Complex compound mitre cuts

Hey all,

So I'm appealing to those who have more experience than I when it comes to calculating compound mitre settings where there is a splay, ie a rectangle. So for the last few days we've been restoring an old gazebo, and after installing a new top and bottom rail we came to the criss cross rails that were lap joined throught the center. The trouble come where we needed to calculate the mitre and bevel, where it joined the gazebo post. The rails had a 30 degree mitre either side and the angle from top of centre post to bottom of gazebo post where it meets the bottom rail was 29 degrees, but because the overall shape is a rectangle if we used those setting on the droppy we would recieve a poor join as it isn't a square. Anyone got some tips for quickly working these out, we did think of using crown moulding tables but didnt think it'd work as they are set for 38 and 52 degree angles. It's all finished now by trial and error until the correct settings were found, but I'm more intersed about how to get it close to right first go.

There's a rough sketch here to.

Thanks.

is it possible for you to hold the uncut member in position and scribe/mark the line? as a carpenter I do this a lot no measuring no mathematics. I Hope I have interpreted your question correctly.regards joel

Nah I scribed the side that meets the centre post. I can't scribe a compounded mitre onto the other end though. I spent a bit of time on google last night and have found the technical answer with a few equations, was just hoping there was something easier out there

Found these:
http://www.pdxtex.com/canoe/compound.htm
http://jansson.us/jcompound.html

They look a bit complex, but there are diagrams to help you get the right numbers in the right boxes

Have a look at http://www.tradestuff.com.au/product...tid=16151&js=n

Dad was a carpenter / builder and used to cut a lot of hip roofs by hand in the early days. Went on to become a truss designer for a Gangnail then a Hydroair truss plant in the early 1980's. Not many chippies even then could cut a hip roof by hand.

a picture of the actual job from a few angles might help.

I usually can work the many angles out from looking at a job and a sliding bevel is great to use. Use on in conjunction with a straight edge or spirit level if you need to project the line further.

These angles if you want on º you can put the bevel against your fence on your drop saw and then rotate the bae till it lines up with your bevel ... you can then write down the º

Love doing a 'stick roof', Id tackle one with a hand saw if I needed to but a power saw of some kind always makes it easier.


Dave the turning cowboy

turning wood into art

Thanks fellas there is a couple of handy links there that spat out the same numbers I got from using the formulas I found. Much easier than trial and error, will just refer to it when I run into the same problem again.

The other solution is don't even try to calculate the angles.

Use a compound mitre saw and set one angle against the other with the timber in the position it should lie in.

visualisation is the issue.....but calculate nothing

You may have to cut the whole thing inverted though.

I have also cut compound miters on the table saw using my protactor sled and the tilt of the blade.

you could do it the old way..and yes that is to mark out the compound using adjustable bevels.

This may help setting up the saw.

The biggest problem is visualisation...it may help to use a square piece of wood to work things out.

you can calculate all you like...there are on line calculators and stuff.....but then you have the difficulty of accurately measuring and marking angles.

easier to bypass the whole process and go straight to the angles themselves and transfer those.


cheers.

I think i must have misinterpreted the original post this roof in my mind sort of goes against the principles of pitching a roof it is effectively creating an irregular pitch roof as you have to different half spans with no ridge. which canges the geometry completely thus i imagine renders the hancocks roofing book useless, as it will give you plumb and side cuts for rafter and hip cuts but only for 45' junctions, now i would go back to pythagoras theorum if you know the pitch, this will get you close but in practice there are too many variables and to get perfect near air tight joins cuts would need to be scribed and adjusted, Sorry for the ramble it is hard for me to explain in written words,

Sorry Soundmn I didnt see your post, you have a far better way with words that I,

Wasn't there some bloke on here that used to post a calculator online for this sort of stuff???

Quote:

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Originally Posted by BrettC

Wasn't there some bloke on here that used to post a calculator online for this sort of stuff???

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Yes, blocklayer

http://www.blocklayer.com/CompoundMiter.aspx