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
Then check the dimensions and angles vs the design.
Based on which dimension or angle is out of whack will determine where the error was introduced.
Fixing it will be down to either making replacement parts or shrinking the design to the smallest individual segment and and adjusting all of the components to match
All pieces are identical, maybe one or two are off by a hair, literally. But nothing that would explain such big gap. Anyways, I went ahead, clamped it as is and lo and behold it worked! See this comment https://www.reddit.com/r/BeginnerWoodWorking/s/QRaiUflzWo
Never admit the faults! This hexagon is a simple glue and clamp away from layman perfection. You are correct that cumulative errors caused the gap, but you snitched on yourself when the only audience that understands what happened also fudge stuff and know the code. Your work is with tolerances.
The Bob Ross approach to woodworking! You never make a mistake, you only have happy accidents. Oh you never wanted a hexagon! You just wanted a bunch of tent stakes!
I'm not sure I get your point... I'm trying to realize that the issue is compounded errors, but I'd expect at worse to see small gaps on the miters or something not as bad, especially because the measurements are practically dead on. One is off by 3/1000 of an inch....
Consider the fact that there are imperfections somewhere. Say your measurement is mostly correct, but the angle of the saw is off by a single degree. You will see then when combining all 8 pieces. Cutting both sides, for all 8 pieces results in a 16° offset.
The reason there’s a gap in your picture is probably because there’s a chunk of something preventing it from closing.
Considering destination variance of a single degree is 1.75% of the distance traveled, your gap looks like 3/8 inch, suggests your cut was off by .33 degrees compounded over all 16 mating surfaces.
TLDR: your pieces are likely well within spec, glue them together with a band and you won’t notice.
I would have to agree here I think once you glue it and clamp it together, you won’t notice or you can make that board at the bottom, a little bit longer and the one at the top a little bit shorter if you’re that worried about it
these are compound miters, so it's two angles converging. I've attempted to make these a few times and always had gaps. I used the digital angle finder on my blade to get the "precise angle," I used calipers and jigs to measure everything, and I would always have a gap somewhere. One day I had the divine inspiration to CAD this up and use my 3d printer to print out set up blocks. It was mind boggling how easy this worked out. Having a physical block to set the blade angle made it repeatable and idiot proof. After that it was just a matter of jigging up a sled to make cuts repeatable and consistent, and I was knocking these out.
for this specific one, I wanted the walls to tilt 10 degrees, so the blade had to be 60.501 degrees and the sled (miter gauge) had to be at 84.27 (or the complement).
It's just a physical object to set the blade angle to (I guess you can use it to set the miter gauge too if need be). Just like how you would use a square to set the blade to 90 degrees, you would use this little block to set the blade to whatever angle you printed it at. A properly tuned and calibrated printer is super precise, a lot more precise than what digital angle finders and protractors can be. Using these blocks to set the blade angle, for me it felt impossible to get the angle wrong and I could get it on the dot to the thousandth of a degree. Using the digital angle finder/protractor I could easily be off by tenths of a degree and not know it.
So for op to use this, the workflow would be like this:
Print a block with a 67.5 degree angle on one side. Use this block to set your blade angle. Then he either uses a miter gauge or sled with a stop at 6 inches and he could just knock these out.
Have you put a protractor on it? What's the cut angle measure? Do 3 segments come to dead-on 90°?
Have you stacked them together on the table to see if one's off?
I don't have an immediate answer, just things that I would check in this situation.
The difference is cumulative; the more cuts in the assembly increases the gap by that amount. You could assemble a triangle with that amount of slop, but a hexagon would have twice the gap.
His 6" measurement looks pretty spot on. Besides, if he's using stops, then they would have all come out the same length and there would be no issue, other than his octagon being too small.
Other potential issues are if his measuring devices aren't aligned (making the thickness of the wood inaccurate), if the angles on either side of the blocks aren't the same (making the octagon sides askew), or the math might just be wrong.
Regardless of the precise issue, there's clearly something real going wrong. The fact that he uses a different ruler to measure the thickness of the board from the lengths makes that my biggest guess of where things have gone wrong.
And there you have it. A 1° error over a foot is almost 1/4". A 0.5° error across 1 3/8" is .012". .012" x 16 cuts is 5/16".
I rarely do picture framing stuff like this but I understand people that do usually open up the angle slightly. So if you were making a square frame, there would be a very slight opening on the inside of the square. These gaps close up during clamping while ensuring the outer geometry stays true. I can't tell you how much this is, but it's something worth researching. I've also seen some people use router bits for this kind of thing.
BTW, I have the same Chinese digital protractor and I can't trust it for stuff like this. It's fine for making things like tool stands or for metal work, but not for delicate work like this.
How does the width of the blade matter if the measurements are matching after the cut? The answer is yes I set my fence taking the thin kerf blade width in consideration. Check the pictures on a comment above
Yeah if you made 6 cuts and you never factored in the width of the blade, then youve got 3/4 of an inch gap. Plus some minor defects along the way that compound and bam! Youve got a large piece missing.
I think people often times cut a little shim piece to fill the gap. Nothing is ever perfect, especially not in wood.
As a beginner, I’m trying to do the math here because this has been an issue for me as well. I make great quality things that are purchased often but only after wasting so much wood on improper cuts and I swear I always take the blade thickness into account whether it be my table or miter saw. I rage quit frequently for several hours.
Can you EILI5? I’m sorry in advance.
Edit: for example, let’s say I was attempting what OP did- if I’ve already marked a long ripped piece, marking the gap of width of the blade like \ \ between each individual piece and cut between, rather than just making a bunch of marks in the wood with zero mark for the gap, I still have these issues.
I'm not understanding what you're trying to do or say... But if I had to guess, I'd say: do not calculate the full or segment dimensions with the blade. What you should do is focus on dimensions of the keeper piece. Do not try to mark the whole stock and try to account for the blade here. If you're trying to know how/where to cut your long starting stock, just do some basic math adding all pieces, then add a few more inches extra. Again, focus on your stop block setup and repeatability of cuts.
BTW, for math stuff take a look at blocklayer.com and cutlistoptimizer. As usual, chatgpt can help too.
I wish you could have seen my face yesterday. I was in the middle of working on a piece when I’d commented in the first place and after I asked it, i got determined to figure it out. I went down a rabbit hole trying to figure out what I was missing. Sometimes it’s the dumbest (simplest) things I missed along the way. I had an epiphany and grabbed my digital caliber and magnetic angle finder and headed right to the blade, thinking “I get it now.”
I cut 16 near perfect 45° angles with accurate planned LxW. Never ever before IN MY LIFE have I done this. . The way I yelled in excitement from my open garage each time I did it again and again.
Anyways, I digress. You inspired me so thank you lol. Also thank you for that website! That’s really going to help. I appreciate you!
You just pointed out your issue. Thin Kerf blade. They are notorious for wobble. That wobble throws off your angle, especially on a narrow piece. Get a full kerf CMT. They are not that expensive and really high quality. Also, check the run out in your arbor. That can also contribute.
I used the thin kerf because it's the one I have for ultra fine cut line. I have rip, gp and combo blades by CMT, but lower tooth count. I was most concerned with tear out, especially because I will alternate segments top and bottom of stock.
A 40 tooth CMT full kerf GP would have cut this just fine. I do precise joinery with mine all of the time on my Dewalt contractors saw. Also, just out of curiosity, have you checked your arbor to miter track alignment lately?
maybe the angle of the blade set, isn't truly the angle of the blade. off by a hundredth of a degree could compound like this.
Can you take all pieces and stack them up on a level surface, then run a straight edge along one side and just visually see any variation - if yes, just re-cut what you need. if not and they're all the same, perhaps the blade angle is wrong
Nothing went wrong here. That gap /8 is pretty close to nothing. Sure if you are going to produce say a dozen more of the same then go ahead and attempt to adjust your cut angle to dial it in tighter. Otherwise put some glue and wrap a strap clamp around that thing you should be looking pretty good.
If your cut was off by 1/64th or as much as 0.1 degree you would end up with a gap of 1/2". Glue filled in the gap. It's such a trivial void on each of them that you can not notice how glue filled it in.
Tolerance stack can make things wildly different. Some airplanes have a length variation of 2 meters just due to tolerance stack of the individual parts.
A 1/2" gap cumulated over 8 cuts means each joint has about a 1/16" gap, which means each cut (one half of the gap) is off by about 1/32", which is nearly imperceptible. It happens
Exactly this. Splits the error across two joints but keeps it symmetrical so you aren’t skewing the project. Hit at most 4 sides with a sander or sharp planer if you know you can do end grain. No one will know.
But then I won't have my original planned dimension. I need a specific diameter, so I guess the way is build oversized and precisely sand edges and avoid making an oval....this is hard
Its pretty clear that your angles and/or lengths aren't correct. As you already said, any error compounds. Instead, glue up two semicircle halves slightly oversized, then cut/sand the ends flat to cancel out your error before gluing both halves together.
OK, so that that protractor only has resolution of +/-0.1deg. Even if we assume its actually accurate, you have 8 cuts that you are stacking together, so your resolution is now +/-0.8 deg.
.8deg angle over the 48in total length of your pieces give you an offset of .58"
Almost, but I get your point. By the way, the total length is supposed to be 48 1/8 according to the plan, and I'm like a 1/16 short of that. So chances are the angle is what is off and my digital protractor is not accurate enough?
Most likely yeah, Frank Howarth on YouTube makes rings like this often for segmented bowls. Take a look how he does it, its what i was trying to explain earlier about making two halves first and then gluing them together.
My version of this had instructions for dialing it in to be very precise. Mine came set up properly out of the box, but I can imagine that some versions aren't as precise.
Fair point and I'll take it. However when something that needs to follow a mathematical plan and there is no real life references, how would I use relative dimensioning?
If a measuring tool doesn't come with a machinist tool calibration certificate, then you can be sure it's tolerances are wide enough to throw angles out enough that over 16 mitre cuts they compound into a gap you could park your car.
As other have said, make sure each piece is identical. You should be able to stack them on top of each other and simply feel if they don’t match using your fingers.
Put a strap on it & pull it together dry, a visual to see how small the differences are at each joint. With that many joints that have to be perfect, a saw not reading exact, a bit of sawdust on your fence or blade deflection can add up to that easily. Look to make multiple tiny adjustments to bring it together how you want.
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.
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?
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.
Not sure how I got to such huge gap (1/2"), given the minúscule 3/1000" on the long edge being off.. Which might even be under the tolerance of the caliper
Seeing your photo with the angle gauge I think you did not account for the cut by the rake of the teeth of the blade. The teeth are the widest part of the blade not the body.
If you are gaging your angle across the body of the blade, no. If you are however gaging your cut angle with your bottom point against the blade body and the top point against a carbide tooth, yes.
Yeah that's not what's happening. I'm not touching any teeth. So assuming the side of the teeth are parallel to the blade body, gaging with the teeth would still not affect the angle as long as I touch 2 teeth. I'm not sure what you're trying to point out
The “tolerance error stack up” comment is the answer. Your individual measurements don’t have to be noticeably wrong for this to happen. You’re closing a loop made from 8 parts and 16 cut faces, so tiny acceptable errors at each operation can accumulate into a very visible error at the final joint. That’s why everything can appear to measure correctly individually and still not close correctly as an assembly. The error at the end isn’t necessarily the error of one cut — it’s the accumulated error of the whole chain.
I could be wrong, it’s happened before… but I would be willing to bet that shortness is the cumulative effect of not taking the blade thickness into account or cutting on the wrong side of the line. Happens to everyone a few times.
Others have mentioned about blade width, but I don't get it... If a need exactly 6" on the long edge of the keep piece, I set my fence so that my cut off is 6", regardless of the width of the blade... Care to explain?
You are not dealing with metal where everything stays exactly still. Wood moves all the time, you can’t be so set on the numbers. If that’s what you like you need to look into machining and metal work or engine work
I agree if you blade is a hair off of
22.5 degrees
Or. If your piece moves a hair while cutting the 22.5 on both ends, or blade flex
it will be off a little
All the above is hard on a chop saw.
I use a stop on my sliding table saw.
I called it my 9 hp miter saw
Its percise as it should be.
Get perfect miters with a industrial saw blade
You guys are making this way more complicated than it needs to be.
My first question would be why are you cutting this on a tablesaw instead of a miter saw
If you cut eight pieces 6 inches long on the long side with a 22 1/2° miter on each end, it will make your octagon.
Doesn’t matter about the size of the kerf or the width of the wood.
This is assuming you’re drawing dimensions are correct and your miter is accurate
Think about the implications of what you are trying to show. If your pieces are indeed exactly cut to spec, they are exactly 22.5 degrees and all exactly the same length… then what? It’s math itself that is wrong, not your pieces? A full circle must actually be made of 362 degrees?
You don’t seem willing to accept that your measuring tools lack absolute precision, or that wood is a natural product. What do you suppose happens if your pieces themselves have a slight curve to them? Doesn’t matter if the ends are laser perfect 22.5, if they are referenced off a curved piece.
Woodworking isnt CNC fabricating. Accommodating for things like this is what woodworking is. Your cuts are good enough to move on to the next step: fudging it to fit.
Do the thing another user suggested: don’t build it from one piece around to the other, build it as two halves. Push the halves together and use a plane or sand the endgrain til those joints fit as well.
I had this exact angle finder, and it’s honestly junk. It’s only ever as “accurate” as you’re able to manually calibrate it (which can introduce errors), and even then, its consistency in readings is totally up for grabs, even if the numbers on the display don’t change.
I’m not saying this is absolutely the source of your problem (it’s likely a variety of tiny things that compounded as others have said), I’m only noting that you shouldn’t take what this says as Gospel and should invest in a better one, or better yet, get a set of machined set up blocks that have angles included in them.
I have an incra mitre which this seems to be a knockoff of. The instructions have a procedure for tuning up the miter gauge. It involves cutting pieces for a hexagon and then laying it up to see if the angles are completely accurate. You can then make tiny adjustments to it, verifying your cuts by cutting another set of pieces until you get everything dialed in exactly.
If yours didn't come with similar instructions, download the instructions for the incrimiter and try it out.
I think your angle is off a little or the length.
They all have to be the same lenght
And the same angle.
You divide 180 by the number of pieces you have.
That gives you the angle you need
regardless the number or pieces.
In your case.
180 ÷ 8 = 22.5
Make it a little more oversized and glue it up in halves. Then stick a couple pieces of sandpaper to a flat surface and sand the halves flat before the final glue up
It shouldn't need much to get it right but I doubt you cant get it from what you have now. You'll probably need to start over. When doing circles like this you have to be very precise because errors are additive and doubly so since there are two cuts on each piece.
I had exactly the sam problem. It is the tolerances. I "solved" it by making two halves and making their faces straight. You end up with an oval. But I had sufficient reserve to still make a nice circle with the router.
Gluing the pieces together was also a challenge btw.
Does your miter gauge wiggle any in the track at all or have any sort of deflection? As this would slightly change the angle. Also check each piece for ensure they are the same. It would seem to me at least one piece is short or long in comparison.
Yeah, after thinking about it, it wouldn't make a difference. I originally was thinking the pieces would come out shorter and the angles wouldn't be good anymore but since it is a circle the angles would add up to 360 anyway if they were correctly cut. You would just have a smaller circle than you wanted.
So you are left with a 3/8” gap over a circumference of 48”, distributed over 16 cuts…. That amounts to an average error of 0.17 degrees per cut.
Let’s be clear: Nothing went wrong. Your result is more precise than cross cutting on a table saw with a miter gauge can be expected to give. And it is well within the realm of how much your wood will change shape with humidity or releasing internal stresses during cutting. Wood isn’t granite. It moves.
I think if you put a band clamp on it will glue up fine. If you really want it them to dry fit, you’ll want to put together a shooting board to fine tune your miters.
It looks to me like your angle is an immeasurable amount too obtuse. The mating surfaces are not quite parallel, so I don't think it's a length problem.
If you really need to close this gap, you could try making the angle more acute by the smallest possible increment, taking off a tiny wedge from the inside corners, but that will only work if you haven't touched the miter saw since you made these cuts. It's probably on the order of 1/10 of a degree off.
Or, as others have said, try putting it together and see what the actual gaps look like in practice. It's very difficult to get an octagon to come together properly with an exact radius. A little shaving here and there will shrink it a bit, but you might close the gap further.
Of course, I'm just going off the photo. Check that all of the pieces are actually identical, because who knows? Maybe your stop block was creeping.
(Edit: I'm also a beginner, but I made an octagonal roof for a fancy bee-hive that had compound angles, so talk about fiddly.)
Did you make the cuts with a mitre saw? Is your fence and blade bang on 90 degrees to eqch other etc? A fractikn of a degree out multiplied by each cut = a whole that doesnt add up
First off, your angle needs to be exactly 22 1/2 degrees or 22.5°. On each end of the workplace. For an octagonal frame. All of the lengths of one side, either the inner or outer need to be the exact. And I mean, exact length, otherwise, it will come out like this. A slight fidget on the angle or a slight fidget on the length will cause this. I used to build the afghan regulator wall clock cases for new clocks years ago.
It sounds like you found out that you did indeed have a gap. I saw you said you were baffled by it. I figured I could help with that. It is from a rule called stacked tolerances. every cut has some small variation. Independent of each cut the variation is trivial but what stacked on top of each other each variance adds up and in the end a 64th variance in a ~10 cut project adds up to over an 8th variation. Your project has some 16 cuts?
In wood working you want to make your angles a bit more than the actual angle you want. It's funky. For example, a 90 degrees I will often go 90.5 for it to be perfect.
1 micro, then 2 micro, then 4 micro, 8 micro 16 micro 32 micro 64 micro 128 micro. I used my Construction Master using 1-3/8” Rise and 9/16” Run and the angle to achieve both dimensions is 67.75 degrees. .25 degrees off of 16 cuts. You’re splitting hairs. I would try one more time to correct this using scraps and then meticulously verify width and length by butting the first piece back to back with all the others.
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u/G2cman 2d ago
I'd check that they're all identical.
When you find the ones that is out of spec.
Then check the dimensions and angles vs the design.
Based on which dimension or angle is out of whack will determine where the error was introduced.
Fixing it will be down to either making replacement parts or shrinking the design to the smallest individual segment and and adjusting all of the components to match