morticing a pedestal table

[johnnyb]

I'm just making a small pedestal table and I've nearly finished but I'm at the stage of doing the dovetail slots for the three legs.
I think my lathe has facility to divide the spindle into 3(havent checked yet but I'm 90% sure)
should I make some sort of box to attach to the lathe bed and use the dividing disc. or make the dividing disk using geometry and the whole device could then be made for use off the lathe which is a bit high(I'd have to operate the router on a step.)
what is the best way to guide and steady the router as well.

 

[TheTiddles]

You could do it one of those ways, or by hand. Are you putting a flat on the spindle before the dovetail mortice or scribing the leg to the curve?
Aidan

 

[johnnyb]

I'm putting a flat on first then with a 1/2 inch straight finally with the dovetail bit. I spent the morning making a suitable jig. it looks as though it should work. I take a few pics shortly. im just wondering the best way to guide the router. mine does have 2 fences I could use. by hand would be a reet pain int but I reckon!

 

[stuartpaul]

I made a 3 legged pedestal some years ago and the sliding docetails were a pain. Steve Maskery had plans for a jig so that was the way I went but it was still quite frought and I needed 3 routers in order to not loose settings.

If you’ve got indexing on your lathe then building a box is probably the easiest option (mine hasn’t) but make sure to think through the process carefully so you don’t reset before you’re finished. Good luck!

 

[johnnyb]

yes I can see that the guide needs to be solid and the depths need careful management.

 

[johnnyb]

heres my morticing box.

 

[recipio]

I make shaker candle stand tables and reckon that dovetailing the legs is the most difficult job. Routing flats at 120 degree angles is ideal as you will never get that level of precision doing it by hand. Having seen a Legacy ornamental mill at a show I bought one on impulse ( that's the problem with shows ! ) and it's so useful. A router sliding box however will also work. The trick is to use a router bit as close as possible to the width of the legs ( or even slightly over ) to rout the flats and to plough a groove for the dovetail with a straight bit which will relieve the pressure on the dovetail bit. A straight groove can't be any wider than the 'neck' of the dovetail bit of course. Its worth taking time to get the setup right as there is nothing worse than finding mm gaps between the leg and post.

 

[Jacob]

Wouldn't it be easier to do it by hand?
Easy to mark the three sockets exactly. Then chisel out a straight mortice, then taper the sides, then fit the DTs.
Looks like the effort to set up using a router is much more difficult.
P.S. You'd need to undercut the shoulder part of the sliding DT so that it'd pull up tight and close the visible joint line.

 

[johnnyb]

I seem to have stumbled on having all the parts in place to accomplish this using a router and lathe(the index seems really good and split up into 24)
but I am heeding recipient advice and carefully choosing the dovetail bit. the parameters are the leg is 3/4 inch thick and the size to the shoulder 1/2inch. I will initially plough with a 1/2 inch. so the dovetail needs to be 1/2 inch wide 1/2 inch from its widest point(or slightly less)
ps normally I'm a big advocate of doing it by hand but I reckon it would be an awkward job requiring regrinding the bevels on a chisel.

 

[Jacob]

Simple way to mark your 3 centre lines is to walk and mark a pair of (outside) calipers round as near as you can guess. If it misses try again with small adjustment - basically divide the error by 3 (by eye). Do it once more if necessary and you are there.
n.b. this is why dividers are called "dividers". It's a tool for accurately dividing a line. But outside a round thing you need outside calipers.

 

[recipio]

I tend to make the dovetails first and then fit the legs for a snug fit. Aim for a thin dovetail - you have to leave enough wood on the leg to rout down to the shoulder. I find an old Leigh jig good for this as it has a bar for sliding dovetails and you can make minute adjustments.

 

[johnnyb]

I finished doing the sliding dovetails on this today. It was challenging but seemed to come together pretty rapidly.
recipio was absolutely correct that the joints need to be tight. otherwise a gap will appear. there was a touch of slop in the index system hence the wooden wedge. the whole mortising probably took under an hour. including making a quick router table as I didn't have an 8mm collet for the big router in the router table(used an 8 80 dovetail bit from a leigh jig)

 

[johnnyb]

the finished table

 

[1275gt]

Looking good John