# Engaging half nut



## Alberto-sp (Sep 20, 2022)

Hello.

I have a minilathe and is a PITA engaging the falf nut. I have a threadind dial, but not always engage where it should and a I have to try it a few times.

 So, Am I clumsy, there is anything I´m missing or just my minilathe doesn´t have the quality that it should?

Thank you

Best regards


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## Just for fun (Sep 20, 2022)

I was having that problem on my PM 1236T.  On the dial the pointer in a rivet head, I have to engage just before it gets to center.  I slowed way down and practiced with nothing in the lathe but learned where to engage.  It has helped.


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## T Bredehoft (Sep 20, 2022)

_practiced with nothing in the lathe but learned where to engage._

That's what you've gotta do. Practice it dry, without intent to cut. Practice till it's automatic, don't try  for fast turning, start slow as the lathe will go with a coarse thread.


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## Gaffer (Sep 20, 2022)

Joe Pie's video below is helpful. Some folks don't care for it, but I like it. Let me know what you think.


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## Wheat.Millington (Sep 20, 2022)

Joe also has an old video on this exact topic:


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## maspann (Sep 20, 2022)

Yep, I just did a 1/2 - 28 on my PM1236T using Joe Pie's method. I was able to dial it in and get a perfect 3 wire reading. Would never have attempted it turning toward the chuck.


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## graham-xrf (Sep 21, 2022)

I have always loved Joe Pie's method, but I can only use it when I have fixed up a way to guarantee my chuck won't unscrew itself off the spindle. It's going to require a modification add-on of some kind.


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## Alberto-sp (Sep 21, 2022)

Thank you for all your answers.

I saw the first Joe´s video, but he uses the dial and in my lathe doesn´t work very well. I´ll see the other video.

But, do you use always the threading dial to engage the falf nut? I mean, if I only machining somethinh (not threading) I´ll need the threading dial?

thank you


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## WobblyHand (Sep 21, 2022)

Alberto-sp said:


> Thank you for all your answers.
> 
> I saw the first Joe´s video, but he uses the dial and in my lathe doesn´t work very well. I´ll see the other video.
> 
> ...


For feeding, you can engage the half nut where ever you can.  You do not need the threading dial for that.


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## great white (Sep 21, 2022)

Alberto-sp said:


> Thank you for all your answers.
> 
> I saw the first Joe´s video, but he uses the dial and in my lathe doesn´t work very well. I´ll see the other video.
> 
> ...


You don’t absolutely _need _the threading dial to engage the half nuts, but it gives you a visual ref as to when the the half nut threads are lined up with the leadscrew threads. Without that, you just gotta flip the lever and hope they’re lined up or the half nut is going to ride on the leadscrew until it lines up and can drop in to the leadscrew threads. Not good for longevity of the half nuts….


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## Alberto-sp (Sep 21, 2022)

Thanks for your answers.

yes, I was talking for normal feeding, not for threadening. Sorry about my mistake not saying at first. Ok so, when you are regular feeding, you simply try until is engaged right? I try 2 or 3 times until engages, but I don´t know if there is a better way without using the thread indicator. 

But if the best way is using the threading dial, As some of you said, I´ll practise with it. I wasn´t using it because I think I heard that it weard down


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## WobblyHand (Sep 21, 2022)

Alberto-sp said:


> Thanks for your answers.
> 
> yes, I was talking for normal feeding, not for threadening. Sorry about my mistake not saying at first. Ok so, when you are regular feeding, you simply try until is engaged right? I try 2 or 3 times until engages, but I don´t know if there is a better way without using the thread indicator.
> 
> But if the best way is using the threading dial, As some of you said, I´ll practise with it. I wasn´t using it because I think I heard that it weard down


Use the thread dial to help you know where to engage the half nut.  It will engage either exactly on the line, or a little before, or a little after.  If you need or want to have the dial exactly line up, you can install a shim or two in between the thread dial and the apron.  I did this on my mini-lathe to make the half nut engagement on the line.  Shim will probably be around 0.5mm or so.  Vary the shim thickness until the thread dial lines up and you are able to engage the half nut without friction.  I would use the 1 on the thread dial for the alignment procedure.

If you practice engagement, even when you are feeding, it will help you develop the muscle memory needed for threading.  Then threading will become a lot easier.

You will wear the half nut if you try to forcibly engage it when it does not want to engage.  (Many many times.)  It is best to time the engagement, by using the threading dial.  Start out with the lowest RPM and learn to engage cleanly and consistently.  Then you can increase the RPM and practice some more.  Eventually you will be able to do it even at higher speeds without thinking about it.  It is just a practiced skill.


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## Beckerkumm (Sep 21, 2022)

Most lathes will also have an adjustment for the half nuts to seat so the engagement clicks in with reasonable force - not too loose of too tight.  Dave


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## homebrewed (Sep 21, 2022)

Improper alignment of the lead screw w/regard to the half nuts can cause difficulties in engaging the half nuts.  To check for that, engage/disengage the half nuts with the motor turned off.  If the lead screw moves up & down or back & forth (or a combination of those) while engaging and disengaging, you have an alignment issue that needs to be addressed.

In the usual procedure for alignining your LS and half nuts, the carriage is moved all the way to the right, then the screws holding the pillow block are loosened.  Engage the half nuts, then _without disengaging them_ tighten the screws back down.  You may find it useful to do the same thing with the left-hand pillow block; but on a mini lathe you will have to remove the speed control box to gain access to the screws. You also may want to remove the gear attached to the lead screw so the adjustment range isn't limited by it; or loosen the banjo to free up the gear.

There is yet another adjustment that can help w/regard to LS misalignment.  There are two screws that attach the apron to the saddle, located on the top front left and right sides of the saddle.  They are recessed in slotted holes.  To perform this procedure, again run the carriage all the way to the right.  Engage the half nuts, then loosen/re-tighten those two screws.  This will only work for misalignment that produces a back & forth motion of the lead screw, since that's the only direction that can be accommodated by the screw slots.

BTW the bottom of the screw heads on my lathe were rounded so they always sought the center of the slot.  This caused me all kinds of grief when attempting the alignment, until I replaced them with better screws.

If these don't eliminate or greatly reduce the misalignment you may have to shim the rack.  Also check for debris in the half nut mechanism, proper adjustment of its dovetail, etc.

On my minilathe, which has two half nuts (some models only have one) there also is an adjiustment which sets the gap between the half nut threads and the lead screw threads.  Due to the fact that single-nut versions can be easily converted to the dual-nut version, it's likely they have the same adjustment.  It's possible that a very small gap might also cause difficulties when attempting to engage the half nuts.

You don't want the gap to be too small because that causes increased friction, nor too little because the half nuts could slip loose.  While the latter wouldn't be that big a deal while power feeding, it would be a disaster if you're cutting threads.


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## higgite (Sep 21, 2022)

FWIW, I regularly engage the half nuts at turning speeds on my current machine which doesn’t even have a thread dial. I use to do the same on my previous machine which did have a thread dial that I ignored. IMHO, the thread dial is only useful when you’re cutting threads at low rpm. At turning speeds, it's spinning too fast to be useful anyway. The trick at turning speeds is to close the half nuts firmly by feel rather than quickly slamming them in like you can do at low speed threading rpm. With a little practice, you'll get the feel for it and it's not going to prematurely wear out your lead screw if you keep it lubricated.


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## Alberto-sp (Sep 21, 2022)

Thanky you a lot for all your help!


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## T Bredehoft (Sep 21, 2022)

Is the half nut the only way you can feed the tool?  The half nut is for threading, usually there is a feed lever independent of the half nut to engage the feed for normal cutting.


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## great white (Sep 21, 2022)

T Bredehoft said:


> Is the half nut the only way you can feed the tool?  The half nut is for threading, usually there is a feed lever independent of the half nut to engage the feed for normal cutting.


Depends on the lathe. Usually, the less expensive models have the leadscrew doing double duty for threading and feeding. My Atlas 10F is like that.


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## evan-e-cent (Sep 21, 2022)

My Boxford lathe has a reliable thread dial indicator but I never use it.  In fact if you are cutting a metric thread on an imperial lathe or vice versa you cannot use the dial indicator, and it is best not to disengage the half nuts at all.  After installing a variable speed DC motor in my lathe I find it quite simple to cut threads without disengaging.  At the end of one pass you withdraw the tool and wind the tool back to the start using the motor at high speed in reverse. 

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.  

While actually cutting the thread I start slow, speed through the middle and slow right down at the end so that I can stop precisely where I want it. Cool! 

My chuck is screwed on but I do not have any problem with it unscrewing with this technique because it is not under load when using reverse.

I think you already have a lathe with a variable speed motor, but for those who do not, you might find my YouTube videos useful. I just posted them on another thread, but thought you might also find it useful.

Evan’s You Tube Channel which includes stuff about steam engines. See the Playlist for engineers lathe.
https://www.youtube.com/evan-e-cent

Engineers Playlist





#35 Installing a DC motor





#37
How speed controllers work





If you need an online computer program to work out geat trains for cutting any thread, see


			Ride The Gear Train software by Evan Lewis


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## homebrewed (Sep 22, 2022)

T Bredehoft said:


> Is the half nut the only way you can feed the tool?  The half nut is for threading, usually there is a feed lever independent of the half nut to engage the feed for normal cutting.


"Power feed" on mini lathes is just a combination of change gears that produces the finest-possible thread.  That's 256 TPI for an imperial lead screw and the maximum gear ratio available in the standard change gear set ( 20 80 20 80 for A...D respectively).  Due to physical limitations it's difficult to get anything higher.

Some folks have implemented an ultra-fine power feed by attaching a gearmotor to the lead screw.


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## higgite (Sep 22, 2022)

evan-e-cent said:


> 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.


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## GunsOfNavarone (Sep 23, 2022)

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.


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## homebrewed (Sep 23, 2022)

GunsOfNavarone said:


> 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....


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## WobblyHand (Sep 23, 2022)

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.


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## RJSakowski (Sep 24, 2022)

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


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## Alberto-sp (Sep 24, 2022)

Thanks for your answers.

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


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## Alberto-sp (Sep 25, 2022)

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?


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## homebrewed (Sep 25, 2022)

Alberto-sp said:


> 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.


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## Alberto-sp (Sep 26, 2022)

homebrewed said:


> 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!
> 
> ...




Thank you for the explanation!


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