Headstock/tailstock alignment

[transatlantic]

I have the Fox lathe (pictured below) that has a rotating headstock, and have noticed an issue. 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. But if I turn an 8"piece between centers, turn a dovetail on one end, and mount in a chuck. Although it appears to spin perfectly true, the live center in the tail stock will now not align with the dimple created when it was turned between centers. The dimple is about 2.5mm too high.

I've repeated this expeiment many times now, and am convinced that the headstock is pointing/rotating slightly upwards, as shown by the red line. It's hardly noticable when the headstock and tailstock are close togeather, but becomes more apparent as you space them out.

How do I go about solving this? if it was a fixed headstock, I see people just stick in some shims and bolt it down, job done. But as it's a rotating headstock (which I make use of all the time), I can't just shim it. Or if I did shim it, I'd have to glue them or something, to keep them secure. Any ideas?

 

[minilathe22]

That's a tricky one with a swivelling headstock. Perhaps you could use the shims method just to determine how/where the misalignment is? Then braze/solder/glue a shim to the base of the headstock.

 

[Phill05]

If it fine between centres it could be a misalignment of the chuck, just had a mate with a problem like this and it was a build up of dust in the chuck register.

 

[Paul Hannaby]

It might be worth checking the bed is straight. I had a similar problem once and the bed was the cause of the issue.

Also, try switching the headstock & tailstock round on the bed to see if it's any better the other way round.

 

[Phil Pascoe]

https://www.axminstertools.com/axminster-lathe-alignment-centre-2mt-102427

 

[transatlantic]

That's a tricky one with a swivelling headstock. Perhaps you could use the shims method just to determine how/where the misalignment is? Then braze/solder/glue a shim to the base of the headstock.

Yep - I'll have to try the shims anyway to see if it even solves the issue.

If it fine between centres it could be a misalignment of the chuck, just had a mate with a problem like this and it was a build up of dust in the chuck register.

It's not the chuck, as I tested it with multiple headstock accessories, including different, chucks, friction drives, Jacobs chuck etc etc. All appear to show the same issue.

It might be worth checking the bed is straight. I had a similar problem once and the bed was the cause of the issue.

Also, try switching the headstock & tailstock round on the bed to see if it's any better the other way round.

If it's the beds not being flat, then I am well and truly ****

https://www.axminstertools.com/axminster-lathe-alignment-centre-2mt-102427

Not sure how that helps? that is for aligning in the horizontal plane is it not, where there is a lot of play to work with? if I use it in my case, isn't it just going to force something into place and perhaps damage something?

 

[Sachakins]

Is it definitely the headstock? Could the tailstock be pointing down, not headstock pointing up?.
I use the MT2 Alignment tool, Great to get centred. Worth trying one out, set it in the headstock first, then use a DTI to check run out along it's length at about 5 points, this will show if headstock is running true. If out it maybe your spindle bearings are worn, and the motor tension on belt is pulling spindle down a tad at back.

 

[Sachakins]

Also try to shim end of bed up, if it's floor mounted, maybe something has sank at bit at either end, or if bench mounted, maybe bench has swollen in middle, throwing of level of the bed. If you could borrow a true engineers reference level, try it along the bed.

 

[transatlantic]

Is it definitely the headstock? Could the tailstock be pointing down, not headstock pointing up?.
I use the MT2 Alignment tool, Great to get centred. Worth trying one out, set it in the headstock first, then use a DTI to check run out along it's length at about 5 points, this will show if headstock is running true. If out it maybe your spindle bearings are worn, and the motor tension on belt is pulling spindle down a tad at back.

It seems to get worse the longer the piece you add to the headstock, which is leading me to think the issue is there. But as a previous poster said, could also be the beds

 

[Sachakins]

It seems to get worse the longer the piece you add to the headstock, which is leading me to think the issue is there. But as a previous poster said, could also be the beds

Could be rear of bed dipping down slightly, this would get worse the further you get from headstock?

 

[Jacob]

Is 2.5mm a prob - what happens if you tap your 8" piece down to fit the tail stock?

 

[Phil Pascoe]

Not sure how that helps? that is for aligning in the horizontal plane is it not, where there is a lot of play to work with? if I use it in my case, isn't it just going to force something into place and perhaps damage something?

It would show any deviation so at least you would be 100% sure of the problem, and allow you to check if using shims under the headstock that you have got them right. Line the head and tail stock up with the headstock slightly loose and see if you can get a feeler under the outboard side?

 

[Duncan A]

If the lathe spindle extends through the headstock at both ends, measure the centre heights to the lathe bed. If one end is higher, that would indicate a headstock issue. Look at the underside of the headstock and use a straightedge to check for any raised areas - it's possible that there's a very slight edge or protruberance from a knock some time in the past - perhaps when putting it onto the bed.
Duncan

 

[transatlantic]

Is 2.5mm a prob - what happens if you tap your 8" piece down to fit the tail stock?

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.

Hope that makes sense. But basically I am describing the 21:10 point in the following video. The center point of the lid runs perfectly true, but the point of the tailstock does not align with it.

 

[Jester129]

How about using a laser level on the bed, then somehow set it up on either/both ends? Just a thought. HTH

 

[Danieljw]

Most likely to be lathe bed, I would start be checking the bed for level and square.
If it is bolted to the floor, release the bolts and recheck

 

[Phil Pascoe]

It may well not be the bed with the misalignment occuring so close to the headstock, it may well be that the spindle isn't parallel to the bed.

 

[Jacob]

It may well not be the bed with the misalignment occuring so close to the headstock, it may well be that the spindle isn't parallel to the bed.

And if you shim , trim, adjust the headstock you are probably going to have to do the tailstock too.
Should be easy check the bed - take everything off and squint along it, or shine a focussed torch beam. 2.5mm over 8" should be visible. But the least likely cause at a guess.

 

[Paul M]

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

 

[Phil Pascoe]

And if you shim , trim, adjust the headstock you are probably going to have to do the tailstock too.

Why probably? If the fault is in the headstock the quill may well be perfectly parallel.