QCTP too tall

[Ischgl99]

I was wondering if there are metric thread indicators like the imperial one so that wasn't necessary. I think the reverse function would be more a priority. Blondihacks had what looks like a cool suggestion for cutting threads backwards, from left to right so your timing is not as crucial for stopping potentially, would be nice to have both directions to turn it seems like. (Coming from no experience of course but in my head it seems handy. So the nicer lever change would be ideal instead of the easier option I posted above which I think takes some effort to switch back and forth.

I’m not aware of any that work with an imperial leadscrew. With an imperial leadscrew, you are stuck with leaving the half nuts engaged while threading.

I thread away from the chuck, it works well not having to worry about stopping at a shoulder. One caution, if your chuck has a threaded mount, make sure it does not unscrew when threading in reverse. With imperial threads, it is very easy to do, but with metric, since the half nuts are engaged, you still have to time stopping before hitting the shoulder when getting to your start point. That is where a jog feature is very handy, power close to the starting point, then use jog to slowly get to where you want to start the thread. When threading away from the chuck, you are still using the forward leadscrew direction. The only difference is the tool is upside down and you are running the spindle in reverse.

 

[chris.epp]

I’m not aware of any that work with an imperial leadscrew. With an imperial leadscrew, you are stuck with leaving the half nuts engaged while threading.

I thread away from the chuck, it works well not having to worry about stopping at a shoulder. One caution, if your chuck has a threaded mount, make sure it does not unscrew when threading in reverse. With imperial threads, it is very easy to do, but with metric, since the half nuts are engaged, you still have to time stopping before hitting the shoulder when getting to your start point. That is where a jog feature is very handy, power close to the starting point, then use jog to slowly get to where you want to start the thread. When threading away from the chuck, you are still using the forward leadscrew direction. The only difference is the tool is upside down and you are running the spindle in reverse.

Running spindle in reverse with tool upside down to thread left to right? That's actually done? I thought I saw video of it being done with tool right side up but the carriage feed in reverse?

 

[chris.epp]

If you have a metric lead screw it is possible, but to do all the threads you need additional gearing or wheels. These extras are usually quite hard to find.

If you have an imperial lead screw, basically it won't work. Technically it could be made to work, with all sorts of sensors, math and computation up the yingyang, but that's the work of a pretty good ELS system. At the moment, even with my own ELS, cutting metric threads requires me to leave the lead screw engaged at all times. I have an imperial lead screw. I haven't solved the math problem yet. It's tantalizingly close, I can feel the answer, but still haven't worked it out. At least for me, handling the modulo stuff, the ratios, various angles, and sensors has been difficult to grasp the total necessary and sufficient conditions. I really need to spend a few days on just this - to work out the details. Bet it isn't quite as hard as I'm making it out to be.

I have not looked at or even really considered the math involved. I thought it would mostly be having just a correct ratio. Not sure if the 10x22 is imperial or metric thread. Has change gears for metric and imperial, but I've heard mixed about these machines. Some have metric threads but imperial guages in the handles, some are real imperial actually etc depending on who had it made. Busy bee's version of this mill is nicer with power cross feed and is driven from a keyway on the rod instead of the threads for example.

 

[twhite]

Running spindle in reverse with tool upside down to thread left to right? That's actually done? I thought I saw video of it being done with tool right side up but the carriage feed in reverse?

Running the motor in reverse will also make the lead screw turn the opposite way. Doing the reverse motor is great to start threads at a shoulder then cut treads outwards to the open end of the part.


Cutting oil is my blood.

 

[Ischgl99]

Running spindle in reverse with tool upside down to thread left to right? That's actually done? I thought I saw video of it being done with tool right side up but the carriage feed in reverse?

Yes, when doing a right hand thread from left to right, the tool needs to be upside down. The spindle will be in reverse, and that will cause the leadscrew to turn in reverse, you are only changing the spindle direction, nothing else. If you cut a thread in the normal direction and then reverse the spindle while keeping the half nuts engaged, the tool will follow the cut you just made. Since the tool is the right side up, it can’t cut in that direction since the work piece is rotating the wrong way in reverse. By turning the tool upside down, you can make that same cut when the spindle turns in reverse.

To cut a lefthand thread from left to right, the spindle needs to spin in the forward direction and the leadscrew in reverse. Or, you can do the opposite as well. Remember, for right hand, both the leadscrew and spindle are going in the same direction, for left hand direction, one goes forward, the other reverse. It doesn’t matter which one, that just determines where your cut starts.

To help understand this, mount a Sharpie in your toolholder, press it against a piece of stock in your chuck and “thread” using the different settings and you will see the threads change depending on your leadscrew direction.

 

[WobblyHand]

I have not looked at or even really considered the math involved. I thought it would mostly be having just a correct ratio. Not sure if the 10x22 is imperial or metric thread. Has change gears for metric and imperial, but I've heard mixed about these machines. Some have metric threads but imperial guages in the handles, some are real imperial actually etc depending on who had it made. Busy bee's version of this mill is nicer with power cross feed and is driven from a keyway on the rod instead of the threads for example.

No, it doesn't quite work that way, at least for metric threads. You are trying to maintain not only the correct ratio but also the exact angle of the spindle at the start of the thread and the lead screw has to be able to be engaged. If you don't then the next pass of cutting of the thread ends in a random place, not where it needs to be. You get a mess. Try it some time, you'll see. My G0752Z 10x22 lathe has a 12 TPI lead screw. Having the correct ratio only guarantees the right pitch, but not where the thread starts. That means at carriage position Z, (the start of the cut in the part), we must guarantee the spindle angle is N degrees for every pass. If a multi-start, the angle of the spindle needs to move for each pass, by a fractional amount corresponding to the number of starts.

Unless you have a metric dial on your metric lead screw, you can't do metric threads the same way as you can with an imperial dial and imperial lead screw, at least not by opening and closing the half nuts. If you keep the half nuts engaged all the time, then you can cut either kind of thread on either system, because the engaged half nuts maintain the relationship of the spindle angle to the carriage position. Once you open the half nuts the relationship is lost.

Recovering the original relationship requires knowledge of the spindle angle and Z position when the half nuts were originally engaged. You also need to know about the lead screw since you can't arbitrarily engage the half nuts at that Z position, the angle of the lead screw must be correct in order for the nuts to properly engage. So you need to sync at least three things to the best of my knowledge. It seems to me that one may need a signal to the operator to know which rotation of #1 is the correct one to engage.

 

[chris.epp]

Yes, when doing a right hand thread from left to right, the tool needs to be upside down. The spindle will be in reverse, and that will cause the leadscrew to turn in reverse, you are only changing the spindle direction, nothing else. If you cut a thread in the normal direction and then reverse the spindle while keeping the half nuts engaged, the tool will follow the cut you just made. Since the tool is the right side up, it can’t cut in that direction since the work piece is rotating the wrong way in reverse. By turning the tool upside down, you can make that same cut when the spindle turns in reverse.

To cut a lefthand thread from left to right, the spindle needs to spin in the forward direction and the leadscrew in reverse. Or, you can do the opposite as well. Remember, for right hand, both the leadscrew and spindle are going in the same direction, for left hand direction, one goes forward, the other reverse. It doesn’t matter which one, that just determines where your cut starts.

To help understand this, mount a Sharpie in your toolholder, press it against a piece of stock in your chuck and “thread” using the different settings and you will see the threads change depending on your leadscrew direction.

Haha, thank you for that. Clearly didn't think that through. Of course. (Unless I was being tricky and mounting the tool cutting from the back side of the workplace I guess...) Hopefully tomorrow I'll actually be looking at this with the lathe in front of me instead of while I'm running errands and other stuff.

Didn't think of people actually cutting upside down. As you don't have the same visibility but I see now. Thanks!

 

[chris.epp]

No, it doesn't quite work that way, at least for metric threads. You are trying to maintain not only the correct ratio but also the exact angle of the spindle at the start of the thread and the lead screw has to be able to be engaged. If you don't then the next pass of cutting of the thread ends in a random place, not where it needs to be. You get a mess. Try it some time, you'll see. My G0752Z 10x22 lathe has a 12 TPI lead screw. Having the correct ratio only guarantees the right pitch, but not where the thread starts. That means at carriage position Z, (the start of the cut in the part), we must guarantee the spindle angle is N degrees for every pass. If a multi-start, the angle of the spindle needs to move for each pass, by a fractional amount corresponding to the number of starts.

Unless you have a metric dial on your metric lead screw, you can't do metric threads the same way as you can with an imperial dial and imperial lead screw, at least not by opening and closing the half nuts. If you keep the half nuts engaged all the time, then you can cut either kind of thread on either system, because the engaged half nuts maintain the relationship of the spindle angle to the carriage position. Once you open the half nuts the relationship is lost.

Recovering the original relationship requires knowledge of the spindle angle and Z position when the half nuts were originally engaged. You also need to know about the lead screw since you can't arbitrarily engage the half nuts at that Z position, the angle of the lead screw must be correct in order for the nuts to properly engage. So you need to sync at least three things to the best of my knowledge. It seems to me that one may need a signal to the operator to know which rotation of #1 is the correct one to engage.

I've never given threads nearly this much thought. So much simpler to use than to make, clearly. (And mathematically, to make with a die and tap...) lots of fun to be had! Thanks!

 

[RJSakowski]

I was wondering if there are metric thread indicators like the imperial one so that wasn't necessary. I think the reverse function would be more a priority. Blondihacks had what looks like a cool suggestion for cutting threads backwards, from left to right so your timing is not as crucial for stopping potentially, would be nice to have both directions to turn it seems like. (Coming from no experience of course but in my head it seems handy. So the nicer lever change would be ideal instead of the easier option I posted above which I think takes some effort to switch back and forth.

The problem with cutting metric threads on a lathe with an inch lead screw is that in order to resync the half nuts once opened is the lead screw has to travel some multiple of 127 turns. When cutting inch threads with an inch lead screw, you regain sync at least once an inch. Metric thread dials are a complex mechanism compare to the inch dials. This is because metric pitches are set up as mm/thread whereas inch threads are threads per inch.

It is possible to use the half nuts when cutting metric threads on an inch lathe.To do so, you make your first pass engaging the half nuts on a designated number on the thread dial. When you reach the left hand end of the thread, disengage the half nuts and shut the lathe motor down. Reverse the lathe and when you reach your designated number on the thread dial, reengage the half nuts and continue until you have passed the right hand end of your thread. Shut the lathe motor down and make your adjustments for the next pass and start the lathe in the forward direction. Repeat this process until you have completed your thread.