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G96 NPT thread programming help

DeSelle

Cast Iron
Joined
Oct 23, 2006
Location
Midlothian, TX
Hi all,

Trying to run off a couple of pipe half nipples for a job and I'm having an issue with G76 lines

I'm shooting for 6" NPT

G00 X6.625 Z-1.750 (start point)
G76 P010060 Q050 R.002
G76 X6.425 Z0.0 R.0545 P1000 Q020 F.125

It appears to be close but it does a little dance at the relief groove where I start and at the end.

I am not sure I fully understand the G76 command. I'm running a Doosan Puma 400LB slant bed. The control is an I series 2008.

Since the tool is in the back and facing up don't I have to feed from Z neg to pos for RH thread?



Any help is appreciated

Nathan
 
...Since the tool is in the back and facing up don't I have to feed from Z neg to pos for RH thread?
Yes, with the spindle in reverse.

Not sure why you want your tool upside-down though? Doesn't that put the insert way above centerline?
 
I use gooseneck style threading holders so I can start out front in the air and thread towards the chuck. If you start at the other end of the thread (in a groove), you're going to see the sync and acceleration issues of the Z axis getting up to speed, so it's going to be a bit out of pitch there.
 
I don't know how you have the tool touched off but I'd feed off the front of the part a few hundred thousands further which will change the R taper in the second line.

Depending on the RPM the control could be jumping back a bit when it starts so it can catch up to the lead.

Brent
 
Yeah, definitely feed out to Z.2 or so, else the retract bugger up the first thread.
 
I may have not been clear about the tool orientation. Hope picture helps. I'll extend the thread off the end of the part and tweak the R accordingly but the hop it does at the beginning is a code issue

IMG_1799.jpgIMG_1798.jpg

Looks like a VTL cause I can never get the iPad pics oriented right:/
 
That thing looks like it's gonna drag the insert out of the holder.
 
It's a Mitsubishi set up. Works great. We have used it for years. We ran these pipe fittings on our Okuma machines with it but this machine is behaving funny. I'm sure it's me but I need to resolve this and move on
 
Your thread hight doesn't look right to me. Your start point in 1.625 the root is 1.425 that the total distance from safe start position to the thread root.

Recalculate the thread hight and try it again. Major diameter subtract the root diameter divided by 2 is the P thread hight.

Brent
 
Look in the machinist handbook under pipe threads it give you the thread hight of a particular pitch of pipe thread. Which is how I get the information to write my pipe thread programs.

Brent
 
Why is the tool oriented up instead of normal? I'll catch a bunch of shit for suggesting that as "normal", but working around all of that is a pain. If all the problems you are having would be solved by using normal holder (RH), and turning the normal way (M3), starting from in front of the part and retracting at the end of the Thread, would cure all your issues, why not?

R
 
Why is the tool oriented up instead of normal?
Normal for me with a turret on the back would be left hand tool for turning, then a dropped head upside-down right-hand tool flipped over in the turret (actually the way it's designed to be used) cutting from out front towards the chuck in M04. Otherwise difficult to get a right-hand thread. The groove width is not enough to get the turret up to speed.

But the Jap stuff likes to put the tools on the wrong side of the central line of the turret and turn things the wrong way, so ymmv.
 
Why is the tool oriented up instead of normal? I'll catch a bunch of shit for suggesting that as "normal", but working around all of that is a pain. If all the problems you are having would be solved by using normal holder (RH), and turning the normal way (M3), starting from in front of the part and retracting at the end of the Thread, would cure all your issues, why not?

R

I'm with you Rob.

And if I might add that starting at what would typically be the end of a thread especially when a shoulder or relief is involved kinda makes it a crap shoot as to how the thing will start if scooting around has to happen to find the lead in the beginning of the thread.

Going the other way if need be the control gets all that jumping around out in the clear blue yonder. Having said that IMO the OP's operation should be able to be completed without issue.

Brent
 
Normal for me with a turret on the back would be left hand tool for turning, then a dropped head upside-down right-hand tool flipped over in the turret (actually the way it's designed to be used) cutting from out front towards the chuck in M04. Otherwise difficult to get a right-hand thread. The groove width is not enough to get the turret up to speed.

But the Jap stuff likes to put the tools on the wrong side of the central line of the turret and turn things the wrong way, so ymmv.

Usually I agree with you SeaMoss....:D But no. If the insert is up (facing the sky), and the Tool is behind the part, and you turn the Spindle M4 (CCW) then you get a left hand thread. So if you are facing the Chuck jaws, M4 turns the Spindle Clock wise, so if the tool is behind the part it will not be RH.

Think of running an Engine Lathe whilst doing a head-stand, behind and below the part, would be the correct orientation, thus right hand tools toward the Chuck for right hand Threads. You can do Right hand Threads the way the OP is doing it, but not toward the Chuck. Maybe I misunderstood you. I hate this argument BTW, always the old guys saying "NO, not like that!!" Sorry that is the way the World does it in 2018. :D

R

EDIT IMO, the other way is a huge hassle of getting the LH tools for RH Threads and turning the Spindle the wrong way, and programming backwards from what would be easy and normal. M3 is CW, M4 is anti clock wise (for the Brits still funny to me--Anti)
 
Usually I agree with you SeaMoss....:D But no.
Terrible description on my part, sorry. Like this :

dropdown%20thread.jpg


Now flip it over so the insert is on the bottom side. Rear turret. On traditional US nc lathes the plane of the top edge of the toolholder intersects the center of the part. Now turn the spindle M04 (counter-clockwise facing it from the tailstock) and drive the insert from +Z to -Z (towards the chuck.) That'll make a right-hand thread.

Mori's (and other Japs ?) run right hand tools upside down on a rear turret turning M04 (which lifts the turret off the ways, ahem), that should work fine for right-hand threading ? But if you normally do rightside up M03 left hand tools on a rear turret, you have to play games to do right-hand threads. Like M04 it and use this weird threading tool holder. Score one for the slant-eyes, threading is easier.

From the confusing photo it looks like the op is doing half-and-half, which probably doesn't work :crazy:

And what's with the G96 in the title ? I thought he was trying to use css when threading which really threw me off.
 
Now flip it over so the insert is on the bottom side. Rear turret. On traditional US nc lathes the plane of the top edge of the toolholder intersects the center of the part. Now turn the spindle M04 (counter-clockwise facing it from the tailstock) and drive the insert from +Z to -Z (towards the chuck.) That'll make a right-hand thread.

Mori's (and other Japs ?) run right hand tools upside down on a rear turret turning M04 (which lifts the turret off the ways, ahem), that should work fine for right-hand threading ? But if you normally do rightside up M03 left hand tools on a rear turret, you have to play games to do right-hand threads. Like M04 it and use this weird threading tool holder. Score one for the slant-eyes, threading is easier.

Okay, we are actually saying the exact same thing. EXCEPT (maybe it's my age) have never seen that command in red work that way. Facing the Chuck, M4 turns the Chuck counter clock wise-not clock wise. Granted the M-codes are simple commands they could be re executed in the parameters, the ladder or probably even Mechanically. But I aint never seen M4 turn it that way afore. And since it comes from the factory that way, I'll continue to call it "Normal". :cheers:

And that gibberish about lifting the weight of the turret off the Casting or Ways is a wives tale. It makes analytical sense, but I have never heard of damage to a machine as a result of it, I've never heard a Tech recommend running it so the cutting forces are toward the Ways, I don't think it makes a big enough difference. JMFingO. But hell it makes no difference to me, I'll run it which ever way you want, I'll run the whole thing hanging from a boom, upside down, horizontal turned vertical, I don't care. But I'm going to single point toward the Chuck, unless I cannot.

out

EDIT> holy hell, I just checked, the Cinci runs it that way....what a POS design flaw :D
 
For heavy interrupted cuts I always advised running tools with the insert up and M4 on a rear turret lathe. Minimizes pounding on the keeper plate bolts. Normal cutting and especially threading always run the tool upside down and M3.

When I was at the Mori Seiki factory for some training in the mid 80s, the maximum clearance on setting lathe gibs and keeper plates was .0002". You ain't lifting a turret off the slide with that fit in normal cutting.
 
Thanks. I’m looking on the Sanvik site now. Not the best website. As always I appreciate the patience and the help!!


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