Drummond B lathe

[Trevanion]

Oh I get it, if you werent turning between centres. Wouldnt it be easier to do it with the cross slide

It would be used for quite long, shallow tapers. By consequence a deeper taper would be less length because it’s traversing more across the material rather than along its length so it’s easier to do those with the top slide.

If that makes any sense

 

[wallace]

Seems strange to move the head stock, I can move the tail stock on my wood lathe for off centre work or for doing long tapers.

 

[Trevanion]

Seems strange to move the head stock, I can move the tail stock on my wood lathe for off centre work or for doing long tapers.

You can do that on a wood lathe between centres because the work isn’t held as rigidly as a metal bar in a three-jaw chuck, on a metal lathe it wants to hold the bar in line with the headstock with very little play possible.

 

[Jelly]

Seems strange to move the head stock, I can move the tail stock on my wood lathe for off centre work or for doing long tapers.

This is also generally the arrangement used on larger metal lathes where the headstock and bed are part of a single casting, or the mass of the headstock is simply too large for moving it to be a sensible design.

But because of the issue highlighted by Trevanion, this does mean that workpieces then have to be turned between centers, potentially resulting in an awkward order of operations, or neccesitating the use of a dedicated arbour of some sort if the piece can't be turned from a long piece of bar stock.

For this reason, many larger lathes have the facility to fit a taper attachment, which will cut shallow tapers by controlling the movement of the cross slide with an external slide which you can set using a sine bar.

 

[wallace]

I wasn't expecting for this little lump to take so long. I thought I'd do some bits in black oxide, luckily the old bottle of solution is still working.

I have so little space I'm spraying on top of a machine that has been waiting to be collected for a few months.

I found this nice little motor in my stash.

I want to use a vfd for speed control so got my motor guy to dig out the star point and make it 2OOv

 

[MusicMan]

For taper turning you do turn between centres but displace the tailstock. You should find out what the calibration means on your tailstock. You can do a taper with the top slide set at the desired angle, but only a short one, the length of the slide. With an offset tailstock you can do one the whole length of the bed.

As AES says, getting it back exactly right is not trivial. The way you check it of course is to turn a long bar and see if it is tapered, adjust till it isn't. You need to do this on most lathes anyway.

 

[Phil Pascoe]

You wouldn't need to turn the whole length, you'd need only to turn a groove or a rebate at both ends and check they were concentric with the bar, surely? (I'm no metalworker.)

 

[AES]

Actually you're quite correct Phil.

I'm definitely not a real good machinist (I just learnt the basics during my apprenticeship and didn't do any more at all until I bought a lathe only about 10 years ago), but personally I find that it's actually much easier to turn a long taper for such purposes.

That's because on my little Chinese Mini Lathe anyway (can't talk about other big machines), you end up making such really minute adjustments on the tail stock position that although wasteful (of material) and of time too, in the long run it's actually quicker/easier to turn the single long taper (which you're actually trying to rid of, of course).

But it may well be easier/quicker to turn just a groove at each end on a bigger machine, I dunno.

 

[MusicMan]

You wouldn't need to turn the whole length, you'd need only to turn a groove or a rebate at both ends and check they were concentric with the bar, surely? (I'm no metalworker.)

No, you have to have the turning tool at the same feed position at each and check that the diameters turned are the same. And you can't keep the tool at the same feed unless you turn all the way along the bar. (though you could turn down the middle part of the bar, then you could do the test just at the ends, and do it again easily after you adjust the tailstock).

All your test does is to check that your bar is concentric with your centre V.

 

[MusicMan]

Ooops I hadn't noticed that the adjustment was on the headstock, for tapers as said it is usually on the tailstock. Is there one on the tailstock too?

What does the headstock adjustment actually do? Does it translate the whole headstock assembly over, or is the back pinned and the adjustment rotates the headstock? If so it would be for ensuring that the lathe spindle is well aligned to the axis of the bed. I think it must be something to do with alignment.

 

[AES]

On my little lathe MM, the tailstock adjustment (in effect a single bolt) can move the tailstock in an angular fashion (around a single point - IF you're un/lucky!) or laterally (side to side). To say that adjusting it is extremely finicky is a major understatement! One of the shortcomings of the breed.

 

[MusicMan]

AES, It's quite easy on my robust Boley lathes. The motion is side to side rather than angular, but I don't think this part is a big deal.

What I do when I have a lathe properly set up is to put centres in headstock and tailstock and adjust till these are accurately touching. Before this, one has to align the main spindle to be parallel with the main bed slideway, or at least check that it is so. A lathe alignment bar is best for this.

My first metal lathe at home (I'd used plenty at work, and had got spoilt with a beautiful Schaublin) was a mini lathe and it frustrated the hell out of me, so I went to reconstructing prewar Boleys!

 

[Wildman]

just one word of caution for you, the traverse wheel is different in direction to most lathes thus if you turn it clockwise instead of moving the apron away from the chuck it does in fact wind the tool into the chuck. Most people at some time introduced a intermediate gear to reverse the direction to the norm