The fixed datum line that you have to align everything to are the rails on the bed of your lathe. When you set your tailstock your movable quill has to run parallel to the rails as it extends out from the tail stock. When you set up your dead centre in the tailstock with your turned centre you should have repeated this with the quill fully extended ..You can set up a dial indicator on your carriage to measure the run out on the quill. One you have the quill parallel to the rails you can move the tailstock in or out to register on centre..(ball park figure) Also , you should reference your head stock to the bed rails..Put a length of straight bar in your colle t chuck then, use an indicator on the carriage to check for run out in that bar , side to side and up and down . Only when your head stock and also your tail stock quill are running parallel to the bed rails can you set a true centre line from head stock to tail stock. I hope your head stock is true as that is a bit more work to align! Good luck

Some here have the correct idea. If you're using a precision ground rod with centers on each end and rotate the shaft using a dial indicator. You're only testing the runout of the chuck and the runout in the live center. If you slide on a stationary shaft from one end to the other. You are testing if the tailstock is out of alignment. Not only can your tailstock be out of alignment, but the headstock can be out of alignment to the bedway.

good work man!!!! i gotta to mine! my lower section of my TS only uses the 2 rear grubs to lock it. so i am gonna build a custom plate and have it go all the way from edge to edge of the 2 Ways and use the 2 raised Vs as alignments so all i have to do is lock it in place.

Oh and I forgot to talk about the center in the tail stock being higher than the one in the chuck. It is totally fine if the tail stock center is a few thousandths higher than the one in the chuck. Some manufacturers build lathes like this, and they will wear in over time. So don't sweat the tial being up to say .005 higher than the chuck center.

Now Please don't take anything I say as criticism but let's stay focused on the tail stock. The tail stocks only job in life is to run true to the ways and the spindle, don't worry about drilling a hole yet. First step would be to take a light cut on some stock using the live center. Then measure the stock with micrometers on each end of the cut and see if you have a taper. if you do have a taper that's what the side to side adjustment screws are for on the tail stock. once the taper is removed back off the tail stock and extend the quill to the maximum working length and lock it with the lock handle on top. Put your mag base on the carriage and the dial indicator on the side of the quill and run the indicator back and forth or end to end on the quill with the carriage. This will show you if the tail stock is cocked or twisted and of course adjust the rear screws to correct anything you find. This will throw the first side to side setting off but it's how I do it and it will true up after a few attempts. Once the quill is 100% straight to the ways by checking it like I stated above, you no longer have to worry about the tail being the cause of any miss aligned holes you drill. Drill bits can and do wonder and are not for precision work. The deep hole you made for that roller, I would have drilled halfway from one end then flipped the part in the chuck and drilled the other half. You can also use a axial indicator to true up a tail stock for side to side but it will not tell you anything as far as if it is cocked, that's what the dial riding on the carriage will tell you. Hope that helps

You should just buy the Edge Tech tail stock alignment bar and follow their instructions, pretty straight forward and simple. ymmv

Would holding the material you are test drilling in a collet eliminate the possibility that your 3 jaw chuck is not holding the material perfectly centered?

;) Nice!

Some of the things you are measuring are not the things you want to measure. When you put the dead center between the tailstock and the chuck and spin it you are measuring either the run out of the chuck (when at that end) or the run out of your live center (when at that end). Nothing you can adjust on the tailstock will make any difference to that particular measurement, and in fact there is no way with that setup to even center the tailstock. Also, using a drill on a piece of stock to check center is also not actually measuring center. A drill will tend toward the center of the axis of rotation, and is pretty flexible, so your results are not a reliable indication of center. That is why precision hole placement cannot be done with drills and reamers, it must be done by boring. There are two things you care about, whether the tailstock quill extends parallel to the ways, and whether is on the same axis as the spindle rotation (centered). Centering doesn't really work until you know the quill travel is parallel. The most common way to center a tailstock is to put a reasonably long piece of stock between centers. It is done between centers to remove the chuck from the equation. If the goal is just to center the tailstock, then you leave an inch or so at both ends of the stock, relieve the center part 20 or 30 thousandths just to get it out of the way. Then you turn both of the sections you left at the endsjust enough to clean them up, but make sure you do not move your cross slide as you go from one end to the other. It needs to be a light pass, with the same depth of cut at both ends of the stock so tool pressure is the same. Then use a micrometer to measure the diameter at both ends. If the tail stock end is smaller your tailstock needs to move away from the operator half the difference, if it is larger then toward the operator half the difference. It is an iterative process, and you may need to relieve the center more if you cut the ends down to the center diameter. Start with a reasonably stout piece of stock, 1 inch is a good size. Aluminum is fine, because it cuts easier you have less tool pressure and flex in the lathe. It is possible you do not need the shim under the front of the tailstock anymore, since the block you ground down was holding up the rear of the tailstock, so the front of the tailstock would be tilted down, and the live center would have been lower the further it was extended. Measuring how straight the tailstock is to the ways in horizontal and vertical is a completely different measurement. The simplest way is to extend the tailstock quill, and set up you indicator on carriage, indicating either the front or the top of the quill, and traverse the carriage. if this measurement is off that means centering your tailstock is kind of useless, because the point of the center will move up/down or left/right as you extend and retract the tailstock quill. Those methods don't cost you anything but the piece of stock for the centering measurements. If you want to throw money at it you can actually buy a centering bar that has a precision ground diameter at both ends, which you place between centers and indicate the diameters from the carriage. This is basically the same bar you end up with when you do it yourself and have it adjusted correctly, except if you buy one it is probably hardened and should have a specified tolerance much smaller than +-0.001. You can also buy Morse Taper alignment bars that can be used to check tailstock alignment, the difference being that you will be measuring the alignment of the taper in your tailstock, not the travel of the tailstock quill. Theoretically should be the same, but that depends on the run out when the taper was machined in the quill. This same type of alignment bar can be used in the morse taper of your headstock to check how true the heastock is to the ways. Also, beware, chasing zeroes here feels really important, after all this affects everything you do that involves the tailstock. Just remember you have a lightweight relatively flexy lathe, and you have been successfully enjoying making stuff with it. Don't let the quest for precision ruin the fun of the hobby.

On a bigger hole, definitely try a boring bar(but thats a toolpost mount not tailstock mount, so it doesn't fix your issue), or if your chasing hole size accuracy, then maybe a set of machine type reamers?👍👌🇦🇺

Your comments seem to indicate you are missing the point. As someone else pointed out, rotating the live center has no relevance to the tailstock offset. The tailstock could be offset by 6", and your live center should still run true. There are a couple of ways you can align your tailstock, but as someone else mentioned, first you need to get your headstock and tailstock parallel to the bed ways. In any case, you should remove your 3 jaw chuck. Then you can either buy a precision ground round bar and place it between centers or else you can turn down a piece of round stock between centers and measure the amount of taper, adjusting the tailstock per its amount of taper. And yes, the Vevor tailstock is a real 0piece of crap. I have one, and it is junk. Putting all the adjustment at one end is a bad Idea. I am going to modify mine by putting a pair of steel plates on the side with fine thread adjusting bolts at the front and back so both the yaw angle can be adjusted to zero and the offset can be adjusted to at least 1" or so.

HI, YOU SEEM TO BE MEASURING THE RUNOUT OF THE DEAD CENTRE IN ROTATION USING THE CENTRE DRILL HOLE WHICH MIGHT NOT BE BANG ON CENTRE. IF ITS OUT IT WILL ALWAYS BE OUT NEVER MIND HOW MUCH YOU MOVE YOUR TAILSTOCK. WHEN I ADJUSTED MY TAILSTOCK ALIGNMENT I FOUND IT TO BE VERY AWKWARD AND TIME CONSUMING. I ENDED UP INSTALLING AN EXTERNAL ADJUSTING BLOCK FIXED ON THE SIDE, MADE THE JOB MUCH EASIER.

Is that piece of stock not a cylinder? Is it cone shaped so the side with more meat around the hole is actually bigger?

There is an assumption that your chuck is true. The tailstock adjustment seems like a minor hell there must be a better system. Better is better but I expect you will be coming back to this regularly as you get more demanding with your accuracy.

I would be more concerned with how parallel your jaws in your chuck are. Tailstock or bit issues you would feel drill drag, drill chuck wobble, oversize hole etc. Try your collet chuck.

You might be interested in Xynudu's quick tailstock alignment checking process near the end of the video kzfaq.info/get/bejne/b6ijdZaZqcmbdX0.html

A drill bit is just a ruffling tool, it’s by far not precision . Your chuck on a good day is probably off by 3or 4 degrees, try it with your collets, it will be better, and of course, I can’t get a straight hole with a drill bit 6 inches deep, I’d be lucky not to run it out the side of the part lol