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Arron
4th Feb 2010, 10:50 AM
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
4th Feb 2010, 11:35 AM
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
4th Feb 2010, 11:43 AM
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
4th Feb 2010, 02:27 PM
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
4th Feb 2010, 02:42 PM
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
4th Feb 2010, 03:00 PM
I guess the centre line of the timber.

Arron
4th Feb 2010, 03:02 PM
I guess the centre line of the timber.

I dont get that ?

Arron

steck
4th Feb 2010, 03:15 PM
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
4th Feb 2010, 03:26 PM
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
4th Feb 2010, 03:51 PM
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
4th Feb 2010, 04:36 PM
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
4th Feb 2010, 04:53 PM
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
4th Feb 2010, 05:07 PM
I guess the centre line of the timber.


I dont get that ?

ArronI 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 yearsA few. :wink:

Pat
4th Feb 2010, 06:54 PM
A few.
Centuries:q

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
4th Feb 2010, 08:51 PM
Centuries:q 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.

joe greiner
4th Feb 2010, 10:24 PM
Several years ago, Nawm (Abrams, NYW) turned end features on some odd-shaped pre-forms by attaching them to a flat fixture that spun along with the piece. I forget the details, but I think the fixture provided some counterweight to reduce vibration. The fixture was stiff enough to not need a steady. For raw timber, the fixture would need adjustable clamps.

If the fixture doesn't clear the banjo, relocate the banjo with the stationary flat part horizontal. Or remount flipped end-for-end.

Cheers,
Joe

oldiephred
5th Feb 2010, 09:50 AM
Maybe it is already obvious but -- just in case not-- should you not first roughly center it in the lathe then measure the runout to determine the largest size spindle you MIGHT get? Is it possible that you will suffer all the stress of beating it to somewhere near round only to find it will end up too small to be useful?
I apologize if I have offended anyone but -- just wondering:;

RETIRED
5th Feb 2010, 10:44 AM
Maybe it is already obvious but -- just in case not-- should you not first roughly center it in the lathe then measure the runout to determine the largest size spindle you MIGHT get? Is it possible that you will suffer all the stress of beating it to somewhere near round only to find it will end up too small to be useful?
I apologize if I have offended anyone but -- just wondering:;I am under the impression that he is building rustic furniture and only needs the tenons on the ends to fit into something else.

I could be wrong, have been before.:D

oldiephred
5th Feb 2010, 11:07 AM
Sorry:B Only part way through my new literacy classes, so my comprehension is not what it should be. Will get my dog to confirm my understanding of the next item before I reply:doh:. Actually she is a sheep herder and, as many of you aussies know, some of them are very intelligent.

rodent
6th Feb 2010, 04:11 AM
Multi-center woodturning by ray hopper isbn no 0-946819-35-1
He does walking sticks ( page 37 ) using a off centered and counter weighted face plate with home made cup chuck .And slowly does it your mc 900 does a minimum of 500 rpm use it .as for center of balance a v cut into to bits of ply two nails . screw one bit of ply onto your bench one in workmate or watever gess your centers lightly nail into wood ( one in both ends ) and spin in v blocks if it keeps dropping to one point re position the nails till it's as balanced as you can get it there's your centers . ta da .

Tim the Timber Turner
6th Feb 2010, 10:23 AM
(quote)
I could be wrong, have been before.
__________________
Ian () Robertson
"We do good turns every day"



I thought I was wrong once but I was mistaken.
___________________
Tim

stuffy
6th Feb 2010, 01:02 PM
If your drive centre has a long enough point put your work piece between centres with just the point engaged and gravity will let the weight fall to the bottom. If your point isn't long enough put a tail centre in the headstock so both ends move freely. Adjust either or both ends, spinning by hand, until it is balanced.
:)
Steve

Gil Jones
6th Feb 2010, 04:28 PM
There are tenon cutter tools, but they are NOT cheap.

Rockler - Search Results for 'tenon cutter' (http://www.rockler.com/search_results.cfm?filter=tenon%20cutter&ne_ppc_id=776&ne_key_id=3424592&gclid=CMGOnd773J8CFRGfnAodX0mpIg)

Tenon Cutters + Tenon Cutter Blades | Power Tool Accessories | Power Tools | Northern Tool + Equipment (http://www.northerntool.com/webapp/wcs/stores/servlet/category_6970_97+146+771482)

rsser
6th Feb 2010, 04:31 PM
Jest need a whittlin knife and a steady hand ;-}

cultana
7th Feb 2010, 12:28 AM
Jest need a whittlin knife and a steady hand ;-}

:rotfl:
With the sense of wit that falls out of this place I would have expected that one earlier.. :D

Arron
7th Feb 2010, 06:57 PM
sorry, I've been away for a few days and just caught up on this.

, youre right, I only need to cut short tenons.

Rodent and Steve, your ideas seem to amount to pretty much the same thing, the difference being in the way you temporarily suspend the workpiece. Anyway, it seems to work OK.

and thanks to those who recommended tenon cutters. They are pretty pricey, and when you've already got a lathe it seems smart to use it. Also, I was surprised when watching the YouTube videos on tenon cutters just how rough the tenons produced are. I guess the problem is that there is nothing to keep the cutter aligned so the working edges are always digging in. A lot of the videos show people cutting tenons and then proudly showing off jobs I wouldnt be seen dead with. I know this is rustic stuff, but I still want joints as strong as possible so to me that means maximum surface contact.

thanks for the replies
Arron