Engaging half nut

[higgite]

There will always be some backlash between the half-nuts and the leadscrew. When making the next pass cutting the thread you have to make sure that the carriage has taken up the backlash, otherwise the tool will not engage with the groove of the thread you are cutting. Simply wind the tool a few cm past the beginning of the thread while running in reverse, so that as the motor starts it takes up the slack before hitting the thread. During this stage I put my hand on the big carriage wheel and apply a bit of friction to make sure it takes up the slack.

I’m not saying it’s a wrong thing to do, but I don’t understand your need to apply pressure to the handwheel until the backlash is taken up. My carriage handwheel is often disengaged when I’m threading with the half nuts closed. I’ve never detected carriage movement before the lead screw has taken up all the backlash in either direction.

 

[GunsOfNavarone]

Mine was much more difficult than it should have been, loosed the half nut a touch and it helped loads. I also loosened the dial's face and set it to be more accurate in where it engages and tightened it back up there.

 

[homebrewed]

Mine was much more difficult than it should have been, loosed the half nut a touch and it helped loads. I also loosened the dial's face and set it to be more accurate in where it engages and tightened it back up there.

I never thought about adjusting the dial face. Good idea. Makes sense (in retrospect) -- like many parts of these cheap lathes, why wouldn't that need to be adjusted too? Learned something new today, all good....

 

[WobblyHand]

On my mini lathe the dial face is not adjustable. That's why I put a shim between the apron and the dial block. It slightly rotates the dial. The thicker the shim, the more the offset.

On my G0752/G0602 the dial is adjustable.

 

[RJSakowski]

On my 602, the dial markings were not concentric which caused uncertainty when engaging the half nuts on certain marks. I made a new dial and all is good now.

Threading On A Grizzly G0602

On March 19th, I replied to a thread begun by Cody Killgore entitled "Threading, Something Went Wrong Here" (post #19) where I show evidence of an problem with the threading dial on my Grizzly G0602. I had determined that the dial markings were not concentric with the gear shaft, creating an...

www.hobby-machinist.com

 

[Alberto-sp]

Thanks for your answers.

I engage the half nut for the last pass to have a good finish

 

[Alberto-sp]

Ok I have been practising and I have realized that my dial is not very precise.



The half nut engages slightly after 2, almost in 3, and sligthly before 4, so I supose that Ill have to remember that positions right?

By the way, when threading, instead using the falf nut, Can I reverse the direction of the rotation right?

 

[homebrewed]

By the way, when threading, instead using the falf nut, Can I reverse the direction of the rotation right?

Yes. In fact, that's one of the ways to cut metric threads on an imperial machine. The threading dial doesn't work for that, so the most straightforward way to do it is to stop the motor, back the cutter out with the cross slide and put the motor into reverse without disengaging the half nuts. The lead screw and change gears have enough backlash that you can't leave the cutter in the threads when going in reverse -- you will mangle the threads you just cut. So at the start of each pass you have to advance the cross slide back to its "zero" position (set when you started cutting the threads), then advance the compound to actually cut the threads.

The above method is easier if you cut a runout groove so you don't inadvertently crash the cutter into an un-threaded part of your work. I usually stop a bit short and finish each pass by hand-turning the chuck. A lot less drama that way, especially while cutting coarser threads -- the carriage can move awfully fast when doing that!

Many lathe owners don't power-thread at all, they attach a handwheel to the spindle and turn the chuck by hand. There are a bunch of designs out there for one of those.

There is another way to do it that does allow you to disengage the half nuts but you have to keep track of the position of the threading dial so when you re-engage the half nuts (while running the lathe in reverse) they drop into the same exact relationship to the lead screw they had when cutting the threads. Joe Pi has a videa regarding that method. I haven't tried that method yet.

Finally, with the right toolholder you can cut the threads in reverse so the cutter naturally moves away from the work. The cutter has to be upside-down. You can't use a toolholder designed to cut from the front, it has to be one that raises the tool back up to the spindle centerline. I'm not aware of one that is commercially available for mini lathes so you'd have to make one.

If you're cutting any nonstandard threads (say, for a differential screw) you also will need to employ one of these cutting methods.

 

[Alberto-sp]

Yes. In fact, that's one of the ways to cut metric threads on an imperial machine. The threading dial doesn't work for that, so the most straightforward way to do it is to stop the motor, back the cutter out with the cross slide and put the motor into reverse without disengaging the half nuts. The lead screw and change gears have enough backlash that you can't leave the cutter in the threads when going in reverse -- you will mangle the threads you just cut. So at the start of each pass you have to advance the cross slide back to its "zero" position (set when you started cutting the threads), then advance the compound to actually cut the threads.

The above method is easier if you cut a runout groove so you don't inadvertently crash the cutter into an un-threaded part of your work. I usually stop a bit short and finish each pass by hand-turning the chuck. A lot less drama that way, especially while cutting coarser threads -- the carriage can move awfully fast when doing that!

Many lathe owners don't power-thread at all, they attach a handwheel to the spindle and turn the chuck by hand. There are a bunch of designs out there for one of those.

There is another way to do it that does allow you to disengage the half nuts but you have to keep track of the position of the threading dial so when you re-engage the half nuts (while running the lathe in reverse) they drop into the same exact relationship to the lead screw they had when cutting the threads. Joe Pi has a videa regarding that method. I haven't tried that method yet.

Finally, with the right toolholder you can cut the threads in reverse so the cutter naturally moves away from the work. The cutter has to be upside-down. You can't use a toolholder designed to cut from the front, it has to be one that raises the tool back up to the spindle centerline. I'm not aware of one that is commercially available for mini lathes so you'd have to make one.

If you're cutting any nonstandard threads (say, for a differential screw) you also will need to employ one of these cutting methods.

Thank you for the explanation!

 

[pjf]

I know this post is older but I wanted to share my final technique after studying several metric thread cutting 'threads' and videos. It took me 5 tries to finally get threads that didn't look terrible and settle on a technique.

I was having serious trouble cutting an M24 x 1.5 thread on 1018 cold rolled. The threads\chips were rolling over and welding back onto the material, the cut just looked really bad. I tried HSS and Carbide I had laying around with limited success, I didn't want to drive 1 hour to use my dads grinding equipment for HSS and the carbide from grizzly (JCL15-120 insert) was just garbage.

I ended up purchasing a RH ER16 style carbide holder\insert from amazon. As soon as I put it in the toolpost i realized that I couldn't use the 'upside down cutter' method without a LH toolholder for my particular application - so I was stuck using the high anxiety methods.

I ended up cutting at 600RPM using the method shown in this video with my own flavour:

• My FWD\REV leaver is a bit tricky so I used the e-stop instead.
• I also hand-wound the spindle back into the half-nut index for the first passes until I was confident with the rest of the sequence.

Here's are the video's I used for reference (in addition to the videos in this thread):