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cuemaker
02-22-2005, 11:35 PM
Need help with tailstock alignment.

I am now cutting a 5 inch crs which is now at .844 thick. Using my Mitutoyo dial calipers (.001) I get the exact same measurement at the front, middle and end of the stock and all around the bar too. And if there is a difference, I don't see it.

Now, when I use a live center with the tailstock, I get a taper.

Question #1 When using a live center, is it best to drill a small center hole?

Question #2 If you do use a center hole, do you mark out the hole, or having a (in the future) dialed in tailstock use it with out laying out a hole first

Question #3 Best way to align a tailstock.

My live centers do not have a carbide tip.


Thank you for your help.

precisionworks
02-23-2005, 12:29 AM
Cuemaker,

When you posted yesterday about lathe leveling, this topic came to mind, as the two go hand-in-hand.

Question #1. Yes, using the size center drill appropriate for the diameter of the stock being turned. Center drill sets containing #1-#5 cover most needs, here's one source (scroll down to combined drill & countersink sets):

http://www1.mscdirect.com/CGI/NNPDFF?PMPAGE=138&PMK0NO=00000414355


Question #2. Whenever possible, mount a drill chuck in tailstock & use it with center drill.

Question #3. You'll need a good, sharp-pointed dead center to mount in the headstock & the tailstock. Bring the tailstock up to the headstock, lock tailstock down. Advance tailstock ram until points nearly touch (I use OptiVisor to see clearly). If they don't align perfectly, adjust tailstock offset to realign.

Sound like you've already leveled the machine, this is the last step to "straight" turning.

------------------
Barry Milton

BillB
02-23-2005, 02:01 AM
Question #3:
Chuck a test indicator in the headstock, in a collet if possible, with the tip bearing on your tailstock center. Rotate the spindle by hand and use a mirror (unless you _like_ standing on your head) to read the runout. Don't be surprised if you find it's off a bit in the vertical plane as well.

BillB

speedy
02-23-2005, 06:28 AM
Another method and in the same vein as setting up tooling.
Dead centre your headstock and tailstock. Bring your tailstock up to the headstock and lock it in place. Now, have a piece of flat plate or a rule will do,place in front of the h/stock centre, advance the t/stock until it contacts the rule . The inclination of the rule will tell you the position of the t/stock in relation to the h/stock in both planes and you can adjust accordingly.

I like your idea BillB.

cheers, Ken

Orrin
02-23-2005, 12:02 PM
All the suggestions you've received are good ones. The one that gives me the best results is to put an indicator in a collet as has already been suggested.

I got tired of using a mirror, however, and Have switched to using a Blace co-axial indicator. It is slick!

The first time I did this I was shocked to see the amount of vertical mis-alignment. I've since shimmed up the tailstocks in all my lathes and as a consequence many of my deep hole drilling problems have gone away.

Regards,

Orrin

precisionworks
02-23-2005, 01:53 PM
No way, thought I, is my tailstock vertically out of alignment...so on goes the little B&S dial test and ARGGHH!?*#@...it will be done soon...thanks for the tip.

BillB
02-23-2005, 07:45 PM
And when you think you've finally gotten it just right, check again with the tailstock locked at different points on the bed, and with different extensions of the tailstock ram. I'l join you in hoping that your ways & tailstock aren't as worn as mine.

Obviously, I don't turn between centers often, or I'd have to start scraping. As is, I just shim for the most used distance & extension, and use a chuck mounted on the QCTP for drilling.

BillB

BillB
02-23-2005, 07:55 PM
Almost forgot, your idea is great too, Ken. I use the 6" rule all the time for finding/checking center height of lathe tools, but never thought of that one. The best ideas are usually the simplest ones, and they're usually the hardest to see.

BTW, I read somewhere that some mfgs send new lathes out with the tailstocks a bit high, so that they will wear into perfect alignment, and be closer to correct for longer. Can't say if this is true as I have no personal experience with the "new lathe" concept.

BillB

nheng
02-23-2005, 08:28 PM
Harrison specs the tailstock limit to be 0.001" higher than the headstock center at the end of a 24" test mandrel.

Mori Seiki specs it as 0.0008" high, period.

Den

cuemaker
02-23-2005, 10:48 PM
Thanks for all the reply's. I already knew that my tailstock was low. I dont see how to set it higher and dont know where to add shims, but I havent spent much time on this yet.

I will perform the dial indicator in the collet test soon. I am expecting lots of fun (read frustration)

I may need to have my indicator worked on. I noticed its "jumpy" as opposed to smooth. Its a Mitutoyo .0001.

Do you sent it back to Mitutoyo for calibration?

hamerhead74000
02-24-2005, 05:03 AM
Re: Question 3 -- Make an alignment bar - take a length of drill rod 1/2 to 1 in. diameter (the largest you can easilly get that will fit through your headstock), check that it's not tapered (shouldn't be , but I've seen stuff wind up in the wrong bin before, and you're making a precision tool here), chuck it *exactly* centered (use the 4-jaw and your dial indicator) with about 1/4 in. sticking out, and drill a center hole in each end (remember: if it's sticking out the back end of the headstock, go REAL SLOW rpm-wise!) Then, put a dead center in the headstock, your live center in the tailstock, and your dial indicator on the cross slide (perhaps in the tool post if yours will accept it - I have one mounted in a tool holder for my quick-change post just for this purpose), and the new alignment bar between the centers. Run the dial indicator across the bar, and adjust to zero runout across the bar. Also, rotate the spindle and bar and check that you are getting zero (or at least minimal) runout. Because of tolerance-build-up and wear, it is probbably a good idea to make several alignment bars, for the various tailstock distances you might be working at. With this setup, alignment can become a 30-second procedure. :-)

sradel@ncresa.org
02-25-2005, 12:00 PM
The vertical alignment of your tailstock should not be a problem if you are just turning a diameter. Your problem would be the X axis alignment.

To align a tailstock with 3-jaw chuck:
face and centerdrill both ends of a length of round stock (8 - 10 inches would suffice)

Mount a dead center in the chuck. ALWAYS recut the dead center that is mounted in a 3-jaw chuck. The action of recutting (60 degree included angle) finds the exact center of the chuck.

Place the shaft in a lathe dog and mount between centers. Take a cut until you have a full cut diameter. Measure the shaft at the tailstock end and the headstock end. If there is a difference your tailstock is out of alignment.

If the measurement at the tailstock is larger than the measurement at the headstock your tailstock is moved to far back. Bring is forward 1/2 the difference in the dimensions (use a plunge type indicator on the base of the tailstock). If the measurement of at the tailstock is smaller than the measurement at headstock, your tailstock is too close. Move it back 1/2 the difference in the dimensions.

Using ground and polished round stock is also a good suggestion. Center drill both ends mount between centers. Mount an indicator and magnetic base on your carriage. Measure the run-out and move the tailstock accordingly.

[This message has been edited by sradel@ncresa.org (edited 02-25-2005).]

precisionworks
02-25-2005, 01:21 PM
SR, gotta take issue with you on tailstock vertical alignment. Say that your tailstock center is vertically 0.500" above the headstock center (or 0.050" or 0.005", the effect will just be less). Start the cut at the tailstock with cutter just touching. By the time cutter reaches headstock, diameter will be greatly reduced and you'll have a truncated cone.

nheng
02-25-2005, 08:59 PM
A 0.005" tailstock drop (or conversely, bed wear under a chuck) at one end of a 0.5000" bar would give 0.5001" at the opposite end, regardless of length.

If your tailstock is 0.5" high or low, it must be on the wrong lathe http://bbs.homeshopmachinist.net//biggrin.gif http://bbs.homeshopmachinist.net//biggrin.gif

[This message has been edited by nheng (edited 02-25-2005).]

precisionworks
02-25-2005, 09:28 PM
RH, the 1/2" I used was just an example...there are quite a few PhD's, engineers, & scientists that read these posts, & examples really help these people <LOL>.

Tom CPM10V
02-25-2005, 10:40 PM
SUGGESTION: don't overlook the possibility that the live center is defective -- the point is not on the same axis as the shank. Recently, my lathe was giving me tailstock alignment fits. Tried everything I could think of ... and in time came to realize that the point and bearing barrel/housing of the MT #4 live center were way out of alignment relativve to the shank. [It was a beautiful American-made live center that looked perfect and rotated oh so smoothly.] Bought a used live center at Cabin Fever, and all is well now.
Recently told the tale to my favorite, full-time machinist, and he had just experienced the same problem with a Morse #5, ... which he solved by buying a new Skoda.

happy02
02-26-2005, 01:51 AM
Why not just turn a piece of stock between centers and adjust the tailstock 1/2 the direction required by measuring the taper. Keep this up til you're turning the same diameter the full length. By the way check your dead center for the headstock with a dti to be sure that it runs true. You will be true for that distance...

[This message has been edited by happy02 (edited 02-26-2005).]

hammerhead74000
02-26-2005, 04:20 AM
>> Why not just turn a piece of stock between centers and adjust the tailstock

That works also, but eats stock each time you need to adjust it - I personally find it inelegant, and depending on what you are using, can get expensive if your tailstock is a bit balky. However, in a pinch... http://bbs.homeshopmachinist.net//smile.gif