big tap, deep hole, no holder

[Kendo]

and I only got two holes to do

its a 3/4-10 tap going 3-1/2" through a soft steel bar

 

I tried it starting by hand already, but the threads wandered away at the bottom of the hole - looked straight to me!

 

anyway, guess Im milling an adapter next to put this thing in a 1" tool holder w/ set screw

 

any words of wisdom?

[Namliek_J@TheeCircle™]

Lots of tapping oil, slow and steady. Is it a blind hole or a thru hole?

 

Maybe a roll forming tap would be a good choice since it doesn't produce a chip. HTH.

 

You could get a single point thread mill and thread mill it.

[3R!< W3NG3R]

make sure it cannot spin!

also , it has to be really true to the spindle if you do it that way.

good luck

[J Coulston]

Does the tap have a center in the drive end? I have put a single flute counter sink in the spindle and hand feed into the tap center. Then turned the tap by hand. Turn, back off, turn, move z down, repeat until the tap is straight.

[MotorCityMinion]

If possible, try thread milling as deep as you can, then that will act as a pilot to drive the tap the rest of the way.

[Kendo]

Thats a good idea J Coulston

 

and thanks guys, but I finished the adapter today right before I left

everything looks good and true in the 1" holder

 

I milled a piece of 1" round bar with a circular pocket the diameter of the tap shank and then a square pocket at the bottom to accept the tap drive

Then I turned it over and milled off one of the four sides of the square pocket so the set screw would contact the tap drive.

[GoetzInd]

Sounds Dangerous. I like it!

 

Mike

[Matthew]

Maybe a bit late for you, but you can get a standard holder tension/compression holder to hold a 3/4-10 tap, as long as the shank on your long tap is the standard size for a 3/4-10?

[Kendo]

Ran my tap this morning using the new adapter, threads look good so I guess it was true enough.

 

I couldn't buy a new holder for $400-500 since It was just two holes, plus I'm like GoetzInd, I like it when it gets tricky.

 

Most of the time I'm milling little notches and slots in aluminum extrusion so I enjoyed this little project.

 

Thanks again yall