I've been looking at videos and explanations online on how to align the tail stock. All recommend using a dial indicator on the front and back of the quill and adjusting the tail stock so the readings are equal. However, all only take a measurement at one point on the quill.
Maybe it's just my lathe... I see the two set screws are used to move the tail stock perpendicular to the headstock. The top of the tail stock has a channel that rides along a raised matching 'tang' on the base of the tail stock. However, this doesn't appear to be ground to any precision so I can actually loosen both set screws then grab the top of the tail stock and rotate it slightly in both directions on the lathe.
It seems this could produce an angle where the axis of the tail stock is crossing the axis of the headstock. Then by measuring just one point on the quill all I'm potentially doing is making it so the distance on both sides is the same but the the axis are actually still crossing each other. In essence I'm just centering the quill to the axis of headstock where I happen to have my dial indicator but the two axis are still crossing. This would mean that any live center/dead center/drill...would actually be off center wouldn't it?
Seems the solution would be to measure the front and back at two spots on the quill and ensure all four readings are the same.
Extend the quill about half way. Mount an indicator to the carriage and move it along the quill. That will tell you if the quill is parallel to the bed. Then mount a precision bar between centers and move the indicator along it. That will tell you if the tailstock is coaxial with the spindle. If I understand your machine description you may have to go through several iterations until you have both alignments correct.
Frank Ford has a very simple method to check tailstock alignment. Running the quill in and out should reveal any serious axial alignment problems, too.
If this simple test reveals anything but minor misalignment you will probably want to get out the gages. This topic was recently discussed on another forum here: Newb help with tail stock alignment
Thanks guys. I guess my question wasn't so much about how to do it, although I appreciate both suggestions, but rather the multiple video's and posts I found that don't seem to take into account that taking a single reading or not ensuring the quill is parallel to the bed first can still create a misaligned setup. I found at least 10 web sites/video's with instructions and none of them took this into consideration.
Is it perhaps so insignificant that it typically isn't a problem?
It should only be an issue when rebuilding a lathe and for checking at the time of manufacture. But if there is possible angular play then it will be an issue every time the tailstock is set over. If that's the case, it might be worth dismantling it and seeing what can be done with shims/gibs/scraping/machining.
You have a problem. Should be no play in that key.
Originally Posted by 72Zorad
Hmm, had a pic I was going to show, it was on metalworking.com/dropbox but thats apparently vanished into thin air.
More or less it was a section of 2" black pipe, 1/4" dowel pin welded to OD with some sticking past the end of the tube. Nothing precision about any of it. Clamp test indicator to the dowel pin. Clamp pipe in the chuck. Now the DTI rotates with the alignment of the spindle. Do a circumference check on the quill with most of it inside the body as that's where you will most likely use it.
Then you can extend the quill and check two "rings" or check with respect to the carriage. It may be easier to visualize what's happening with the test indicator on the carriage.
I have a tailstock with similar play. I don't know WTF the previous owners did to it (exactly) or WHY, but I have got to fix it for REAL, one of these days.
I would like to mention the tailstock is not really faulty here.actually offsetting is only necessary when setting the machine up to
turn a straight ,parallel diameter,such as a shaft for example.
This spline that is machined into those mating surfaces is what resists the thrust against the tailstock,It is more than likely squarely
cut and bearing evenly where it needs to.
When turning most tapers,at least the more usefull ones such as morse tapers,NPT threads,API threads etc,etc,you really can't use the tailstock offset method anyway.It is necessary to use the taper attachment most of the time.
The point I am getting at is ,as far as worrying about whether your tailstock works nicely in an admittedly alien direction,I think you need to get it turning a parallel shaft and leave it as is.
Unless you work as a gunsmith or do other such "decorative tapers" you are'nt gonna make much money offsetting your tailstock.
Thats just my 2 cents worth,but it was free.
I work as a gunsmith and use the modfied boring head for tapering barrels. It is more important to keep the tailstock aligned for chambering work.
"Lofty" in post #6 has got it right; there should be no play in the transverse way and slide, it should be a light interference fit. I've had a couple of lathes with that problem and it's not an easy fix. Perhaps the easiest way to correct the situation is to make the correction on the TS bottom; is to mill out the male section, if this is the case, deeper, and install a piece that is a light interference fit in the female; or if the bottom is the female, is to cut the slot wider an install a piece that will give you the same results- a light interference fit.
The big problem with either fix is maintaining the alignments with headstock. I recommend that you get a copy of Edward Connelly's "Machine Tool Reconditioning" book, which goes into great detail about the alignments needed.
Only one true way to alighn a tailstock. Have a piece of material 12" long in the chuck and with the center in place. Take a 1" long cut at the tail stock and a one inch cut at the chuck. Measure and this will show how out it is. Using the 2 screws reset the tailstock for half the difference nad recut. This is also a method for cutting tapers using your tailstock if a taper attachement is not available.
I'm glad this topic came up as I was just thinking about this issue this morning. Seems my problem is worn ways, and the center will drop depending on where the tailstock is positioned. Yeah, sucks.
I would truly like to have the ways re-ground on my little vintage South Bend lathe. I have resorted to brass shim stock under my tailstock (curling them up on both ends of the tailstock keeps them from sliding out).
Ultimately, I put a collet in my headstock, pull it in to where its a nice sliding fit with a precision rod. I then mount the precision rod in the tailstock. When I can obtain that same, nice sliding fit pushing the tailstock towards
the collet, then I'm satisfied with my center. Not extremely precise, but good enough for the kind of stuff I do.
This is also how we used to set our lathes to cut straight.
Originally Posted by Ursuskoolus
Put a precision rod in the chuck and turn a point. Reverse the rod and with a pointed tool bit cut a tapered cavity ( similiar to a center drilled hole). By cutting the end for the tail stock the rod will be quite accurate. Then pull the rod out aways out of the chuck and put it in the tale stock. Put an indicator in on the cross slide then indicate the top then the side. Repeat this several time and you will get it dead nuts. The trick is to cut the tail stock end and not use the out of center tail stock to center drill.
I also use the cutting the center drill hole when drilling .015" or below holes to keep them straight. I hold the drill in a hand vise, using oil, drll and clear the chips. The smallest I did was a .010 hole that stayed straight thru 3/16 steel.
The lathes at work have a set screw parallel with the bed that pushes the tailstock tight to the front of the keyed slot as well as the two screws to move it sideways. So look below the handwheel near the split line, it may just be backed out. May also be possible for you to put one in. Mine at home has a tapered gib in the keyway to keep it tight.
Checkout post #25
Chamber reaming between centres
Speerchucker uses a centerfinder to align the tailstock - fast and very clever.
This is basically how I was taught with one addition that prevents chuck/taper run out from compounding the error into the tailstock alignment.
Originally Posted by Ursuskoolus
Take a 12" bar like he said, center drill both ends.
Chuck another 5" bar. Cut a bit off the od of 3" to make sure its round. Flip it around and chuck the newly turned shaft . Turn a "bull nose" or true point small enough to fit into the large center drill on the 12" bar.
Then do what he said using the "turned in place" point as your center. Since it was turned in place it its true to the spindle. It can be re-used as long as you take a light cut of the angle every time.
If you're not familur with the theory- after taking a bit off each end if the tailstock end is smaller than the head stock then the tailstock is pointing towards you. (that really is for archival purposes since it doesn't address the "up/down" error.
Setting up a lathe for accurate work is a step by step procedure. Step 1 is leveling the bed. Step 2 is aligning the headstock with the bed. Step 3 is aligning the tailstock ram centerline parallel with the spindle centerline, both verticaly and horizontally. At this point we can trust that the ways/carriage are aligned with the headstock centerline, so we can use a dial indicator between the tool post and tailstock ram. Step 4 is to make both the aformentioned centerlines coincide both verticaly and horizontally.
If you try to start with step 4 and it turnes out that Steps 1, 2 or 3 (or any combination of them are deficient, you will be surprised to find that the tailstock is accurate only in the same spot it was clamped down when you aligned it, but walks off speck in other positions. If steps 1, 2 and 3 are properly done, then using a homemade test bar, between centers alternate test cuts and adjustments to the top part of the tailstock until fresh, light test cuts with a sharp tool give you the same diameter on both bands.
The only thing left then that will affect your accuracy is wear on the ways and that only if one way is worn more than the other to give the effect of a twist in the ways. All variables are much more important horizontally than verticaly, since you are cutting at or near the vertical centerline of the workpiece.
Step 1 is usualy acomplished with a high precision level and is a subject all it's own.
Step 2 can be accomplished with a test bar and trial cuts also, except that the bar is chucked on one end and free on the other.
Step 3 may involve shimming the sliding surfaces between the top and bottom castings of the tailstock, until a sensative dial indicator set up in the tool post will read zero both on the top and the near side of the extended and clamped tailstock ram.
This isn't confusing as it sounds, if you take the time to visualize what is happening at each step..