Three Jaws, Four Sides...

[sparky961]

Hey all,

I was just looking at some of the photos from the recent ball-turning thread, and I noticed a neat little trick used to hold square stock in a three-jaw chuck on one of the referenced sites:

The picture is small, but it looks like the adapter is a piece of round stock with a hold bored to touch the four corners of the square stock, and then slitted to apply pressure to the stock when the jaws are closed. There's also a set-screw there that may also be applying pressure to the stock, but it seems that the forces applied to the stock wouldn't be very even this way.

I was wondering what other methods exist to hold square stock in a three-jaw chuck. It would be great if someone could suggest a method to hold arbitrary square and/or rectangular stock sizes without having to create a mounting fixture each time!

Thanks!
-Brian

 

[Mcgyver]

that’s a common and handy method. bore to the across the corner dimension and split, soon you have collected all the sizes for common square stock. screw is superfluous imo

 

[mklotz]

I suppose that, if you have only a 3jaw chuck, the pictured method is ok for work where accuracy is not a major concern but I wouldn't trust it for anything that matters.

There's a very good reason why most model engineers own at least one 4jaw chuck. It's the most flexible chuck for lathe work.

If you're intimidated by the process of centering work in the 4jaw, read my technique for doing it:

http://www.schsm.com/html/centering_work_in_the_four_jaw.html

 

[GailInNM]

Works for rectangular stock also if the aspect ratio is not too large. I just split mine and then make sure the split is between jaws. For smaller sizes I clamp in a collet instead of a chuck. There is a little better accuracy that way. Most of the error using commercial stock is that the corners are not uniform. The flats are much better. If you need better than run of the mill accuracy the 4 jaw is still best, but the split collet is OK for most of my work.

 

[sparky961]

Indeed, I've dreamed of owning a 4-jaw chuck for a long time now. Two main reasons exist why I don't presently:

1. On the Craftex B2229, the lathe spindle and faceplate/chuck mount are all one piece. It uses a precise groove to align the chuck and three bolts around the diameter. I have yet to positively locate a decent 4-jaw chuck that wouldn't require a lot of modification to fit this.

2. Money. 'Nuff said.

-Brian

 

[Alphawolf45]

I dont turn much square stock. Intermittant cuts are murder on a lathe..
.
anyway.. what about using a faceplate and lathe dog? You'all dont like dogs? LOL

 

[Alphawolf45]

Course I meant to turn the square stock between centers. I should have added that you can grip a 'center' in your 3 jaw and dog leg can be engaged by one of the jaws.It'll work I do variants on the theme all the time..

 

[Mcgyver]

Coincidently, just did this last weekend for part on the triple expansion engine.

http://i20.photobucket.com/albums/b201/michael0100/Stuart Triple Expansion/FRmount.jpg

Marv's right, it goes without saying that if you need accuracy relative to a surface of the square, this isn't the method because 1) it grips the edges and 2) in the first photo its in the three jaw. When you’re making stuff an important aspect is knowing where accuracy matters and to take that into account in your processes. Its good to explicitly note the limitations of a process so the newer practitioners understand.

However, I find, like in the above pic, this set up frequently does not required precision between the sides of the square section and the turned portion, ie making a square head fastener or stanchion with square base etc so it’s a handy technique to know about. In the case of the triple part above, starting with sq stock saved the extra operation of squaring up the small section on the mill.

Brian, if you only have one chuck it should be a 4 jaw - we all use the three jaw but really it is just a semi accurate convenience. Its very limiting to not have one, partially because you can hold odd shapes but more because you accurately centre work when concentricity is required. Most spindle mounts fall into a number of standard type for which backing plates are available. I almost can't BB can't provide a 4 jaw for a lathe they sold?

 

[sparky961]

I must admit that I haven't actually called and asked at Busy Bee about a 4-jaw. Right now, the more limiting factor is money, as I'm between jobs (actually, between careers...)

Seeing as the limiting factor in the precision of a 4-jaw would appear to be the machinist's ability to adjust it, are there any _simple_ designs out there to build one or reasonable quality/capacity?

I have the Gingery books, and there's a 4-jaw in there, but I'm not convinced of it's ability to hold parts securely.

Failing a decent, simple design, I guess I need to upgrade the purchase priority...

-Brian

 

[Alphawolf45]

Theres many ways to do everything..If your lathe makes it tedius to change chucks..Buy a small 4 jaw chuck, put a stub out it's backside then mount that into 3 jaw on your lathe......

 

[mklotz]

I seriously doubt that you can build a reasonable 4jaw for less money than buying one. Take a close look at your 3jaw and ask yourself what it would take to build one.

Here, in no particular order, are some ideas...

Four screw clamps bolted to the faceplate will allow you to handle *certain* shapes that would normally go in the 4jaw. In fact, the faceplate is probably the ultimate in adjustable work holding. There are any number of fixtures one can make to allow it to hold and center all manner of work.

A small, (used ?) 4jaw, fitted with a spud and held in the 3jaw will allow you to do many small-engine-sized parts.

Square collets are available and work very well for small size square stock.

Nevertheless, bottom line is that every model engineer needs a 4jaw chuck.

 

[Tin Falcon]

IMHO if you are going to have just one lathe chuck it should be a 4 jaw not a 3. And I am not pointing fingers at all the guys out there that only have a little seig 7 x that only has a 3 jaw.
you may think I am crazy but the old craftman 109 only came with a 4 jaw the 3 jaw was an option. Forrest Addy who has written for home shop machinist and is active on that board suggests that a newby set his three jaw aside for 6 months to a year and learn to use a 4 jaw. with some practice indicating a part in is quick and easy.
When i set up a 70s vintage hobby lathe for a friend I installed a 4 jaw on that and made a spare back plate to add a 3 jaw later.
Tin

 

[Bernd]

Brian, check out the thread below. It shows a four jaw being used in a three jaw chuck on my Grizzly 9X20 lathe.

http://www.homemodelenginemachinist.com/index.php?topic=1800.msg14027;topicseen#msg14027

Bernd

 

[sparky961]

Thanks for all the great ideas! I hadn't thought of mounting another chuck to the 3-jaw.

I'll be keeping an eye open for some deals in the future.

-Brian

 

[d-m]

Hi all
I have 2- 4 jaw chucks for my Logan and 1- 3 jaw I had never used a 4 jaw before and was having a heck of a time getting it centered I found marv's method long before I found this board . It is vary easy to use and I don't do it any other way. It makes sense and after you do it a few times it is like riding a bike. I use my 3 jaw but I would rather use a 4 if I have a choice. And having 2 is really nice if you are working on one part and get interupted and need a chuck just swap them out, your part is ready to go back on the lathe indexed no fuss. not having a 4 jaw :wall:

Dave

 

[Bernd]

If you're intimidated by the process of centering work in the 4jaw, read my technique for doing it:

http://www.schsm.com/html/centering_work_in_the_four_jaw.html

Marv,

I went and read your write up. Very nice write up by the way. Now you know and have seen that I know how to center parts in a 4 jaw chuck. The first part of your procedure had me reading it several times. I just couldn't figure out how you located your center of the work piece. Then the light bulb came on. You are explaining centering a "round" piece of stock. I had assumed a "square" piece of stock. Perhaps you should mention that in your write up. Perhaps an explination on how to center a square piece of stock also.

I may sound a bit nit picky here, but if I were a newbie I'd be a bit confused. I be wondering how you line up a square or hexonal piece of stock in a 4 jaw. Perhaps a pic or two would also help.

Bernd "the nit picker"

 

[mklotz]

Bernd,

The technique for centering square stock is basically the same with the exception that the DI is now applied to the sides (not edges) of the stock.

This can get awkward because, as one rotates the chuck and stock, the edges of the square stock want to catch the DI plunger and bend it - not a good thing.

I made an attachment for my DI

that is nothing more than a piece of thin, springy sheet steel. As the square stock rotates, the edge hits the sheet steel and depresses the plunger pushing it out of the way. The sheet metal also helps to indicate when you've turned the work such that a face is perpendicular to the DI plunger.

 

[Bernd]

AH, just learned something new. I never thought to use spring steel to put the indicator pointer on. I always laid out the hole on the square using the corners and then center punching and then lined it up in the lathe. Your method would be way faster.

BTW, that pic spoke a 1,000 words. Thanks for getting this nit picker straightened out. ;D Looks like another round-to-it to add to the list. At this rate I'll never get my engine finished.

Bernd

 

[zeusrekning]

Bernd,

The technique for centering square stock is basically the same with the exception that the DI is now applied to the sides (not edges) of the stock.

This can get awkward because, as one rotates the chuck and stock, the edges of the square stock want to catch the DI plunger and bend it - not a good thing.

I made an attachment for my DI

that is nothing more than a piece of thin, springy sheet steel. As the square stock rotates, the edge hits the sheet steel and depresses the plunger pushing it out of the way. The sheet metal also helps to indicate when you've turned the work such that a face is perpendicular to the DI plunger.

Excelant!! I always mount the indicator on the cross slide and move it out of the way in the Z axis while I rotate square or hex material to the next flat. It is a PITA and this method eliminates half the steps.
Marv, I don't need any more explanations either I actually get this one This is on my to do list now.
Tim

 

[mklotz]

Looks like another round-to-it to add to the list.

A fitting punishment for a nit-picker.