Grizzly 9729 half nut
Posted: Wed Feb 15, 2017 3:31 pm
Good afternoon,
First off I would like to admit that I am far from a machinist. Secondly I have had my lathe since 2011. The first machine tool I purchased was my Grizzly 9729. I didn't do a lot of research before I bought it but knew the Grizzly name and thought I would not be that seriously dedicated to this hobby and that the shortcomings of this unit I could deal with. In a way I was right. I now have Grizzly g4000, taig micro lathe 2, Logan 400, Precision Mathews pm2o mill, Jet and Craftsman drill presses band saw, measuring equipment granite plate .........
I like 3 in 1 as it is relatively large (I can turn a rifle barrel on it), easy to understand how the controls work and mine is not really modified. It is the only lathe I have not done a slew of "improvements" on. I think as a lathe it is a really good machine, except for the half nut. My original brass one is completely worn through and makes it useless for threading and leaves patterns in longer work due to the "wrapping effect" that the leadscrew exhibits as the slot comes around to take another "cut" from the half nut. Being new to this I looked everywhere as to why this was happening only to discover it after the warranty expired and I am staring at a 80 dollar parts that weighs in at a few ounces. By reading a few posts here I was able to diagnose the problem and a cure was put into place. I spent a huge amount of time deburring the slot in my leadscrew so it would behave less like a one flute mill. I thought I would make my own half nut only to be set back again by not being able to purchase a tap for the incredibly odd .767 (if I remember the number right) by 6 tpi left hand thread. Lots of ideas went through my head from an electronic leadscrew with ballscrews to all out cnc (another area I have no knowledge in).
Last week I had just finished the Logan lathe set up clean up and realized this lathe could turn left hand threads. This machine is missing a few gears but I had everything except a 72 tooth gear to do it. Ebay solved the problem for about 50 bucks. So what I did was turn a left hand 6 tpi tap blank that matched the diameter of my leadscrew (again .767?) I used a form tool I ground myself and used the leadscrew as a gauge to get it right. The material was water hardening drill rod. I did not photograph any of it (disappointed) because at first I did not think I would get very far and later because I was superstitious. . It actually came out very good! Before I cut the slots to make it a tap I remembered someone saying something about Acetal being a wonderful material for half nuts on another forum for a different lathe. I had a foot of this in 1 1/2 inch diameter so went about measuring the old part and turning a blank to try and mould a half nut. Using the tap blank, propane torch, bench vise and water I carefully heated the metal and tightened the vise until I forced the blank into the plastic. I could not figure an accurate way of measuring this so I "eyeballed" it until the blank tooth just bottomed out and I stopped cranking and poured water over everything to stop the process. After a little cleanup on the bandsaw I installed it and to my amazement it worked. I played with it a little bit last night but was wondering if anyone else has any experience with this material. More importantly will this material hold up or should I complete the tap and make one out of brass.
Sorry for the length of this essay but I wanted to explain my thought process so as to make it easier to point out any errors in my logic.
Thank you
Kenny
First off I would like to admit that I am far from a machinist. Secondly I have had my lathe since 2011. The first machine tool I purchased was my Grizzly 9729. I didn't do a lot of research before I bought it but knew the Grizzly name and thought I would not be that seriously dedicated to this hobby and that the shortcomings of this unit I could deal with. In a way I was right. I now have Grizzly g4000, taig micro lathe 2, Logan 400, Precision Mathews pm2o mill, Jet and Craftsman drill presses band saw, measuring equipment granite plate .........
I like 3 in 1 as it is relatively large (I can turn a rifle barrel on it), easy to understand how the controls work and mine is not really modified. It is the only lathe I have not done a slew of "improvements" on. I think as a lathe it is a really good machine, except for the half nut. My original brass one is completely worn through and makes it useless for threading and leaves patterns in longer work due to the "wrapping effect" that the leadscrew exhibits as the slot comes around to take another "cut" from the half nut. Being new to this I looked everywhere as to why this was happening only to discover it after the warranty expired and I am staring at a 80 dollar parts that weighs in at a few ounces. By reading a few posts here I was able to diagnose the problem and a cure was put into place. I spent a huge amount of time deburring the slot in my leadscrew so it would behave less like a one flute mill. I thought I would make my own half nut only to be set back again by not being able to purchase a tap for the incredibly odd .767 (if I remember the number right) by 6 tpi left hand thread. Lots of ideas went through my head from an electronic leadscrew with ballscrews to all out cnc (another area I have no knowledge in).
Last week I had just finished the Logan lathe set up clean up and realized this lathe could turn left hand threads. This machine is missing a few gears but I had everything except a 72 tooth gear to do it. Ebay solved the problem for about 50 bucks. So what I did was turn a left hand 6 tpi tap blank that matched the diameter of my leadscrew (again .767?) I used a form tool I ground myself and used the leadscrew as a gauge to get it right. The material was water hardening drill rod. I did not photograph any of it (disappointed) because at first I did not think I would get very far and later because I was superstitious. . It actually came out very good! Before I cut the slots to make it a tap I remembered someone saying something about Acetal being a wonderful material for half nuts on another forum for a different lathe. I had a foot of this in 1 1/2 inch diameter so went about measuring the old part and turning a blank to try and mould a half nut. Using the tap blank, propane torch, bench vise and water I carefully heated the metal and tightened the vise until I forced the blank into the plastic. I could not figure an accurate way of measuring this so I "eyeballed" it until the blank tooth just bottomed out and I stopped cranking and poured water over everything to stop the process. After a little cleanup on the bandsaw I installed it and to my amazement it worked. I played with it a little bit last night but was wondering if anyone else has any experience with this material. More importantly will this material hold up or should I complete the tap and make one out of brass.
Sorry for the length of this essay but I wanted to explain my thought process so as to make it easier to point out any errors in my logic.
Thank you
Kenny