Using a rotary table.

[radfordc]

I purchased the Harbor Freight 3" rotary table today and spent some time playing with it today. When setting up an operation on the rotaty table I assume you first must center the table under the mill quill and then center the work on the table. Is this about right?

Charlie

 

[kvom]

You got it!

 

[gbritnell]

You're right Charlie. You have to initially center the rotary table to your spindle centerline, set your dials to -0-, mount the piece and center it to the center of the radius to be swung. Sometimes you will have a piece that doesn't have enough stock to put a centerline on it so in that case you would put some reference marks on the piece to be cut, move your mill off center to the desired radius, line up your spindle with your reference marks, clamp the piece and then start machining.
gbritnell

 

[kd7fhg]

Here is a good link on how to align a rotery table on a the mill.

http://techtv.mit.edu/collections/ehs-videos/videos/84-machine-shop-5

Best wishes to all!
KD7FHG

 

[radfordc]

Aligning the table is fairly easy. Since the small table doesn't have a machined center hole I used the outer edge of the table and zeroed it under the spindle using an edge finder. The hard part is locating the work accurately. For practice I popped the work piece and held it in place with a center in the drill chuck while clamping. I can see much difficulty trying to locate and clamp an actual part. Looks like the technique may be to lightly clamp the part, indicate with a DTI, and then tap the part into position before final clamping. Is there a better way?

Charlie

 

[SBWHART]

Hi

I've got a small Vertex rotary table its got a M2 morse taper up the middle, a quick way of centering the table I use is to put a centre in the quill wind it down onto the table, tighten the clamps on the rotary table, and zero your dials, job done.

Her's the table in use http://madmodder.net/index.php?topic=820.15

Cheers

Stew

 

[joeby]

I usually get a good many arguments started about rotary table setups. I worked in a large forge die shop, and I still do the setups the way we were shown in that shop. Probably 95% of the time you used a rotary table on a rotary head milling machine, so getting stuff on center was step #1.

The first thing to be pointed out is that the center hole and OD of the table aren't necessarily on the axis of rotation. Easy to check, take the worm out of engagement and pull the table around by hand with an indicator zeroed on the center hole. Just like indicating a part in a four jaw.

If it is on center, that's great. If not, you can eyeball your part on center and lightly clamp while you indicate it in by pulling the table around by hand and tapping it. If you don't have a concentric hole or OD to use an indicator on, a center punch mark and a pump center can be used.

Once the part is on the center of the rotary tables axis, it's a simple matter to center it under the machine spindle by locking the table and rotating the machine spindle and indicating like you would normally.

It all sounds like a lot of extra work, but it only takes a few minutes to do.

Kevin

 

[radfordc]

I made the assumption that the outer diameter of the table was concentric with the rotational axis...but better check it to be sure.

The part about centering the work on the table first and then centering the work and table under the quill makes sense. Sounds easier than doing it the other way around.

Thanks,
Charlie

 

[joeby]

You would assume that on a rotary table that the OD and center hole would be on the rotational axis, it makes sense that it would be.

I have checked a few and was surprised to find that wasn't always the case. Even on some of the better (name brand made in USA) rotary tables the runout was more than reasonable. Whether due to wear, abuse, manufacturing, or who-knows-what.

Kevin

 

[radfordc]

OK, I did check and the table is accurate to within .001 inch. At least that helps.

Charlie

 

[Andrew_D]

In Harvey's "Machine Shop Trade Secrets", he describes a different way to do this:

1) Align the part on the RT with the axis of the RT. The RT could be under the spindle, but does not have to be. Simply set a DTI against the inside or outside surface you are indicating. Spin the RT. Bump the part in until it runs true. Now you know the part is centered on the axis of the RT.

2) Put the DTI in your spindle with the needle indicating on the part. With the RT stationary, spin the spindle. Adjust the X & Y handles until the feature on the part is running true to the spindle.

Doing it this way, you avoid trying to indicate on the inside bore or outside edge of the RT, which may or may not be concentric with the rotational axis of the RT.

If you want to check and see if the axis is concentric with the inside or outside, remember that you just guaranteed that the rotational axis is centered under the spindle. When you are done with the part, you can always check the inside and outside bore at this time. Hopefully they are concentric, but they may not be.

Andrew