A discussion got started on the IAP pen turning site and so far not any good answers have come forward. So I thought i would post the question here because it does have merit. Now the lathe refered to there was the Jet 1014 but the question can be applied to any lathe.
When you go to test a lathe you push the tailstock and headstock together and check the points using a steb center or other centers. Now if they line up perfect you are saying great. But what happens when you slide the tailstock back, is there a way to check if the points still line up perfectly that distance away. Maybe the ways are machined out of wack. Is there a way to check intermediate points as well??? If they are not lined up what would be a cause and what would be a fix??? Does this happen often and how many people bother to check this??? Thanks for the replys.
Wood lathes are not "super" precision machines (like a Hardinge toolroom lathe, for example), so an "eye ball" test is perfectly suited to verify the alignment.
With centers installed on both the tailstock and headstock:
Crank the tailstock out to its maximum extension (but with a 1 to 1-1/2 turn of thread still engaged).
Slide it up to the headstock and clamp it down. Observe how the two centers meet point-to-point.
Note any misalignment. Retract the tailstock as far as it will go without ejecting the center (if you have a model that self-ejects). Slide the tail stock back to the headstock to see if the two centers meet point-to-point. Note any misalignment.
If the two centers meet point-to-point in both tests, your lathe is aligned good enough for the most part. You could still have some misalignment in the headstock, for example, but it's probably not a big deal.
If the two centers are misaligned the exact same amount in the same direction in both tests, the tailstock (or maybe the headstock) is offset from the spindle centerline. Fixing this could be somewhat involved. Same goes for a condition where the two centers are misaligned different amounts. In that case the tailstock is askew.
The time to do this test is before you buy, so you can pass on any machine that isn't reasonably aligned.
Most lathe beds are pretty straight, but the gap is usually less than perfectly machined. There has to be some clearance for the tailstock to slide. The issue is typically the gap is too wide in some spots and the tailstock can lock down askew from the spindle centerline. Is a this a big deal? On long spindles it shouldn't be, but stubby parts between centers can be really sensitive to misalignment.
If your lathe bed has some slop and the tailstock can be angled, you have to work out the "sweet spot" that when held just right, it will lock down more or less lined up.
(How do I know these tricks? I used to own a Grizzly lathe.)
It seems to me that a lathe that has a sliding headstock could have several places along the ways to check alignment.
I would slide the headstock almost the where the end is and check it there, then again in the middle, bringing the tailstock up to the middle as well, and then to the other end, bringing the tailstock up to that end as well.........If you see points not aligning on any area, then go through the bed leveling process.
A level bed end to end and front to back is a must, especially for larger lathes. This proceedure should tell if the ways are machined correctly or if a shim is needed on the tail stock or head stock.
I know how I check it on a metal lathe but not sure it could be done on a wood lathe. You mount a bar between centers (after facing it off and center drilling it) and turn it from end to end. Of course your using the cross feed to do this which we don't have on a wood lathe. Measure the bar with a dial indicator at the headstock end. Then flip the bar over and measure. if it's off then the tailstock is off. In this case the tailstock can be adjusted until the bar is running true.
Using a wood lathe I think it would be enough to simply check the flatness of the inside and top portion of the lathe bed with a good straight edge. If both areas are flat and the tailcenter lines up when you slide the points together then I think it would be fine when move out.
Now that does not take into account any diagonal tilt of the headstock spindle itself or even if you had dirt under the headstock tilting it upwards or out a bit. I had that problem once with my Nova with the rotating head. In most cases I think this would not matter at all. However it might matter if you were turning things mounted solely in the headstock. A good description would be if you could use a lazer gun sighting tool. When mounted in the headstock it could miss the tailstock center even if the bed was perfect and the tailcenter alignement was perfect.
What we need is a good #2 morse taper tool with a lazar centered in it. This would check for that kind of misalignment.
Another tool that might work is the double morse taper that is sold to align lathes with rotating headstocks.
Is there a way to check intermediate points as well??? If they are not lined up what would be a cause and what would be a fix??? Does this happen often and how many people bother to check this??? Thanks for the replys.
The headstock on my lathe slides and swivels which is a wonderful feature, but when locked down, it doesn't always line up perfectly. The alignment is a little bit on the sloppy side and for many turning operations, perfect alignment is unnecessary. The only time it has been a problem, is when I turn a foot on a form between centers and against a faceplate or jamb chuck. Only 'between center work' is affected.
When perfect alignment is required, I check alignment by firmly clamping one end of a 2" x 2" x 10" piece of wood in my chuck along the axis. With the lathe spinning and the tool rest in place, I mark a bull's eye on the end of the 2" x 2" with a pencil. This extends the location of the axis of the spindle out to the end of the 2" x 2" stock. I usually make a 1/8" diameter circle for the bull's eye. At this point, I can slide my tailstock up to the bull's eye to check alignment.
The bed of the lathe could be twisted. If the lathe feet are not "balanced" then the lathe bed can twist. Poor construction can result in a twisted bed, which is very unlikely. You can adjust the lathe so that the bed is level front to back along the length of the bed and level along the length of the bed.
The drive centers could be off. This is to say that the points don't run true. Having a selection of centers can help eliminate this possibility from be a source of error.
The centers might not be fully seated. It is a good idea to mount a hunk of wood between centers. Turn the lathe on a slow speed and advance the live cent to be sure the centers are well seated in the headstock and tailstock.
The MT of the headstock may not be centered in the headstock spindle. You would be surprised at how often the MT in the headstock spindle is off. You can check this with a dial indicator. While you are checking the MT check the spindle for runout.
The simple way might be to mount a laser pen in the tailstock. This could be easier than you might think. Think of ways that you could mount a revolving laser in the tailstock with some "micro adjustment".
Robert I had the headstock alignment issues when I had the Nova 3000. What I did was to align it perfectly once. Lock it down really good in this position. Then I took a drill bit and drilled a hole exactly on the joint between the headstock and lathe bed. Visualize a half a hole in each piece. Now whenever the headstock was twisted I could go back to the original position by simply aligning the headstock until the drill bit slips back into the same hole. This worked perfectly every time. It also helped keep the headstock aligned while tightening the bolt. I found it would sometimes slip before I did the hole alignment thing.
We have discussed this problem at length on this side of the Atlantic.
The solution we use is to turn a cylinder, with a morse taper at each end.
We put one in the MT of the headstock and the other in the tail stock. THis should allign the tail stock.
Of course, if it does not match that means that you have one or more of the problems written in the previous message
Put a block of wood in a chuck length to suit you.
clean the face.
put some non revolving center with a point in the tailstock.
turn on the lathe advance the point of the center slowly to the wood so that it just touches it. You will either scribe a circle with the point or a point.
Point is good. big circle bad. small circle not so bad.
The center point at a specified distance is critcal for supporting a thin stem goblet. drilling an accurate hole and a few other things. Most of the time close is good enough for wood.
Last edited by hockenbery; 01-07-2011 at 08:08 PM.