Confusion With Machining A Blank On A Chuck Mounted To Rotary Table

M

Machinehead

Registered
Registered
Joined
Nov 3, 2015
Messages
18
It's a simple operation of milling a .250 diameter out of .375 round stock and putting a hole in the center after machining the diameter. I have my rotary table centered in the mill table, with my X,Y zero set on the dro. Then, I indicated in the 3 jaw chuck to the same zero. After I machine the diameter true to the rotation of the table, shouldn't my hole go directly on center to that diameter when I go back to zero? It appears off center, and I thought it would be good to the outer diameter after machining. Am I missing something?
 
Depends. First off, I have to ask so I apologize, did you indicate the rotary table? You state it was centered. Also there are some things you may not realize. This is easiest done in a lathe, but it can be done in a mill. You have to indicate the rotary table, taking into account WHICH direction you last moved the table to get t either the X or Y axis to zero. This is because if you don't, the slop in your table will NEVER allow you to get the hole back in the center. I say never, but I digress, everyone gets lucky once in a while. Sorry for babbling, but in my mind I can do this in my sleep but to describe it in words that are easy for others to understand can be challenging. Once you see my description you will understand why this is best done in a lathe..

Ok, so you must indicate the rotary table, you have to know which direction you moved the table last as that is the direction with NO slop. This needs noted for the X and the Y axis.
Then mount the 3 jaw must be centered to that same point AND with the table being last moved in the same direction as the rotary table. That is gonna be tough.


Let me change the entire course.... Try this...

Buy a piece of .25 stock, using a small V-block, clamp it in a good strong vise mounted to your table, Indicate the .25 stock to zero, lock the table from movement, you will be centered, then drill your hole, done... You will have so much hair left over....hope this helps...

(EDIT)And if you don't have a good V-block or a vise, use your 3 jaw chuck clamped to the table and indicate the .25 material in there, will work just as well.
 
Last edited:
Got the backlash going the same way when you come back to your zeros?
 
A chuck mounted on a rotary table will more than likely have some runout.

When I machine a cylinder using the mill with a rotary table, I get an approximate center and offset the table to mill an oversized cylinder. The cylinder will now be true the the RT axis. Indicate the cylinder in the x and y directions to determine the RT axis coordinates and set your DRO to coincide.
 
I hesitate to ask this, but why are you putting yourself thru all this when all you have there is a job for the lathe. Info so far is all good but you are, IMHO going about it with the wrong machine. Chuck it up in the lathe, turn the OD and bore the hole., done deal.
 
Last edited by a moderator:
RJSakowski said:
A chuck mounted on a rotary table will more than likely have some runout.

When I machine a cylinder using the mill with a rotary table, I get an approximate center and offset the table to mill an oversized cylinder. The cylinder will now be true the the RT axis. Indicate the cylinder in the x and y directions to determine the RT axis coordinates and set your DRO to coincide.
Click to expand...
One may find the center of rotation of a rotary table mounted on a mill by indicating the convenient center hole provided for this purpose amongst other uses.
Many have a hollow spindle with a reference diameter produced during manufacturing, can't get much closer to center then that.

I have a Walter 18" Horizontal/Vertical with a vernier dial (1 minute resolution) that is in excellent shape that I would like to unload at a very nice price, with a wheeled storage cart included, it weighs 300+ pounds.
Looks exactly like this.
http://www.maschinensucher.de/bilderuploads/1074679.jpg
 
When using a chuck on a RT, I indicate the work true to the axis then center the spindle over the work I just indicated in. This way I'm not relying on the inside hole of the RT for a reference. Plus, Import 4" RT's don't have a bored hole in the center, rather it's threaded M6 (I think, I chased it with a 1/4-20 UNC tap for convenience)
 
Bill Gruby said:
I hesitate to ask this, but why are you putting yourself thru all this when all you have there is a job for the lathe. Info so far is all good but you are, IMHO going about it with the wrong machine. Chuck it up in the lathe, turn the OD and bore the hole., done deal.
Click to expand...

Right now I don't own any tool bits to create a sharp inside corner, so I needed to use an end mill on the RT to get it.
 
You must log in or register to reply here.
Back
Top