3 Jaw Vs 4 Jaw Chuck

[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]

...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]

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]

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]

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.