What chuck size for rotary table?

[Brian Rupnow]

I am playing about at mounting a chuck on my rotary table. I do not currently have a chuck, so will have to buy one. There is not a great deal of price difference between a 5" chuck, which is the largest I can use, and a 3" or 4" chuck.---my heart tells me "Go for the largest possible, to maximize on what I can fit into the chuck."--However, in this situation I don't know if that is realistic or not. My mill is a relatively small CT129 from Craftex. When the head of my mill is raised to its highest position, it is 11" from the bed up to the tip of a Jacobs chuck mounted in the quill, or 12" from the bed up to the end of a 1" diameter endmill (which is the largest endmill my machine can handle). So, assuming I want to mill something, this still leaves a distance of 4 3/4" from the top of the chuck jaws to the underside of the milling cutter, or 3 3/4" from the top of the chuck jaws to the underside of the Jacobs chuck. What is the general feeling out there in machinist land?---Brian

 

[kvom]

If the height of the jaws above the table is similar, then the larger chuck seems to make sense. Otherwise it's a tradeoff between space under the spindle and the size of work you can chuck.

 

[b.lindsey]

Brian,

Would the chuck ever be used with a lathe also. Normally I would say go as big as possible, but if you plan on using it now or in the future with a lathe you might want to add that into the size consideration.

Bill

 

[Bogstandard]

Brian,

For my 6" rotary tables I have survived for many years with an 80mm (3 1/4") chuck.

I am just swapping over to 4" now that I have a bit more room under the quill.
It is the table to quill distance that is the governing factor.

I used to struggle sometimes to get the drill chuck with a largish drill over my RT and small 3 jaw if holding a bit of thickish material.

John

 

[Brian Rupnow]

I have edited my original post to show the clearances that I would have over top of the chuck jaws with tooling in the mill. My lathe currently is running a 5" chuck (that is where I got the dimensions on the drawing). If I buy one for the rotary table, it will be a dedicated chuck and will live permanently on the rotary table.--Brian

 

[kvom]

Looking at the drawing, I'm guessing that you could gain some quill room by machining down the thickness of the adapter plate and probably some of the chuck as well.

 

[mklotz]

Indulge me for a moment while I offer a different viewpoint...

I've had an RT for ages and never saw the need to mount a chuck on it. I've never yet had a part that I couldn't mount directly to the enlarged, sacrifical plate I have mounted on the RT table.

Ok, maybe it's just me, the way I work and the type of work I do (although I build small engines just as the rest of you do) but it seems like an unneeded complication. No matter what size chuck you use, it won't have the capacity of the bare table. Furthermore, a chuck introduces an additional source of misalignment and it eats up vertical space.

My recommendation to Brian is to use his RT as is until he encounters a situation where he can say with assurance that a chuck is required.

 

[Brian Rupnow]

Bear with me fellows---I just went over to BusyBee and picked up an MT2 blank, which has an MT2 hardened taper on one end and a 1" diameter x 1.5" long unhardened section at the other end which can be machined, for $10.00.
I have modelled an adapter plate which will allow me to use the 3 jaw chuck off my lathe and mount it on my rotary table, without modifying either. I am not as handy at centering the independent 4 jaw chucks as many of you seem to be, so if I have to make any adapter, I may as well make one which is going to center things for me. I am not even convinced that I will make this, but I bid a 4 week design contract yesterday, and I'm setting around here waiting for my phone to ring, and I need to be doing something to keep from going stir crazy while I wait. The drawing shows what i have in mind.---Brian---"EDIT--EDIT---EDIT"--This design was abandoned after I taken a close look at it. In order to use the purchased MT2 blank, It would have required an extremely thick adapter plate and a ton of machining. I decided to redo it, using a "home made" MT2 adapter stub---this would allow me to make the adapter plate from 3/4" thick stock, with much less machining.

 

[Brian Rupnow]

Okay---I'm on a roll now. this design uses an adapter plate that is made from 3/4" thick stock and a "home made" MT2 tapered plug.--a lot cheaper and considerably less machining to do.

 

[Divided He ad]

Hi Brian, I have a Vertex 6" rotary table and on it a 5" 3 jaw chuck..... sound like what you want?

My check has 3 holes through from the front so mounts directly to my RT using 'T' nuts and bolts.

No need for the plate and just required a centre making for quick alignment ;D


An old photo of it....

Hope this doesn't put a spanner in the works!



Ralph.

 

[Bogstandard]

Brian,

In a few weeks, I will be converting my RT's, dividing head and lathe to accept myford backplate threads. That will mean I will be able to accurately swap between RT's, dividing head and lathe in a matter of seconds with the part still held in the chuck.

I will be using the little adaptors as shown in the pic. They are designed to lock semi permanently into the MT2 taper on RT's, but by using a drawbar and taper adaptor can be mounted onto my lathe. So each chuck will have a Myford backplate and screw onto any of them.

John

 

[Brian Rupnow]

Divided He ad and Bogstandard---Definitly no spanners in the works!! I am trying to use tooling that I already have, and "Make do". I have set my compound rest up to the MT2 taper. (or as close as I can get it) and turned a taper on a peice of 3/4" aluminum. Lord bless me---It actually works!!! I have no "Prussian blue" and I'm trying to not get to far away from my telephone ---Still waiting for that contract call). I tried a bit of red layout die instead to see what the contact area looked like. Now to try it on a peice of 3/4" steel before I get excited and screw up the setting on my compound rest----

 

[kvom]

Brian,

I'd expect that, given relatively little torque on the chuck in the RT, a "pretty close" taper will be secure.

 

[Brian Rupnow]

Brian,

I'd expect that, given relatively little torque on the chuck in the RT, a "pretty close" taper will be secure.

There shouldn't be any torque transmitted thru the center at all. It is purely a locating device to keep everything centered. All the torque will be taken thru the 3 bolts arranged at 120 degrees on each side of the adapter plate.---Brian

 

[Brian Rupnow]

I made the MT2 tapered part yesterday--(the green part in the center) --had to leave off when I went to tap the 3/8-16 thread in the end of it, as I didn't have the right sized drill.--Will remedy that today.

 

[Brian Rupnow]

Well boys, all I can say is, its a good thing I don't do this for a living!!! Nobody would be able to afford the parts I made, based on the time it takes me to make them. The MT2 tapered arbor is made of steel and the adapter plate is made of aluminum. (I didn't use the MT2 blank from Busy Bee). All I have left to do now is put in an accurate and concentric counterbore into the adapter plate to receive the straight shank on the MT2 peice. I had to use the 4 jaw chuck to hold the adapter plate while turning the "registered " diameter that fits into the back of the chuck. Today is the very first time I used my dial indicator to mount the adapter plate "concentric" in the 4 jaw chuck, and My god, I found it difficult!!! I must have tightened and loosened that sucker about 40 times, and never did get it perfect. I am not the kind of person to "throw things across the shop", but if I were the whole lathe might have flew across the shop today. All you experienced machinists will laugh at me, but honestly, that has to be the most difficult thing I have had to do yet with my lathe. Based on the immense difficulty I had setting up that 4 jaw today, I'd say it was a pretty good idea to mount my chuck concentric to my rotary table with an adapter plate. If I had to go thru that centering business every time, I would probably never ever use it.----whine, whine, whine---

 

[rake60]

Brian I am an experienced machinst and I AM laughing.

Not be cause you had difficulty, but because I've been to that level of frustration
myself. When I get to that point I start talking to myself. Very LOUDLY!

Then the wife yells down to the basement.

"I take it things aren't going well down there. Is the potty mouth really necessary?"

Sometimes that comment puts it into prospective.
Sometimes is makes for a bigger dent in the concrete walls of the basement.

THAT'S why I'm laughing! :big:

Rick

 

[Bogstandard]

Brian,

It does get easier after a time, give it another few hundred attempts and you might get close.

For a few years I would rather have drilled holes in my head than do four jaw work, but now I do enjoy the frustration sometimes, it is like an anti relaxation thing.

John

 

[chuck foster]

brian, like every thing else in life the more you do some thing the easier it gets.
when i left high school the first job i had was making boat propeller shafts, we never used a three jaw chuck cause those shafts had to be running dead on when you turned the taper on the end.

the one guy i worked with challenged me one day to see who could set up the shaft it the lathe the quickest.
well i thought i'm younger so i'm better :big: well i took 13 or 14 minutes and he took 5 or 6 minutes

so what i'm trying to say is just use the four jaw and the more you use it the better you will be............ and remember this hobby stuff is not a race.
and most of all have fun cause if you are like me, when you throw parts around the shop in a fit of rage............they some times come right back at you.............don't ask me how i know this, i just know it is a fact
chuck

 

[mklotz]

...it is like an anti relaxation thing

ROFL. I'm going to borrow that one and add it to my repertoire.