Accurate Mortice & Tenon Joints for floor standing lamp?

[Martin]

Hello all - I don't post very much on these forums but read them often, and find them a great source of ideas and inspiration! Thanks to all for making this such a great site

I was hoping someone could give me some advice on making mortice & tenon joints for a standard lamp I'm making as a gift for my Mum.

The main body (upright section) of the lamp will be in 3 sections (my lathe's not big enough to turn it as a single peice), so I'll need to join the pieces somehow.

I've decided to try to use mortice & tenon joints (round ones of course) to join the bits together, but I'm struggling with how to make accurate (perfectly centered) holes for the mortices. My fear is that if they're off center, or not at perfect right angles to the peice, the resulting lamp will end up looking "wonky" when fitted together.

When making lamps from a single peice I would of course turn the stock to a cylinder, and then bore a hole right through the center for the flex.
But, having done this, how do you bore a larger hole in one end for a mortise whilst ensuring you remain centered with the axis of the lathe?

I've been racking my brains and come up with a few ideas:

(1) Drill the mortise hole first before even mounting in the lathe using a pillar drill (but I'm worried this will give complications when you come to mount the stock afterwards on the lathe)

(2) Use a jig mounted on the bed of the lathe to support one end of the peice whilst the other is mounted on a centre peice, drilling the mortice with a drill bit mounted in the headstock (but again, I'm worried about the accuracy of this method).

(3) Give up and use some other mechanism for fixing them together

I'd really appreciate any advice from those of you that have done this before - what methods did you use? Did you use any special tools/jigs? I probably haven't explained this very well, so I hope you get what I'm on about :?

Thanks in advance.
Martin.

 

[Dewy]

Have you got a pillar drill?
You could offset the drill head away from the table then make something to clamp the workpiece perfectly upright & centred for the drill then use a forstner bit to produce the mortic. You could use the same setup to drill the through hole for the flex.
Back in the lathe. Turn the tenon to fit the mortice already drilled.

It's easier to do than explain.

 

[Chris Knight]

I would have thought that you could use a hole saw that typically comes with a quarter inch bit (or the metric equivalent these days, I suppose). Having turned your piece and having drilled a quarter inch hole for the flex, just mount the holesaw in the chuck and use the quarter inch bit to centre it (by poking the bit into the hole you have drilled) then saw deep enough for your tenon.

 

[Martin]

Thanks for your suggestions guys...

Chris:
That's a great idea with the hole saw (and luckily I have one). The only prob I can see is getting the waste out afterwards - but I guess that's a secondary problem - provided the hole is accurate...

Dewy:
I do have a pillar drill and have been thinking about the same sort of solution. It's floor standing, so theoretically I could even rig something up in the table provided it drops down low enough.

Overall I think I just need to have a go at this and see what happens (but not on the nice new turning blanks I've bought for this project - I'll practise on some scrap first...). I'll let you know how I get on...

Thanks once again for your suggestions.

Cheers,
Martin.

 

[Aragorn]

Hi Martin
If you are able to set up a rigid jig to hold the piece vertical to your pillar drill, then why not just use the right sized Forstner bit?
I agree that removing the waste from the hole saw will be a bit fiddly!

 

[Anonymous]

Martin,

If you can cut the mortice with a Forstner bit first, you could then make a loose tenon to fit on the lathe, and use this to hold it between centres while turning later. This way the mortice is guaranteed to be central in the finished piece and the accuracy of drilling is not so important. I think that maybe what Dewy's already suggested, but I couldn't resist posting too...

AG

 

[Chris Knight]

Since removing the waste from the holesaw solution presents a problem, here's what I would do

1. If possible cut it out whilst still on the lathe - implies you have a steady or that you will make one.

2. Take it to a pillar drill and use a Forstner bit to drill it out (because the hole saw has already defined the sides of the mortice, subsequent steps don't need to worry about doing this, so in this case, an undersized bit would work OK

3. Take an out-cannel gouge to it and just chop it out

 

[Anonymous]

Thanks once again guys (& gals?) for all the great suggestions... :idea:

I think Afterglow's suggestion is looking like the most viable to me - I just never thought of it that way (Dewy: apologies if that's what you were suggesting all along - didn't occur to me when I read your post).

I suppose in effect your suggesting using a shop-made friction chuck to hold the workpeice. Don't know why this never occured to me before (I've read about them but never used them).

On balance I think this will give me the result I want since it guarantees that the turning I do subsequently will accurate in relation to the mortice/tenon.

Anyway, I'll give all this a try on some scraps and let you know how I get on.

Cheers,
Martin.

 

[Martin]

....wish this forum software wouldn't let you post without logging in... :?

 

[cambournepete]

I think you need a chuck mounted on the lathe and a forstner bit.

Drill a hole in a piece of scrap to use as a gauge to size your tenons.

Mark your centres and turn the 3 sections to shape, including the tenons, sizing the tenons using the gauge you've just made.

Mount the chuck with forstner bit in the headstock, and using the previously used centre point as the centre for the point on the forstner bit drill the mortice (on slow speed), winding the wood onto the bit using the tailstock.

You can now drill the through hole with the sections turned the other way round, using the centre point left by the forstner bit to centre the hollow tailstock centre (using its centre pin) as you would for a single section lamp.

Hope this makes sense !

This is how I've done it before - and the lamp is still in my friends living room!

 

[Martin]

Thanks Pete,

Yet another excellent suggestion For some reason I'd got it fixed in my mind that I'd need to drill the hole for the flex before tackling the mortices.

In fact, I guess I could still drill the flex hole and mortice holes before doing the final turning (I prefer it this way - the idea of the drilling going wrong after spending hours doing the turning doesn't bear thinking about!).

Cheers,
Martin.

 

[Chris Knight]

Pete,
I like your idea best!

 

[Argee]

I know this is a very late reply, but I've only just joined! It doesn't look like anyone's suggested using a counterbore drive centre. These usually have a 5/16" pin on which to seat the flex hole when reversing the spindle. To make a mortice, stop the lathe, slacken the tailstock and grasp the spindle firmly. Switch on, then drive the piece forward with the tailstock until the counterbore drive cuts the mortice deep enough. There's an example to be found at http://www.axminster.co.uk/product.asp? ... 57&recno=2

Works like a charm every time.

Ray.

 

[Martin]

Ray,

Many thanks - ironically this was the method I ended up using (having read about it in a woodturning magazine), but I forgot to post back the final answer...

Martin.