# G9729 Half Nuts



## LX Kid

I have the Grizzly G9729 17x31 and would like to try my hand at making my own half nut. At $75 a pop I need a spare or two. I've already replaced it once and they wear fast even when frequent cleaning and lubing. Question "is" does anyone know what the Acme type/TPI/pitch is for the lead screw. A tap is around $100 and want to order the correct tap. American Standard/ Metric etc.

I called Grizzly Tech Support and they didn't know.  The guy said he would try and find out but was not too optimistic.   Thanks


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## LX Kid

The lead screw is a left handed thread and because the lathe cuts towards the chuck there is more pressure against the half nut.  If the G9729 had a reversing lead screw the half nut would not wear so fast because it would with the thread instead of against it.  From the pic above you can see the wear on the right side of the half nut "fighting" against the lead screw.


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## Bob Korves

I think half nuts are more usually single pointed than tapped.  You might also look into material choices.  The photo looks a lot like brass, and I think some bronze alloys might serve better.  Also, does the carriage move freely with the handwheel?  If not, that could be a source of the wear.


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## LX Kid

Bob Korves said:


> I think half nuts are more usually single pointed than tapped.  You might also look into material choices.  The photo looks a lot like brass, and I think some bronze alloys might serve better.  Also, does the carriage move freely with the handwheel?  If not, that could be a source of the wear.



Well yes I've had a lot of problem with the binding of the rack and gear box pinion gear.  I had to add about .008" shims to the gear box to make it so it wasn't binding.  Moves "much" more  smoothly now just since last week.  Lathe has been sitting for past six months un-used.  First half nut failure was because I had locked the saddle and engaged the lead screw!  (Dumber than dirt!)  I replaced the steel lead screw pin with a brass one now hoping this will save my half nut next time.  When I take the lead screw out of gear, and engage half nut, turning the hand crank runs smooth.  When I hand crank back towards the chuck it is a lot harder to crank.  Wondering if I already have wear on the half nut for that direction?


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## LX Kid

I'm also wondering if it would help to file each sharp corner of the lead screw at the swarf opening?


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## Bob Korves

I was speaking about moving the carriage with no feeds or half nuts engaged, carriage lock loose.  Does the carriage run freely then?


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## LX Kid

Bob Korves said:


> I was speaking about moving the carriage with no feeds or half nuts engaged, carriage lock loose.  Does the carriage run freely then?



As I explained above it was binding until I added shims to the gear box.  The pinion gear was too tight against the rack.


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## Bob Korves

OK, it sounded like you were also traversing it with the half nuts engaged but the gear box disconnected.  I have never tried that, could be hard on the half nuts.  If it was tight traversing the carriage earlier, that may have added some wear to the half nuts as the carriage was being powered.


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## LX Kid

I just ordered another half nut, $75, so I can have a spare.  As you can see, from my first half nut, the wear on right sides of the acme thread.  Gotta be something that I can check, adjust better,  different lead screw lube etc.  I believe the wear is caused by  the lead screw, as described above, from the pinion and rack having too much pressure against it when engaged.  I haven't removed the one I'm running on now but can see with a flashlight that it is wearing and will be another early failure.  I also found the belt idler bearing starting to make noise so I ordered another, $3, from Grizzly.  If I don't get this particular bug worked out this lathe may soon be on Craigslist!


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## mmcmdl

Amco bronze or possibly oillight may be a good replacement material . Acme taps are available but chasing the thread is a better option . They sell inserts if you have a holder . TIP..... thread that bad boy with a 60 degree tool then dig the rest out with the Acme insert . Make 2 or 3 extras also !


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## LX Kid

Taps run about $200-$350 for an Acme thread.  I'm still haven't learned to thread yet and it's my understanding that it can be made by single point cutting.   It still has the same question to be answered, "why is it failing and what will make it reliable?"  And I know that I'll be asked how deep cuts am I making?  Just light cuts, little by little!


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## mmcmdl

If its brass it will wear , period . Once you find out the pitch look for a cheap tap . I have some and will let you use it . Single point cutting is chasing btw , so that is true .


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## jbolt

C932 Bronze is better suited for this. I've seen them made from Delrin, 6061 and cast iron.


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## Bob Korves

You can single point the half nut, and it looks like you can make the nut full round and cut it in half for two usable pieces.  You can also grind the tool yourself.  It still looks to me like there is drag in your carriage somewhere.  Are you sure you release both the carriage locks when you thread or feed?  Is the lathe reasonably clean, no grit hanging around back there by the half nuts?


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## LX Kid

Bob Korves said:


> You can single point the half nut, and it looks like you can make the nut full round and cut it in half for two usable pieces.  You can also grind the tool yourself.  It still looks to me like there is drag in your carriage somewhere.  Are you sure you release both the carriage locks when you thread or feed?  Is the lathe reasonably clean, no grit hanging around back there by the half nuts?



There are two locks on the cross feed table and one lock on the ways gib.  The two locks on the cross feed don't effect the half nut "unless" using it under power feed, which I don't really use.  The ways lock is not interfering and is loose.   I do clean and lube my lead screw often.


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## LX Kid

mmcmdl said:


> If its brass it will wear , period . Once you find out the pitch look for a cheap tap . I have some and will let you use it . Single point cutting is chasing btw , so that is true .



That would be great if you have a .780" x 6TPI x 29 deg Acme tap.  I do have some round delrin that I could try it out with.  If that works out for me I could also buy some bronze round stock.


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## Bob Korves

I looked at the operation manual online.  Are you using the half nuts for feeding when you are turning metal to size?  The feed lever is for that, and the half nuts are only for threading or other precision feeding.  Normally it takes a LOT of threading to wear out the half nuts.  Use the feed lever for feeding, and the half nuts for threading.  Also, and it is usually not even possible to do, but make real sure that the feed lever and the half nuts are not engaged at the same time.  The manual did not seem to address that.


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## mmcmdl

Good point Bob . That would be a pretty high feed rate thus wearing them out .


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## BGHansen

Bob Korves said:


> I looked at the operation manual online.  Are you using the half nuts for feeding when you are turning metal to size?  The feed lever is for that, and the half nuts are only for threading or other precision feeding.  Normally it takes a LOT of threading to wear out the half nuts.  Use the feed lever for feeding, and the half nuts for threading.  Also, and it is usually not even possible to do, but make real sure that the feed lever and the half nuts are not engaged at the same time.  The manual did not seem to address that.


I think Bob is correct about the wear.  I have a Clausing 5418 that started its life in a high school shop in 1963 (my dad was the shop teacher and bought the lathe from Atlas/Clausing).  It had a lot of use in the shop for around 10 years, then not so much.  The half-nuts are cast iron and look like new.

Either Grizzly has a really bad design, bad half-nut material choice or you have something causing your carriage to drag putting a real load on the half nuts.  I can freely push my lathe carriages back/forth the length of the bed with no drag.  If yours is moving really hard maybe your carriage gibs (manual page from my Grizzle G0709 is below) need adjusting.  Good luck!

Bruce


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## Smithdoor

One way is to use epoxy filler (bronze type) to may one I have never did others have
It looks like Grizzly is using cheep brass for the nut.
They not hard to make I like bronze pins for large truck transmission

Dave


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## tomh

Can you post a pic of the back side of the half nut?
Is it held in place with a cross pin?
Looking at the manual, that lathe only uses one piece of what most is commonly known as a set. If so then its going to wear out rather fast because it is pushing /ridding  and not clamping the leadscrew  as half nuts are designed to do.
Folks have been making half nut from derlin/actel.   The projects in metal group seem to be  having success from what I have read,
so that might be a possible solution for you to look into.     

Your leadscrew is 6 tpi


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## LX Kid

The  feed lever, lower hand wheel, is engaged all the time!  No way to disengage it.  The half nut is  engaged when cutting threads and the feed wheel turns as it moved along.  With half nut "not" engaged I can not "easily" move my carriage by hand.  I could try loosening the gib screws under the table, just above the gear box to see if they might be too tight.  Being a "newbie" I could have tried to take too much play out of the carriage.


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## LX Kid

The carriage lock would not stay put, just flop around, unless held in place by hand so I made a mod to the shaft.  This put friction on the gear box hole to hold it in place.


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## tomh

Without the half nut engaged the carriage should glide with out any effort when you move it with your hand, so I suggest loosen the carriage gib a little at  a time till you can slide the carriage easily.  The brass half nut has my curiosity up, can you post a pic of the back of the brass half nut.


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## tmarks11

Yet another reason to hate 3IN1 designs.  Using the lead-screw and (half of a) half nuts for power feed is a trick found on cheap 7x14 mini lathes.  turning.

What is even crazier is that the G9729 has the slot in the lead screw, so it shouldn't have to use the half nuts.  But Grizzly put the "feed lever" (really the leadscrew engagement lever) on the headstock instead of the carriage.  Only the cross-slide power feed uses the slot on the leadscrew; longitudinal feed relies on the half-nuts.

Even the 9x19 lathes have a separate feed lever (nothing to do with the half-nuts) on the carriage to engage/disengage the slot in the lead screw so you don't have to use the half-nuts for turning.

Since you obviously use your lathe a lot, you might start looking for a 12x36 to upgrade to.  You will be very happy with the additional features.



LX Kid said:


> The  feed lever, lower hand wheel, is engaged all the time!  No way to disengage it.


That is true on every lathe.  The carriage hand wheel is engaged to the rack on the bottom of the bed all the time, moving the carriage moves the carriage hand wheel (whether while threading or by hand or by power-feed).

The "feed lever" on most lathes (as I said above) is mounted on the apron and is used to engage/disengage power feed (both longitudinal and cross).


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## Bob Korves

http://cdn1.grizzly.com/manuals/g9729_m.pdf
This is a link to the operation manual.  Read pages 35-44.  Page 35 shows the feed lever and what it does.  I just noticed that the feed lever is part of the headstock, not part of the apron.  You do not have a separate feed lever on the apron, like most lathes do.  So the half nut needs to be engaged for any power movement of the carriage on your machine.  The combination of a single half nut and the half nut being used for all power traversing is the root of your problem with half nut wear.  It is a far from ideal design, apparently not designed for much usage.  I would go back to your earlier idea of selling the machine if I intended to use it more than occasionally and even then only for light work.

Edit:  Looks like tmarks11 beat me to it...


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## LX Kid

Ok, here is what I've discovered.  I tried pushing my carriage by hand and I could not budge it!  I "evidently" had the gib adjustments too tight.  I adjusted the gib screws just to where I could move the carriage by hand.  That said it's not as smooth as silk.  When making cuts I will adjust the carriage lock for best final cut using power feed.  Accuracy will suffer.  Here is a pic of the back of the half nut and my pinion gear.  I replaced the pinion gear early on cause it was really rusty and badly pitted.  The new one wasn't much better!


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## tmarks11

Bob Korves said:


> Looks like tmarks11 beat me to it...



great minds think alike... just some people type faster than others...


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## mmcmdl

tmarks11 said:


> great minds think alike... just some people type faster than others...



Every time a see this thread title pop up I'm reminded of my current situation ! Rummaging thru drawers , containers , boxes , buckets and coolers looking for stuff I know I have has driven me past half nuts . Waaayyy past !


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## tomh

Lets try a couple ideas.
I hope this helps in some insane way

On the carriage are you getting plenty of oil on the bed ways between the carriage and the bed? think of the oil as millions of tiny ball bearings, it will help the carriage slide without causing  friction/drag that can effect carriage movement and  the cut finish.

Now for the half nut.
That is what I needed to see. looking at the manual and the half nut and wear on it, it appears that the halfnut rest in a cradle and held in place with a pin and that assembly  possibly threads on to the half nut lever shaft? if so you should be able to adjust the halfnut assembly  closer to or away  from the lead screw,  does that make sense or am I out in left field?  the halfnut thread wear appears to be primarily on the outside of the thread  if so I am thing that the halfnut needs to be closer to the lead screw.


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## jbolt

tomh said:


> Lets try a couple ideas.
> I hope this helps in some insane way
> 
> On the carriage are you getting plenty of oil on the bed ways between the carriage and the bed? think of the oil as millions of tiny ball bearings, it will help the carriage slide without causing  friction/drag that can effect carriage movement and  the cut finish.
> 
> Now for the half nut.
> That is what I needed to see. looking at the manual and the half nut and wear on it, it appears that the halfnut rest in a cradle and held in place with a pin and that assembly  possibly threads on to the half nut lever shaft? if so you should be able to adjust the halfnut assembly  closer to or away  from the lead screw,  does that make sense or am I out in left field?  the halfnut thread wear appears to be primarily on the outside of the thread  if so I am thing that the halfnut needs to be closer to the lead screw.



I was thinking the same thing. Looks like the half nut is not fully engaging the lead screw or the lead screw is deflecting some under load.

Also check the lead screw threads along the key-way cut for sharp edges and burrs.


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## LX Kid

jbolt said:


> I was thinking the same thing. Looks like the half nut is not fully engaging the lead screw or the lead screw is deflecting some under load.
> 
> Also check the lead screw threads along the key-way cut for sharp edges and burrs.



I also was concerned about these sharp edges of the key way.  I had asked earlier about the possibility of rounding each and ever  thread edge on both sides of the key way.  What the heck does this key way do anyhow?  I don't see any real function for it unless it is to collect chaff out of the threads.


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## jbolt

LX Kid said:


> I also was concerned about these sharp edges of the key way.  I had asked earlier about the possibility of rounding each and ever  thread edge on both sides of the key way.  What the heck does this key way do anyhow?  I don't see any real function for it unless it is to collect chaff out of the threads.



It drives one of the bevel gears on the apron which gives you the cross slide power feed. I have the same setup on my Smithy Granite 1324 except it drives a a full gearbox in the apron that does the power feed for both X & Y(Z on lathe). The key-way slot allows the apron to move while driving the bevel gear.

A full featured lathe will have a feed screw and lead screw. The lead screw has no slot and is used only for threading. The feed screw is a smooth rod with the key-way slot that drives a bevel gear in the apron gearbox.


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## LX Kid

LX Kid said:


> I also was concerned about these sharp edges of the key way.  I had asked earlier about the possibility of rounding each and ever  thread edge on both sides of the key way.



What about using a pencil die grinder, with a conical stone attached, to grind in between each two threads?  Then just touch up the crest of the thread for any burrs.

I'm also thinking of pulling the gib out, for the way lock, and do some polishing with 600 grit paper to smooth out any possible high spots.  I'll also round and  polish the detent holes where the adjusting screws mate.


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## LX Kid

Things are getting better and better with all the help that is being offered here!  Thanks!

I removed the carriage gib and polished it with 600 grit paper and used valve grinding compound to smooth the detent holes to fit the adjustment bolts I made.  I made the bolts with a rounded end instead of the pointed set screws that came installed.  I found I could now adjust the gib more  accurately.  I also lubed everything with motor oil and that really made a difference!  Everything is operating much better and I'm now more optimistic about about my new machine.  I also made a  way scraper from a piece of acrylic material.

Before properly adjusting the gib I could not turn the hand crank, on the lead screw, to move carriage back towards the chuck.  (Lead screw in "neutral" with half nut engaged.)  Now that works so much better and I'm sure when my new half nut gets here it will even be better.


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## jbolt

LX Kid said:


> What about using a pencil die grinder, with a conical stone attached, to grind in between each two threads?  Then just touch up the crest of the thread for any burrs.
> 
> I'm also thinking of pulling the gib out, for the way lock, and do some polishing with 600 grit paper to smooth out any possible high spots.  I'll also round and  polish the detent holes where the adjusting screws mate.



I would just use a jewelers file to knock the edge off is there is one. It does not need much.


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## jbolt

Sounds like your getting there. One comment about motor oil. Most motor oils have detergents in them that are designed to suspend particles in the oil. Good for engines but not as good for machines that see more abrasive materials. Non-detergent motor oils are fine. True way oils are really unnecessary for the hobby size machines that don't have much mass. Generally use standard 30w machine oil on my Smithy. I do use way oil on my CNC mill which sees more severe duty.


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## LX Kid

Well it's been raining here all day so it was a good day to stay out in the shop.  "What to do?"  Sooo I took the whole carriage off, table, gear box and cleaned everything in solvent.  Blew every nick and cranny with air, oiled and put everything back together.  Did an inspection of the half nut and there is wear but not as bad as I had thought there would be.  Now I'll have a spare when it get's here from Grizzly.  This was the second time that I have tore everything down and was really surprised at how much casting sand, grit and grime was "still" in the parts.


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## 4GSR

One thing not mention, when I get ready to do any threading, I squirt oil on the lead screw in the length I'm going to be using.  Sure extends the life of the half nuts.


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## LX Kid

4gsr said:


> One thing not mention, when I get ready to do any threading, I squirt oil on the lead screw in the length I'm going to be using.  Sure extends the life of the half nuts.



I'm pretty sure that my excessive half nut wear is going to be a thing of the past!  Since I properly adjusted the gigs and using better oil, it has really been  a much smoother operation.   It's like the old saying goes, "Experience cost!  How much you wanna pay!"


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## tomh

"Experience cost! How much you wanna pay!"

Been there done that


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## LX Kid

I'm not going to worry about the half nuts for awhile.  Seems like the "newbie" has learned a little bit with the help of the folks here.  I adjusted the carriage gib to where there wasn't so much pressure and put more oil on the ways and things are looking a lot better now.  I also bought another half nut as a back up because there is some wear on the current one I'm using.  Thanks for everyone's help and  advice.


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## Johnnybar

Do not use the carriage feed for roughing cuts, including finish cuts  if you can hand feed a decent finish.  A HSS shear tool will allow really nice finishes when slow hand feeding.


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## LX Kid

Johnnybar said:


> Do not use the carriage feed for roughing cuts, including finish cuts  if you can hand feed a decent finish.  A HSS shear tool will allow really nice finishes when slow hand feeding.



Thanks I'll give this a try.  Haven't been out in the shop for a while now due to the Florida heat.  Cooling off now so I be out there soon making some nothings!  LoL


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## Johnnybar

If you decide to give half nuts a try eventually, you might go ahead and get a reversing idler made since it will be required.  Even if you decide against making your own nuts, it will come in handy for those odd ball LH threading jobs occasionally.   Here's one I made and it works well in the existing empty slot on the change gear plate.


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