Hey guys so i have been at this for the better part of the afternoon today. I have a Harrison M300 lathe circa 2000 era think Colchester 13 inch by 40 pretty much the same machine. Any way It tends to cut tapers even though I have no taper attachment so figured its time to level it up and get the twist out of the bed. So I first threw my 12 inch Starrett level on the machine and got the lathe dialed in level both longitudinally and then across the ways as well on the headstock and tailstock end. This was easy just four jack screws at all four corners of the cabinet.
SO I then took a piece of 1.5 inches by 1414 inches aluminum bar to be a test piece and chucked it up into my 3 jaw chuck. Took some .020 passes to get the bar true and running concentric with the spindle. I then took a very light pass at about .002 depth the length of the bar. I then got out my micrometer and measured the tailstock end as well as the headstock end. Well, I noticed there was about a .003 inch difference in diameter with the tailstock end smaller than the headstock end. No problem I just loosened the tailstock front jack screw and took another pass. The measurements improved but still about .002 inches difference with the tailstock end smaller than the headstock end. Well at this point the jack screw at the front on the tailstock end was pretty light I could move it by hand so the machine was pretty much just resting on the two feet back and front on the headstock end as well as the back foot on the tailstock end. So I am out of adjustment I decided I would unbolt the tailstock end of my lathe from the cabinet and put a shim under the backside to try and add more twist forward to improve the measurements. I unbolted the four bolts on the tailstock end and then put a hydraulic bottle jack under the tailstock end and lifted it up ever so slightly and slide a .008 inch piece of aluminum flashing under the back part of the tailstock mount point to the cabinet. I then bolted it back down with the four bolts and took another test cut.
So now the measurments from both ends was off by about .001 inches and the tailstock side was larger than the headstock side. This was good I then lowred the front foot on the tail stock end to compensate for this and took another test cut. Finally I got both sides to be within about .0003 inches of each other over a 12 inch bar. Then I thought to myself the middle should be about .00015 inches between the two. I took a measurement at the middle and to my surprise, it is .0009 inches larger than the tailstock end of the bar and the headstock end of the bar.
I have been scratching my head on this now and am unsure if I can do anything about this. I think this points to wear in the machine as I get closer to the headstock. What I don't understand is how I can be almost the same at both ends of the bar but the middle is almost one thousands of an inch larger than the tailstock and headstock end. Should I worry about this or call it good? I am just a home shop hobby guy making one-off parts for whatever arises. I am no journman machinest hence im asking these questions. Is it unrealistic to be expecting my machine to be able to hold .0001 inches across a 12 inch peice of stock? Is it bad to shim the tailstock end of the lathe to help reduce the twist in the bed?
I have attached a few photos to show what I was doing. Really appreciate any insights or help. Thanks again!
Lee
SO I then took a piece of 1.5 inches by 1414 inches aluminum bar to be a test piece and chucked it up into my 3 jaw chuck. Took some .020 passes to get the bar true and running concentric with the spindle. I then took a very light pass at about .002 depth the length of the bar. I then got out my micrometer and measured the tailstock end as well as the headstock end. Well, I noticed there was about a .003 inch difference in diameter with the tailstock end smaller than the headstock end. No problem I just loosened the tailstock front jack screw and took another pass. The measurements improved but still about .002 inches difference with the tailstock end smaller than the headstock end. Well at this point the jack screw at the front on the tailstock end was pretty light I could move it by hand so the machine was pretty much just resting on the two feet back and front on the headstock end as well as the back foot on the tailstock end. So I am out of adjustment I decided I would unbolt the tailstock end of my lathe from the cabinet and put a shim under the backside to try and add more twist forward to improve the measurements. I unbolted the four bolts on the tailstock end and then put a hydraulic bottle jack under the tailstock end and lifted it up ever so slightly and slide a .008 inch piece of aluminum flashing under the back part of the tailstock mount point to the cabinet. I then bolted it back down with the four bolts and took another test cut.
So now the measurments from both ends was off by about .001 inches and the tailstock side was larger than the headstock side. This was good I then lowred the front foot on the tail stock end to compensate for this and took another test cut. Finally I got both sides to be within about .0003 inches of each other over a 12 inch bar. Then I thought to myself the middle should be about .00015 inches between the two. I took a measurement at the middle and to my surprise, it is .0009 inches larger than the tailstock end of the bar and the headstock end of the bar.
I have been scratching my head on this now and am unsure if I can do anything about this. I think this points to wear in the machine as I get closer to the headstock. What I don't understand is how I can be almost the same at both ends of the bar but the middle is almost one thousands of an inch larger than the tailstock and headstock end. Should I worry about this or call it good? I am just a home shop hobby guy making one-off parts for whatever arises. I am no journman machinest hence im asking these questions. Is it unrealistic to be expecting my machine to be able to hold .0001 inches across a 12 inch peice of stock? Is it bad to shim the tailstock end of the lathe to help reduce the twist in the bed?
I have attached a few photos to show what I was doing. Really appreciate any insights or help. Thanks again!
Lee