Center For A 3” Rotary Table (second try at posting)

[bmac2]

Ok. See if can put this in the correct thread. The weather here in sunny Alberta Canada has been hovering in the high 20’s and I don’t have air conditioning so it looked like a good time to hide in the basement workshop. I have a small 3” rotary table for my mini mill and thought it would be nice to have a center for it. The ones I can find locally either cost more than I paid for the mill or are just crap.

 

[bmac2]

So I decided to make one. The center would need to be around 2 1/2“ high. I often fit a 3” Taig lathe chuck to the table and this has to be set on a 123 block so the jaws clear. I wanted a simple but useful height adjustment and came up with this. I stressed out over how to get the angle perfect till it dawned on me that the angle wasn’t all that critical. All that mattered was that the two wedges had to be the same angle. With the angle set at around 12 deg. I should get about ¼” vertical travel.

 

[pkastagehand]

Did you mix up pictures? That doesn't look like any center I've seen before... oh that's better. The first pic that came up was not what I was expecting.

Seems like it should work. As you said the actual angle less critical than that they match to make the lift stay parallel.

Paul

 

[bmac2]

All good things start with a 4x6 band saw.
Cut off 2” from my precious length of 1 x 4 aluminum and then cut that down again to get the 2x2 block for the body and two 1x1x2 blanks for the wedges. Cut out a 2 ¾ x 2 ¾ from some ½” stock for the base and it’s downstairs to the shop. Somehow it looked bigger on the cad

 

[bmac2]

After squaring everything up I like this vid for squaring up stock. He explains it well and doesn’t stick his hands into a running mill like the MIT (I think it was MIT) vid I saw.
Tom's Techniques - How to square up stock on the milling machine [ame="http://www.youtube.com/watch?v=igfqYZPdQ78"]http://www.youtube.com/watch?v=igfqYZPdQ78[/ame]
I started with the fixed wedge set in the vise at around 12 deg. and milled it down to ½” at the small end. Milled a .375 x .375 slot just over 1.9” down the middle. Flipped it over and milled a flat area big enough for the adjusting bolt to ride on 90deg. to the wedge.

 

[bmac2]

Set up the sliding wedge using the fixed one in the bottom of the vice to set the angle and milled it down to the same dimensions as the first leaving a .375 x 375 x .5 hub in the center.

 

[bmac2]

I needed a bolt threaded to the top so I ran a die up a cap head screw (those are made of some tough stuff). Drilled and taped the hub ¼ - 20 again using the fixed wedge to set the angle. Checked it with a dial indicator and its out just under a thou end to end (must have got the angles right)

 

[bmac2]

Next came the side plates. Ok. My history is basically a wood guy so some of my setups might not be quite right. Glued the two plates together (in wood I’d use veneer tape) and milled them to size. Laid out the holes, drilled, milled, and ready to go. Well after some heat to separate them.

 

[bmac2]

Hogged out a slot 1.25 wide .25 deep slot in the base and test fitted the parts.

 

[bmac2]

Milled and drilled a small boss (not sure what to call it. Half a piece of 3/8 brass?) from .375 brass to give the lock nut on the angle screw something to run against. Drilled and taped the 6-32 holes in the fixed wedge using my mini tap follower and bolted everything tougher.
My tip here is that when you mount your vise to the milling table put an extra T nut under the vise so you can assess it between the jaws. Handy when setting up small stuff.

 

[bmac2]

The center is just a 2” length of .5 drill rod (was going to be .625 but I didn’t have any) machines with the taper at one end and taped ¼-20 1 inch deep on the other. Drilled and taped for the 2-56 cap screw used to keep the center from rotating.
Note to self “drill and tap all holes before hardening” I remembered this time

 

[bmac2]

The main body is nothing special. Drill the 2 ¼” cross holes. Slit the top. Mill a ½” long slot for the guide screw. And drill and tap four 6/32 holes for the back plate. The ¼-20 screw that seats (?) the center into the work piece gets a locking nut like the one on the slide. Counter sunk for the 10-32 clamp screw using my shop built counter bore I made following the instructions from Dean Williams page. Check it out Great workmanship and ideas. (http://www.deansphotographica.com/machining/projects/projects.html)
Go ahead. Check it out. I’ll wait . . . . . . . . . . . . .

 

[bmac2]

LAST PIECE! The back plate is a piece of 1/8” plate cut down to 1x2” and drilled for the four 6-32 mounting screws and the ¼-20 screw. The 6-32 mounting screws are set below the center so they don’t interfere with the clamping action. A little Myford gray (green?) and DONE.

 

[RichD]

That's real nice work there Bob!
I like the design features. Clever setup.
Rich