Stack cutting is a great method for making a large number of items quickly. If everything works correctly that is. So what is stack cutting you ask? As the name implies, you stack multiple pieces of wood and cut them all out at the same time. There are some limitations and a few things could go wrong if you don't prepare the stack correctly.
You can stack cut a variety of different thickness but the most common is 1/8" or 1/4". This technique is particularly useful for fretwork cutting. You spend the same amount of cut time but instead of one item you end up with up to 8 duplicates.
The magic number isn't necessarily 8 but I would not recommend going beyond that as the chances for things to go wrong increases. Stack 8 layers each 1/8" thick and secure all the layers together. You could tack glue the layers in negative waste areas to keep them all together. If all the sizes are similar, you can run a line of tape along the edges to secure them. You could also use some double sided tape but with intricate fretwork, this method can be long and tedious and tricky to remove the tape without damaging the piece. You could use layers of wood less than 1/8" thick but at that point, the wood becomes very fragile and if the blade catches the piece on the upstroke of a cut and slams it onto the table (always a cringe moment), strong chance that something will break.
So why not 10 layers? Well, the thicker the stack of wood the greater the chance of angled cuts. I've cut many fretwork pieces out where the top layer looks perfect but once you separate the layers, the cuts become less and less accurate and can ruin the bottom few layers. Cutting at 1" or less is a rule that I follow but it can certainly be done on a thicker stack.
One of the other possible occurrences that spell almost certain doom is if the stack of wood shifts. This can happen if the layers are not secured well enough. You want all the layers to be perfectly rigid to each other or cut will not match on the top and bottom layers.
You can sometimes get away with angled cuts on a scroll saw but in the majority of projects, a perfect 90 degree angle is critical. There are a variety of factors that can lead to angled cuts. Some of them can be a quick fix and others will make you tear your hair out. Hopefully after reading this post, angled cuts will be a problem of the past.
1. This may seem obvious but the first thing that you should always check is if the blade is 90 degrees to the table. Even if you set the table at 90 degrees earlier in the week, there is always a chance that it somehow shifted. Leaning or pressing your hand down on the surface can tilt the table a fraction of a degree which can make all the difference. A quick and easy way to check if the blade is a perfect 90 degrees is to take a small piece of scrap wood and make a shallow cut. Turn the saw off and spin the scrap piece of wood around and try to feed the blade backwards into the kerf line. If the blade slides in perfectly, you're all set.
2. Blade tension or really lack there of can be a factor. A blade with too little tension will bow often in the middle creating a cup shaped angled cut. If you notice this, do a few test cuts and increase the tension to see if the angled cut reduces or goes away. Blade tension can be a difficult thing to master and usually needs small adjustments for different types and sizes of blades. Some advice that's given in the scrolling community is when you pluck the blade, if you hear a sharp C note, its tension is correct. If you're anything like me, figuring out what a C note sounds like is like figuring out theoretical physics. I do pluck the blade and listen to the sound but I'm clueless if it's a C note. Practice is the best solution for proper blade tension.
3. Improper blade selection can sometimes result in an angled cut. For instance, If you try to cut a 3/4" piece of purpleheart (a very dense wood) with a number 1 reverse blade, your going to have a difficult time getting cuts without an angle (not mention a good chance of charred wood and a pile of broken blades). The thickness and hardness of the wood are big factors in blade size. In general, we use 3/4" to 7"8 wood for everything we make and I alternate between a #5 and a #7 blade. For very dense woods such as yellowheart, use a #7 blade. Lesser density woods such as American cherry, use a #5 blade. Wood less than 1/2" thick, use a #3 or a #1 blade. Wood thicker than 1" will often create a whole mess of issues. It the cuts are not very intricate, use a #9 blade (This blade is fairly thick and doesn't take kindly to tight curves.)
This is the first of our tutorial blog posts. Since 2010, we have focused heavily in both puzzle making and intarsia. We have developed a lot of useful tips and techniques and we would like to share that which we have learned. This basic guide should be enough to take you from start to finish for most simple puzzles. Other detailed posts will be forthcoming. Please add your comments and questions as they will ultimately shape future posts.
The style of puzzles that we make are often referred to as free-standing puzzles. This basically means that they are able to stand up freely on any flat surface without the need of additional support. They are two sided and are usually completely interlocking. If you want more visual examples, take a gander at our free-standing puzzle gallery. For this post, I will only be referring to free-standing puzzles. The only tool that you will need to make one of these puzzles is a scroll saw. Of course there are many tools to make the start to finish process easier and save a bit of your sanity, but they are not necessary.
Before you make a single cut, you need to know what you will cut with. Scroll saws can use either a pin end blade or a plain end blade. For the sake of puzzle cutting, avoid pin end blades all together. They are much thicker which makes intricate cutting and tight curves near impossible to cut accurately. Always use plain end blades when cutting puzzles.
The next thing to consider is the type of plain end blade. They come in a variety of different sizes and styles and there is no real answer to, "What is the best blade?" Every scroller has their own personal preference. For blade size, I would recommend either a #5 or a #7. When you cut the puzzle pieces out, the kerf line is just the right size to allow the pieces a little wiggle room to slide apart easily but not too much to detract from the appearance of the puzzle. These sizes also work well for a large variety of wood species and thicknesses. As for the style, since the puzzle is a two sided project, it is very useful to have a reverse cut blade of some kind. This reduces the amount of tear out on the bottom of the project and requires less sanding in the end (always a good thing!). There are a few different types of reverse blades out there. Try a few out and stick with the one that seems to work best for you.
So now that you have your blade all picked out, there is one last thing to do with the blade before cutting and it is perhaps the most important. Make sure that the blade has a perfect 90 angle to the table. If its off even by a single degree, the puzzle pieces will cut at an angle and may not fit together. This problem is very time consuming to fix (if it can be fixed at all) and is also the most common issue. Angled cuts can still happen with a 90 degree blade which I will cover in a future post.
One of the great things about using a scroll saw is that you can use wood that would otherwise be unworkable. Twisted boards, cracks, knots, and other board defects, while annoying, can generally be worked around. However, it's best to avoid these defects until you become very comfortable with your saw.
The wood you select should be surface planed on both the top and bottom. The sides can be left rough. Having a nice smooth bottom will prevent the board from wobbling, decrease vibration, which reduces the chance of angled cuts and blades breaking. For beginners, I would recommend a softwood to practice cutting on such as cedar, cypress, or pine. Once you get the hang of cutting, try out some hardwoods such as cherry or maple. When making puzzles, its best to use hardwoods. Softwoods like pine are too fragile and the pieces are more likely to break.
You have your wood and blade selected and now its time to cut your puzzle out. There are a number of different methods to transfer your pattern onto wood. I will go over the method I use. It will save you a lot of time if you sand the top and bottom of the board prior to pattern placement. A brief 220 sanding is generally sufficient. Take your paper pattern and cut out about 1/4" from the puzzle outline. Then cover the top of your board with a layer of blue painters tape. The tape serves two purposes that saves you a lot of time. Most importantly, it greatly reduces the chance of burning. Sanding off burn marks is very time consuming. Place your pattern on a piece of cardboard and use an adhesive spray to spray the back side of the pattern. Then place the pattern on the board on top of the tape.
The other benefit of using tape is easy removal of the pattern. Without the tape, the pattern would be adhered directly to the wood. If you manage to peel the paper off, you will be left with a sticky residue from the spray. You would have to clean and re-sand the top of each piece. Painters tape peels off easily leaving no sticky residue and the paper pattern comes with it. Now its time to cut the puzzle out, do some touch up sanding, and use the wood finish of your choice.
That covers all the basics on puzzle cutting. Now all you need to do is practice. If you have any questions, just send us a message or leave a comment below.