Centering a Link on a Rotary Table

[Matt_Isserstedt]

Here is a procedure using a couple pictures of a technique I use for setting up round-end links on a rotary table. The procedure is for links which will have a hole bored or drilled at the center but the technique could be slightly modified for non-drilled link ends or other arc forms.

http://www.metalworking.com/dropbox/rotary_table_1.jpg

Here are the "raw materials"…My workpiece which is rough-bandsawed oversize to reduce the amount of stock to be removed with the milling cutter. The centerlines have been jig-drilled using the x-leadscrew on my Bridgeport mill, first with a center drill, then a 1/8" drill bit. Other raw materials are R8 collets with a stub of ¾" CRS round stock, and a stub of 1/8" drill rod.


http://www.metalworking.com/dropbox/rotary_table_2.jpg

Here is the basic setup for centering the rotary table. The ¾" CRS stub is tightened in the mill's spindle, and the center bushing of the rotary table is located with the X and Y leadscrews, until the stub slips cleanly into the bushing when operating the quill. At this point, the spindle is centered over the center of the rotary table.

http://www.metalworking.com/dropbox/rotary_table_3.jpg

Without moving the table from the photo above, put the workpiece on a parallel and locate the hold-down clamps with finger-tight bolts. Insert the collet with the 1/8" stub and then lower the quill into the drilled hole on the workpiece. Now it is time to tighten the hold-downs with a wrench. Using either X or Y leadscrews, move the table an amount equal to (radius of link end) + (radius of milling cutter). You are ready to cut the radiused end.

http://www.metalworking.com/dropbox/rotary_table_4.jpg

Finished workpiece after some other operations compared to the drilled blank. Not that it really matters but the "links" are designed to hold a long tool-rest for my Dad's woodworking lathe.

Future upgrades planned are to replace the stubs with standard case-hardened dowel pins for greater accuracy in the centering process. Also more fluorescent shop lights so my pictures aren't so dang dark.

[Michael_Az]

Good show Matt. Looks like it came out great. I guess if you didn't have a hole to locate from, you could machine the end of the link and then use an indicator to locate the three edges and then locate the spindle on the radius.
Michael

[cprucha]

Hi Matt,

Thanks for sharing the procedure you used to locate the link in the mill on the rotary table. The photos you posted are great and really help explain your process. Thanks again, and in the last photo the link looks good.

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[Roy]

I use a ground center that is adapted to the R8 on my BP, and just giggle the X and Y feeds while working the quill to line up the center of the RT. Then I lock the X and Y feeds, zero the indicator knows and the DRO. Then lower the Knee or raise the quill insert part, and I usually have a small indent to which I index off of on what ever it is I am milling, so I bring the knee back up and set the point of the center in the indent, and clamp the part to the table. It has proven to be repeatable with the DRO and feed knobs and sure is quicker than setting up a DI to index it in. It may not be the most accurate but it is pretty darn close if not dead on, as it all depends on how carefull your setting and clamping proceedures are. Up until I obtained a center I used the plug method as you did.
Great looking part Matt.
Regards