Headstock/tailstock alignment

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Jacob

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Why probably? If the fault is in the headstock the quill may well be perfectly parallel.
They could end up both being parallel to the bed but at different heights.
PS I'm just being pessimistic - I think it's a set-up prob as PaulM says above.
 
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Tris

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Is this a new problem or one that has always been there?
If it's a new problem I'd start by looking under the headstock for accumulated crud, sawdust and finishes.
Once that's cleaned up and whilst the headstock is off I'd check the bed is straight and not in wind. Wind probably won't be an issue on this style of bed, more so on parallel bars like record cl lathes.
If you have a through headstock use a straight metal rod to check the alignment of the head and tail stock along the bed length, if it's still out you may have to file a little off the front of the headstock casting or shim the back edge as described in earlier posts.
If it has always been a problem you might have an issue with the headstock casting. My jet lathe required a bit of fettling as there was a ridge on the edge of the casting that gave the problem you describe, a light filing sorted it out.

Hope this helps
Tris
 
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Hi is this a setup problem. When mounting in the chuck, the tailstock revolving centre should be engaged at same time. Then tighten chuck jaws equally, whilst rotating checking concentricity, lightly tap to correct. Use a DTI or scribing block to check
If you place stock in chuck & tighten up, you have no support at tailstock.
I'm was a mechanical turner (apprentice trained). When we reversed chuck we would do the above, use a DTI to check concentricty (whilst equally tightening the jaws supported with centre) and tap with a plastic mallet to get running true. Hope this helps

When the piece was between centers I added a dovetail so I can secure the ends in a chuck, so if everything is as it should, I should be able to place the wood in the chuck and have no gaps where the end of the jaws meet the side of the dovetail.

If I do as you say, and use the tail stock to align the piece with the center point (from where it was between centers) before tightening the jaws, then it skews the other end in the chuck, and there is now a gap on one side.
 
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Is this a new problem or one that has always been there?
If it's a new problem I'd start by looking under the headstock for accumulated crud, sawdust and finishes.
Once that's cleaned up and whilst the headstock is off I'd check the bed is straight and not in wind. Wind probably won't be an issue on this style of bed, more so on parallel bars like record cl lathes.
If you have a through headstock use a straight metal rod to check the alignment of the head and tail stock along the bed length, if it's still out you may have to file a little off the front of the headstock casting or shim the back edge as described in earlier posts.
If it has always been a problem you might have an issue with the headstock casting. My jet lathe required a bit of fettling as there was a ridge on the edge of the casting that gave the problem you describe, a light filing sorted it out.

Hope this helps
Tris

It may have always been there, not sure. I've basically only started to notice it as I have been doing more and more pieces that aren't simply held between centers, and are long enough (more than 8") for it to be noticeable. I've previously only done bowls.

Last night, I took off the headstock to have a look underneath. It's all clean, no muck or anything that would cause an issue. However, it turns out that it does not rest on the casting of the headstock itself. It rests on what looks like a precision piece of machined steel, which again , is clean of any muck.

I'll take some photos in a bit to show you
 

Phil Pascoe

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They could end up both being parallel to the bed but at different heights.
PS I'm just being pessimistic - I think it's a set-up prob as PaulM says above.
If I move the tailstock close to the headstock to check alignment of centers (a cone shaped live center at each end), all looks good.
The tailstock is probably OK - you'd adjust the headstock to suit? Only one is at "a different height".:)
 

Jacob

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The tailstock is probably OK - you'd adjust the headstock to suit? Only one is at "a different height".:)
But it might then be easier to machine the tailstock down to meet the new level of the headstock, rather then shimming the head stock up - unless it is easier to do.I imagine there is no point you could shim - it's swivelling casting straight on to the bed as far as I can see.
 
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PS I'm just being pessimistic - I think it's a set-up prob as PaulM says above.

As I said in one of the previous posts, I can reproduce the issue with other accessories in the headstock, such as a Jacobs chuck with a drill bit in it, or a chuck with a machined piece of round bar in it.

Sure, the Jacobs chuck might have error, and the drill bit might have error etc, but visually it runs true, and there is no vibration when you place something on it, and yet still does not align with the tailstock.
 

Jacob

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As I said in one of the previous posts, I can reproduce the issue with other accessories in the headstock, such as a Jacobs chuck with a drill bit in it, or a chuck with a machined piece of round bar in it.

Sure, the Jacobs chuck might have error, and the drill bit might have error etc, but visually it runs true, and there is no vibration when you place something on it, and yet still does not align with the tailstock.
Right - it's the headstock then!
 
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Here are some pictures of underneath the head stock. There was no muck or dirt. Just oil for lubrication.
 

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MusicMan

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The process is
1. Check that your bed is flat and straight. An engineers' quality level (can usually find them secondhand) and straight edge. Check it doesn't have any funny bumps.
2. Mount a lathe reference bar in the headstock, on the Morse taper (nothing else will work). Check that it is parallel to the bed (use the level). If it is not, shim below the headstock support (where it doesn't rotate)
3. Do the tailstock alignment to the headstock at close distance again. It should now work when far away.
 

Tris

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If the bed is true and you turn the ring that sits on the bed bars 180 degrees and clamp the headstock back on it do you then get the axis pointing down (ignore the alignment stops for the moment)?
I think you are chasing an accumulation of small errors here
 
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The process is
1. Check that your bed is flat and straight. An engineers' quality level (can usually find them secondhand) and straight edge. Check it doesn't have any funny bumps.
2. Mount a lathe reference bar in the headstock, on the Morse taper (nothing else will work). Check that it is parallel to the bed (use the level). If it is not, shim below the headstock support (where it doesn't rotate)
3. Do the tailstock alignment to the headstock at close distance again. It should now work when far away.

What do you mean by lathe reference bar?

If the bed is true and you turn the ring that sits on the bed bars 180 degrees and clamp the headstock back on it do you then get the axis pointing down (ignore the alignment stops for the moment)?

It only fit's one way. [Edit] actually that won't be problem, so I can try that!

I think you are chasing an accumulation of small errors here

Quite possibly
 

MusicMan

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transatlantic, a lathe reference bar is, for example

You have to get the correct Morse taper (probably MT1 or MT2) that fits directly in your headstock (clean it first). Then you know it is pointing directly along the spindle axis and you can align it to the bed.

If you don't have a Morse taper in your headstock, there isn't a really accurate way of doing it, I'm afraid.
 
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transatlantic, a lathe reference bar is, for example

You have to get the correct Morse taper (probably MT1 or MT2) that fits directly in your headstock (clean it first). Then you know it is pointing directly along the spindle axis and you can align it to the bed.

If you don't have a Morse taper in your headstock, there isn't a really accurate way of doing it, I'm afraid.

hmm, I was picturing something much longer. The 2MT says 280mm overall length, so thats only around ~220mm sticking out. Is that really enough to reference against?

Also - is the hole in the end to check it aligns with the tail stock?

Edit : Ah - so these are designed for machinist metal lathes, which is why I assume they're quite short.
 

bussy

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The problem is with turned boxes. When I have hollowed out both the lid and the base (both ends still have their dovetail and initial centering dimple), I then fit the lid to the base, and mount the base in the chuck (using the dovetail), and then bring up the tail stock for support. At which point, even though the piece runs perfectly true, the tail stock does not match up to the centering dimple. If I force it, the lid is forced to not be on straight.

If you have removed the base from the chuck to do the lid, then replaced the base in the chuck, in my experience the base is never going to sit in the exact same position as it was when first turned, i think this could be your problem.
Try fitting the base without tightening the chuck fully, bring up the tail stock then tighten the chuck, if I have to remove a piece from the chuck I always put a mark on the piece and on the chuck so I more or less have the original position of the work piece.
Hope this helps
Marty
 
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If you have removed the base from the chuck to do the lid, then replaced the base in the chuck, in my experience the base is never going to sit in the exact same position as it was when first turned, i think this could be your problem.
Try fitting the base without tightening the chuck fully, bring up the tail stock then tighten the chuck, if I have to remove a piece from the chuck I always put a mark on the piece and on the chuck so I more or less have the original position of the work piece.
Hope this helps
Marty

I really don't think this is a setup issue. The reason this has cropped up is because I kept seeing the same issue with different boxes, and as I have said a few times now, I can reproduce the same issue with other accessories in the headstock.

- I can put the base back on the chuck. Runs very true (no bumping when you lay a tool on it)
- I can then put the lid on the base. Runs very true (there is no visible distoration of the 'between centers point' on the end of the lid as it rotates)

Yet when I bring up the tail stock, that same center point on the lid is 2.5mm too high. And keep in mind now, that it's running very true, so it's always 2.5mm too high no matter where it is in the rotation. To get it to align I have to undo the chuck and skew the base such that it is not seating correctly, but then the base obviously doesn't run true.
 

Gavlar

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I have exactly the same problem with my Record DML24 lathe. This has a twin tube bed and I had convinced myself that the tube(s) were bent or that they were sitting somehow other than flat. I'd acquired it 2nd hand and partly assembled. I noticed the issue when turning a spindle between centres and then putting in the chuck to drill out the end, e.g. for a candlestick. It ran true, but not centred. On finding a manual online, I discovered that the various castings that hold it all together are handed and need to be assembled the right way round, although that's not obvious when you first look at them. Mine was partly put together wrong. I stripped it down and put it back together, thinking I'd found the problem. Nope, still there. So the lathe is in a box awaiting a decision on its future. Having read this thread, I'll look again at the headstock alignment.
 

MusicMan

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hmm, I was picturing something much longer. The 2MT says 280mm overall length, so thats only around ~220mm sticking out. Is that really enough to reference against?

Also - is the hole in the end to check it aligns with the tail stock?

Edit : Ah - so these are designed for machinist metal lathes, which is why I assume they're quite short.
Yes their main use is on metal meths but they are quite long enough for fairly long ones. But it is assumed that you check heights (parallelism) with a dial gauge or test indicator with a sensitivity of 0.001 - 0.01mm. Then you are good to 0.004 - 0.04 mm even at a metre out, which is far less than the problem you are seeing.

If they were much longer, the sag under gravity would become significant.

If you don't have one of these, a good compromise is an internal caliper that is screw adjusted (the sort of thing you will use to measure the inside diameter of a box lid). By carefully checking the distance from bed to alignment bar along its length, you should easily achieve 0.1 mm check on whether this distance is varying. You don't need to know the distance, just that it is constant.

Once you have set the parallelism to the bed, yes you can use the hole in the end to check the tailstock. It is probably more accurate to check the tailstock against a short turned centre close to the headstock. If your bed is humped or hollowed, you will see this with the calipers.
 

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I have a similar problem with my rotating head lathe, however I've not been able to work out what exactly is causing the mis-alignment and have resorted to shims on the tail stock. Obviously whenever you rotate the head you will need to re-align when it goes back to normal. The main issue is that you are probably never going to find out where the error is without some sophisticated (expensive) measuring equipment and probably a lathe specific jig; even if you can there's probably not much you can do about it. I came to this conclusion and whenever I need the accuracy I shim. The problem with shims are that it may only cure the problem at one position i.e. if you are drilling a long hole then it may be centred where you enter the piece but as you drill further it will try to follow the tail stock alignment which may be pointing up or down and you can hear/see this as the drill begins to bind and vibrate the deeper you go. Here I tend to drill very slowly and accept the hole will be slightly bigger at one end than I want. I also use longer pieces of wood fashioned to a point (each time it's mounted) so that I can shim the tail stock to centre at the point I need it to be i.e. at the end of the piece, which still may be pointing up or down. This process works for me and hope that helps. if anyone has a better and more permanent solution I also would be very grateful.
 

IanB

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Sorry I can't contribute any suggestions, but I've recently noticed that when I turn the inside of a bowl, it is not perfectly aligned and I get a rim which varies in thickness by about 1 or 2mm over the circumference - so I'm grateful for some of the suggestions above, which I will look into to find what the problem is.
 

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