trochoidalpath
Cast Iron
- Joined
- Jan 17, 2016
I ran into a weird problem tapping 316 and I'm kinda scratching my head.
The part in question is made in two operations: the top, where I hit five surfaces, and the bottom, where I surface the bottom (it's at an angle to the top). The top has 2 M3x0.5 blind holes. The part mates to three others, and it's a little fussy, so I made a prototype in 6061 to check fit -- works perfectly. The environment is wet and the part needs to last for decades so I made a final version out of 316. The part design is identical, I just reprogrammed it to account for the new material. The drill and tap are identical between the 6061 and 316 version. The tap is an OSG Exopro XPF form tap. The drill is a no-name HSS-TiN 7/64ths, which has cut exactly 4 holes in its entire little life.
Before I broke the first setup, I checked the thread fit with a M3 screw, which was perfect. After the second operation, I went to assemble the part, and the M3 bolts won't thread. They turn in maybe two or three turns and then bind up.
The thread looks good on visual inspection. I can chase the hole with the tap with zero resistance, the fit feels perfect. And this worked perfectly in the aluminum part -- same drill, same tap. But no bueno in stainless.
What am I missing?
The part in question is made in two operations: the top, where I hit five surfaces, and the bottom, where I surface the bottom (it's at an angle to the top). The top has 2 M3x0.5 blind holes. The part mates to three others, and it's a little fussy, so I made a prototype in 6061 to check fit -- works perfectly. The environment is wet and the part needs to last for decades so I made a final version out of 316. The part design is identical, I just reprogrammed it to account for the new material. The drill and tap are identical between the 6061 and 316 version. The tap is an OSG Exopro XPF form tap. The drill is a no-name HSS-TiN 7/64ths, which has cut exactly 4 holes in its entire little life.
Before I broke the first setup, I checked the thread fit with a M3 screw, which was perfect. After the second operation, I went to assemble the part, and the M3 bolts won't thread. They turn in maybe two or three turns and then bind up.
The thread looks good on visual inspection. I can chase the hole with the tap with zero resistance, the fit feels perfect. And this worked perfectly in the aluminum part -- same drill, same tap. But no bueno in stainless.
What am I missing?