2022)

Do you have outside jaws for the 3 jaw chuck?


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## jwmay (Jan 10, 2022)

I don't know if you can find what you want. But for me, best is to have 4 chucks. Two 4 jaws; one with inside jaws, one with outside jaws. Two 3 jaw chucks...same scenario. And then a collet chuck.  So five chucks...yeah..five chucks minimum. Lol


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## Alberto-sp (Jan 10, 2022)

Yes, I have outside jaws but they have less grip "surface" and about having more than 1 chuck, in my minilathe changing the chucks is a PITA.


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## woodchucker (Jan 10, 2022)

jwmay said:


> I don't know if you can find what you want. But for me, best is to have 4 chucks. Two 4 jaws; one with inside jaws, one with outside jaws. Two 3 jaw chucks...same scenario. And then a collet chuck.  So five chucks...yeah..five chucks minimum. Lol


oh come on now, stick to the question, stop giving advice on buying 5 chucks and stick to his question...

You can get a bigger chuck, but it's a matter of your lathe. when you go bigger you risk the jaws hitting the cross slide.
So a few things will have to be known.

what is the size of your mini lathe?
need to know either radius or diameter swing. just tell us what you are giving.
next we need to know the center to cross slide distance.. measuring (where the tailstock center point  to the top of the cross slide where it would hit . *Then that same center point to your carriage arms  (that's the most important)..*
For some reason, they always recommend a smaller 3 jaw, and a larger 4 jaw.
My 9" lathe for instance handles a 5" 3 jaw, and a 6" 4 jaw.  Why? I don't know the answer to that.  But your 3 jaw should not hit your carriage arms, and  your jaws should clear the carriage.


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## jwmay (Jan 10, 2022)

Seriously. Sometimes I need two chucks just for one job.
But yeah I guess the answer is that you have to buy a larger chuck. But of course, besides the things woodchucker pointed out, you will always be limited by the ID of your lathe spindle.


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## Ken from ontario (Jan 10, 2022)

Here's a 4 jaw self centering 4"chuck:








						4-Jaw Self-Centering Lathe Chuck | Lathe Chucks for Sale
					

Hold work up to 80 mm in diameter. Made of high-grade steel, this 4-jaw self-centering lathe chuck includes a chuck key and inside and outside jaws.




					littlemachineshop.com
				



and 6 jaw 4" :








						Lathe Chuck, 6-Jaw 4", Self-Centering 2276
					

Lathe Chucks 2276 6-jaw self centering lathe chuck; 4" (100 mm) diameter; Includes chuck key and mounting bolts; Plain back mounting; Excellent for ho...




					littlemachineshop.com


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## brino (Jan 10, 2022)

Alberto-sp said:


> in my minilathe changing the chucks is a PITA.



Do the different chucks bolt on to a single fixed plate that is part of the lathe spindle?

Some pictures of your current chucks would help us to help you.

Brian


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## Nogoingback (Jan 11, 2022)

6" sounds like a lot for a mini lathe, but a 125mm  might work. 
Perhaps something like this: https://littlemachineshop.com/products/product_view.php?ProductID=2337&category=566826475

 If you want a chuck
that's the same  size but with a larger aperture, you'll just need to research 
manufacturers drawings until (if) you find one.


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## NC Rick (Jan 11, 2022)

A couple thought I’m having:
scroll chuck (self-centering) is likely to have less jaw excursion and you NEED to have a couple “teeth” engaged on each jaw.
3 jaw chuck holds a lot of things better than a 4 jaw. Using the outside clamping jaws of the three jaw works well for shorter parts because the “shelfs” support the part against cutting forces.

a 3jaw scroll chuck in 6” size needn’t be very expensive and if you are careful not to extend the jaws where they hit your ways or cross-slide could benefit you by having a larger a d deeper aperture through the chucks body.  I do not like the idea of a chuck in a chuck on any lathe but on a mini lathe the loss of rigidity and forces on the spindle bearings seem totally unacceptable to me.  So, my answer is to have 3 chucks.

by the way, your English is fantastic!  Welcome.


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## Ken from ontario (Jan 11, 2022)

@Alberto-sp, One thing you need to consider is the size of the motor on your mini lathe,, if  it comes with a brushless motor ,it can (barely) handle a 5" chuck but that same 5" chuck would be too heavy for the " classic" mini lathes .  I have a 5 " four jaw independent chuck and can tell you it is the maximum weight /size I'll ever use on my lathe even though the motor on mine is the more powerful brushless type but you can still hear it laboring on the initial start , it also takes twice as long to stop .



			https://littlemachineshop.com/products/product_view.php?ProductID=2345&category=


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## woodchucker (Jan 11, 2022)

guys, the 5" and 6" was my example of the 3 and 4 jaw for MY SB9. I was explaining that generally they are different. 
We need to figure out his lathe and available options.

I can't believe how sideways his simple question went multiple times.


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## NC Rick (Jan 11, 2022)

Sorry for ruining the thread!  It seemed likely to me that if the lathe would swing a wide open 4” (that close to 100 mm) then a 5 or 6 inch chuck may well work.  Dimensions and inertial limitations seem like would be more obvious to the lath owner.
please accept my apologies and I’m out.


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## Ken from ontario (Jan 11, 2022)

NC Rick said:


> Sorry for ruining the thread!  It seemed likely to me that if the lathe would swing a wide open 4” (that close to 100 mm) then a 5 or 6 inch chuck may well work.  Dimensions and inertial limitations seem like would be more obvious to the lath owner.
> please accept my apologies and I’m out.


I am confused, I don't know why "you're out" , I re-read (and liked) all your posts here, please let us know who you think is upset and why , the main point you made was that we still need to know more info about the mini lathe and what the OP is actually searching for.


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## epanzella (Jan 11, 2022)

Learn to love your 4 jaw!


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## brino (Jan 11, 2022)

woodchucker said:


> I can't believe how sideways his simple question went multiple times.


What? Where?
(meant with NO reverence to Vinny Barbarino!)

Okay, perhaps a small reference to needing a few dozen different chucks minimum, but I took it as a joke....
It was followed with a "Lol"....but maybe that doesn't translate well....



NC Rick said:


> Sorry for ruining the thread!
> please accept my apologies and I’m out.


No harm, no foul!
Rick I see no reason for you to apologize, please stay and help!

I think we need more info from the OP to fully understand the situation.

Brian


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## woodchucker (Jan 11, 2022)

I thought you guys were stuck on the 5 and 6 because I mentioned my SB using 5 and 6.
I immediately saw responses to that effect, also the recommending many chucks.
I just didn't think we were trying to help in in an efficient manner. We know nothing about his chuck, his mount, his measurements from center.

Sorry, I just thought it went off the rails.


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## brino (Jan 11, 2022)

I believe we are all-good here guys!
I just would like to avoid any misunderstandings or finger pointing.

We can wait for some more input from the originator.
Some pictures of the existing chuck mount and some diameter measurements would help a lot.

@Alberto-sp No worries about your english ..... please feel free to post and ask anything you want!
Just know that we are a passionate group dealing with technical details, so we will be asking some questions too....

Brian


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## Alberto-sp (Jan 12, 2022)

Thanks for all your answers.

I´m still learning english so I sometimes have problems to explain myself. These are my chucks. 100mm diameter





I don´t mind 3 or 4 jaws. The 4 jaws is non self center, but its aperture is much bigger than the 3 jaws wich is self centering. I could use the external jaws, but the grip surface (Blue line) is much less.

So, what I want is a self centering (3 or 4 jaws) chuck with the aperture of the left one.

This is a pic of the backplate (100mm diameter) I posted it here some time ago (When I asked for the 4 jaw chuck) 





And this is the specs of my lathe





Thank you


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## NC Rick (Jan 12, 2022)

I feel like it is worthwhile to bounce around ideas.  I was aware of the things we don’t know about our friend Alberto’s lathe.  I don’t have answers and hoped I might be offering another set of things to think of.  I have never owned a mini-lathe so I’m pretty under experienced, the small lathe I upgraded from was a Rockwell 10”.  Maybe I was being over sensitive but I felt like Woodchucker was complaining of me derailing the thread with non-valid suggestions without reading all the information (something I am fairly likely to do).  Thanks for clarifying folks.

Alberto, while most are pretty hard, it is possible to bore out the body ID on many chucks using carbide tooling.  It would be necessary to disassemble your chuck and make your own judgment of how much you can get away with. A ridged setup and strong carbide tool is needed to deal with the highly interrupted cut.

I think most of us get into situations where we are wishing to extend the capability of our equipment and ourselves.  these situations lead to learning and sometimes (many times for me) mistakes where I learn how NOT to do things. I don’t know your application but don’t forget about the possibility of building some kind of fixture on a faceplate.

i may well have been feeling a little snippy yesterday. My wife and I both have Covid and both have been fully vaccinated and boosted.  We run a business from home with employees and there are some frustration and problems in making things work.  I’m essentially locked out of my shop which is enough to **** off anyone!


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## woodchucker (Jan 12, 2022)

@NC Rick he is not talking about boing out the  hole. He is showing you the limit of the jaws.

@Alberto-sp You have exceeded what the jaws can handle on the 4 jaw. That's not safe. 3 things can happen:
1 you break the chuck because there's not enough support there.
2 you have a jaw fly out while it's spinning.  
3 you hit the carriage with that jaw out that far.

First, your jaws can be turned around on the 4 jaw, when you need to go out that far, yes it will only be grabbing by a smaller amount, but it will be safer.

Your lack of space on your 3 jaw:  I see you have another jaw there. You should have 3, those are for grabbing a big part, you put those in, the opposite way of the current jaws and you can grab a bigger part, the same as the 4 jaw.

The entire jaw will not grab, you need to use the landing. But it is safer, if it's a flat part you are good to go, if it's a long part, you need to use the tailstock or steady rest to hold the rest of it.


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## woodchucker (Jan 12, 2022)

being that this is a 7"  180mm lathe, a 4"  100mm chuck is the right size 3 jaw. You could go one size up, but you are not going to gain more than 1"  25.4 mm  diameter, or 1/2" 12.7mm radius, which is still short of your goal.

I know that's not going to help, but if you really need to turn big stuff, you need to get a bigger lathe, for multiple reasons.
capability, power,   The smaller lathe doesn't have the rigidity for bigger parts.


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## RJSakowski (Jan 12, 2022)

As a rule of thumb, I never extend my chuck jaws more than the first step past the outer diameter of the chuck.  As a result the maximum safe diameter of work held by the inside jaws is the chuck diameter less twice the distance from the first step to the inside of the jaw.   The maximum safe working diameter of my 4' chuck is 4"-2*1.1"= 1.8"(46mm).  For my 5" chuck, it is 5" -2*1.4"=2.2" (56mm).  While not having a 6" chuck, I would guess that the distance from the first step to the inside of the jaw would be more like 1.7" so the maximum work that could be safely held would be  6"-2*1.7"=2.7"(67mm)

However, the maximum possible work diameter that could be held with the inside jaws is the swing of the lathe less twice the length of the jaws.  The OP's lathe has a 180mm ( 7") swing.  Guessing that the overall jaw length of a 6" chuck is something like 2.4", the maximum work diameter without the jaws hitting the bed of the lathe would be 7"-2*2.4"= 2.2" (56mm)

From this analysis, there is little or nothing to be gained in terms of work diameter held by the inner jaws by going from a 5" chuck to a 6" chuck.  There is some advantage in having a longer grip length with the 6" chuck but this has to be balanced against swinging a greater mass.  My 5" chuck and back plate are about double the weight of mt 4" chuck and back plate.  I would guess that a 6" chuck would weight close to double my 5" chuck.  That extra weight will icrease the stress on the motor and  on the spindle bearings possibly leading to an early failure.  Additionally, there will be some spindle sag  caused by the additional weight which could cause problems when machining.


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## mikey (Jan 12, 2022)

woodchucker said:


> I know that's not going to help, but if you really need to turn big stuff, you need to get a bigger lathe ...



I've been following this thread and I have to agree with woodchucker. If you are going to *regularly* work with materials that require a larger chuck then you really need to step up to a larger lathe. Your spindle and spindle bearings are not meant to handle the weight of a larger chuck or the weight of the work it will have to carry plus the cutting loads imparted by the tool.


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## Alberto-sp (Jan 12, 2022)

Thanks for all your answers. So now it´s clear, I´ll have to use the other 3 jaws in combination with the tailstock.

But I don´t open the jaws of any of the chucks  so big. That was only for show you how far can go each one of them. 

@NC Rick I wish you the best for you and your wife

​


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## woodchucker (Jan 12, 2022)

Alberto-sp said:


> Thanks for all your answers. So now it´s clear, I´ll have to use the other 3 jaws in combination with the tailstock.  Good
> 
> But I don´t open the jaws of any of the chucks  so big. That was only for show you how far can go each one of them.  Ok, that's good too. I Think you were trying to express that it is the opening you were referring to then? Correct?
> 
> ...


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## Alberto-sp (Jan 12, 2022)

Yes.

One question off topic. I know a nylon hammer is useful in the shop. But I have pieces of delrin at home. Can I make that hammer with delrin instead nylon?


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## RJSakowski (Jan 12, 2022)

Alberto-sp said:


> Yes.
> 
> One question off topic. I know a nylon hammer is useful in the shop. But I have pieces of delrin at home. Can I make that hammer with delrin instead nylon?


Delrin will work perfectly well for a soft blow hammer.


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## Alberto-sp (Jan 12, 2022)

Thank you!


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