'Perceive v2.0' Construction Diary

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#1,062
Re: Reminds me of thick as a brick,

Ed Lafontaine said:
and I rather like that album, though I don't think of you as thick at all...I would rather lapse into admiration, but more to the point...

Before you cut the wood, take the 2 pieces which will join at the miter. Set them together on a flat surface in aproximately the orientation you want to achieve. Angle them in to aproximate the 16 degree slope.

The wood you will remove by cutting is that which is touching...and a little further out...so make a pencil mark across the edges and faces of the wood to represent where the saw has to enter. These marks have been helpful to me many times with saw set-up.
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Ah, now I get you, thanks and will do!

Right really am off now.
 
#1,063
alexcd said:



Because as you tilt the two sides (16*) then the angle between the pieces is no longer 45* even. I may be wrong but I'm somewhat confident that it's a 1.75* difference.

If straight down on a saw is 90*, then you want to set the blade to 46.75*. It's not a big deal but you would end up with a gap otherwise.

Ant, I dont blame you for signing off. My head hurts too.
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I felt the same way when I first looked at it, I tricked myself into thinking that angle changed when I thought that was the original question. After strong concideration I feel very confident now that it does not. Anyways, good luck Shin. Damn, it's getting late here too, took longer than I thought to work through all this mess :cannotbe:. Time flies when it comes to math I guess, fun question though.
 
#1,065
m0tion said:



I felt the same way when I first looked at it, I tricked myself into thinking that angle changed when I thought that was the original question. After strong concideration I feel very confident now that it does not. Anyways, good luck Shin. Damn, it's getting late here too, took longer than I thought to work through all this mess :cannotbe:. Time flies when it comes to math I guess, fun question though.
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Change that 16 degree angle to 90 degrees and see if that 45 doesn't change.

Sheldon
 
#1,066
Sheldon said:



Change that 16 degree angle to 90 degrees and see if that 45 doesn't change.

Sheldon
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I see exactly what you're saying, and I know I've been saying 45 degrees the whole time, we all have, but the truth of the matter is everyone just picks 45 degrees because it's easy to do on both sides of the pieces. You could pick any two angles for that joint that add to 90 degrees and it would work the way you wanted, even in the instance of the pieces being tilted all the way to 90 degrees. My mind, my thoughts, I'm always willing to concede the fact that I might be wrong, I'm just trying to convey what makes a whole lot of sense to me.
 
#1,067
Its not going well guys.

I tried 12.5 and 45 but it doesn't mate up correctly by a fair way. Something is wrong.

Both angles are likely wrong as the 45 degree bevel is causing the wood to lean into the work. I was thinking that mitre saw wasn't accurate but it was spot on the money for the bits I did on the Perceives.

I'm off out to buy some more MDF to practice on :xeye:

Might be another trial and error job this one.
 
#1,070
If I have issues like this, I resort back to my technical drawing days, and actually draw the thing to scale, then measure off with a protractor from the various projections. I can't be having with that maths stuff. 😉

m0tion, youre quite right in saying the angle is always 45 degrees, but that is only normal to the actual joint, if you're cutting from another plane it does change.
 
#1,071
Try a different angle...

Leave the 45 degrees as the crosscut. Don' fiddle with it.
Size a block of wood to be used at the bottom of the fence to induce a 16 degree slope into the stock to be cut. In this arrangement the stock is held to the fence rather than the table.

How wide are the pieces to be cut? If the pieces require being laid down, this arrangement will still work. However the bevel setting would become 45 degrees and the stock would be square in crosscut.

This approach reduces the variables and should make the cuts easier to set up.

Hope this helps.
 
#1,072
I posted the same question on a UK chat forum that isn't really related to DIY but does have a number of bright individuals, I've now got a physisist looking into it 😀

Apparently its more complicated than we originally thought and yes the bevel does change from 45. Can't get my head around that but anyway...
 
#1,073
OK here's how its done according to our well informed Physisist:

The first thing to do is to work out the coordinates of the various points. So the top edge where they meet has values for x,y,z of sine 16, sine 16 and cosine 16, assuming the bottom of that edge is 0,0,0. You want the length of that intersection, so first you need to divide it into the various triangles you need to get lengths. The top forms a square so you use pythagoras to get the length of the hypoteneuse, which in this case is the square root of sine 16 squared x 2. The next triangle is the one formed by the height, the diagonal displacement from the origin and the length of the intersection, so again the length of the intersection is the square root of sine 16 squared x 2 plus cosine 16 squared.
You ought to get a value larger than one for this. Then it's a matter of taking the inverse cosine of the inverse of that number to find the resulting angle.
For 45 degrees you find you need to cut at more like 35 degrees to get the two to line up.
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Using that lot, the cut angle is 15.4 degrees and the bevel is 43 degrees.

And using those figures results in near perfect joints:

An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


🙂
 
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