Threading away from the chuck on my lathe...

[schemer]

What? Nobody mentioned Joe Pie yet?

I fast forwarded through his video last night but realized he was cutting an ACME or square thread so I wanted to be sure I knew if the 60 degree single point would be the same or not.

 

[Bob Korves]

I have used a right side up tool on the back side of the work, spindle turning the opposite direction, feeding away from the chuck. Same as WreckWreck showed. Even also used a boring bar. It works fine, no fear of a crash during the cut. It does the same thread that we usually do, but in a reverse path.

 

[schemer]

I have used a right side up tool on the back side of the work, spindle turning the opposite direction, feeding away from the chuck. Same as WreckWreck showed. Even also used a boring bar. It works fine, no fear of a crash during the cut. It does the same thread that we usually do, but in a reverse path.

Bob,
Do you feed with the cross feed only too? I need to buy a few more threading tools. In this case I need to cut an 8 TPI thread so I was just doing a quick crash course on finding a tool and proper inserts. Do the IR16 AG60 inserts sound like a good choice? Or go with the IR16 G60?

 

[Bob Korves]

I typically only feed with the compound. As long as the thread is not too coarse, it works fine. The cutting tool is ideally ground a bit differently for a compound cut than for a cross slide cut. The only thread I have done from the back side was 32 TPI. It turned out nice. Here is a link to the work:
http://www.hobby-machinist.com/thre...th-starrett-196a-back-plunge-accessory.48595/

 

[whitmore]

No I won't. You have to put the cutting tool in upside down and run the chuck in reverse.

Or (it'd work on some lathes) reverse the headstock so it's on your right, not your left. Tool force still
bears down onto the bed, that way.

 

[darkzero]

Threading away from the chuck using the compound you'd want the compound at the 7:00 position rather than the 5:00 position (I'm not mentioning degrees as the markings vary on lathes but you get the idea). Doesn't matter if you are cutting a LH thread or spindle in reverse with the cutter upside down to cut a RH thread.

As for AG60 or G60, as you know both will cover 8 TPI. Choice really matters on how close to a shoulder you are threading to or how wide the thread relief is. G60 has a wider tip so it's more stout, in theory stronger, better for heavier DOC. If your thread relief is narrow or you are threading closer to a shoulder the AG60 would be the btter choice. Another factor is how usefull the insert will be. AG60 covers a wider range of threads. You have a 12x lathe, it's not likely you'll be taking heavy cuts. IMO the AG60 would be the better choice as it would be more useful for other thread pitches.

Which leads to another thing. I mentioned threading close to a shoulder or to a thread relief. If your threading away from the chuck, obviously you're not threading to a shoulder or into a thread relief so this doesn't matter right? And one of the advantages of threading away from the chuck is you can thread at a faster speed.

Yes but if your thread starts close to a should or your thread relief is narrow, this is where you are starting, you'll have a much smaller margin for error when engaging the half nuts. At 8 TPI the thread dial is already spinner faster than a finer thread. Then add the thought of wanting to thread at a high RPM. If your thread is starting close to a shoulder or in a small thread relief, better engage the half nuts with precision. Make a mistake & chances are you'll destroy your threads.

I thread close to a shoulder or into a very narrow thread relief often cause the stuff I make is small. Sometimes I don't make a thread relief at all. When threading conventionally (into the chuck) you don't have to worry about making a mistake when engaging the half nut. This is why I prefer to thread conventionally & not away from the chuck. It's much easier for me to disegage the half nuts at a mark than trying to catch the thread dial spot on when starting close to a shoulder or in a narrow thread relief if the thread dial is spinning at 10K rpm.

But if you're not starting close to a shoulder or in a narrow thread relief, then ya got nothing to worry about.

My post is already long but I wanted to add anyway since the subject of cutter upside down came up. As said I always single point external threads with the compound feeding towards the chuck, that's how I was taught & is what I'm used to. But when I single point internal threads, I mount my cutter upside down the the spindle in reverse but it's not threading away from the chuck nor is it a LH thread. I'm still using a RH cutter & I'm threading on the backside of the internal bore. Allows me to actually see what I'm threading easier & I don't have to reposition my compound, it stays the same as for external threads.

 

[RJSakowski]

You will have left handed threads! Good luck!

No I won't. You have to put the cutting tool in upside down and run the chuck in reverse.

Forward or reverse, tool in front or tool in back, right side up or upside down, you will not cut a left hand thread.

In order to cut a left hand thread, you have to have a reversing gear which reverses the rotation of the lead screw in your gear train. The reversing gear is an idler gear that reverses the direction of rotation of the lead screw relative to the spindle. Each gear set (one or more gears locked together on the same shaft) rotates in the opposite direction to the gears it meshes with. If you have a RH lead screw like my Atlas/Craftsman, the lead screw will turn in the same direction as the spindle to cut RH threads and in the opposite direction to cut LH threads. My Grizzly 602 has a LH lead screw so it turns opposite to the spindle for RH threads and in the same direction for LH threads.

Lathes that are set up for this usually have a tumbler or banjo that moves the reversing gear in and out of the gear train. The 602 doesn't come with one so I made my own.

Cutting threads with the tool facing up and and in the front is essentially the same as turning the tool upside down and cutting from the rear. If you think about it, you simply rotating the entire cutting mechanism 180º around the spindle axis. If you are cutting toward the tailstock by reversing the spindle rotation, the tool must be flipped so it is upside down at the front or right side up at the rear but you will still cut a RH thread.

As to whether the compound angle should remain at 29.5º. The reason for setting the compound at 29.5º is that setting the compound at an angle and advancing the cutting depth with it will cut primarily on one side of the thread v. This reduces the likelihood of chatter from cutting both side at once. The effect is similar to what is experienced with a parting tool or a form tool. The 29.5º angle is designed to primarily cut one face of the thread but take a very light skim cut on the second face.

I expect that you will be OK leaving the compound angle set as for inboard threading. You are still cutting primarily one side of the thread. I would personally rotate the compound to 29.5º in the outboard direction if it didn't create an interference issue. You wouldn't want to set the angle to 30.5º though. A 30.5º angle can result in a step on the near face.

Concerning forgetting about the compound and advancing with the cross slide, here are my thoughts. Using this method is fine for a rigid and tight lathe. Problems can arise when threading with a smaller lathe or one which is not at tight as it should be. These are the same issues we experience with parting. Some people can part with no difficulty while others just can't seem to get the right technique. My personal experience with threading is that once I started using the compound , set at 29.5º, my thread quality improved significantly.

Additionally, by separating out the tool back out from the compound tool feed, I don't have to remember what my dial is set to. On completion of a pass, I disengage the half nuts, back the cross feed out one full turn, move the carriage to the start of the next pass, return the cross feed to zero, advance the compound feed, and engage the half nuts. The cross feed is always at zero for a pass and I know how much I have advanced my feed from the compound dial.

The only problem that I see with outboard threading is the amount of backlash in the lead screw gear train. If the lathe is tight, it shouldn't be an issue. My tired old Atlas has quite a bit of lash so I like to start a pass four or five threads before engaging the work. For outboard threading, this may be an excessive amount of thread relief.The Grizzly has considerably less backlash so I should be OK with it.

Note: As I finish this, I see that a number of other posters have put forth similar thoughts. I am posting this anyway because it bears repeating.

 

[Bob Korves]

The easier and safer but slower way to cut a thread from a shoulder is to cut to the right, leave the half nuts engaged for the entire job, and back the tool up under power to near the shoulder with the tool away from the work, and then move the tool up against the shoulder by rotating the chuck by hand. Dial in the feed for the cut and run the cutter toward the tailstock. Repeat as required.

 

[schemer]

Threading away from the chuck using the compound you'd want the compound at the 7:00 position rather than the 5:00 position (I'm not mentioning degrees as the markings vary on lathes but you get the idea). Doesn't matter if you are cutting a LH thread or spindle in reverse with the cutter upside down to cut a RH thread.

As for AG60 or G60, as you know both will cover 8 TPI. Choice really matters on how close to a shoulder you are threading to or how wide the thread relief is. G60 has a wider tip so it's more stout, in theory stronger, better for heavier DOC. If your thread relief is narrow or you are threading closer to a shoulder the AG60 would be the btter choice. Another factor is how usefull the insert will be. AG60 covers a wider range of threads. You have a 12x lathe, it's not likely you'll be taking heavy cuts. IMO the AG60 would be the better choice as it would be more useful for other thread pitches.

Which leads to another thing. I mentioned threading close to a shoulder or to a thread relief. If your threading away from the chuck, obviously you're not threading to a shoulder or into a thread relief so this doesn't matter right? And one of the advantages of threading away from the chuck is you can thread at a faster speed.

Yes but if your thread starts close to a should or your thread relief is narrow, this is where you are starting, you'll have a much smaller margin for error when engaging the half nuts. At 8 TPI the thread dial is already spinner faster than a finer thread. Then add the thought of wanting to thread at a high RPM. If your thread is starting close to a shoulder or in a small thread relief, better engage the half nuts with precision. Make a mistake & chances are you'll destroy your threads.

I thread close to a shoulder or into a very narrow thread relief often cause the stuff I make is small. Sometimes I don't make a thread relief at all. When threading conventionally (into the chuck) you don't have to worry about making a mistake when engaging the half nut. This is why I prefer to thread conventionally & not away from the chuck. It's much easier for me to disegage the half nuts at a mark than trying to catch the thread dial spot on when starting close to a shoulder or in a narrow thread relief if the thread dial is spinning at 10K rpm.

But if you're not starting close to a shoulder or in a narrow thread relief, then ya got nothing to worry about.

My post is already long but I wanted to add anyway since the subject of cutter upside down came up. As said I always single point external threads with the compound feeding towards the chuck, that's how I was taught & is what I'm used to. But when I single point internal threads, I mount my cutter upside down the the spindle in reverse but it's not threading away from the chuck nor is it a LH thread. I'm still using a RH cutter & I'm threading on the backside of the internal bore. Allows me to actually see what I'm threading easier & I don't have to reposition my compound, it stays the same as for external threads.

Thanks for the explanation and thoughts on the carbide choices. The main reason I am trying to figure this out and test other methods is because I don't cut many threads in the first place although I would love to be really good at it, and because I am making an adapter for an important personal project. This requires a 2 1/4 - 8 tpi thread and that would be the largest thing I have ever threaded. I would think it would be easier but after 2 tries, the thread was looking pretty rough and not symmetrical. Of course it looked "ok" and it actually threaded into one of the 2 plates (back plate and face plate), but not the other. So I figured something was wrong with the threads on the ebay purchased faceplate although they looked great to me. I ordered a tap to clean up the threads and rechecked all my setting on the lathe to figure out why the threading looks so bad. I checked my compound angle which I have set at 60.5 which also checks out fine with a protractor and is actually 29.5 degrees. I counted the teeth on my thread dial as I read that Grizzly had been shipping the G4003 with the wrong gear (15t instead of the correct 16t) and that was fine. I checked for slop in the more than likely "like new" half nuts as they don't see a lot of action and that was fine. I was running at 70 RPM and the gearing and settings are all good too. So last night I went back out there to the shop and had a closer look at my threading tool and it looks like hell. So that is likely my main problem. The tool like mine is shown below. What is the best way to sharpen that style of tool? Just flat onto the face of the grinder and assume all other angles are built-in and correct? I will get and post a pic of my handy work on the adapter and post it here later.

 

[schemer]

Forward or reverse, tool in front or tool in back, right side up or upside down, you will not cut a left hand thread.

In order to cut a left hand thread, you have to have a reversing gear which reverses the rotation of the lead screw in your gear train. The reversing gear is an idler gear that reverses the direction of rotation of the lead screw relative to the spindle. Each gear set (one or more gears locked together on the same shaft) rotates in the opposite direction to the gears it meshes with. If you have a RH lead screw like my Atlas/Craftsman, the lead screw will turn in the same direction as the spindle to cut RH threads and in the opposite direction to cut LH threads. My Grizzly 602 has a LH lead screw so it turns opposite to the spindle for RH threads and in the same direction for LH threads.

Lathes that are set up for this usually have a tumbler or banjo that moves the reversing gear in and out of the gear train. The 602 doesn't come with one so I made my own.

Cutting threads with the tool facing up and and in the front is essentially the same as turning the tool upside down and cutting from the rear. If you think about it, you simply rotating the entire cutting mechanism 180º around the spindle axis. If you are cutting toward the tailstock by reversing the spindle rotation, the tool must be flipped so it is upside down at the front or right side up at the rear but you will still cut a RH thread.

As to whether the compound angle should remain at 29.5º. The reason for setting the compound at 29.5º is that setting the compound at an angle and advancing the cutting depth with it will cut primarily on one side of the thread v. This reduces the likelihood of chatter from cutting both side at once. The effect is similar to what is experienced with a parting tool or a form tool. The 29.5º angle is designed to primarily cut one face of the thread but take a very light skim cut on the second face.

I expect that you will be OK leaving the compound angle set as for inboard threading. You are still cutting primarily one side of the thread. I would personally rotate the compound to 29.5º in the outboard direction if it didn't create an interference issue. You wouldn't want to set the angle to 30.5º though. A 30.5º angle can result in a step on the near face.

Concerning forgetting about the compound and advancing with the cross slide, here are my thoughts. Using this method is fine for a rigid and tight lathe. Problems can arise when threading with a smaller lathe or one which is not at tight as it should be. These are the same issues we experience with parting. Some people can part with no difficulty while others just can't seem to get the right technique. My personal experience with threading is that once I started using the compound , set at 29.5º, my thread quality improved significantly.

Additionally, by separating out the tool back out from the compound tool feed, I don't have to remember what my dial is set to. On completion of a pass, I disengage the half nuts, back the cross feed out one full turn, move the carriage to the start of the next pass, return the cross feed to zero, advance the compound feed, and engage the half nuts. The cross feed is always at zero for a pass and I know how much I have advanced my feed from the compound dial.

The only problem that I see with outboard threading is the amount of backlash in the lead screw gear train. If the lathe is tight, it shouldn't be an issue. My tired old Atlas has quite a bit of lash so I like to start a pass four or five threads before engaging the work. For outboard threading, this may be an excessive amount of thread relief.The Grizzly has considerably less backlash so I should be OK with it.

Note: As I finish this, I see that a number of other posters have put forth similar thoughts. I am posting this anyway because it bears repeating.

RJ, Thanks for the detailed explanation. I also learned the compound way of doing it and it seems natural. It also has less backlash but that doesn't matter if you compensate for the backlash on the cross feed. I also have a DRO so I can really be sure and accurate. Still, I manage to cut ugly threads. My G4403G seems to be a pretty tight machine other than the usual backlash. I Have never crashed my lathe yet and don't plan to so I was going with the regular way of threading and using a purchased 60 degree threading tool as pictured above. In the end I should just grind my own threading tool. But I will spend the money on a few threading tools that use the inserts just so I have them in my toolbox. I think my dull tool is causing most of my frustration but I didn't realize it was dull until after the fact. I likely too too big of a cut or maybe my tool got above center but I checked all of that when I set it up. I did find later though where the tool was above center when I tried to figure out the problem. I also have a BXA tool post that has the piston as opposed to the wedge design and I noticed when I tightened the tool holder in the TP, it cocks up on the front a little. That may have been what I noticed when the cut seemed to be deeper than I turned the compound at one time and made a thicker chip. Anyhow, I will learn as much as I can with all the good help here and be better for it and have more new tools too.