Cutting obtuse angles... Which technique, what tool!?

[will_s87]

So I tried to outline the problem below

I need to cut the obtuse triangles from full lengths of 2x4, this timber dimension can be changed but this seems a good trade of between strength, weight and cost.

... I have no table saw and I probably cannot afford one either!

Any help would be greatly appreciated.

Thanks, Will.

 

[Jacob]

Wossa problem?
Your layout is difficult (black rectangle). Easier if the apex of the triangle is on the outside edge (of a 2x2"?) rather than in the middle of a 2x4 - for which you would need a no-back saw or a band saw.
So you just mark them up with the apex outermost and saw close to the line with a tenon saw, then plane to the line if necessary.

 

[bugbear]

So I tried to outline the problem below

I need to cut the obtuse triangles from full lengths of 2x4, this timber dimension can be changed but this seems a good trade of between strength, weight and cost.

... I have no table saw and I probably cannot afford one either!

Any help would be greatly appreciated.

Thanks, Will.

How many do you need to cut?

BugBear

 

[will_s87]

Wossa problem?
Your layout is difficult (black rectangle). Easier if the apex of the triangle is on the outside edge (of a 2x2"?) rather than in the middle of a 2x4 - for which you would need a no-back saw or a band saw.
So you just mark them up with the apex outermost and saw close to the line with a tenon saw, then plane to the line if necessary.

On a length over 2m there is no way I would be able to achieve the accuracy I desire relying on the trueness of my arm. I ain't got the skills. Also, do you have arms like hercules? It would take me a long time to cut that with a rip saw, let alone a tenon!?

With regards to the number it's hard to say. Over 100 I would of thought, probably all longer than 2m. I'm about to get some lunch so I will try and draw up your suggestion of leaving the apex on the fixed side, rather than in the middle. ...

Will

 

[bugbear]

With regards to the number it's hard to say. Over 100 I would of thought, probably all longer than 2m.

Will

If your joint shapes are 2m long, and 4" = 10cm high, your angle, assuming both ends taper to zero, is tan -1 (10/100) = 5 degrees (so your apex angle is 170 degrees).

That's certainly obtuse, and in the quantities you mention, I'm not sure manual techniques are practical.

BugBear

 

[jasonB]

With over 200m to cut you would be better off buying a cheap tablesaw from one of the sheds for about £50. Stand teh 2x4 (4x1 would do) on edge and with the blade angled cut one triangle off, flip it over and do the other side. You could also do it with a handheld power plane but it will be a lot slower.

How strong is this structure going to be as drawn you will only have about 1/2" to screw into and any flexing will likely crack the softwood.

 

[Jacob]

Oh I see! The drawing is an end view - what you want is a long triangular "glue block".
Either make a set of smaller blocks to fit together, or make a long one by hand planing the two bevels to marks. But if you want 100 this will be difficult, so take the job to a machinist - spindle moulder with a tilting arbor? Table saw?

 

[will_s87]

Hi guys! Thanks for all the fast reply's I will try and clear up all the things I didn't make clear... Doh!! In this first diagram I didn't show any depth to the wood... I've changed this now so hopefully it makes more sense

I've put on another file attachment that will make it easier to visualize ...

@BugBear - No tapers here thank goodness, just a long triangular glue / screw block for re-enforcement.

@ Jason - looking at the diagram do you think this would be a safe way to cut? Perhaps I can make some sort of jig/fence to provide some extra support...

@Jacob - The thing about taking this to a machinist is that every piece will be slightly different... I'd rather spend some cash on the tools (looks like a table saw haha) and be able to do it myself...


thanks, Will.

 

[bugbear]

Oh I see! The drawing is an end view - what you want is a long triangular "glue block".
Either make a set of smaller blocks to fit together, or make a long one by hand planing the two bevels to marks.

Depending on the cosmetic requirments, easier to just hand plane one bevel at twice the angle, which results in an asymmetric block. Still a huge amount of labour though.

But if you want 100 this will be difficult, so take the job to a machinist - spindle moulder with a tilting arbor? Table saw?

Agreed, seems the obvious solution.

BugBear

 

[Eric The Viking]

What are you making? Are there any alternative ways of going about it?

 

[will_s87]

Eric: This is for a climbing wall. I believe this will be an effective way of re-enforcing the joints between panels...

see: http://www.bigrockclimbing.co.uk/shopim ... dering.jpg

 

[jasonB]

You wont need any other jigs if you saw it like your drawing, done it plenty of times. The main thing to watch is that whatever saw you use has sufficient depth of cut to ensure the crown guard does not rub on the workpiece.

Jason

 

[AndyT]

On that scale, how about this:

To reinforce along the angled joint between two ply boards, use a table saw with the blade angled over to make a bevelled rip-cut along the length of a chunky piece of softwood. Glue and screw along the join. Plenty of area by making it full length.

Then, to hold the angles right, use the same timber and make bevelled cross-cuts at the ends of fairly long pieces (about 3 or 4 foot) and screw through the ply into the ends of these. They make quite large triangles, a bit like roof construction. Big triangles will give better rigidity.

 

[Jacob]

Eric: This is for a climbing wall. I believe this will be an effective way of re-enforcing the joints between panels...

see: http://www.bigrockclimbing.co.uk/shopim ... dering.jpg

In that case you don't want long pieces at all.
Assuming there is some sort of framework structure holding the whole thing together you can then go around putting small individual glue blocks behind the joints, in the old fashioned way. You'd have the grain crossing the joint and each one would have a final trim if needed, to make sure it was a tight fit - it's quite likely that the structure will vary from the design drawing for one reason or another. You could fit as many as you want, fill the space or leave gaps. Glue, and screw in from the outside, or just a rubbed glue joint, or perhaps screw every fifth one and the others just rubbed.
This would be much stronger than having a long fillet with the grain going same way as the joint.

On the other hand a much better idea would be a glass fibre bandage with resin.

 

[barkwindjammer]

So, its not going up the wall of your bedroom and across the ceiling then?
If members of the public are going to be using it ?, then I'd take the drawing to a welder/fabricator.

 

[Eric The Viking]

I'm with Jacob - much depends on the framework behind, and grain across the joints will be far stronger and easier to fit. Fibreglass reinforcement will hold the panels together, and in any case you're going to need to fill the gaps with something strong (on the climbers' side of it), to avoid splinters, etc., and attach to the framework.

Can you have a good look at the way they've been made elsewhere?

If you get or can borrow a rail saw ('plunge saw': Festool, Makita, Mafell, DeWalt all make them), you can have good long straight cuts with whatever bevel angle you need, without needing a huge saw table (just something sacrificial underneath the sheet - I use a slab of polystyrene usually).