Two Collar Test Method of Alignment

Halligan said:

So after seeing iwananew10k's video with the collars I wanted to do the two collar test found in HTRAL for tailstock alignment and compare it to that other method I showed. After levelling my bed and readjusting my tailstock by my original method I made and mounted a two collar bar between centers and took a cut. The bar is 12" long and the collars spaced two inches on center from the ends, I got a deviation of less than .001 between the headstock and tailstock collars the tailstock being larger. I tweaked the tailstock towards me about .001 according to my dial indicator and repeated the test with the results being both collars pretty much exactly the same or within a few tenths. The video can be found on my channel Here:

Two Collar Lathe Alignment Test - YouTube

Part 1- Making the bar
Part 2- Making the test cut @ 15:15
Part 3- Results @ 18:38

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SE18 said:

Also, I see you're drill didn't flex too much but one trick some people use that I've seen is to put a dog on the drill so the tail rests on carriage to prevent flex. Also another method is to press the back of toolholder against the bit. I haven't tried either method but probably will.

Dave

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SteveM said:

An alternate to the bar shown in the video is to use a piece of all-thread; the largest you can fit in the bore in your spindle. Yes, cheap all-thread from the hardware store (this method is for the cheapskate).

Chuck it up and center drill each end. Accuracy is actually not important, so you can just use your 3-jaw.

Then take two nuts and two large washers (you can make your own washers out of free-machining material instead of using the junk that washers are made from) and mount a washer maybe an inch or so from each end.

Put a dog on the end and mount it up between centers using a faceplate or dog driver to drive the dog (MUSH!).

Machine both collars to get them round and a nice finish.

What you now have are two collars that are concentric with the line between the two centers. This is why the accuracy of the centers with the all-thread is not important.

Now here's where it gets different:

Machine the collar at the headstock end a small amount in one pass. Do not move the cross slide or compound.

Pull the bar out, put the dog on the other end (I suppose you could use a pair (team?) of dogs) and then move the carriage to do the same pass to the washer at that end.

Now you have a test bar with two collars the same size. You could measure to verify.

Put an indicator on the carriage and indicate one of the washers. Then move the carriage to the other end and read the indicator. If it's the same, you are good. If not, make adjustments until it is.

Note that you can measure tailstock offset as well as height.

You could use the bar in 10k's video this way as well.

I think that the advantage is that you machine it once and then measure and adjust until you have it set.

If you save the test bar in a safe place. you can always use it to re-test, without even having to take any cuts.

If I have any of this screwed up, let me know. This is a method someone showed me and I've found it to work well.

I would like to make a bar like 10k's in the future and use it this way. I'd also make a nice fitted case for it.

Steve

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SE18 said:

Halligan, forgot to mention. Nice 1" standard to use to calibrate your mic, although really it doesn't need to be calibrated to measure the 2 collars as it's all relative, but I enjoy that you explain things as you go along

also, I like the idea to use plumbers tape for the dog. When I built my test bar, my dog was too small so I made my own dog out of thick copper and it cannot mare the steel, being softer (I'm not sure if the tape you use is to prevent maring or to reduce tendency to spin or both)

I'll look forward to other videos you have planned, as you indicated; great help to those of us beginners who don't know it all like some

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kgize said:

Halligan – I am amazed at the length and breadth of your 2 collar test bar video – Nice bar you made.
I was lazy when I made mine and it doesn’t deserve a wooden box as yours does – but I enclose pic just for those that might want to make a quick and dirty one. Made mine from 1.25 inch all thread which was the cheapest ‘rod’ of any thickness I had then. I think the rod was meant for mounting studs holding freeway lights bought at auction for about 5 cents a pound, but any rod or pipe with plugs welded in the end might do. Then I cut some sections of larger pipe (for the collars) that easily slid over the rod and crudely centered those collars with the threaded rod by hammering in a few nails, and then welded the pipes to the rod. It's not the best material to turn - but i think it still works
I got my lathe (13” South Bend) to one thou over that 16 inch ‘test bar’ – where I gave up trying to get ‘perfect as I spent about 2 hours including leveling with machinist level to get it there (besides I know my concrete floor moves from season to season)
A note of something I saw in your video – at about 5:30 when you are drilling with larger drill - have you noticed your drill bit keeps slipping a little bit with each peck of the drill? Not sure if your taper is spinning in tailstock or ? – but doesn’t seem like a good thing going on there.
Also wondering why not put the collars close as possible to the centers for rigidly – instead of 2 inches in?

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