Made a simple gizmo - lathe is not in alignment

WobblyHand

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No surprise to most everyone here, my mini-lathe isn't in alignment. I cut a simple 6061 rod, trimmed it to diameter and drilled a hole in it using the lathe. I then tapped the hole by hand. The screw is loose. Now, I've used this 8-32 tap before, just a few days ago, and it cut a decent set of threads, that were ok. (Slightly loose) The difference is in one case, I used my lathe to drill the hole, and in the earlier case, I used a drill press. I used the same #29 drill. The lathe drilled hole is larger diameter than it should be.

So I checked the alignment of a MT3 dead center in the spindle and a MT2 dead center in the tail stock and they seem to be kind of far apart. Like guesstimating 0.01" in height and about the same in displacement. It's noticeable by eye. It seems that the tail stock is higher than the spindle, which from reading - isn't good. By that I mean, I can't shim the tail stock and be done with it.

I found this thread https://www.hobby-machinist.com/threads/mini-lathe-tailstock-alignment.30208/ by @petcnc on this subject. I've read it about 4 times now, each time understanding a little bit more. I thought I had access to the lower adjusting bolt #1, but I just don't have a long enough 4mm key to be able to really tighten and loosen it effectively while the tail stock is on the ways. So I think I'll have to do some of his modifications.

Reflecting on this, I don't actually know that my spindle is aligned to the ways correctly. How can I check that?

Assuming that it's close enough, then I should proceed with the thread above?

Down the rabbit hole I go...
 
Does it change with the TS quill extended and retracted? Height difference should only be acouple tenths 3-4 I beleive. Have you cleaned and checked the mating surface to ways and surfaces on upper and lower parts of TS? And that the halves are tightened down to each other with the lock screw?
 
I haven't measured that yet. The quill was slightly extended, only 3/4" or so. I did clean the ways and the mating surface of the TS to the ways. Not sure what you mean by the halves. The TS was locked down when I did the measurement. I also remembered to clean the inside of the MT sockets as well as the tapers on the dead centers. One other thing I did was to remove the TS DC rotate it 180 degrees and try it again. No significant change.

I'll take things apart again to check for swarf, etc. and check with the quill extended and retracted.
 
Cleaned everything up. Didn't find any obvious problems, but cleaned all the surfaces anyways. Locked down the tail stock.

The quill can extend around 2.5". I mounted the indicator on the carriage and ran it along the top of the extended quill. The tail stock end of the quill is about 0.002 to 0.0025 higher than the extended end. It varies roughly linearly along the way. I used 2 different dial indicators, my Harbor Freight one that measures thousandths, and one I got from my late Dad that measures tenths of thousandths. They basically agreed with each other. (To the extent that they could given that one indicator has 10x the resolution)
 
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Umm, remeasured. Apparently I wasn't thinking to clearly. I had forgotten to snug the quill. Along the top of the quill, when the quill is locked is 0.0002". If the quill is totally unlocked, it droops 0.002" due to gravity. In my measurements above, the quill was totally unlocked and loose. If the quill is slightly snug, so that it can still move via the hand wheel, then it's back to 0.0002-0.0003". Redoing the dead centers with the slightly snug quill still shows a slight tilt in the vertical direction, say 0.25" from true vertical. (6" rule, points at 4", 0 almost touching the saddle) Side to side there is a twist, or horizontal tilt. It's a lot more. If you view from overhead, the points are off. If I attempt to rotate the tail stock, by pushing the tailstock away from me, I see a slight movement of the point towards me.
 
The tailstock should have two pieces. The base part which mates to the ways of lathe. Then the upper part which holds the quill. The upper half can be offset to correct taper. There is a locking bolt that holds these two halves together beside the two bolts that allow side to side of tailstock. after making adjustments I’ve forgot to tighten that bolt which changes the measurement of the height of tailstock.
As you found you want to take measurements with quill lock snug. Sounds like the fit between the quill and TS are alittle loose. The quill should not be able to spin in housing. A sloppy fit of the key is the fault.
From your description it sounds like the tailstock is pointing downward chuckside is lower than handwheel side of TS?
 
The tailstocks that come with minilathes are notorious for being poorly aligned. I'd be surprised if you DIDN'T need to adjust it. Mine was so bad I broke off the tip of one of my spotting drills when I tried to use it!

FYI, the vee in the tailstock base often is poorly machined, which can lead to reproducibility problems. The sides, not the top, of the vee need to be in good contact with the bed's vee. For starters, make sure there aren't any globs of paint or debris stuck to the vee or back reference surface -- that will really cause problems in getting repeatable alignment. To check how good the contact is, you can mark the base's vee with a sharpie and run it back & forth across the bed a few times. Areas where the sharpie is gone indicate the contact points.

I cleaned mine up by cutting some strips of PSA-backed sandpaper to the same width as the vee, stuck them to each side of the bed's vee and ran the base back & forth over it a few times to increase the contact area some. I also shimmed the back reference surface so the front and back of the bed were the same height, so both sides of the vee were in equal contact. The idea was to just improve the contact area, not make it perfect.

Don't lap the vee -- that will alter the bed as well. You want to use the bed as a reference surface. After you're done make sure to thoroughly clean both the bottom of the base and lathe bed to remove any grit that was knocked off the sandpaper.

For another take on addressing problems with the tailstock, see here, about 1/3 of the way down the page.

To get the tailstock exactly parallel to the bed also may require shims. I had to use them on mine to get rid of the vertical height variation as I extended the quill.
 
The tailstock should have two pieces. The base part which mates to the ways of lathe. Then the upper part which holds the quill. The upper half can be offset to correct taper. There is a locking bolt that holds these two halves together beside the two bolts that allow side to side of tailstock. after making adjustments I’ve forgot to tighten that bolt which changes the measurement of the height of tailstock.
As you found you want to take measurements with quill lock snug. Sounds like the fit between the quill and TS are alittle loose. The quill should not be able to spin in housing. A sloppy fit of the key is the fault.
From your description it sounds like the tailstock is pointing downward chuckside is lower than handwheel side of TS?
Sorry about the delay. I've been having trouble actually measuring things. My indicator holder is no good, ie flimsy. Have been struggling to measure stuff. Hard to quantify the problem if the measurements are not repeatable. Made a hack dial indicator holder out of 1/2" CRS and a dial indicator clamp. This is much more rigid, but there still are too many degrees of freedom. I'm already designing V2.
IMG_20200110_154404.jpgIMG_20200110_154029.jpg
V2 will have a hex instead of round, so I can get a wrench on it. Also I will screw a piece of 3/8" x 1.25" steel to 3/8" squared stock, to form an "L". Then drill the longer part of the L to mount the hex on one side and the indicator on the other.

It would be nice to mill a slot for the hex into the L, so it wouldn't rotate. Alas, I don't have a mill. Shoot, if I had a mill, I'd mill the L rather than bolting it together.

From your description it sounds like the tailstock is pointing downward chuckside is lower than handwheel side of TS? Yes
 
so the tailstock is pointing downward but is still .0002 above center line. Maybe extend the quill and lock, then shim to get parrallel with the ways of machine. Then compare the height to a center in the spindle. Then see if the amount can be taken of the mating surfaces of the two tailstock pieces?
 
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