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jaybird
07-19-2004, 05:31 AM
I am doing an alignment of may lathe tailstock and headstock. I have made/using a test bar. My question is how close dose the height of the tailstock and headstock have to have to be? And what would be and effective way to measure the differnace in height?

J

I did a search after posting and did find some good information.....J

[This message has been edited by jaybird (edited 07-19-2004).]

Forrest Addy
07-19-2004, 07:32 AM
Alignment tolerences depends on the quality of the machine and its condition.

In the absense of factory specs a rebuilt lathe when level and in correct alignment should safely be within:

Spindle parallel to carriage motion 0.0002"/12" horizontal plane 0.001" in 12" vertical plane (spindle rising)

Tailstock quill 0.0005" in 12" parallel to the ways in horizontal plane 0.001 in 12" in vertical plane (quill rising).

Spindle and quill at the same height 0.0005" with the quill high.

As for a checking set-up. Jump the tailstock ahead of the carriage and sweep in the quill with an indicator mounted directly on the faceplate. Do not use a mag base or a collection of rods and snugs. Use soemthing stout bolted directly to the face plate. Gravity takes a terrible toll from the usual indication set-up that inversion doubles.

[This message has been edited by Forrest Addy (edited 07-19-2004).]

jaybird
07-19-2004, 09:05 PM
Forrest,

Is it ok to mount the indicator in a chuck instead of mounting to a faceplate?

J

[This message has been edited by jaybird (edited 07-19-2004).]

BillH
07-19-2004, 09:46 PM
Geez Forest, you trying to bum me out about my southbend?

nheng
07-19-2004, 11:09 PM
BillH: Don't get too bummed out http://bbs.homeshopmachinist.net//smile.gif Even if your cutting tool (or the work due to the tailstock) drops as you traverse the carriage, the error is down in the 5th or 6th decimal place UNLESS the wear on the front and rear ways is not equal or unless doing VERY small diameters.

If the front to rear wear is not equal, then the drop on one is immediately transferred to diameter error.

For example, a 0.002" drop of the cutting tool on a 0.250" diameter will give a radius of 0.1250160" instead of 0.125".

For a simplified view, the effective radius would be the square root of (drop^2 + radius^2) since you're just solving for the hypotenuse of a right triangle. That's why unless the diameter is extremely small, the drop is overshadowed by it when squared.

Feel better now http://bbs.homeshopmachinist.net//smile.gif

added - that was real clear ... let me know if you need a sketch

Den

[This message has been edited by nheng (edited 07-19-2004).]

jfsmith
07-19-2004, 11:17 PM
I start with a dead center in the tail stock and a precision dead center in the chuck. When those two are touching tip to tip, then you can get the "mikes" out and start doing the rest of the alignment.

The lathe I just got came with both center, and had the specs for the alignment. So I did the same thing with my old lathe, which didn't come with any centers or documents. It is now aligned and it was easier this way.

BillH
07-20-2004, 10:12 AM
The 2 things that concern me on my lathe is my tailstock and chuck backplate.
I can align the tail stock centered with the headstock, but if I move the tailstock ram out, it moves to the side and down.
As for the backplate, I had to turn down the shoulder since the south bend has a very short spindle. I flipped the back plate around, and tigthened it against a ring I made. Unfortunetly this ring was not perfectly flat as I found out. Now both sides of the back plate are out of phase so to say. No matter how many times I flip it around, and turn both sides to get them flat again, Im affraid that my zero changes by how tight the backplate is tightened. If I zero a piece in the 4 jaw chuck near the jaws, I can get it to within .001, but if I move the dial indicator a few inches out, it changes to .002 or .003. Its enough to annoy me.

Dave Opincarne
07-20-2004, 12:09 PM
Lots of good information on an important topic. But as I'm reading I'm also recalling the stories of the machinists who knew their machines shortcomings and how to compensate. I'm not suggesting that we shouldn't strive to tune our equipment as acuratly as possible, only that we not let it become a crutch or excuse for not developing a more simbiotic relationship with our equipment. I used to use an old and well used Logan 10x24 when I was working on composite tooling. If I needed to turn an accurate diamater the whole leangth of a long shaft I new that as I neared the headstock I'd have to lean in on the cross slide starting with gradual preasure about 8" out and increase as I got closer to the headstock.

That being said, I have an EMCO V10 mounted on the original sheet metal stand. Making the stand as level and ridged as possible greatly improved the ability to level the lathe. I do use a Starett machinist level to tune the lathe, so having the stand level to begin with is a must for this method. Spirit level aside, having a ridgid lathe stand is a must, otherwise any adjustments will flex the stand as much as the lathe. I began by installing Hilti anchor bolts into teh concreate slab. The stand is suspended on each anchor bolt between two nuts and washers. Adjusting the nuts alows me to level the stand. After I did this I still found that the lathe did not feel very stable on the factory stand. Further investigation showed that the stand was essentialy two sheet metal boxes open on the top and bottom. A strap was welded across the top to mount the lathe and a cover that was loose, being captured by the mounting bolts. By pushing the lathe for and aft I was able to see the boxes twist (torsion). Even if the lathe was relativly stiff any attempt to use the level would be negated due to the uncertanty of the error thrown in by the flexing stand. I removed the lathe from the stand and welded in a heavy guage gusset at the top of each box. I can now place the level on the lathe, push hard against the stand and observe less than half a gradation's movement in the bubble. each gradation is aprox. 0.002"/ft.

Dave