All,
If you've been following my buildlog at all, you know I am interested in using this laser to cut all the parts I need to make a cart to set my laser on and eventually even make a 4x8 router. One of the methods that I am working on to be able to make parts that are larger than the table is the douchman method. Douchmans are bow tie looking pieces of wood that can be used for decorations, patching dents and holes, or clamping joints together. I am using them in the later sense to keep joints tight during glueup.
I first tried just cutting pannel pieces in a straitforward way aligned during the cut as they would be when they were assembled. However, I found out that though my edges were fairly square, they were definately not perfect... far enough off that they wouldn't joint properly during a glue up. The main problem isn't alignment of the laser, but the fact that the laser cuts in a V shape... that is wider at the top than at the bottom. It may be about 1/64 of an inch wider at the top than at the bottom. While this is fine for most applications, jointing is not one of them. The strongest joints will come from a joint that starts with a joint that is basically seemless (can't even fit a piece of paper in it). Thats why we use a jointer in the wood shop to put a flat, perfectly 90 degree edge on before we glue up.
After thinking about the problem a little bit, I thought I would try flipping 2 of the 4 pannels upside down during the cut so that when they were assembled, one would be cut with the "V" up and the other down. I was banking on the idea that the "v" angle would be pretty consistant and give me a better joint
Here's a pic of what I cut out:
- Pannels cut
Notice that pannels 1 and 4 are upside down. When I assemble them they look like:
- Assembled pannels
The douchmans are also cut and in place. When I cut the douchmans, I reduced the height by about 0.002" and increased the width by about 0.007-0.008". I wanted them to be fairly tight in fit and have to somewhat pound them in. I found that you will have to cut several of them at various width increments and fit them to each cut to really draw them in good and tight. That's probably no big deal as we can cut several and put them in a bin to have for assembly.
I also found that the wood does affect the straitness of the joint and kerf width, so these joints aren't perfect. There is a variety of reasons for it. Most notedly, the wood isn't flat, my table is not perfect (yet) and the wood is not really a homogenious material so it cuts differently along the lenght.
That said, over all, I think the cut may work for many applications. In some cases, there may be some gaps that you have to fill with a sanding compound, especially around the top/bottom of the douchmans, but for the most part, the joints seemed to be pretty good. It may be best to use a glue which expands to fill gaps like a polyester foam glue (gorrila glue). I think that may work better than plain yellow wood glue, but we'll see. It's in glueup right now. I put wax paper on the table and glued up the joints and then put wax paper on the top and stacked heavy books on them to keep it flat. Hopefully, that will be enough to get it flat.
Edit: It is also worth noting that the gantry has to be very square to the y axis to get this to work right, espeically if you are flipping the pieces over. If it isn't it will create gaps no matter how square the edge is or how perfect the material is. If you don't flip it over, it doesn't matter as much. The fact that I got gluable joints out of this means that I must have done a decent job squaring up the gantry. I am not 100% convinced that it is perfect yet, but it is darn close. I will know when I start to do larger glue ups.