Finally stopped the spin...

[dubby]

I've tried lots and lots of different methods to tap these little 1/2" thick, 1.25" rounds to 5/16-18. Lots. Some methods have worked, some have failed. Every one of them has had some sort of drawback.

Using a vise to hold them, I ended up with either severely scarred up edges from the teeth on the jaws, or I'd end up with an out of round thread where I actually tightened the vise down so much it would oval-shape the center hole.

I've tried clamping them from the top, using v-blocks, tapping in my lathe, tapping in my drill press, and even holding the tap in the vise and trying to spin the work on by other means. Lots of time the actual setup to tap the hole took longer than the process. Either way, it's just been frustrating.

Finally, I believe I've hit upon a method that works. It's fast. It's simple. It has minimal scarring on the workpiece. The drawback is that it's not adjustable for any other sizes than the two that I built the rig for. I put this little chunk of aluminum in the CNC mill and programmed it to cut two pockets, one 1.5" and one 1.25". I had it go ahead and clear out a 1/2" hole in the center all the way through the piece so the tap and chips could clear. I then changed tools and ran a line to help me find the center of the holes on the edges. I pulled it off the mill and drilled a couple holes for 1/4-20 threads into the upper pockets.

Again, not real complicated but it proved to be extremely effective. Here's the block in my hand tapper ready to work. I need to find or make a speed handle to manipulate the screw but had a water leak to fix and had to stop for the day...

[Lew Hartswick]

Looks like a piece of cake with a collet in a lathe. drill / tap /faceoff / etc .
...lew...

[GWIZ]

clamping from the top would be an option.

[LKeithR]

Originally Posted by Lew Hartswick

Looks like a piece of cake with a collet in a lathe...

Pretty hard to find collets that size. Depending on quantity my choice would probably be soft jaws on a lathe...

[digr]

That looks like it would work mighty fine. I think I would have made my own collet or collets to put in a three jaw. Bore your I.D.s and use a slitting saw to cut three cuts in it to make a collet. you could use the same collet for at least two different sizes.

Ted

[Scotts]

Sometimes if it is not a critical super tight torque down job you can cheat a little and have a little less thread engagement by stepping up the drill bit size to help with this, it may not be applicable in this situation though.

What are you using for lube?

Scott

[Lew Hartswick]

Originally Posted by LKeithR

Pretty hard to find collets that size. Depending on quantity my choice would probably be soft jaws on a lathe...

Machinable collets are readily available. We "inherited" a handfull several years
ago.
...lew...

[dubby]

Again, facing the undersized lathe problem I have. Collets would be ideal, as would doing everything in one setup on the lathe. On a 7x14 lathe you just don't have the bulk to pull off that sorta thing. I've tried to tap a number of different ways on it, and the motor just bogs down and everything comes to a stop. By the time I throw it into reverse two or three times and start back over, I could've had it done by hand.

Until the lathe fairy brings me something better, it's adapt and overcome

I do drill out the holes oversize to make it easier. Usually I can spin the tap in without backing up to clear the chips more than once. I use A9 fluid for tapping in these and it all works decently enough.

[Scotts]

thanks for the info.

Scott

[dreamcutter]

For milling and tapping round items, I use lathe chuck to hold the work piece. On the vertical mill the chuck is mounted on a rotary table, although I have also have a low profile plate for applications where I need more vertical clearance. In the images below I a 32x8 inch plate with (4) 3" 3-jaw chucks on center (height trammed too,using shim) that was needed for a high volume project. Its suitable-for CNC and has perimeter coolant troughs. Its available for local loan if someone needs it. Attached are images with vises mounted and trammed, and the underside of the plate with bolt patterns. Redesigning the plate, I would mount vises from surface dogs rather than from bolts underneath.
hmm I see i took some raw video of the gang mill attempt, could be entertaining...