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trouble taping 18-8 ... help?!

bTanZ

Plastic
Joined
May 4, 2016
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!!
 

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'' -(2) McMasterCarr "economy carbon steel taps" a plug chamfer 1st & then a tapper chamfer have been tried

Therein lies a lot of your woes, SS is a pig to tap on a good day, .....SS bolts even worse, .and ordinary el cheapo CS taps are no good for it, ...get some HSS taps for Stainless (it won't be $ wasted they work great on carbon steels etc etc.
 
I certainly agree with Limy that tapping SS bolts can be a bitch sometimes. I realize you have already put a good amount of work into this project but if it were me I would not use SS for leveling bolts. SS is a great material for certain things but it is not particularly strong and tends to gall because of its "sticky" qualities. Why not make them out of bolts that are easier to machine and glob them up with anti seize?
 
'' -(2) McMasterCarr "economy carbon steel taps" a plug chamfer 1st & then a tapper chamfer have been tried

Therein lies a lot of your woes, SS is a pig to tap on a good day, .....SS bolts even worse, .and ordinary el cheapo CS taps are no good for it, ...get some HSS taps for Stainless (it won't be $ wasted they work great on carbon steels etc etc.

This is great feedback... i ordered a HSS coated tap from McMaster Saturday and i hope it arrives today to try!
 
I certainly agree with Limy that tapping SS bolts can be a bitch sometimes. I realize you have already put a good amount of work into this project but if it were me I would not use SS for leveling bolts. SS is a great material for certain things but it is not particularly strong and tends to gall because of its "sticky" qualities. Why not make them out of bolts that are easier to machine and glob them up with anti seize?

Yes after this experience, and if a good HSS coated tap doesn't make things work more smoothly I think a good old grad 5 bolt will be my next stop ...

2. things ...

1. i mistakenly thought i ordered HSS uncoated "economy taps" until I made this post and looked closer at the McMaster Carr invoice and realized the taps I ordered were not HSS. that's on my for sure and def. a screw up!
2. i didn't want to go mild steel with anti-seez globed on. even though my shop is clean i was hoping to avoid dust, chips, etc. from sticking to the threads. I was hoping stainless with a lil dry lube would run well ... clearly now I see a grade 5 bolt may be the lesser of 2 evils #Learning

THNAKS!!
 
Perhaps "globed on" was a bit misleading. Although it may attract a bit of dust, I doubt if a thin layer on the threads would have swarf hanging off it. How often do you intend to level this table anyway? I would think it would be pretty much a one shot deal. I completely agree with you that the table should be level. When I am welding up material I often throw a magnetic torpedo level on vertical components.
 
This is a good exercise to single point the threads in your adjusting feet. You don't have to cut the thread to final size, but if you get it close the tap will thread in much easier and will start straight.
 
I hear ya .... thanks!

my shop is undersized so for small TIG jobs i can leave the table in place and that part of the slab is about 1/8" per 12" out of level. For bigger, MIG or messy jobs (lots of grinding, etc.) it will roll outside on the 5" casters to a more level surface and upon completion rolled back into the the shop again to the crooked slab. So sadly I'm probably adjusting level more then most..
 
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!!

Your trying to use a cheap cut thread tap. Cut thread tap aren't worth there cost. Try a better tap that is ground 1/2-20gh3 HSS. The g is a ground tap. The h3 is .0015 over the basic thread dimension for the fit. Grade 8 and Stainless is over kill. A light film of lube on the screw, go gob and no mess.

Good Luck
Roger
 
Your trying to use a cheap cut thread tap. Cut thread tap aren't worth there cost. Try a better tap that is ground 1/2-20gh3 HSS. The g is a ground tap. The h3 is .0015 over the basic thread dimension for the fit. Grade 8 and Stainless is over kill. A light film of lube on the screw, go gob and no mess.

Good Luck
Roger

this is great learning thank you!
 
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!!

15/32 tap drill is the right size for SS (50% thread). Molly lube and a good quality HSS tap (Spiral point H3) and you should not have
any problem. No cheap Carb. Steel etc. but a brand name.
 
2. i didn't want to go mild steel with anti-seez globed on. even though my shop is clean i was hoping to avoid dust, chips, etc. from sticking to the threads. I was hoping stainless with a lil dry lube would run well ... clearly now I see a grade 5 bolt may be the lesser of 2 evils #Learning

THNAKS!!
This is where your reasoning went wrong... You could use "normal" black or galvanized steel bolt even dry without any lube but never stainless steel!

Stainless steel galls and friction welds to single-piece assembly amazingly easily and fast when things go south.
I have had 8 mm SS bolt-nut pair gall when turning to finger-tight. Attempting to back up with a wrench and it moved maybe quarter turn and after that galled totally solid shearing off the bolt.
 
thanks for everyones help ... I had accidentally procured "junk taps" and that was the problem!
 
...even though my shop is clean i was hoping to avoid dust, chips, etc. from sticking to the threads...

Jeezuz....if you think a few chips sticking to your threads is going to be a problem you're getting into the
wrong business. Machining, drilling, welding and fabricating all produce chips and dust; something you're
just going to have to learn to live with...
 








 
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