Guys, I'm sorry to flog this subject, I know there are 1500 posts about threading but I have been searching & reading on-line for WEEKS and still haven't found what I need to know.
This is for maintenance and R&D, not production, and I buy my own tools so I'll be using the cheap stuff on Ebay like Shars, etc. That stuff always works fine for me. Not worried about details like coatings & grades & chipbreakers, & speeds & feeds etc. because it's all random mystery metal scrap. (Not really, I usually know what it is, but sometimes 12L14, H13, M2, S7, 4140, whatever is lying around.) I am willing to deal with the deflection, chatter, finish & thread form issues, etc. as required. Using a Clausing with DRO but no threading stop or "clock."
1) I will ALWAYS cut RH threads away from the chuck. That means the spindle is "reversed", and the tool is in "back" of the bar.
2) Assume there is always a blind hole or external flange on the left, hence the reversed feed. If there wasn't, I'd just use a tap or die anyway.
3) Can't turn the tool upside down on this lathe. It lifts up the saddle. I have done it with care from necessity but it is not a good plan.
3) I have learned to NEVER, EVER unclamp the halfnut once I get started, even though I theoretically know how to do it, I have always managed to ruin a good thread on the last pass because I wanted to try the fit on a workpiece and get the tool out of the way in a hurry. I start with a relief groove with about 0.01in of clearance and after each pass, slowly jog the DRO back to zero. After sweating bullets for 10 passes on S7 I just don't have the nerves to risk opening the nut without blowing it. If I really have to, I'm better off just re-locating the groove from scratch instead of trying to phase the leadscrew properly.
About the biggest I have to deal with is 7/8-9. I'm going to buy four boring bars, two each inside & outside for size 11 and 16 triangle laydowns. With non-topping inserts in a couple of radii to cover a wide range. The cheap holders I'm looking at dont have shims, that's OK. Basically "SNR/L0010K11" type bars.
So my question is, what the hell is the difference between 11IR, 11NR, and 11EL inserts (which look the same in pictures). Or their mirror-images, 11IL, 11NL, 11ER.
It seems to me, cutting a right-hand thread on the "back" side, the helix angle is reversed. For example, holder SNR0010K11 with 11ER is apparently made for External Right-hand threads cut on the "front", it looks positioned correctly for Internal threads on the "back." Except the helix angle would be reversed! So I don't know which inserts to buy. The IR and ER are by far the most abundant online. My budget is low, I'm spending about $100/wk on tools & parts, but it is the ebay lead time that is killer if I buy the wrong stuff. (Wrong stuff always finds a use, anyway.) None of the mfr.s web sites that I've been able to find explained the real difference between R & L inserts.
Am I the only guy that cuts threads backwards? (BTW I have already cut left threads by mistake, reversed the tool AND the spindle, and cut another beautiful left thread!
)
This is for maintenance and R&D, not production, and I buy my own tools so I'll be using the cheap stuff on Ebay like Shars, etc. That stuff always works fine for me. Not worried about details like coatings & grades & chipbreakers, & speeds & feeds etc. because it's all random mystery metal scrap. (Not really, I usually know what it is, but sometimes 12L14, H13, M2, S7, 4140, whatever is lying around.) I am willing to deal with the deflection, chatter, finish & thread form issues, etc. as required. Using a Clausing with DRO but no threading stop or "clock."
1) I will ALWAYS cut RH threads away from the chuck. That means the spindle is "reversed", and the tool is in "back" of the bar.
2) Assume there is always a blind hole or external flange on the left, hence the reversed feed. If there wasn't, I'd just use a tap or die anyway.
3) Can't turn the tool upside down on this lathe. It lifts up the saddle. I have done it with care from necessity but it is not a good plan.
3) I have learned to NEVER, EVER unclamp the halfnut once I get started, even though I theoretically know how to do it, I have always managed to ruin a good thread on the last pass because I wanted to try the fit on a workpiece and get the tool out of the way in a hurry. I start with a relief groove with about 0.01in of clearance and after each pass, slowly jog the DRO back to zero. After sweating bullets for 10 passes on S7 I just don't have the nerves to risk opening the nut without blowing it. If I really have to, I'm better off just re-locating the groove from scratch instead of trying to phase the leadscrew properly.
About the biggest I have to deal with is 7/8-9. I'm going to buy four boring bars, two each inside & outside for size 11 and 16 triangle laydowns. With non-topping inserts in a couple of radii to cover a wide range. The cheap holders I'm looking at dont have shims, that's OK. Basically "SNR/L0010K11" type bars.
So my question is, what the hell is the difference between 11IR, 11NR, and 11EL inserts (which look the same in pictures). Or their mirror-images, 11IL, 11NL, 11ER.
It seems to me, cutting a right-hand thread on the "back" side, the helix angle is reversed. For example, holder SNR0010K11 with 11ER is apparently made for External Right-hand threads cut on the "front", it looks positioned correctly for Internal threads on the "back." Except the helix angle would be reversed! So I don't know which inserts to buy. The IR and ER are by far the most abundant online. My budget is low, I'm spending about $100/wk on tools & parts, but it is the ebay lead time that is killer if I buy the wrong stuff. (Wrong stuff always finds a use, anyway.) None of the mfr.s web sites that I've been able to find explained the real difference between R & L inserts.
Am I the only guy that cuts threads backwards? (BTW I have already cut left threads by mistake, reversed the tool AND the spindle, and cut another beautiful left thread!
)
