9 x 20 half nut problem

I did a lot of fettling when I first recieved this lathe but as it was the first lathe I had ever used there was everything I didnt know or have experience with.
I adjusted and checked everything I could after heaps of research on line.
Mostly I used logic to work out how to do it and Cletus's books.
The first set of half nuts were damaged in a crash, totally my fault.
I rebuilt the worm carrier with brass inserts that stopped the key dropping out from excessive end play on the worm.
drilled larger holes in the half nut dove tails so they could be aligned fully and removed all the play.
Made sure they opened and closed fully.
Everything worked well and I have cut heaps of threads with no problems.
I think the main problem was having removed the saddle a couple of times since and never checking how they clamped before tightening the saddle bolts is what caused the problem this time.
I've run a quick experiment regarding the bicycle innertube cover idea and it looks like a good possibility. I will report back if I get it working.
There must also be a better way of preventing swarf from entering the rear of the saddle.
Oh how I love these type of problem solving exercises:bang head:
 
Seems Half Nut not disengaging enough might be a good thing to look into.

I crashed my cross slide early on. Since rebuilding it, I cannot recall if the auto feed is reversible when the chuck is not reversed. Did I mess up & lose that function or just wish I had it? Grizzly G0773 must be very similar to all of yours.
 
C-Bag said:
My 9x20 had the half nuts not set up correctly so that's why they wore quickly. Don't know if it was previous owner or factory. I replaced them with Grizzley units. Like Savarin in order to get the correct alignment had to set the half nuts and then tighten the saddle. I also rigged an old tooth brush to clean the lead screw but wasn't really happy with the mount. I recently came up with something better. Still a tooth brush but old brushes off our SoniCare brushes that have really strong magnets in the base. This really simplifies mounting after modding the brush. This seems to knock all the swarf off the lead screw. I also put a bellows between the carriage and under the chuck and it overhangs the side eliminating the amount of swarf that can even get slung onto the lead screw.View attachment 279234View attachment 279235
Click to expand...
C-bag, I thought this was a fantastic idea. Just had a bit of concern about losing some leftward travel, as the toothbrush in this position would run into the QCGB ahead of the carriage. I did a bit of looking at my own 9x20 and came up with this alternative:

Step 1 - I had some brass brushes, as shown in the first photo. The orange handle brushes came from Home Depot, the grey handles form someplace else, long forgotten. I cut the handle off one and plucked out the tufts sticking out on the diagonal. Found a place on the underside of the carriage where the head would fit, though the bristles were "too long" and bent against the leadscrew. So I milled a bit off the back of the head. This let the bristles reach all the way into the leadscrew threads without too much bending. Added two threaded holes.
kHPIM5555.jpg


Step 2 - Found some 2" x 1/16" aluminum angle and cut off a chunk about 1" wide. Narrowed down the part under the brush, added two holes for brush mounting and two more for mounting on the carriage. Shortened the mounting "leg."
kHPIM5556.jpg


Step 3 - Mounted the brush assembly on the leading face of the carriage, below the leadscrew (after first having checked that there were no carriage parts in the way, either during threading or power feeding). The low profile of the brush mount allows full leftward carriage travel.
kHPIM5557.jpg


Step 4 - Unless power feeding or threading, I've always disengaged the QCGB by lowering the selector all the way down to disengage the gears. My theory is that this saves wear and tear on the leadscrew, as well as reducing noise. I turned the leadscrew to place the drive notch at the bottom, marked the top of the coupling with some paint. This will be the "default" leadscrew position and will let the brush clean the power feed groove whenever the carriage is run back and forth. When the leadscrew is turning, the brush will clean the threads.
kHPIM5559.jpg


UPDATE:
I sent Savarin a spare brush setup for his 9x20 lathe. Turns out that his lathe is "the other kind" of 9x20 - with the carriage crank on the right side of the carriage. Mine is on the left, as shown in my third photo. He had to mount his brush outboard of the carriage (see post #34), because his did not have the nice little cubbyhole underneath the leadscrew on the left side. Check your own lathe for the location of the crank, and plan accordingly!
 
Last edited:
hman said:
C-bag, I thought this was a fantastic idea. Just had a bit of concern about losing some leftward travel, as the toothbrush in this position would run into the QCGB ahead of the carriage. I did a bit of looking at my own 9x20 and came up with this alternative:

Step 1 - I had some brass brushes, as shown in the first photo. The orange handle brushes came from Home Depot, the grey handles form someplace else, long forgotten. I cut the handle off one and plucked out the tufts sticking out on the diagonal. Found a place on the underside of the carriage where the head would fit, though the bristles were "too long" and bent against the leadscrew. So I milled a bit off the back of the head. This let the bristles reach all the way into the leadscrew threads without too much bending. Added two threaded holes.
View attachment 279306

Step 2 - Found some 2" x 1/16" aluminum angle and cut off a chunk about 1" wide. Narrowed down the part under the brush, added two holes for brush mounting and two more for mounting on the carriage. Shortened the mounting "leg."
View attachment 279307

Step 3 - Mounted the brush assembly on the leading face of the carriage, below the leadscrew (after first having checked that there were no carriage parts in the way, either during threading or power feeding). The low profile of the brush mount allows full leftward carriage travel.
View attachment 279308

Step 4 - Unless power feeding or threading, I've always disengaged the QCGB by lowering the selector all the way down. My theory is that this saves wear and tear on the leadscrew, as well as reducing noise. I turned the leadscrew to place the drive notch at the bottom, marked the top of the coupling with some paint. This will be the "default" leadscrew position and will let the brush clean the power feed groove whenever the carriage is run back and forth. When the leadscrew is turning, the brush will clean the threads.
View attachment 279309
Click to expand...

That looks like a very well executed mod, should work a treat. I like the concept of marking the coupling so that the power feed groove is always parked in the down position.
 
I like that brush idea, so simple so brilliant.
Grooved the cross slide and de-burred yesterday.
But, I think I may have made a bit of a boo, I forgot the cross slide doenst fully cover the saddle so the oil grooves at each end will be exposed allowing the oil to squirt out when pumped in. Hopefully its still better than no oil and will help.
The oilers are in and two more gibb screws are in.
Starting on the saddle today.
The "V" way showed a wear stripe on each side almost the full length but the flat only showed wear on one end about 15mm long and a narrow strip at the other end about 3mm wide and 50mm long.
I've started scraping to obtain full length contact and its getting better, there is also a casting defect half way along running almost the full width across the flat.
 
Regarding the cross slide ... did you groove the slide or the saddle? It's best to groove the shorter of the two (ie., the slide). The slide being on top, gravity is also your friend - less chance for crud to fall into the grooves than if they're on the bottom. But as you've said, it's gotta be better than no oil!
 
The slide is grooved.
In thinking about this further I think it will be a method of flushing the oil ways of crud. Move to one end and pump then move to the other end and pump. Or pump when there is a small overlap at each end which will flush from both ends replacing the old oil with fresh.
Just trying to find a positive here :laughing:
 
I cannot believe how much I had to scrape the saddle to fit the bed.
Added two ball oilers to the "V" groove and two to the flat way, just have to add an oil groove to the flat.

It felt very smooth when pushed from end to end (without the gibbs)
Got to admit its getting better
cue for a song
 
I had watched a video on utube I think Stefan G where he put grooves in the compound slide. He talked a lot about finding the limits of the travel of compound so that the groove didn’t go past the saddle. Which as youve found releases the pressure of oil. Either way oiling is way better than not. She will sing like a dream. Good job.
 
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