guys I've gotten so much learning from reading all of your posts but this time I'm stuck and could really use some expert help ...
i'm building a new steel 26"x60" weld/fab table for the shop and i'll be fastening casters (hollow kingpin style) via 1/2-20 grade 8 bolts to 1" dia 18-8 stainless steel bolts at each of the 4 corners/legs of the table. the 1" dia 18-8 bolts will be used as leveling/jack screws to level the table. i'm drilling facing and trying to tap the 1" 18-8 (basically grade 5) bolts and no matter what tap method I employ I'm seeing the same failure.
failure - the tap will run ever so slightly out of parallel with the hole in the 18-8 stainless and once it's approx. 1/4" deep it will of course bind and stop
what I have tried -
- all attempts include a lead in chamfer on the drilled hole greater then the max. dia. of the 1/2-20 thread
- drilling both 29/64 to start & then tried 15/32 dia on the lathe (see pics attached)
- there is no work hardening concern
-(2) McMasterCarr "economy carbon steel taps" a plug chamfer 1st & then a tapper chamfer have been tried
- tap magic cutting fluid is being used
- tap method (1) - manually taping in lathe w/a live center in the dimple on the back of the tap, head stock locked and tap wrench on tap (note i don't have a spring loaded live center so i'm manually maintaining pressure on tail stock)
- tap method (2) - manually taping in lathe with the tap in the drill chuck, tail stock floating and manually turning head stock... note the tap seems to quickly grab and HSS shaft spins in the drill chuck so I slid the tail stock back and tried to finish taping with method (1) above
- tap method (3) I machined a guide block, fixtured the bolt in a bench vice, used guide block to try and maintain perpendicularity while taping by hand through the guide block
considering all combinations/possibilities above I consistently get the exact same result ... the tap runs ever so slightly out of parallel.
please help?
thanks!!
i'm building a new steel 26"x60" weld/fab table for the shop and i'll be fastening casters (hollow kingpin style) via 1/2-20 grade 8 bolts to 1" dia 18-8 stainless steel bolts at each of the 4 corners/legs of the table. the 1" dia 18-8 bolts will be used as leveling/jack screws to level the table. i'm drilling facing and trying to tap the 1" 18-8 (basically grade 5) bolts and no matter what tap method I employ I'm seeing the same failure.
failure - the tap will run ever so slightly out of parallel with the hole in the 18-8 stainless and once it's approx. 1/4" deep it will of course bind and stop
what I have tried -
- all attempts include a lead in chamfer on the drilled hole greater then the max. dia. of the 1/2-20 thread
- drilling both 29/64 to start & then tried 15/32 dia on the lathe (see pics attached)
- there is no work hardening concern
-(2) McMasterCarr "economy carbon steel taps" a plug chamfer 1st & then a tapper chamfer have been tried
- tap magic cutting fluid is being used
- tap method (1) - manually taping in lathe w/a live center in the dimple on the back of the tap, head stock locked and tap wrench on tap (note i don't have a spring loaded live center so i'm manually maintaining pressure on tail stock)
- tap method (2) - manually taping in lathe with the tap in the drill chuck, tail stock floating and manually turning head stock... note the tap seems to quickly grab and HSS shaft spins in the drill chuck so I slid the tail stock back and tried to finish taping with method (1) above
- tap method (3) I machined a guide block, fixtured the bolt in a bench vice, used guide block to try and maintain perpendicularity while taping by hand through the guide block
considering all combinations/possibilities above I consistently get the exact same result ... the tap runs ever so slightly out of parallel.
please help?
thanks!!