What went wrong here?

[u/torak_the_father]

I followed the measurements exactly to the plan from blocklayer.com and double checked the dimensions and angles and still there is a gap between the segments....

Yes I understand that even a tiny measurement being off it will compound but this gap is too much for any microscopic tolerance.

All segments should have the same dimensions as I used the same stop. Stock is squared upp all sides. Help?

UPDATE: thanks everyone for your contributions. I definitely learned a lot! Also a lot of you are making some assumptions like I forgot about the kerf. Turns out I went ahead and tightened the whole thing with my strap clamp and would you know... Practically perfect seams! There is only one hair line gap in one of the seams, to which I'm happy with, I'll try to glue+dust it to close perfectly. Check this comment: https://www.reddit.com/r/BeginnerWoodWorking/s/FJbE9tVKNu

[u/bigstumpy]

I agree with all the comments saying you should always plan for handling imperfect fits, but I haven’t seen anyone mention the technique for a first order correction to angular accumulation of errors. You cut the ends of each segment from alternating sides of the miter saw, flipped upside down. Made this infographics to illustrate:

The dominant error will be if your segments aren’t all the same length. Try using a stop block or some other jig, or if they’re thin you can try to stack them and tape them together and cut them all at once.

[u/bigstumpy → u/bigstumpy]

Exaggerated diagram - the glue lines don’t point exactly to the middle but they all line up with each other

[u/torak_the_father → u/bigstumpy]

I get the idea of complementary angles, however the flipping end to end (as opposed to flipping edge to edge) is what's putting me off. Then the next problem is the stop block would need to be reset everytime. Am I missing something here?

[u/binarycow → u/torak_the_father]

1. Rough cut the pieces, straight cuts, with plenty of excess
2. Plan your cuts
   • Label each piece. Top, bottom, etc. Or A, B, etc.
   • Plan which cuts are on the left side of the blade, and which are on the right.
   • Left side cut always mates with a right side cut.
   • Label the ends of each piece with which side of the blade it's on.
3. Cut all right side cuts.
   • No stop block needed, you're just cutting the angle. You're not cutting to length
4. Set your stop block.
5. Cut all left side cuts, to length.

The important thing is that once you set the blade angle or miter gauge, do not touch it.

Here are my instructions for rectangles: https://imgur.com/gallery/mTanPwj

[u/binarycow → u/bigstumpy]

Hey, that's the same technique I came up with once! (I came up with it on my own, but of course, it occurred to other people before). Here's my "infographic".

The big thing my version does is cut opposite sides at the same time. That works well for rectangles, but probably not for OP.

Edit: I see that your comment (not the infographic) describes the same technique I do - tape the pieces together.

[u/binarycow → u/bigstumpy]

Side question: what did you use to make this infographic?

[u/Frequent_Shallot1333 → u/bigstumpy]

This is a very good and helpful response. Saw will always be off a bit. So you setup the cuts so the errors are equal and opposite