Rotary Table questions

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Brass_Machine

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So I have a small rotary table for my small mill. I didn't get a chance to use one in shop class, so... how do I align the spindle and the center of the table? I am assuming thats what I want to do. what is the best way to center the work? Anyone have some good pictures of a RT in use? I saw your post Bob W. about making a square plate round... anyone have anything else?

Eric
 
The beauty of an RT is that you don't need to line up the centre but just the edge of circle (or arc or whatever) from more or less anywhere under the quill, left, right ,in front or behind, depending on the workpiece.

Giles

 
Giles,
That is only true if the centre of the radius is on the same centre as the RT. There are times when we have to go back to basics and start from the beginning.

Eric,

A lot depends if you have a chuck fitted to your RT or not, or whether the RT has a spigot hole in the centre (most do).
For a basic setup of the RT to spindle, you fit a spigot into the centre of the RT (you can buy blank MT spigots that usually fit, or if it is a straight bore, turn one up yourself). Then roughly centre it under the spindle using the table adjustments. Once there, mount a DTI in the spindle chuck or collet, bring it down so that the DTI can be pushed into contact with the protruding spigot. Then turn the spindle gently by hand so that it rotates the DTI around the spigot and mentally note the high and low spots as you go around, and adjust the table in small increments until you get very little deflection as you move the DTI around the spigot. Depending on how accurately you set the centre of the table inititially will depend on how many times you have to bring the DTI back into contact with the spigot. It does sound difficult, but once you get the idea, you can usually recentre your RT in about 5 mins.
Many people fit a 4 jaw independent on their RT. To me that is tantamount to self flagellation. If you can get a decent 3 or 4 jaw self centreing on there, and centred onto the RT using the centre spigot, that will be perfectly sufficient for most peoples needs. Use the same method of centreing as using a spigot, but come off a piece of round stock in the chuck. If you then want to be super accurate, you can fit soft jaws into the chuck and machine them in situ to fit the job size required (as long as it will fit on the jaws).

Maybe someone can try to explain it a bit better, but I hope this is enough to be going on with.

John

 
Brass_Machine said:
So I have a small rotary table for my small mill. I didn't get a chance to use one in shop class, so... how do I align the spindle and the center of the table? I am assuming thats what I want to do. what is the best way to center the work? Anyone have some good pictures of a RT in use? I saw your post Bob W. about making a square plate round... anyone have anything else?

Eric
Hi Brass Machine
It depends on your RT. If it has a taper in the center hole, get a blank with the correct taper and use your edge finder to locate the center (Lautard method). If you have a stright hole in you RT then just put a tight fitting dowel in it and do the same.
 
I have a page on rotabs and their care and feeding: http://www.cnccookbook.com/CCRotabToys.html

As stated on the page, to set up the table, I follow the method outlined in Machine Shop Trade Secrets:

First, you want to make sure your part is properly centered on the table. To do that, I clamp the table down on the mill table (no special place is needed), put my Indicol indicator holder on the mill spindle, and find some round feature on the part to indicate on. For example, on the plate milling fixture above, indicate on the round boss, or on the center hole. Spin the table and bump the part in until spinning the table doesn't move the indicator.

Second, locate the center of rotation directly under the mill spindle. You can simply use the X and Y table handwheels to do this. Use that Indicol to indicate off of a circular feature you want centered under the spindle. Turn the indicol around on the spindle and adjust the handwheels until the indicator stays put relative to the spindle position. A Blake Coaxial indicator will make this last even simpler.

Is there some other particular operation you'd like to understand better? Lots of possibilities with a rotab. I'm a noob myself. Someone here will know.

Cheers,

BW
 
Bob's advice on centering the table is right on the button.

For less finicky work, you can make a plug to fit the bore in the table. Drill it through and thread 8-32 [or thereabouts], then use a center drill to make a 60 degree center in the exposed end. Now you can drop the plug in place and use the pointy end of an edge finder to center the table accurately enough for many operations without the hassle of setting up an indicator. A long 8-32 screw with a sliding weight will pop the plug out when you want to mount your part.
 
Sorry guys ,I misunderstood the question there!, I've never done any work off the RT centre but I've been thinking about doing a curved spoked flywheel ,now I've got more of an idea how to go about it!

Giles
 

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