Trying To Align My Lathe

B

BigSpike

Registered
Registered
Joined
Jul 13, 2013
Messages
9
I previously aligned my tail stock to the head, but didn't use a test rod. I knew it was a little off but put it on my list of ToDo's.
So I started off by making a 10" long test bar from 3/4" drill rod, This was about the largest diameter that would fit through my spindle bore of .787". With minimal stick out I faced, chamfered & center drilled each end.
I then made a dead center for the chuck. I cut the 60° angle with my compound set at 30° and a boring bar angled to the rear of the material. Running the lathe in reverse I cut .005" per pass using the compound for the cut & moving the cross feed out .005 per pass. This took a while until I had a sharp point. I used my fish scale to check the angle & was surprised that I had succeeded in getting the correct angle.
Next I made a light cut from the taper to the chuck jaws to check the chuck/spindle runout. This measured .0002" runout.
Next I mounted up the test bar & using a dial indicator I took a few measurements & found it was out of round by .008".
I took a couple of passes off the entire length from the tail stock to the chuck. Then I used a micrometer to measure the diameter of each end. The diameter at the tail stock end is bigger by .032".
WTH? - chuck end is .705" -- tail stock end is .737"
I measured several times at different points radially with my Mitutoyo 1" micrometer; same results.
Using a dial indicator perpendicular to the rod, I measured a taper of .001 plus about a third of the space between line. but... I started at 0 and it went to +1.3 at the tail stock.
The taper is measured with a near new Peacock dial indicator that has been reliable in the past.

So I'm thinking, maybe the cross feed shifted during the cut. I move the carriage & get a tool touch with the cross feed dial reading 15; I back off to 80. Move the carriage to the tail stock end, cross feed in to 15 then finally touch at 20.
On this lathe the cross feed dial is divided into 100, each division = about .002" (or so they claim). That would indicate a taper of .010".
double wth

I removed the test bar & brought the live center up to the dead center in the chuck
using a steel rule between, it held vertical & looked even horizontal.

Where am I going wrong?

Enco 3in1 lathe, minimal use, gibs reworked & adjusted, new cutting tool on centerline, new tight live center , tail stock was locked.
 
Is the lathe bed level in plane?
Is the lathe bed and the legs/bench/frame to which it is mounted solid and not shifting?

Leveling in plane takes the twist out of the bed.
Think about a drill spiral/helix. A lathe bed will twist in the same way, such that as you move the tailstock closer or farther from the spindle center moves with the twist.

Are the gibs in the crossfeed and compound snug enough to move freely but tight enough so that they don't slip under load?
When you hold the spindle and tailstock quill and attempt to move them are you getting any noticeable movement?

Daryl
MN
 
Your own suspicion that the cross slide didn't hold its setting would be my guess too based on the numbers.
What with backlash and vibration the cross slide could be slipping away from the cut.
Does your lathe have a feature for locking the cross slide? the compound?
 
Last edited:
Mark an inch or so section at each end of the bar. Machine between these two sections to remove excess metal. Then take your precision cuts on each of the two "collars"
By removing the metal between the two "collars" you reduce the possibility of the bar springing under the pressure of the tool bit. Hopefully each collar will be the same diameter. If they are then investigate why you have a taper when machining the full length of the bar. If they aren't then re-level the bed of the lathe etc.
Just my .02
 
Reeltor said:
Mark an inch or so section at each end of the bar. Machine between these two sections to remove excess metal. Then take your precision cuts on each of the two "collars"
By removing the metal between the two "collars" you reduce the possibility of the bar springing under the pressure of the tool bit. Hopefully each collar will be the same diameter. If they are then investigate why you have a taper when machining the full length of the bar. If they aren't then re-level the bed of the lathe etc.
Just my .02
Click to expand...
Yes. The bulk of the bar should not be used for the test. It's called a "two collar test" for this reason. You turn it all down to a reasonably consistent and concentric size. Then you remove .200" or whatever from the bulk of the bar, leaving a collar near the headstock and another near the tailstock. Then in one single operation, without changing any settings except the movement of the carriage, cut both collars to the "same" size. Then check to see if they actually are the same size. It minimizes the spring of the workpiece and entire system, and it eliminates the concern about the tool wearing during the length of the cut.
 
intjonmiller said:
Yes. The bulk of the bar should not be used for the test. It's called a "two collar test" for this reason. You turn it all down to a reasonably consistent and concentric size. Then you remove .200" or whatever from the bulk of the bar, leaving a collar near the headstock and another near the tailstock. Then in one single operation, without changing any settings except the movement of the carriage, cut both collars to the "same" size. Then check to see if they actually are the same size. It minimizes the spring of the workpiece and entire system, and it eliminates the concern about the tool wearing during the length of the cut.
Click to expand...

Your explanation is a bit clearer than what I wrote

Here is Adam Booth Abom79 doing the 2-collar test on his Monarch

Mike
 
intjonmiller said:
You turn it all down to a reasonably consistent and concentric size. Then you remove .200" or whatever from the bulk of the bar, leaving a collar near the headstock and another near the tailstock.
Click to expand...

Is .200'' a typo? cause .020'' would be enough to take off.
 
No typo. The idea is that you keep this test bar around to recheck your lathe for years to come.
 
I would rather recut the centre portion only as needed to minimize deflection in the work.
 
I'm just sharing the "standard practice" as I've read it in multiple books. You're not taking a heavy cut for the test. That would completely defeat the purpose. Assuming you already know you're close you could do it with a vertical shear bit. The tailstock and headstock will be the deflection points since you're running on at least the tailstock center and only barely cutting the collars right where they are well-supported.

Obviously it will work either way. The idea, to me anyway, is just to minimize the work of rechecking it later on (such as after setting up a taper, for instance), so you will be more likely to do it since you know it will be fast and easy. Set it up once and you never have to touch the center section of the test bar again.
 
You must log in or register to reply here.
Back
Top