Alignment of headstock and tailstock centres

[LiviChris]

I'm a hobbyist woodworker but haven't ever done any turning. I have just bought a second hand Luna BWL 406 lathe, it's in great shape, looks like it's been well looked after but I've noticed the tailstock centre is 1 or 2 mm lower than the headstock centre.

is this a problem, do i need to work out how to adjust the tailstock upwards so they match exactly?

 

[marcros]

are the centres seated correctly? In theory it doesnt matter for spindle turning because it is always a straight line between 2 points, but I think that it is worth looking at the cause.

 

[MusicMan]

Yes, they should align correctly, but as Marcros says it is not too important for spindle turning. If you were doing copy turning with a tool held in a machine, then it would matter as it would turn a taper not a cylinder. But for hand held tools, you adjust automatically to wherever the axis lies.

The sort of time you would get into trouble would be if you held the work on the headstock and turned an indentation, then tried to put the tailstock centre into the indentation. But more commonly, you would out the indentation in with the tailstock, or else have it indented before mounting the work.

The only time you would notice is if you make a piece, then use a drill in the tailstock to put in a central hole. A big drill will be so stiff that it will still drill OK but make a hole bigger than the nominal size. A small drill will be flexed by the workpiece having a different centre, and might break.

I am not familiar with the Luna, but looking at the pictures it seems a good design and should not be that much out if assembled correctly. I suggest taking it to bits and reassembling, making sure the slides are all seated properly and (see above) that the centres are seated correctly. It does not look as if it has an adjustment for that alignment, but I don't have a manual to hand.

Keith

 

[CHJ]

You will often see reference to the 'Kiss Test' for centre alignment.

As mentioned above the precise alignment is not critical for between centres turning but for anywhere near accurate drilling for size and alignment it's essential that the centres are also on the same axis both horizontally and vertically, as soon as you move the tailstock away from the headstock centre and mount a drill chuck in it the drill will be pointing and moving in an axis far removed from the headstock centre alignment.

Additionally lathes with a rotatable headstock must also be capable of accurate alignment for drilling and tailstock boring.

The sketch below is exaggerated but even half a degree misalignment can render accurate drilling with the tailstock impossible as the front end of the drill will be several millimetre off centre before you start.

 

[boomerang bender]

I have the same problem on my old Coronet Major and since the tailstock alignment is governed by the locating grove in the tailstock slide bar any wear on the locating pin will allow a slight deviation on a sideways movement, on a modern lathe with a flat surface for the tailstock to sit on it may be possible to insert a shim to raise the tails stock. I am pleased to see that spindle turning is not affected by this deviation. I have only tried once to drill a hole driving through the end grain and the drill tends to follow the easiest route through the grain and any deviation as Keith says makes the hole bigger which is awkward if fitting a dowel or tenon.

 

[MusicMan]

boomerang, if your main slide bar is straight then the solution to your alignment would appear to be to adjust or replace the worn locating pin. I don't know the details, but If it is tapered, it may be possible to screw it in a bit. If parallel sided it should not to too hard to find or make a replacement pin.

Keith