Aligning a lathe headstock

[lane]

Been their done that. Beg ,borry ar steal a precision level an level the lathe ,length wise AND cross ways jest in front of the chuck an at the end make shure the tops of the v ways frpnt an back are the same hight to start with, if not set the level on parallel`s on the front an rear flat ways get it level.Tahe test cut on piece of meterial about 1.250-1.500 dia hanging out of chuck about6-7 inchs. IF tail stock end measures big. set level at tail end cross ways an raise frontjach bolt at tail stock end if big at chuck end raise back bolt at head stock end .You can make it cut straight with in 2 or3 10th of an inch.

[Cardhammer]

Hope this isn't too basic of a question, but here goes. I have a JET 12x36 lathe in my home shop that I have had to realign the headstock (I mean the part with the chuck and spindle in it) in relation to the bed. Making some test cuts with a piece of steel bar about 1.5" diameter that extended from the chuck about 6" and using a lot of patience and little luck I was able to get to the point that on the end of the stock (about 5" or 6" from the chuck) the diameter was about .001" less than at the chuck. The stock was some sort of unidentified steel. I took cuts about .010" deep and fed as slow as the automatic feed would go to minimize any possibility of stock deflection. I also made multiple cuts between adjustments and the diameters were consistantly off by pretty close to the same margin. I was measuring with micrometers to 4 decimal places for my checks. The surface finish was pretty good.

This is probably plenty close enough for anything I will be doing for the forseeable future. My question (finally) is, ignoring any stock deflection, how close to no taper should I be able to expect to achieve? Will a good lathe go as low as "tenths" in taper. I want to know just in case I decide to try to improve my adjustment. If anything, because of stock deflection, shouldn't the diameter increase (slightly) as you travel away from the chuck? Do you adjust the headstock somewhat angled "forward" to compensate for spindle and stock deflection? I haven't checked with an indicator across the top of the stock to see if the spindle is aimed up or down. Is this check necessary? For what it is worth I am a self taught chip maker (I wouldn't dare call myself a machinst). I learned the hard way, by breaking a lot of cutters and starting over a lot.

Thanks for any help. I have learned a lot by reading the postings on the site.

[J Tiers]

Just as a point of information, did you "level" the bed of the machine first?

While "level" isn't important, it is a great reference for getting the whole bed to be straight and parallel.

Most issues with taper turning like that are due to twists in the bed.

Deflection in the stock normally makes the far end larger, and usually isn't much of an issue with thick stock. Most machines don't have adjustments for H/S "aiming" (they are scraped-in if anything), but I have heard that some asian ones do.

If the H/S aims up or down, then depending on the direction , amount, the stock diameter, and what the cutter is set on-center with, it is possible to get small tapers either way.

If teh H/S pointed up or down, and the cutter were on-center at the end of the work, it could turn tapered smaller at the end. If the tool were set centered at the chuck, it could turn tapered the opposite way.

But I think the first move should always be to use the level to check the bed. Only after that can you be sure you have a decent standard to compare to.

As a point of comparison, after leveling as well as I could with a medium sensitive level, then fine adjusting with a variation of your method, and "sanity checking" with the level again, my machine turns to about 3 tenths in a similar distance.

[This message has been edited by J Tiers (edited 02-22-2006).]

[Cardhammer]

By leveling, you mean across the front and rear ways (x-axis?), not necessarily along the length (z-axis?) of the bed? No, at this time I don't have the means to accurately check the levelness (if that is a word). I will have to look into that further before I try to improve my adjustment.

Thanks for the info.

[Scottike]

If your using a 3 jaw chuck your doing good!
If it's a collet chuck it's not bad. From what I understand, Most Cheaper 3 jaw chucks are doing good if they're within .003" If it were me, I wouldn't trust anything except a collet chuck for what your trying to do, but at any rate, being within a thou at 6" from the chuck should be great. I can get mine there if I play with it and breathe right.
Not to hijack this post but maybe I'm doing something wrong?

[This message has been edited by Scottike (edited 02-23-2006).]

[J Tiers]

Actually, as long as you turn at least a section at each end, and the chuck holds securely, the off-centerness of the chuck is not part of the equation.... you re-centered by doing the cuts. If the ends are the same diameter, you are "on".

I like a piece that has a chuck spigot, a 1/4" or so wide raised ring, a section of smaller diameter, and another section of 1/4 or so ring, counting from chuck end of the piece.

Then you can take a cut over the ends without waiting to have the whole middle cut, and you are sure you don't have tool wear.

[Cardhammer]

Yes, this is with a three jaw chuck. I don't think I can use collets on this lathe. For what it is worth, this is a lathe that I basically got for free. It needed a motor, a gear and a bit of TLC to revive it. The gear train is a bit noisy, but otherwise it works great. It also had new feed screws and nuts for the cross slide and compound feed. I think .001" taper at around 5"-6" is probably going to be acceptable for most of my projects. I was just wanting some input for future reference. I may try to get use of a precision level later and try to improve the alignment, but for now this seems OK.

Thanks for the input.