Hello everyone,
I recently had a job making 100 small stub axle parts turned from 3/4" 303 SS round bar. Simple manual turret lathe part (that's what I'm using), with a 1/2" long shoulder on one end,threaded 1/2"-13 UNC. I turned the pre-threaded dia. to .495", and had a generous undercut at the shoulder for the thread to run out into. I planned to use my Geometric 3/4"DS self opening die head to thread them. The first few parts I tried, I kept having trouble with the head not opening when the stop tripped, and instead running into the shoulder with he usual results...chipped chasers, and ruined threads.
After disassembling the head I found the cam spring had broken, and was only just barely throwing the head open, so I ordered a new spring,(and new chasers) from Detroit Automatic, and cleaned,and reassembled the head. The head opens much more forcefully now, but when I started trying to thread these parts again, SAME PROBLEM ! Die head over-runs the stop, and just keeps threading until it crashes into the shoulder ruining part, and more importantly (and expensively)the chasers. I ended up using an Acorn die which threaded 100+ parts beautifully without missing a lick.
I should mention that the chasers were brand new,Geometric USA, Projection,45* chamfer,15* hook, which is what is recommended for stainless in the Geometric Die head book. I was threading them at 60 rpm, which is only slightly below,and as close as my machine will get to the recommended 10 SFPM. and brushing a generous amount of Moly-Dee on the part and the chasers before threading.
I have read in other posts,about some folks threading in two passes,(rough, and finish). and the style D die heads have a cam lever that makes that possible without using two heads.My DS head doesen't have that option. Geometric doesn't mention anything about it in their book on these die heads though, so I'm wondering, is that what I'm doing wrong? Is 1/2-13 too course and heavy to thread in one pass with a 3/4"DS head? I haven't used this, or any other self opening die head a lot, but I have made several parts with smaller, or finer threads with it before, and never had this much trouble, even with the broken cam spring. Chasers are too expensive to spend too much time learning. What the hell am I doing wrong???
And please don't say "just buy a cnc and single point them".
Thanks for any help you can offer, Brian.
I recently had a job making 100 small stub axle parts turned from 3/4" 303 SS round bar. Simple manual turret lathe part (that's what I'm using), with a 1/2" long shoulder on one end,threaded 1/2"-13 UNC. I turned the pre-threaded dia. to .495", and had a generous undercut at the shoulder for the thread to run out into. I planned to use my Geometric 3/4"DS self opening die head to thread them. The first few parts I tried, I kept having trouble with the head not opening when the stop tripped, and instead running into the shoulder with he usual results...chipped chasers, and ruined threads.
After disassembling the head I found the cam spring had broken, and was only just barely throwing the head open, so I ordered a new spring,(and new chasers) from Detroit Automatic, and cleaned,and reassembled the head. The head opens much more forcefully now, but when I started trying to thread these parts again, SAME PROBLEM ! Die head over-runs the stop, and just keeps threading until it crashes into the shoulder ruining part, and more importantly (and expensively)the chasers. I ended up using an Acorn die which threaded 100+ parts beautifully without missing a lick.
I should mention that the chasers were brand new,Geometric USA, Projection,45* chamfer,15* hook, which is what is recommended for stainless in the Geometric Die head book. I was threading them at 60 rpm, which is only slightly below,and as close as my machine will get to the recommended 10 SFPM. and brushing a generous amount of Moly-Dee on the part and the chasers before threading.
I have read in other posts,about some folks threading in two passes,(rough, and finish). and the style D die heads have a cam lever that makes that possible without using two heads.My DS head doesen't have that option. Geometric doesn't mention anything about it in their book on these die heads though, so I'm wondering, is that what I'm doing wrong? Is 1/2-13 too course and heavy to thread in one pass with a 3/4"DS head? I haven't used this, or any other self opening die head a lot, but I have made several parts with smaller, or finer threads with it before, and never had this much trouble, even with the broken cam spring. Chasers are too expensive to spend too much time learning. What the hell am I doing wrong???
And please don't say "just buy a cnc and single point them".
Thanks for any help you can offer, Brian.