Bobw
Diamond
- Joined
- Feb 8, 2005
- Location
- Hatch, NM Chile capital of the WORLD
I had never really messed with form tapping, now I'm running two jobs with it at the same time. Both are in 1018, tank stuff. One is 3/8-16 half inch deep, I've run in between 40-80 sfm and an 11/32 drill. The threads are on size, but they look like crap, I went back to a cut tap on this one.
The other is 1/4-28 full form to 1" in a blind hole. Running an A drill, the treads look pretty good, when they stay with the part. Wrote the program yesterday, and had another guy (we'll call him Jose) set it up. Came in in the morning 2:59am (couldn't sleep) and the program has run, the first parts are in the vises, ops 1 and 2. Cool. Threads look good, the second op looks good, except, threads are undersized. Run a piece of scrap, threads are undersized. Running 250 rpm 8.964 or something IPM. Hmm slow it down to 5ipm, with coresponding RPM change. Oversized threads, Interesting, so I spent 3 hours messing with speeds to try and get a good thread on the Go/NoGo. Turns out 7.5 ipm gives an oversized thread, 8ipm gives an undersized thread, and 7.75ipm gives an oversized thread for the first half of the hole, and undersized for the bottom half, screw it, theres only 50 parts with 1 hole a piece, I'll just have a part timer chase them. (I'm not being mean, they get to sit in a recliner in front of the swamp cooler while they are doing it). Now the problem is chasing with a form tap, they threads are either good or big, crap, try a cut tap, and ripped all the threads out.
My 'lubrication' method from my 3 hour experiment this morning was that flood coolant was out, tap oil was OK, but still losing some threads (tapmatic, not tapmagic, that smells good). I was putting some tap oil in the hole, making sure that the tap was clean (visual and air blast) coating that and then putting some synthetic grease on the tap and in the hole, then adjusting that to following the tap with a brush and making sure on the pull out that the tap was covered in oil. That prevented the top few threads from ripping out.
So what am I doing wrong? I'm thinking that these 1/4-28 taps blow. We ran a bunch of nuts on the lathe in 416 with 10-32 threads, and they worked just fine, though the tap was basically round, these have a slight square shape to them.
The other is 1/4-28 full form to 1" in a blind hole. Running an A drill, the treads look pretty good, when they stay with the part. Wrote the program yesterday, and had another guy (we'll call him Jose) set it up. Came in in the morning 2:59am (couldn't sleep) and the program has run, the first parts are in the vises, ops 1 and 2. Cool. Threads look good, the second op looks good, except, threads are undersized. Run a piece of scrap, threads are undersized. Running 250 rpm 8.964 or something IPM. Hmm slow it down to 5ipm, with coresponding RPM change. Oversized threads, Interesting, so I spent 3 hours messing with speeds to try and get a good thread on the Go/NoGo. Turns out 7.5 ipm gives an oversized thread, 8ipm gives an undersized thread, and 7.75ipm gives an oversized thread for the first half of the hole, and undersized for the bottom half, screw it, theres only 50 parts with 1 hole a piece, I'll just have a part timer chase them. (I'm not being mean, they get to sit in a recliner in front of the swamp cooler while they are doing it). Now the problem is chasing with a form tap, they threads are either good or big, crap, try a cut tap, and ripped all the threads out.
My 'lubrication' method from my 3 hour experiment this morning was that flood coolant was out, tap oil was OK, but still losing some threads (tapmatic, not tapmagic, that smells good). I was putting some tap oil in the hole, making sure that the tap was clean (visual and air blast) coating that and then putting some synthetic grease on the tap and in the hole, then adjusting that to following the tap with a brush and making sure on the pull out that the tap was covered in oil. That prevented the top few threads from ripping out.
So what am I doing wrong? I'm thinking that these 1/4-28 taps blow. We ran a bunch of nuts on the lathe in 416 with 10-32 threads, and they worked just fine, though the tap was basically round, these have a slight square shape to them.