tapping suggestions

[gahydtoolman]

trying to tap on a small (fairly new) mazak lathe. 3/4-16 thread. was running a guhring tap in live tooling, as it dulled it started stalling the live tooling spindle. decided to switch to tap collet and rigid tap the hole. now go-gage won't start, put in new tap, still won't gage. my thinking is misalignment, but there is no indicator here that i can rig up to check the pocket. put new tap back in live tooling position, still can't get go-gage to go more than one turn??? any ideas?

[Chrliev]

Usually if the go-gage won't "go", it's an indication that the thread is undersize, however in your case with a new undamaged tap it is probably an indication that the very first thread or lead-in to the hole, is damaged.

Make sure that the machine leads out away from the part far enough to ensure that the first thread is not rolled back into the hole. Also make sure that the hole has plenty of chamfer at least 45 degrees or even 30 degrees if you can get away with it.

Alternatively if the problem persists you can go to a GH4 or GH5 oversize tap...

[gahydtoolman]

thanks! we have been changing our taps over to H5 due to welding causing the hole to egg shape on some parts. i'm pretty sure our lead in is far enough out to not cause a problem, but will double check (previous tap was fine until it dulled). this is a -5SAE port so there is a really nice starting chamfer built into the porting tool. appreciate the response!