I originally joined a while back in order to get some assistance with utilizing Sketchup on the browser. This time though, I’m hoping someone can help me with a different problem. I’m coming here because I believe tools like Sketchup can help analyze a problem that my brain can’t quite figure out. However, I also don’t trust my less than amateur sketchup skills to attempt to analyze this problem.
The issue I’m facing is while making an actual chessboard out of wood. The issue is with the alignment of the corners (attached picture).
To make a chessboard out of wood, you first cut 4 strips of a light wood and four strips of a dark wood, then glue those strips together. Once the glue has cured, you cut the block perpendicular to the original cuts to once again get a total of 8 strips. This time, each strip has dark and light spaces. The last step is to simply rotate every other strip 180 degrees and glue them all together. There’s obviously some nuance in there, but that’s the general idea.
When doing the second glue up, I align the corners on the top perfectly (not an easy thing to do) and those corners are still perfect once the glue has cured. However, the corner alignment on the underside is what you see in the picture (very not perfect).
In the past, I’ve attributed similar corner alignment issues partially to my mediocre power tools and partially to my execution. This time, I really thought I had everything figured out (tools and all), but am still facing this issue. So I was thinking about it and realized a potential issue occurs with the first glue up and that issue is that I didn’t clamp the strips to a flat surface, so they slid up and down during the glue up. I’ve never seen this as an issue because I can just re-flatten the board after the glue-up and prior to cross-cutting the next set of strips. However, now I’m wondering if that sliding around is contributing to the corner alignment issue since the strips won’t all be sliding up in a straight/parallel line.
I’m trying to envision this problem in my head and it seems like I’m wrong about the vertical sliding of the strips being the source, but I’d really like to be sure. Is there any way someone out there is willing to go through the process digitally while exaggerating the potential source of the problem to see if it causes the corner alignment issue I’m experiencing?
I don’t see how SketchUp will help you solve this issue.
As you guess, one reason and probably the most likely, for what you see is that the strips shifted while clamping up. One option to prevent that is to sprinkle a little salt onto the glue before clamping up. The sharp crystals with create enough friction between the strips to prevent them shifting. You could think of them like tiny randomly placed loose tenons. It won’t take a lot of salt for this.
How did you create the strips of walnut and maple? Did you rip them at the table saw? Did you also run them through the planer?
To add to Dave’s comment, I’d check that your saw blade is aligned correctly, if the corners are correct on top and not on the bottom it suggests an angled face.
I’m hoping Sketchup can help to confirm the issue. To clarify, the shifting of the strips I’m referring to is only in the vertical direction and I’m wondering if the shifting in the first glue up can be the problem. I know that the strips shifting side to side can will cause a problem in the second glue up, but I can prevent that by visually confirming that the corners align on the top while clamping it all together.
I’ve thought about salt to help address the sliding but I’m not sure about whether or not that will effect the strength of the glue bond. I did just remember though that a little bit of the particles from sandpaper can be used and shouldn’t effect the glue bond. All of that being said, I’m not positive the vertical sliding is the issue. I will try to not be stupid and utilize the grit in the future to prevent sliding either way though.
As for how I cut the strips, I did use a tablesaw, and probably didn’t need to utilize a planer because the surfaces seemed perfect off of the tablesaw, but I did use a planer just in case and to confirm the thicknesses were identical between the two sets of strips.
To elaborate on the process some, after the initial glue up, I flatten one side of the board with a router sled and then get a perfectly square edge with a cross-cut sled on the table saw. This way I have a perfectly plat reference against the table and a perfectly flat/straight/square reference against the fence.
I guess you model the blocks as components and shift them with the Move tool to see what things look like.
You don’t need that much salt. You shouldn’t have any problem with the bond.
Assuming the planer knives are parallel to the bed, the top and bottom faces should be parallel however is the blade isn’t perfectly square to the table your strips could wind up as parallelograms in cross section. You could check that, as well.
To add to Dave’s comment, I’d check that your saw blade is aligned correctly, if the corners are correct on top and not on the bottom it suggests an angled face."
Assuming the planer knives are parallel to the bed, the top and bottom faces should be parallel however is the blade isn’t perfectly square to the table your strips could wind up as parallelograms in cross section. You could check that, as well.
Good thinking, but that’s one of the issues I alluded to when I mentioned my mediocre power tools and my execution. I used to have a contractor level table saw that was very under powered for 8/4 stock and I also hadn’t taken the time to make sure the blade was a perfect 90 to the table. Since then, I’ve upgraded my table saw and invested in a tool magnetic device that sits on the table and then “sticks” to the blade. This time, the blade was indeed a perfect 90 (according to the tool at least).
Are you using a jointer on the edges after cutting on the table saw? Are you using parallel bar clamps for the glue-up?
Try this site for ideas and suggestions: Wood workers Guild of America
Are you using a jointer on the edges after cutting on the table saw? Are you using parallel bar clamps for the glue-up?
Try this site for ideas and suggestions: Wood workers Guild of America
No jointer, but I did use a thickness planer just in case there were marks from the tablesaw blade and to get the strips to exactly the right thickness. I also confirmed with calipers after that the strips were within .01mm of each other along their lengths. No parallel clamps either, but this is 8/4 stock so they’re really not necessary.
I have a woodworking forum I can consult for most things, but I’m here because I was hoping to get help visualizing a specific aspect to see if it could be a contributing factor. The more I think about it though, the more I don’t think it is a contributing factor. I’m resurfacing the bottom which gives a nice flat surface for the the table of the tablesaw to reference and giving myself a fresh square edge to reference on the fence of the tablesaw meaning each strip of dark/light should be consistent which should mean I have problem that isn’t the strips moving vertically during the first glue-up.
Whelp, I did some more investigating of the wood and the tablesaw and found that the blade itself might be the issue. Every time I’ve compared the angle of the blade to the table, I compared the left side of the blade. It’s been 90.0 every time. Well, I checked the right side and found that it’s 90.4. The right side is the side that matters in this case because I set my fence to be 2 1/4” from the blade (on the right side) to repeat all of the cuts. So I think it’s safe to say the vertical shifting in the initial glue up isn’t the issue and I’ll be referring to my usual woodworking forum to determine if this is normal for high quality blades or not.
Turns out, the angle finder is the most likely culprit. I got a fancy new combination square in today, squared the blade on one side of the table then checked the other side, and according to the square, it was perfect there as well. I also did a test cut which resulted in both sides being square to the table.
I still don’t understand how the digital angle finder could be wrong in the same way so consistently regardless of the configuration and I’ll continue to be skeptical until my next chessboard, but the angle finder does seem to be the problem.
