Help needed lining up the centres on a Perform CCSL

[AndyNC]

Hi,

I've a Perform CCSL and the tailstock has a large amount of play between itself and the bed. I'm making some guide blocks to bolt to it with adjustment so I can line it up and fix it in the correct position.

My problem is how to line up it with the head stock and also to line up the head stock.

As many will know that although the headstock has index positions it will not line up to within a millimeter or so.
I currently am turning pens an would like to get it lined up as well as possible. At the moment when I insert the live centre into the pen mandrel it pushes the end over.

Is there a text book way of lining the head and tail stock up. I can imagine using a straight bar and centre, lining up as well as possible and then swapping over the ends and lining up finer.

Cheers

Andy

 

[Spindle]

Hi

There is little point in stressing over aligning centres on a woodturning lathe, anything mounted between centres will rotate about the axis created between the centres. Adjust for the best alignment you can by eye and using a centre in both the head and tail stocks.

Where alignment is required is when the work is being held in a chuck or on a faceplate and supported by a tail centre. In view of this it is sufficient to grip a large twist drill in the chuck and align the tail centre to this, (again, by eye).

Regards Mick

 

[Inspector]

If you're willing to ditch the pen mandrel and get a dead centre for the headstock you can turn between centres and eliminate any of the out of round issues stemming from the misalignment. We went that route after making a few dozen pens with the mandrel and it improved the fit immensely.

Because it is useful to drill on the lathe, having the tailstock and headstock in line is important. There are double ended morse tapers available that let you align and bolt the headstock to the bed and shim or as you intend, add guide blocks to the tailstock. With a little care you could turn one in a dense hardwood that should do the same.
An example. http://www.recordpower.co.uk/product/2- ... ent-centre

Pete

 

[Spindle]

eliminate any of the out of round issues stemming from the misalignment

Hi Pete

What issues are you referring to?

Regards Mick

 

[nev]

something like one of these? ..
http://www.recordpower.co.uk/product/2- ... ent-centre

 

[Paul Hannaby]

one way is to use a double ended morse taper but I guess if you have lots of play in the tailstock that won't help much because you would have to move the tailstock before using your pen mandrel.

One way I use is to put a longish piece of wood in the chuck, turn the end so it's cleanly cut and then bring up the tailstock with a live centre to see if it locates in the centre of the piece of wood. If it's slightly out, the point of the tail centre will scribe a small ring in the end of the piece of wood. If it's spot on, it will just leave a single mark.

 

[Inspector]

eliminate any of the out of round issues stemming from the misalignment

Hi Pete

What issues are you referring to?

Regards Mick

With the tail and headstock not aligning, the mandrel has to bend in order for the tailstock to support that end. The bend plus play in the bushings in order to slide on the shaft creates an out of round condition. You will have a small amount more removed from one side of the pen blank that shows up when you look at the ends of the tube and blank. That leaves you with a ridge/step condition where it mates with the hardware. Unacceptable to me at least. You can simulate the same with a good lathe by cranking hard on the tailstock and induce a bend in the mandrel.

Pete

 

[AndyNC]

Sorry guys I did reply last night but the post is missing.

eliminate any of the out of round issues stemming from the misalignment

This my major problem at the moment.

one way is to use a double ended morse taper but I guess if you have lots of play in the tailstock that won't help much because you would have to move the tailstock before using your pen mandrel.

This another point I'm struggling with. The double ended morse taper will only line it up at the point of application. As soon as you move the tails stock it could become out of alignment.

One way I use is to put a longish piece of wood in the chuck, turn the end so it's cleanly cut and then bring up the tailstock with a live centre to see if it locates in the centre of the piece of wood. If it's slightly out, the point of the tail centre will scribe a small ring in the end of the piece of wood. If it's spot on, it will just leave a single mark.

This is close to where I was heading but use a straight steel rod in a drill chuck or collet and a centre. Put it in the head stock and line the head stock up as well as possible to the tail stock, then reverse them and repeat lining up the tail stock and so on. Then clamp up the guide block I've made and it should be good.

If you're willing to ditch the pen mandrel and get a dead centre for the headstock you can turn between centres and eliminate any of the out of round issues stemming from the misalignment.

This is a good alternative for the pen making. I think there are two methods for this, one just between centres and use a caliper (digital etc) to judge the final diameters or make up bushes at the finished diameters to go in the ends of the brass tube and turn down to these.

Many thanks

Andy

 

[Phil Pascoe]

Hi

There is little point in stressing over aligning centres on a woodturning lathe, anything mounted between centres will rotate about the axis created between the centres. Adjust for the best alignment you can by eye and using a centre in both the head and tail stocks.

Where alignment is required is when the work is being held in a chuck or on a faceplate and supported by a tail centre. In view of this it is sufficient to grip a large twist drill in the chuck and align the tail centre to this, (again, by eye).

Regards Mick

I've read and reread this, but I must be missing something - the first sentence states it's not important to align centres as anything between centres will rotate around the axis, and the second states that alignment is important when the work is held in a chuck and supported by a tail centre. (which as far as I can see is "between centres" - the headstock centre is going to be the same no matter what the chosen drive is.)
Edit- having read the post underneath, I can see what you mean - sorry!

 

[Phil Pascoe]

If it weren't important to line up centres, there'd no point in turning on multiple centres.

 

[AndyNC]

I think I may be able to help here.

As soon as you add any device eg a chuck, that forces the work piece to be in line with the head stock now requires the tail stock to line up.
Whereas between centres the centre can be considered a a point contact, although it is more of a small circle.

Andy

 

[Phil Pascoe]

Yes, sorry. I can see what you both mean. Of course the axis on which the item is rotating is fixed by the mounting at the headstock end.

 

[Spindle]

With the tail and headstock not aligning, the mandrel has to bend in order for the tailstock to support that end. The bend plus play in the bushings in order to slide on the shaft creates an out of round condition. You will have a small amount more removed from one side of the pen blank that shows up when you look at the ends of the tube and blank. That leaves you with a ridge/step condition where it mates with the hardware. Unacceptable to me at least. You can simulate the same with a good lathe by cranking hard on the tailstock and induce a bend in the mandrel.

Hi Pete

Thanks for your take on the situation but in my opinion you are incorrect - with the stocks out of alignment you may induce a bend into the mandrel, however the mandrel rotates but the bend remains fixed in space, (think flexible drive shaft), therefore the distance between work and tool will remain constant as the work rotates. You are correct in highlighting that poor matching of tubes to mandrel can give uneven wall thickness but this would happen on an aligned set of stocks as well as a misaligned set.

Inducing a bend into a mandrel by increasing the tailstock pressure is a different scenario which will, if the stocks are aligned, permit the bend to rotate - however this should never happen with something as substantial as a pen mandrel.

Regards Mick

 

[Paul Hannaby]

Thanks for your take on the situation but in my opinion you are incorrect - with the stocks out of alignment you may induce a bend into the mandrel, however the mandrel rotates but the bend remains fixed in space, (think flexible drive shaft), therefore the distance between work and tool will remain constant as the work rotates.
Regards Mick

You are assuming that the bend remains in the same place on the mandrel - theoretically there is no reason why the bend can't "move" up and down the mandrel as it rotates, effectively causing the mandrel to run eccentrically at different points along its length.

 

[Spindle]

You are assuming that the bend remains in the same place on the mandrel

Hi

I think that's an accurate assumption based on the fact that the mandrel is of the same material and section along it's length and therefore the bend / flex should be evenly distributed along the length.

Regards Mick

 

[Inspector]

Spindle I don't know you or you work very well so please forgive the question, but how many pens have you made? Often the theory isn't born out in practice. The lathe we have isn't the best and the tailstock centreline is out vertically and horizontally. That resulted in out of round for the first 40ish pens Marla (my love) made with 2 different mandrels. The next 400+ pens were turned between centres on the same lathe, virtually eliminating the fit problems from being out of round.

Andy it often helps to push or pull the tailstock to one side or the other, against the bed when tightening it down. If you align the headstock to match the tailstock when it is tight to one side, the tailstock should be in line along the length of the bed, assuming it doesn't flex too.

Pete

 

[Spindle]

Hi Pete

I've been turning for in excess of 15 years now and have turned all manner of items. I've probably turned around 40 pens but now my focus is on furniture, mainly chairs and spinning wheels.

I think you may be laying the blame for the lack of concentricity at the 'wrong door' and as you have correctly identified, anything turned between two centres will revolve around the common axis of these centres and this is why you do not see out of round condition when turning your pens between centres.

When using a mandrel the following can produce a lack of concentricity:

Poor fit of the brass tubes over the mandrel
Poor fit of the bushes to the mandrel
The axis of the mandrel not being co-incident with that of the headstock

It may be worth revisiting your mandrels to see if they exhibit any of the above faults - the third case can be demonstrated by fitting the mandrel without bringing up the tail stock for support,. rotate the lathe by hand and observe what the tail stock end of the mandrel does - it should rotate around the central axis of the mandrel, if it describes a circle it's axis is not co-incident with that of the headstock.

Finally, in my experience, proven theory is always born out in practice - when it appears not to be the case it is usually misinterpretation of the symptoms leading to the selection of the wrong theory :wink:

Regards Mick

 

[Inspector]

Thanks Mick. We gave the mandrels along with some other pen stuff not being used to someone getting started, so I can't check them even if I wanted to. After moving on to turning between centres I can't see why anyone would use a mandrel but suppliers like to sell beginners tools they "need" so why would they let them know there are other methods. I've gotten interested in custom pens (kit less) so only occasionally make a kit pen when house renovations and work don't interfere. :roll:

All the best
Pete

 

[Paul Hannaby]

I think that's an accurate assumption based on the fact that the mandrel is of the same material and section along it's length and therefore the bend / flex should be evenly distributed along the length.

Regards Mick

Assumption - a supposition often later disproved by fact! :wink: