Question: Finding center of stock for the Lathe (tail end)

[anaminal]

Hi to all Lathers!

Question: How do you set stock dead-center on the lathe? The drive end has a 4-jaw chuck so is fine, but it's the tail end that being even slightly off-center ends up giving me cuts too deep on one side and too shallow on the other. Is there a way to find the absolute dead center of rectangular stock?


Many Thanks,
Chris

 

[blackrodd]

Is this a trick question? Rodders

 

[carlb40]

This?
http://www.workshopheaven.com/tools/Ric ... inder.html

 

[CHJ]

Hi to all Lathers!

Question: How do you set stock dead-center on the lathe? The drive end has a 4-jaw chuck so is fine, but it's the tail end that being even slightly off-center ends up giving me cuts too deep on one side and too shallow on the other. Is there a way to find the absolute dead center of rectangular stock?


Many Thanks,
Chris

Is this a serious question?
For rectangular stock you just draw two lines with a pencil.

For round or irregular shapes you can use some callipers to scribe centre arcs or a set of pre-cut circle discs to locate the centre of the mass.

 

[anaminal]

thanks for quick responses!

Nope, not a trick question... tried the 'two diagonal lines with a pencil' technique, but with the thickness of a pencil line, difficulty of holding the ruler in exactly the right place... this still doesn't give me the *exact* centre... I'm after total precision and repeatability - i don't like measuring

Just seen this:
http://www.axminster.co.uk/veritas-centre-finder
It's expensive, but like the idea of having a blade set into it so removing need to draw a pencil line. anyone tried this?

 

[Jacob]

Marking gauge. Make a few marks from the edge. If they haven't hit dead centre first go; adjust slightly, more or less, until it scratches out a neat little square (or polygon if the stock isn't square) and the centre is in the middle of that.

 

[CHJ]

I've never had a piece of wood that was fine enough grain or cut square enough that locating the tailstock centre within a pencil line cross was not as near the centre as practically achievable.

 

[blackrodd]

I've never had a piece of wood that was fine enough grain or cut square enough that locating the tailstock centre within a pencil line cross was not as near the centre as practically achievable.

Me neither!
perhaps it's the sheltered life we lead! Rodders

 

[nev]

whether the tailstock is dead centre or not is irrelevant with square stock. The moment you rough it to cylindrical the point of tailstock contact becomes the dead centre.

If your problem is RE-mounting the stock centrally then thats a different kettle. Check the headstock and tailstock line up with a simple kiss test etc.

BTW I purchased one of those centre finders (albeit a cheaper rutlands version) and i find it no more accurate than pencil lines, in fact i only use it for round stock that has lost its centre mark , or been cut etc.

Edit: Thinking about it, if you are finding you are creating ovals or getting a lot of chatter check for play or sideways movement in the tail stock drive.

 

[anaminal]

whether the tailstock is dead centre or not is irrelevant with square stock. The moment you rough it to cylindrical the point of tailstock contact becomes the dead centre.

It remains an issue for me as I'm not removing all the material from the original outer dimension. The lathe then cuts deeper on one side than the other

...I have just realised that, as I'm actually cutting rectangular stock, the Veritas tool wouldn't help me! it would just give a diamond shape close to the middle.

Marking gauge. Make a few marks from the edge. If they haven't hit dead centre first go; adjust slightly, more or less, until it scratches out a neat little square (or polygon if the stock isn't square) and the centre is in the middle of that.

I think this will be the best solution, unless anyone has another theory for use on rectangular stock?

Chris

 

[nev]

I couldnt get my head around what you were saying and then :idea: you mean when creating something like ...

all makes sense now #-o
In which case the veritas or rutlands 'jig' is as quick as you will get. If you rotate the wood as you mark it, even if the stock is not square you will end up with a small square around the centre point like using Jacobs suggestion.

 

[CHJ]

..
It remains an issue for me as I'm not removing all the material from the original outer dimension. The lathe then cuts deeper on one side than the other Chris

You are never going to get a guaranteed centralisation within a 1/4 -1/2 mm using a pointed tailstock centre regardless of how accurate you find the centre of the stock.

The very nature of wood grain is such that it has varying density across each grain boundary, as soon as you press a pointed centre into the end grain it will take the path of least resistance and veer off a fraction dependant upon the wood sample.

The only way to overcome this is to not use a pointed tailstock centre but to use a cone centre to locate on the corners, even then there is no guarantee that you will hold a finite accuracy as the corners of the stock will have differing density as they too will be from different years growth and grain orientation.

The same applies to your statement that holding stock in the four jaw chuck automatically centres it, not true, the inaccuracy may well be of no significance to 99.9% of spindle work but if you are being so pedantic about centring a square spindle you must take into account that the wood density may vary on all four sides and that the chuck jaws may compress the wood differently on each side.

If the accuracy that you get taking the latter factor into account is adequate for your needs, then a cone centre should meet the same needs at the tailstock end.

But you are now into the realms of tool control and absolute control of wood removal and not letting the differing wood densities across the piece influence the ability to keep it truly round.
Of course it will go out of round just as the perfectly square stock will go out of square as soon as the moisture content varies, whether the eye will detect this is another matter.

 

[Random Orbital Bob]

The real question here is WHY. What is it about your project requirements that is driving this need for engineering style precision?

 

[AndyT]

If the project is to make spindles with square parts as shown by Nev, maybe part of the solution is to
plane the flat parts after turning, if you really want to take out every trace of variation.

Before doing that I suggest looking at some real life examples - in my experience even quite large'deviations' go unnoticed.

 

[Jacob]

Sorry to be repeating myself but they do make me laugh these daft gadgets from Veritas and R.Kell.
A marking gauge is all you need, round or square stock. A proper one that is i.e. cheap and made of wood, not one of the expensive all metal daft gadget options. On round stock you just swing a little arc, much the same as Chas's photo above, using a divider.
Why make it more complicated?

 

[Spindle]

Hi

I use a metal version of the one Chas has in wood - I prefer it to a marking gauge as I find it easier to see a pencil line in end grain than a scribed one - also for smaller spindle blanks a I find a marking gauge less easy to control.

In irregular and rectangular blanks it results in a central area rather than a point but it's easy enough to mark the centre by eye from there. I use an automatic centre punch for centre marking

Regards Mick

 

[anaminal]

Chas - interesting points. I'd not considered the grain density producing differing compression at the chuck end or the grain folding at the tail-stock. Also I'd never heard of cone centres, so I could look into. Many thanks!

AndyT - planing after turning is something I had thought about, and I think should work very well where the turning has been slightly off-centre, thanks!

Nev - that is indeed the problem, cheers for the info on jig you tried.

Jacob - Marking Gauge method sounds good, I'll give that a try tonight.

The [current] project is making tool handles with a ferrule holding a blade in place. As the ferrule outer diameter is just 1mm less than the outer diameter of the wooden handle it buts up against, it is very obvious when it is off centre. (it's basically in line with the handle on one side and set back from the edge on the other).

As I see it there are so many sources of error (below) I'd like to make sure I'm not introducing any additional ones with the wrong method. Thanks all for your input, given me plenty to think about.

possible sources of error:
Rounding errors / inaccuracy in measurements
Difficulty of holding a ruler in place while drawing the line corner to corner
width of pencil line
Grain folding towards path of least resistance
Human error in holding the turning gouge!


P.S. to Rodders: I have not (and I'm sure this applies to many others) received any woodworking education other than Youtube videos, library books and the people on this forum; so when someone asks a question with an obvious answer it's not really helpful to open with sarcy post belittling em.

Chris

 

[CHJ]

I'm afraid that if you are starting with stock that close to the finished diameter for your handles then you are more than likely going to fall foul of another factor that will have far greater implications than the location of the tailstock centre.
It is virtually impossible to drill a hole down the centre of a spindle blank that is true within the tolerances you are referring to.

Hence for minimum disappointment with mis-aligned tool shaft holes it is not unusual to drill the tool location hole in the stock first and use this hole as the mounting on a shaft in a counter bore drive similar to this :-
<<<< Linky Img.
or a home made equivalent mounted in your chuck.

When using this system you locate the tailstock centre in the natural position presented at the tailstock end regardless of blank off-set due to hole alignment wander.

This does of course mean that your spindle stock has to be wide enough to accommodate any drilled hole alignment error but does result in a finished tool with a very good Tang-Handle alignment.

 

[Jacob]

......
Hence for minimum disappointment with mis-aligned tool shaft holes it is not unusual to drill the tool location hole in the stock first and use this hole as the mounting on a shaft in a counter bore ......

Yes.
Or drill the hole first and actually fit the tang to the blank. Then locate the centre point by eye - lining it up with the tool in situ. Need to have an oversize blank of course; very difficult otherwise.
Free wood for tool handles - 2" dia bits of ash (or almost anything) branches. Keep them dry but cool (to avoid splitting) for a year

 

[NickWelford]

A ring centre in the tailstock is also useful to overcome the point wandering into the softer grain.