# 3 Jaw Vs 4 Jaw Chuck



## Bray D

I have a PM 932M with an 8" Vertex rotary table that I'd like to outfit with a chuck. I've never used one in real life, but I realize the benefit of being able to clamp on the outside of a piece rather than flat clamping to the rotab surface. 

What are the pros/cons of a 3 jaw and 4 jaw chuck? I'll likely be clamping on square and rectangular stock frequently. Intuitively, this would drive me towards a 4 jaw chuck. 

Any thoughts?


----------



## JimDawson

Given that much of your work involves square and rectangular stock, then the independent 4 jaw would be the best option.  The 4-jaw is more time consuming to center but is more versatile.  If it's in the budget, buying both a 3 and a 4 jaw might speed things up.


----------



## RJSakowski

The only advantage to using a three jaw scrolling chuck is rapid fixturing.  There are four jaw scrolling chucks available.  The four jaw independent chuck can do anything the three jaw can plus mount workpieces off-center, precisely center a workpiece, and work with irregularly shaped workpieces.

One thing that I would like to see is a thin X-Y table that could be mounted to an RT.  It would allow you to perform many of the 2D machining operations that would otherwise require a CNC.   The DRO on mold mill/drill  has an arc cutting feature but it requires a large number of small X-Y steps to make a reasonable arc.  I also have a 12" RT on the mill and if I could precisely move the workpiece to the center of the RT, cutting that arc would be a piece of cake.  

Years ago at work, I had programmed cutting an Archimedes spiral in G code (we didn't have a CAM program at the time).  My recollection is that there were about four thousand lines of G code by straight line interpolation.  We later investigated having an outside vendor make the product with a CNC diamond wire saw but their machine was limited to a few hundred lines of code.  I rewrote the G code, changing to arc interpolation and the same precision was obtained with only a dozen lines of G code.

In theory, this operation could have been done fairly painlessly with a manual process an X-Y table on an RT.

(I got a Tormach, which ended my quest for the slim X-Y)


----------



## Bray D

Thanks for the responses. The quick fixturing that comes with a three jaw is appealing, though the versatility of a 4 jaw has its benefits as well. 

I'll ponder it a bit more before I pull the trigger. I'm so new to machining, it's difficult to ascertain what jobs will lend themselves more to the rotab than others. 

I agree that having one of each would be ideal; I'll just have to decide which one I'd like to add to the arsenal first.


----------



## brav65

My suggestion is to not fight and just join the club with us other tool junkies.  I am new to machining and have had to buy another rolling tool chest to fit all of,the new toys I have acquired.  If  you don't want to join the club then get,out now before your hooked.  It is a truly debilitating condition that leaves you perusing craigslist and eBay almost constantly...


----------



## Bray D

Oh yes, Enco and others have been draining my bank account regularly. I've become a self proclaimed tool junkie. The mill purchase was simply feeding the addiction, which I've found has now compounded the issue, haha. The chuck is a relatively large purchase, so I'm doing a bit more legwork before picking one up. Im sure I'll have one of each flavor before too long. Im leaning towards a 3 jaw right now, simply due to the auto-alignment property. I think I could get by with the square and rectangle stock in my vise. We'll see what I decide in the next few weeks.


----------



## itsme_Bernie

If you already know yo are going to be doing a bunch of square stock, the four jaw is a better place to start.   
Second- are these pieces that have been worked on before getting to the lathe?  Or is it just starting at square stock?   If these are second ops, DEFINITELY go Independant four jaw. 

Bernie


----------



## JR49

One other thought, that I didn't see mentioned. With the 3 jaw you will always have the 3 to 5 thousandths  run out ( more or less) which is normal (or so I've read) for a 3 jaw. With the 4 jaw you can dial it in "dead nuts", but you do have to dial it every time.  Good luck with whatever you decide,  JR49


----------



## kingmt01

Well depending on what you really need of doing all the same size you can leave two jaws in place only losing the other two & change the stock out. I do this often on the lathe when a 1/16th is close enough I don't even remeasure. I can set a 4 jaw up about as fast as I can true a piece in a 3 jaw. Now if I'm doing something like junk pipe I'll through that in a 3 jaw. I also usually use a 3 jaw if I'm going to be turning a concentric shaft for another part to ride on but that probably won't be likely on your rotary table but you never know. A 4 jaw independent can do almost anything a 3 jaw can but the other way isn't true.


----------



## Pat of TN

If you're doing square/rectangular work, a four-jaw is a must.

Let me also put this out there - four-jaw chucks hold far better than a three-jaw, even without biting the work. At the shop I work at, I've seen ol' Dave do things with a four jaw I could never do with the three jaw on the Haas TL-2 I run. We've had a lot of big work in - 10, 11, 12" diameter pucks, usually 4 to 5 inches long. He can put one in his four jaw chuck, holding by the ID jaws - I think they're 3/4" thick - and take .050+ deep facing cuts with no problem, plus well over an eight-inch deep on the OD...

I have tried that with a three jaw, and have in fact had disastrous results. I've launched 10" parts before. The only time I've praised the obnoxious chuck guard on the TL series lathes!


----------



## randyc

If you really, really can only afford one chuck at the moment then, in my opinion, it's a no-brainer, it _has_ to be a 4-jaw.  But if you insist on the self-aligning 3-jaw type, then there are other ways to secure rectangular parts on a rotary table:




In these photos, a 3 inch toolmaker's vise is clamped to the rotary table.  (The clamps are left loose until the vise is tapped into position to align the desired work axis to the rotary table spindle.)

FWIW when this _heavy _rotary table isn't in use, it is parked on a plywood stand (with casters).  This allows me to roll the rotary table along the workbench to the closest location of the mill on which I want to mount it, saving my back from potential damage 




Some notes on toolmaker's vises and a useful modification can be found here:

http://www.hobby-machinist.com/threads/improvement-on-toolmakers-vise.32564/#post-274986


----------



## Bray D

I think you guys nearly have me talked into a 4 jaw. I was on the fence at first, as I wasn't sure if I could disengage the drive wheel on my table. I was using it again today and found that I can indeed release the drive allowing the table to spin freely. This makes truing up a 4 jaw much more plausible. I wasn't looking forward to having to crank through the revolutions to access each jaw as I dialed in the alignment. With the drive disengaged, I can easily spin the table from jaw to jaw. 

Sounds like 4 jaw is the way to go. I'll start researching which particular model I'd like to get. We'll see how I like the 4 jaw, and I may end up snagging a 3 jaw down the road sometime. 

Thanks a bunch for all of the insight!


----------



## randyc

Bray D said:


> ...Sounds like 4 jaw is the way to go...



Most guys don't care for the 4-jaw because they think that it is a time-consuming PITA, involving chasing their tail for five or ten minutes.  That _definitely_ doesn't have to be the case, as experienced machinists will quickly tell you.

The post below describes aligning work in a 4-jaw chuck on the lathe but it is equally applicable to a _rotary table_.  After performing this method a couple of times, it would surprise me if it took you more than a minute or two to align a workpiece within .002 !

http://www.hobby-machinist.com/threads/quickly-aligning-a-four-jaw-lathe-chuck.34609/


----------



## John Hasler

randyc said:


> Most guys don't care for the 4-jaw because they think that it is a time-consuming PITA, involving chasing their tail for five or ten minutes.  That _definitely_ doesn't have to be the case, as experienced machinists will quickly tell you.
> 
> The post below describes aligning a 4-jaw chuck on a lathe but it is equally applicable to a _rotary table_.  After performing this alignment method two or three times, it would surprise me if it took more than a minute - two minutes at the outside - to get a workpiece concentric within .002 !
> 
> http://www.hobby-machinist.com/threads/quickly-aligning-a-four-jaw-lathe-chuck.34609/


That's the process I use except that, having only a DTI, I do the first pass with the DTI ball just short of touching the work and estimate the distance by eye.  This avoids the problem of the initial runout exceeding the range of the DTI.

I'd still like to have a 3 jaw in addition to my 4 jaw, though.


----------



## ronboult

Hi BrayD

Just a thought on the type of chuck and rotary table you are going to buy. If you buy a front mount chuck you may be able to mount it direct to the RT without a backing plate. This will give slightly greater clearance under the spindle which may be important on smaller Mills such as mine. Also rotary tables come with different numbers of mounting T slots. I have a vertex HV6 which in Australia is supplied with  3 T slots at 120Deg which is great for mounting a front mount 3 jaw chuck which has 3 mounting bolts. In contrast the Vertex HV6 in USA seems to be supplied with 4 T slots at 90 deg which would better suit a 4 Jaw with 4 mounting bolts. Just something you might like to consider when you have chosen what type of chuck you need to hold your work ( I prefer a 4 jaw independent Chuck because of its greater versatility but then have to use a backing plate on my silly RT which limits the height of the work I can machine)
If you have a large mill this probably doesn't matter but I hope this helps you make the right choice for your situation
Ron


----------



## Bray D

Even better. I have a Vertex HV8 with 4 slots. Hopefully I could install a 4 jaw onto the plate without an adapter. I've never had to max out my head travel, but the lower I can keep my head the better. 

Any recommendations for a decent quality 6" 4 jaw chuck?


----------



## randyc

Bray D said:


> Even better. I have a Vertex HV8 with 4 slots. Hopefully I could install a 4 jaw onto the plate without an adapter. I've never had to max out my head travel, but the lower I can keep my head the better.
> 
> Any recommendations for a decent quality 6" 4 jaw chuck?



I've had the 6 inch 4-jaw chuck in the photos below for some years and used it often without a problem.  It was ordered from CDCO but there are several caveats regarding this vendor:


They are simply a distributor of Chinese parts - there is no guarantee that ordering the same part number will get you the same part from day to day.
Their quality is no better/no worse than other distributors, however their return policy is outstanding - no questions asked.
There is a thread here regarding CDCO indicating that some members have recently encountered problems with them.









The backplate for the chuck (seen in the lathe photo) was also ordered from CDCO then finished machined on the lathe.  Because CDCO had an 8 inch backplate with the correct spindle mount for my Sheldon lathe, I ordered it rather than a 6 inch.

I'd intended to turn down the excess diameter to suit the chuck diameter but after mounting the chuck, I found that the hackplate made a very convenient handwheel for rotating the spindle so I left it alone.


----------



## darkzero

I choose not to got with a 4-jaw independent on my RT as I didn't need one. Another option is to use a 4-jaw scroll chuck. You can still have the quick ability to hold round stock & square stock as well since you mentioned it. But it can't really hold rectangular stock & it can't hold hex stock like a 3-jaw can. Grizzly offers an inexpensive 4-jaw scroll chuck. http://www.grizzly.com/products/6-4-Jaw-Plain-Back-Scroll-Chuck/G9835

I never need to hold square or rectangle & I just indicate directly off the stock so I choose to go with an inexpensive 6-jaw.


----------



## ronboult

Brady D
I have no idea what chucks are easily available in USA. I did notice that Will(Darkzero) thought Fuerda /Gator chucks were OK amoung the cheaper brands.

If you use a front mount chuck you should be able to fit an 8" chuck to a 8" RT  to give you max work holding capacity

Will
I looked at your Vertex RT in the above post. It seems to have 4 T slots. Is it a 6" and do you have any idea why they supply RT's with 4 T slots in USA but in AU we get them with only three? Seems strange to me.
Ron


----------



## darkzero

ronboult said:


> Will
> I looked at your Vertex RT in the above post. It seems to have 4 T slots. Is it a 6" and do you have any idea why they supply RT's with 4 T slots in USA but in AU we get them with only three? Seems strange to me.
> Ron



Ron, yes my RT shown has 4 slots. It's an 8" with a 6.3" chuck. That's interesting, I was not aware, no idea why you guys are only offered 3 slots. That was one of my main concerns in buying a RT. Although 3 slots would allow direct mounting for front mount chucks, I prefer to have 4 slots.

What I didn't understand when shopping for a Vertex, Vertex lists 3 slots on their website for their 4", 6", & 8" RTs. I've seen them on ebay with both 3 slots & 4 slots. I originally bought a Rutland branded 6" Vertex RT & it 4 slots instead of 3 as listed by Vertex. I sold it cause it was too small for my mill. Photo of the 6" below with a 5" chuck.


----------



## Bray D

I was hesitant to post here for fear of someone snatching it up before I do, but I've decided it's worth the education even if that happens. 

Is there any reason I shouldn't buy this 4 jaw? It seems super cheap for an 8" Bison. 

http://www.ebay.com/itm/Bison-8-4-J...685?pt=LH_DefaultDomain_0&hash=item20fcdf0cb5


----------



## ronboult

Hi BrayD

The Bison has a A2-5 taper. I suspect your lathe has a D 1-4. From the front it seems to be  a plain back chuck with a A 2-5 backing plate (4mounting screws). You would have to make/buy a new D1-4 backing plate for your lathe. Whether you wish to do this is your decision


----------



## The Liberal Arts Garage

Simple question-- will you carry the operation through without re- chucking the
workpiece; three- jaw, O.K.      Re- chuck,use four- jaws.......BLJHB


----------



## ezduzit

randyc said:


> ...when this _heavy _rotary table isn't in use, it is parked on a plywood stand (with casters).  This allows me to roll the rotary table along the workbench to the closest location of the mill on which I want to mount it, saving my back from potential damage ...



My 12" rotary table must be close to 200 lbs. So I don't want to have to move it far--just lower and move the mill table over far enough to slide it on and off its shelf. I haven't set it up for a chuck yet.


----------



## Bray D

ronboult said:


> Hi BrayD
> 
> The Bison has a A2-5 taper. I suspect your lathe has a D 1-4. From the front it seems to be  a plain back chuck with a A 2-5 backing plate (4mounting screws). You would have to make/buy a new D1-4 backing plate for your lathe. Whether you wish to do this is your decision



Hmm, am I concerned with the taper since it's going on my rotab? So long as it has a flat back and 4 mounting bolts, I should be able to secure it to my 4 slot table via 4 T nuts, correct?


----------



## JimDawson

Bray D said:


> Hmm, am I concerned with the taper since it's going on my rotab? So long as it has a flat back and 4 mounting bolts, I should be able to secure it to my 4 slot table via 4 T nuts, correct?



It looks like it would bolt to your RT just fine.  That looks like a plain back to me, if that's the picture of the actual chuck.


----------



## Bray D

I emailed the seller and confirmed that the back is similar to a plain back chuck. It has the taper also, but that shouldn't matter for my application. I went ahead and bought it. Should be here Tuesday. I'll post up pics once I get it unpackaged. 

Thanks for all of the insight guys. Much was learned and I'm looking forward to adding another quality piece of tooling to my arsenal.


----------



## Bray D

The chuck came in this morning so I ran home during lunch to check it out. It appears to be a nice piece, but I won't know how it checks out until I get an indicator on it. 

The whole assembly is tall! I'm sure that will be a blessing for some things - and a curse for others. I need to whip up some t-nuts so I can mount it on my RT. It's just resting on there right now. Head is at max Z in the photo.


----------



## projectnut

If you want accuracy and repeatability the 4 jaw independent chuck is the way to go.  A 3 jaw scroll chuck not only isn't as accurate, it's meant to be used when all the operations can be done without removing and relocating the piece.  Since the 3 jaw has some run out, when you remove and reinsert a part, if the part isn't reinserted in the exact same orientation with the exact same pressure on each of the jaws the part will no longer be on center.

When using a 4 jaw independent chuck the part can removed and reinserted as many times as you like and you'll still be able to center it.   I have a number of 3 jaw scroll chucks and a number of 4 jaw independent chucks.  The only time I use a 3 jaw scroll chuck is when  the part can be finished and parted off the stock with a single setup.

It takes a little time to get used to setting up a part in a 4 jaw independent chuck.  Once you are familiar with the process it doesn't take much more time than using a scroll chuck.  As mentioned earlier other advantages are being to do an off center setup (as in making a cam lobe), and the ability to grip and hold irregularly shaped stock.  The 4 jaw independent chuck is far more versatile, and allows the operator to perform a number of operations that cannot be completed with a 3 jaw or 4 jaw scroll chuck.

If you're only able to afford a single chuck at this time I would definitely make it a 4 jaw independent one.  In the long run you'll find you will use it more often than a 3 jaw one, and be able to make accurate parts more easily.

After typing this response I went back to the main page of this thread.  The last responses by the OP didn't appear until long after I refreshed the page.  Sorry for coming late to the party.  It looks like the OP made a wise decision


----------



## Bray D

projectnut - That wasn't a wasted post by any means. I appreciate the quality response!

I haven't have a chance to try out the 'new' chuck yet, but I hope to in the next couple weeks. I'm building a heavy shelf right now to store the RT and chuck when they're not in use. It seems the majority of my projects have been shop development lately. One of these days I'll have everything arranged so I can settle into some other projects.


----------

