Thread: Square funnel .. sort of thing

I may well be wrong, but I think that in fact, if the funnel is "square":

1. each side of the funnel will be a quadrilateral with two parallel sides (top and bottom) and two sloped sides which will each be sloped out from bottom at the same >90 degree angle,
2. the length of the top parallel side will be equal to that of the bottom plus twice the allowance for the double angled slope plus twice the thickness of the material
3. each joint of the sloping side to the other sloping side can be treated in itself as a right angle and can be dovetailed in the usual way.

At the moment I haven't calculated the allowance for the slope, but a little 3D trig should do it (or cut up a carton to make a 1:1 scale model and fiddle (practical trig for the lazy)

Himzol,

I have the method for making something like what you want. If it was a funnel then two sides would be vertical and the other two would be sloping.

I haven't made this joint but if you want details, PM me with your EMAIL address.

I am not absolutely sure, but I think that you can do skew dovetails. Try the following:

On the face side of the tails board draw the tails.
Extends the lines of the tail on the end grain, but instead of making the line square to the face make it parallel to the top of the funnel. That is, if the sides slope by 30 degrees, the lines should be at 60 degrees to the face.
Cut the tails.
Transfer tails to the end grain of the pin board.
Extend the the lines on the face of the pin board - again make them parallel to the top of the board - not square to the end grain edge.
Cut pins.
You're done.

Picture and SketchUp model of tails attached.

Have a look at the Keller Dovetail Jig web site - they claim to be able to dovetail curved & angled faces, and anything you can do with a jig can be done by hand - eventually. Should have some ideas.

HI Himzo,

I'm frantically preparing for today's work so can't give an extended response, but if you google on

canted dovetails,

and

compound mitre OR miter angle

as the search terms, you should get enough to get you going.

Cheers,

eddie

Himzo,
The joining edges are are NOT square any way.
What you are looking at in a hopper is an upside down hip roof.
Same geometry. You are looking at purlin top cuts for the face of your boards and the dihedral angle for the ends.
Check out my roofing angles page for the geometry of it.
http://www.builderbill-diy-help.com/roofing.html. on that page is a lnk for the dihedral angle.
If you wanted to mitre the corners you would use the purlin side cut.

I would say, cut and fit your material as though you were butt jointing it first, then mark out your dovetails. You are in for some fun.

If you can't follow my geometry do a search on "crown mould angles" which is what they call cornices in the US. There are heaps of sites that do the calcs for you.

Best of luck
Bill

Thanks to all that contributed,
I will work through your answers and work out the best form of attack.

You are in for some fun.

Bill I'm sure you are right, but the way I see it is that it will be a interesting exercise, where if I screw up, it isn't going to impact on anybody else. Also more practice at hand cutting dovetails. You see I've worked out that my biggest problem with handcut DTs is that I don't do enough of them.

Rob.. PM sent

regards,

Himzo.

Do a search on these forums for 'compound mitres'. Someone posted a spreadsheet that you can use to calculate the mitre gauge settings given the angles of the sides - last year if I recall correctly.

Originally Posted by AlexS

Do a search on these forums for 'compound mitres'. Someone posted a spreadsheet that you can use to calculate the mitre gauge settings given the angles of the sides - last year if I recall correctly.

Hi Alex,

Thanks for the input, I've done the search but nowhere does it say how to do DT's on these & thats what I'm really interested in. Javali is (I think) on the right track as to what I'm talking about. So hopefully I can put that into practice..
BTW I hope you put that marking guage to good use, I have to say I'm extremly envious.

H.

Info being EMAILed as we type Himzol.

Originally Posted by Wood Borer

Info being EMAILed as we type Himzol.

Thanks Rob,

I had a quick look before work and it looks like what I'm after. I'll try it over the weekend and let people know how I go.

H.

If you still need more info, I've got a couple of books that describe the method, Let me know, and I might be able to send you a p'copy.

Himzol, If you havent found out how to do it yet, go to CARBATEC and download the manual for their KL 15 dovetail jig.
It shows you how to do jsut what you want. The theory would probably be transferable or adaptable to other jigs.