Centering misshapen work between centres

[Arron]

Hi. I need to turn some short tenons on a few rough-cut branches, such as the one shown in the photo, or even more twisted. The problem is centering them so that they will spin reasonably smoothly. The way I'm currently doing it is by mounting them in the lathe, turning them by hand and noting where the heaviest side seems to be, then repositioning the point of contact with the tailstock; and doing this repeatedly until they seem to be balanced. It works, but its tiresome.

Is there a way of figuring out how to mount an eccentric or misshappen object easily and quickly.

cheers
Arron

[wheelinround]

just the way your doing it even if you had the wood trimmed down it could still be weighted different as grain and density differ

[rsser]

Not that I know of Arron.

But COG is misleading.

You want centre of the wood volume, no?

So maybe start with best guess between drive spur and tail centre.

Do a shallow rough out, then reposition first at drive spur centre. See what it looks like, then change the spur centre and the tail end if nec.

Good luck

[Arron]

You want centre of the wood volume, no?

No, I dont think so, though I'm not really sure. I just want it spinning nicely and not sounding like its going to fly off and hit me, or shaking my rather light-weight lathe to bits. The tenons dont have to be in the centre of the end of the stock - this is deliberately rustic stuff.

I'm currently thinking of things like this :

1. Put a nail in a vice, point upwards.
2. Hang a string above the nail with a plumbob on the end. Hang it in such a position that the tip of the plumbob touches the tip of the nail.
3. Shorten the string by the length of the workpiece in question, plus a couple of mm.
4. Now take the workpiece and fit the lathe spurdrive by bashing it into the centre of one end of the workpiece. This end is just lined up by eye and doesnt really matter much where it is.
5. Knock the spurdrive out.
6. Position the workpiece vertically above the nail, with point of the nail resting in the hole made by the spurdrive.
7. Cup one hand around the workpiece, which is captured at the bottom by the nail but free to respond to gravity at the top, and move it around till it feels to be balanced vertically.
8. With your free hand, mark where the plumbob is pointing at the other end of the workpiece. Punch a hole where the mark is because this is where the point on the tailstock will go.

Actually I just made that up and would be surprised if it works. At this stage I'm just wondering what the recommended way of dealing with this problem is (if there is one).

cheers
Arron

[Ozkaban]

Another idea is to put a couple of 20kg bags of concrete/sand/whatever on the shelf of your lathe. Actually, more than a couple. Should weigh it down a bit and reduce the rattle somewhat.

Cheers,
Dave

[RETIRED]

I guess the centre line of the timber.

[Arron]

I guess the centre line of the timber.

I dont get that ?

Arron

[steck]

Not really a how to do it on the lathe answer , but, I have seen some tenon cutters around that look like big Pencil sharpeners.
Have you had a look at these?
$35 a set of 3 from carbatec.

[Sawdust Maker]

Arron

I think what is saying is that he looks at the log carefully and eyeballs where he thinks the centre even weight would be. But then again he's been doing it for a couple of years

Steck

I think that piece of tomber is a lot thicker then the carbi tenon cutters - they only go up to 30mm

Arron

btw, How is me old lathe going?

[Arron]

btw, How is me old lathe going?

Good, I used it quite a bit after I bought it from you - for about 3 months. Then I didnt use it for about 18 months due to repetitive strain injuries - which didnt really arise from the lathe work but were not helped by it. I've just returned to doing a few things on it lately.
Due to the RSI I will probably from now on be using it as I originally planned - just to make a few furniture components every now and again.

cheers
Arron

[Texian]

Arron,
The procedure outlined in your original post might very well be the best. This is especially true if you need the tenons on the two ends of the workpiece to be coaxial. Beyond that, as Steck showed, there are tenon cutters available that are designed for use in construction of "rustic" furniture. Just need to do a bit of searching.

[Frank&Earnest]

Done a lot of that, attempting through the years to get "blanks" out of prunings.

There is no escaping the fundamental principle, what Ern said, summarised and Sawdust Maker explained. It then depends whether you want to maximise the diametre of the resulting cylinder, which has been my case, or retain the natural profile and structural soundness for rustic furniture parts, which appears to be your case.

If it is so, probably the lathe is not the best tool for the job anyway. The way I would do it would be to design life size with straight lines each piece of what I want to achieve, say a stool or a small table, then make each piece choosing a log that approximates the shape and ensuring that the end tenons, cut by hand, are exactly where the ends of the designed straight piece are. Then you can be sure that the natural form in the middle of the piece is not going to cause you any problems, without the need for complicated guesses.

[RETIRED]

I guess the centre line of the timber.

I dont get that ?

Arron

I look at the timber and roughly work out where the centre line of the rotating timber will be.

I then mark the centres where I think they should be and put the piece in the lathe.

I then rotate the timber by hand to check my guestimations.

In your case as you are putting a tenon on each end I think it is irrelevant where the centre line is as you can make the tenon where you want it on the end. Just spin it slowly.

I think what is saying is that he looks at the log carefully and eyeballs where he thinks the centre even weight would be. But then again he's been doing it for a couple of years

A few.

[Pat]

A few.

Centuries

I have found as long as the ends are as close to square to the drive and tail, you can guess, turn by hand and spin at lower speeds safely. A 3 point steady may help as well.

[RETIRED]

Centuries Just feels like it sometimes.

I have found as long as the ends are as close to square to the drive and tail, you can guess, turn by hand and spin at lower speeds safely. A 3 point steady may help as well.

A steady will not help out of whack or out of round work.