- Joined
- Oct 24, 2019
- Messages
- 52
I answered the phone in my shop while in the middle of threading a rifle barrel. When I got off the phone, I had forgotten that I was threading away from the headstock with the tool upside down. I started the lathe, engaged the half nut and immediately let out a stream of obscenities' that would make a sailor blush.
I ran the tool into the chuck. The chuck came to a complete stop from 300 rpm in about 1/4 inch of rotation. (estimated by the depth of the gouge in the tool).
Checking for damage, I threaded a 1.062 inch piece of cold rolled 18 threads per inch. (just like the rifle barrel) My ring gauge would only go about 4 threads onto the part. Measuring the part, I found almost 2 thou of taper in 1 inch! Previously to this incident, I had less that about 4 tenths of taper over a foot long cut. I couldn't ask for anything better because I cant measure any closer.
There are a lot of great videos on you tube about lathe head and tailstock alignment. All say that the proof of the alignment is in the cut. They all want you to make a "barbell" test bar, take a skim cut, and measure the diameter of the bar at the ends. That is great advise. It works. That is also a lot of "up and down", cutting and measuring. It would have taken days. Since I hadn't checked the level on my lathe in about 6 months, I got out my levels. An 8 inch Starrett, a 4 inch Starrett, and a 12 inch South Bend. I calibrated them and proceeded to level the lathe to as close to perfect I could get it. I left everything set for a day for temp stabilization and cast iron settling. After I checked the level again, I made a test bar (6061 about 3 inch diameter, 5 inches long.) At that point, I had about 2 1/2 thou difference at the ends of the bar. I ordered a mt5 (headstock taper) alignment bar but it will not be here for a couple of weeks. Being impatient, I needed another solution. I do have a MT5 to MT3 adapter, a MT3 to MT2 adapter, and an MT2 test bar. That is a whole lot of tolerances stacking up (one of them Chinese). After a lot of playing around, I got the 6 inch MT2 bar to run out less than a thou at the headstock end. Now I could see the taper with a .0001 drop indicator on a mag mount stuck on the carriage.
Now there was nothing to do but crack the headstock loose. Only 4 hex head screws. Just moved them about 1/8 to 1/4 of a turn. They were very tight - needed a short pipe. I had to modify the short end of the Allen wrench (shortened it by 1/2 inch to get into the opening at the chuck end of the headstock) I could not get to the adjustment screws because the change gears were blocking access to them. I pulled the banjo and the change gears, reached in with a 12 mm open end wrench and proceeded to adjust the headstock to less than 1 thou difference over the length of the test bar! I was shocked! The actual alignment took about 5 minutes after everything was prepared. I ended up doing the alignment 3 or 4 times as it moved when I tightened up the screws. Re-mounting the chuck and re-skimmed the aluminum test bar resulted in both ends being the same (as close as I can measure with an igaging digital micrometer and my Mitutoyo digital calipers. As long as I have the lathe cutting well, I will use my Edge technology tailstock alignment tool and check that too.
I suggest getting a test bar (headstock taper correct for your lathe) and using it to verify the amount of mis-alignment prior to trying to correct taper issues by leveling. I was lucky. That very loud noise was a good indicator that I had a headstock issue rather than just a leveling issue.
I ran the tool into the chuck. The chuck came to a complete stop from 300 rpm in about 1/4 inch of rotation. (estimated by the depth of the gouge in the tool).
Checking for damage, I threaded a 1.062 inch piece of cold rolled 18 threads per inch. (just like the rifle barrel) My ring gauge would only go about 4 threads onto the part. Measuring the part, I found almost 2 thou of taper in 1 inch! Previously to this incident, I had less that about 4 tenths of taper over a foot long cut. I couldn't ask for anything better because I cant measure any closer.
There are a lot of great videos on you tube about lathe head and tailstock alignment. All say that the proof of the alignment is in the cut. They all want you to make a "barbell" test bar, take a skim cut, and measure the diameter of the bar at the ends. That is great advise. It works. That is also a lot of "up and down", cutting and measuring. It would have taken days. Since I hadn't checked the level on my lathe in about 6 months, I got out my levels. An 8 inch Starrett, a 4 inch Starrett, and a 12 inch South Bend. I calibrated them and proceeded to level the lathe to as close to perfect I could get it. I left everything set for a day for temp stabilization and cast iron settling. After I checked the level again, I made a test bar (6061 about 3 inch diameter, 5 inches long.) At that point, I had about 2 1/2 thou difference at the ends of the bar. I ordered a mt5 (headstock taper) alignment bar but it will not be here for a couple of weeks. Being impatient, I needed another solution. I do have a MT5 to MT3 adapter, a MT3 to MT2 adapter, and an MT2 test bar. That is a whole lot of tolerances stacking up (one of them Chinese). After a lot of playing around, I got the 6 inch MT2 bar to run out less than a thou at the headstock end. Now I could see the taper with a .0001 drop indicator on a mag mount stuck on the carriage.
Now there was nothing to do but crack the headstock loose. Only 4 hex head screws. Just moved them about 1/8 to 1/4 of a turn. They were very tight - needed a short pipe. I had to modify the short end of the Allen wrench (shortened it by 1/2 inch to get into the opening at the chuck end of the headstock) I could not get to the adjustment screws because the change gears were blocking access to them. I pulled the banjo and the change gears, reached in with a 12 mm open end wrench and proceeded to adjust the headstock to less than 1 thou difference over the length of the test bar! I was shocked! The actual alignment took about 5 minutes after everything was prepared. I ended up doing the alignment 3 or 4 times as it moved when I tightened up the screws. Re-mounting the chuck and re-skimmed the aluminum test bar resulted in both ends being the same (as close as I can measure with an igaging digital micrometer and my Mitutoyo digital calipers. As long as I have the lathe cutting well, I will use my Edge technology tailstock alignment tool and check that too.
I suggest getting a test bar (headstock taper correct for your lathe) and using it to verify the amount of mis-alignment prior to trying to correct taper issues by leveling. I was lucky. That very loud noise was a good indicator that I had a headstock issue rather than just a leveling issue.