Introduction: Fix the 12 Piece Burr Puzzle Pieces
In another Instructable, I show how to make a 12-Piece Burr Puzzle out of 1/2 inch square blocks. Each of the puzzle pieces are the same, but there's just one issue with them. There's a weak spot in the design. Two of the connection points have a tendency to break easily, and I've narrowed it down to 3 reasons why. First, those joints were the last for me to glue together, and I don't have a clamp big enough to clamp the whole part. Second, it's a small contact point compared to all of the other glued points. And third, it's the highest leverage point for the whole piece. In this Instructable I'll be showing you what I did to strengthen this weak spot.
If you would like to see a video version of this Instructable, you can see that here: https://youtu.be/xueNx9zrviY
Supplies
Step 1: Mark the Joint
This process will involve separating and reconnecting the weak joints, so the first thing I did was to add pencil marks at the joints to help me when I'm ready to realign them. The one in the picture is already broken, but for the ones that aren't I'll break one of the joints after marking them.
Step 2: Drill a Pilot Hole
The way I chose to reinforce the part is by adding a dowel. You'll need to drill a hole through the middle of these pieces, so mark an X on the face of the joint that's broken to help you drill in the center. Start with a pilot hole using a 1/16" drill bit. The bit that I used was barely long enough to go through 2 of the blocks, but that's fine for the pilot hole. Try to get the hole as straight as possible, because that will help guild the larger drill bit.
Step 3: Drill a Bigger Hole
Use a 3/16" brad point drill bit for the larger hole. You need to make sure that this drill bit goes in farther than 2 blocks, so go ahead and align the bit with 3 blocks, then mark it with some tape. Now it's time to drill this bigger hole. The pilot hole you drilled earlier will help guide this bit, but it's still important to try to drill this hole straight.
Step 4: Break and Reattach
Using a 3/16" dowel, double check to make sure you drilled deep enough. If it looks good, then now it's time to break it at the other weak joint. If you didn't get the hole perfectly straight, that's fine just as long as the hole doesn't come out on the side.
Now you want to glue the other 2 pieces together. On the piece with the hole, make sure to glue the side with the X onto the other piece. Once the alignment is good, grab your clamp and clamp it together. I used some other blocks so that when I tightened the clamp, it wouldn't shift the glued joint.
Step 5: Drill Another Hole
After the glue sets, drill into this piece the same depth that you did the other piece. No need for a pilot hole this time, you can just use the existing hole in the square that you glued on as a guide.
Step 6: Measure and Cut the Dowel
In order to cut the dowel to the correct length, it helps to measure and mark it. Put it into the hole in the first piece, then mark the dowel at that depth. After removing it, you can measure it to that mark. I'll describe (and show with pictures) 2 ways to measure it, depending on what tools you have.
Notice with the tape measure, the mark is at about half an inch. Put the dowel into the hole of the second piece, then measure out the same amount from there. But make sure to mark it a little bit shorter. This will give you more room to work with later.
The second way to measure it is easier in my opinion. By using a caliper you won't need to remember the measurement. Adjust your measurement, lock it into place, then hold it up and make your mark. Now you're ready to cut the dowel.
Step 7: Test Fit the Dowel
After your dowel is cut, slide it into the hole and put the pieces together. Sometimes it will fit perfectly right away, and sometimes it will be slightly off. You may need to sand the ends of the dowel a little bit if the pieces don't quite connect flush. Sometimes the hole will magically be a little bit crooked. Since the dowel may not be perfectly straight, sometimes you can just twist it a little bit to fix that problem. It may take a few tries. If that doesn't work, you may need to use your drill to straighten the hole up a little bit.
Step 8: Glue in the Dowel
When the pieces and the dowel are aligned good, put a mark on the edge of the dowel to show you which way goes up, then remove the dowel. Put some glue in the deeper hole. Add the glue one drop at a time and add about 4-5 big drops. Then push the dowel in, making sure that the mark is turned up. When the dowel gets hard to push in before it get to the bottom of the hole, you may need some assistance to help push it all of the way in. You can use a hard surface to press the dowel up against.
When it does get hard to push in, it's because glue is trying to push past the sides of the dowel. This is what you want, and you should get some coming out, if you added enough glue.
Step 9: Glue on the Other Piece
Now add some glue into the other hole, just follow the same process. You won't need as much on this side, but you do need enough glue to squeeze past the dowel and also coat the faces of the 2 pieces. As you push them together, twist the piece around to help spread the glue as it squeezes into the gap between the 2 pieces.
Step 10: Finishing Off
Check the alignment and hold the pieces under pressure. If you have a clamp that's big enough to clamp this whole thing, that would better. After the glue fully sets, grab some sandpaper and sand the edges to get rid of the dried glue, and also the pencil marks.
Step 11: And That's It!
Now you have turned the weakest joints in these puzzle pieces into the strongest joints. If you are following this Instructable to help you fix your broken puzzle, you're finished! If you are following this Instructable while still making the puzzle pieces, you're good to go onto the next step of my 12-Piece Burr Puzzle building Instructable. Thank you for checking out my Instructable!