Off centre box

[Tiger]

Hey all,

At the local woodturning club we had a project that involved turning an off-centre box. The end result was a box with 4 shallow (almost rectangular) curved sides. We all found it very difficult to get parallel sides. For those who have accomplished this, is there a trick to this, or is this a project that requires years of turning experience to get right?

[tashammer]

a bit quiet hear aint it.

i started off thinking of 4 ellipses for a same parallel sided piece. Dunno if that would work though.
Then i thought of same centre point at headstock end and 4 equidistant points at the tailstock end for a taped piece. But that don't sound right either. Help!

[Tiger]

Tashammer, you're right, it is a bit quiet here. The method of setting up this box was to draw a couple of circles and scribe some arcs, that wasn't the problem. The problem was achieving straight parallel lines when cutting. Normally when turning down a cylinder, it's no problem getting an even sized cylinder, but on this squareish type box, it was very difficult.

[Skew ChiDAMN!!]

:confused: I'm not sure I understand the problem. It's still spindle turning, isn't it? So long as you've got good lighting and are watching the shadowline (not the solid body) then it should be straight forward.

Unless I've misunderstood? This box is using 4 different centres, yes?

[OGYT]

I don't know either, but I'm listnin'... :o)

[tashammer]

Yer Skew , that's what i thought 4 centres at both ends to give parallel sides or 1 centre at one end and 4 at the other to give taper.

another way might be to cheat and use a router?

[Skew ChiDAMN!!]

Or give me a handplane and ask me to joint it squarely. :D

Ackershully, you might've put your finger on his problem, TH. Assuming he's not tapering the sides, then all four centre points have to be accurately scribed (& preferably pre-punched) on both sides; unless the "imaginary axis lines" through each pair are perfectly parallel, the sides won't be... even 0.5mm out will be noticeable.

This is why I like to use squared blanks for my offcentre items; they allow for accurate scribing of diagonals for accurate reference.

[Tiger]

:confused: I'm not sure I understand the problem. It's still spindle turning, isn't it? So long as you've got good lighting and are watching the shadowline (not the solid body) then it should be straight forward.

Unless I've misunderstood? This box is using 4 different centres, yes?

It is spindle turning and has 4 different centres but I found it anything but straightforward. I tried moving the toolrest slightly to compensate for the tapers I was getting, that didn't really help much. By the way, everything was carefully marked and punched before turning began, maybe I have to watch the shadowline a little more carefully. It really is a good test of whether or not you can keep the tool steady across a distance.

[Skew ChiDAMN!!]

I tried moving the toolrest slightly to compensate for the tapers I was getting, that didn't really help much. By the way, everything was carefully marked and punched before turning began, maybe I have to watch the shadowline a little more carefully.

When working the shadowline I've found that good, close overhead lighting makes all the difference. I also like to put either a large sheet of white paper or an old blackboard behind the lathe, for the wood to contrast against. Which way I go depends on the colour of the wood, of course. :)

If everyone at the club was having the same hassle, it's possible that the toolrest may be skewed slightly. eg. maybe someone's had a bad catch and jammed the tool down onto the end of the rest, bending the spindle a bit. If that's the case, then tapers almost automatically ensue if you're cutting straight! DAMHIKT. :o Next time you're at the club try checking that the toolrest is truly level.

Simply position the banjo so the top LH edge of the toolrest just touches the centre of the drivespur and bring the tailstock up to the RH edge of the toolrest. Any height difference at all and you may've found the reason for your problem.

I'm only guessing here, but it really shouldn't be difficult to do that job without a taper.

[powderpost]

Been following this thread closely. Still can not see where it is heading. I understand a foursided turned box is the goal, turning the outside shouldn't be a problem. But how do you turn the inside, presuming the wall thickness is to be constant? I played with this problem some time back and decided it couldn't be done on a standard lathe, but needed access to a rose engine, which I don't have. I settled on ovals by building the oval turning chuck from David Springett's book.
Jim

[Skew ChiDAMN!!]

You're right, Jim, a constant wall thickness isn't possible this way. But you can, of course, remount it centrally and turn a more traditional round hollow. :)

My rose engine is a bit further along in its' construction. The baseboard is drilled, anyway. 6 months down, 10 years to go... :rolleyes: Did you have any problems building Springetts' chuck?

[powderpost]

Skew, I had no problem building the chuck as in the book. It started to wear out after three jobs even though the slides were made from cooktown ironwood and lubricated with lanolin grease. The next model had adjustment rods on the ironwood slides to take up the wear and a large diameter, narrow roller bearing incorporated. Got some ideas for a further improvements. Got fed up taking it on and off the lathe so I built a dedicated oval turning machine. That was three years ago. Been a bit tied up lately with developing laminating and china cabinet building. About to get back laminating soon then some overdue ovals. This retirement is bloody hard work If there is any interest I can organise some photos and details on the chuck........later.
Jim

[TTIT]

If there is any interest I can organise some photos and details on the chuck........later.
Jim

Bloody silly question Jim - of course there's an interest!;):D

[Skew ChiDAMN!!]

When I first read the book I toyed with the idea of making one, but as 'twas still early days for me I put it in the "too hard for now, maybe later" basket. From whence it has not been extracted... yet. I'm only just beginning to experiment with those types of toys now. :)

As for any interest, well:

Bloody silly question Jim - of course there's an interest!;):D

I couldn't have stated it better. :D

[powderpost]

Okay, I suppose it was a little naive... :D. Almost finished the china cabinet, will look into it shortly with a new thread.
Jim