Introduction: Wedding Cake Saw
Many aspects of our wedding were made rather than bought, and one of the more unique items was our cake saw.
Every time Katya and I went to a wedding, we both found the tradition of cutting the cake a little odd. The idea is that it is done together, but given the knife handle has space only for one hand only one person is really holding it. On top of that the fact that both bride and groom tend to use both hands means there is a strange looking pile of hands at the back of the knife. This is something that once you have spotted really stands out, so we agreed that we would do things differently.
We figured that a miniature two man saw would allow us to use real team work to cut the cake. The only problem was how one goes about making such a thing. This was an important build so I teamed up with my best man to make it. Katya and I were both very happy with the result.
We liked the way it was traditional with a twist.
Step 1: Get the Blade Laser Cut
I spent a lot of time trying to find a suitable blade off the shelf. Unlike a knife that can stop in the middle, the cake saw needs to be comfortably wider than the cake. I started looking for 20" (50cm) knives but found only levelling knives are available in this sort of length and that the long ones are not serrated (beware stock images, I bought one pictured as serrated that wasn't when it arrived). Mark and I then searched for all sorts of wavy edged ninja swords, but nothing had the right look. In the end Mark persuaded me it would be easier to sharpen our own blade; he makes robots and knew how to get 1mm stainless plate laser cut cheaply.
I sketched out what I was thinking, and we chose a tooth profile we thought we might be able to grind to a blade. The next thing I knew Mark had CADed it up and we had the part within a week.
Step 2: Wooden Handles
I had a think and a google to try to find a suitable idea for the handles. I decided I wanted an aged wood look, and after a bit of searching found a set of reclaimed file handles on ebay that were perfect. They have a hole into which the shank of the file fits (normally a tapered square section spike).
Step 3: Handle Adaptors
To attach the handles to the saw, adapters were needed. The adapters have a squared spike to fit into the handle and a slot for the blade to slide into. Two holes through both sides of the slot line up with holes in the blade, allowing pins to be pressed in to hold the blade securely.
These were made by turning round stainless bar, cutting a spike one end facing off the other end and adding a bevel and just neatening up the rest of the surface of the part.
After turning, the spike was squared off using a coarse file. The holes were very carefully drilled to line up with the holes in the blade. The slot was sawn by hand again carefully to make it straight enough to fit the blade. Sand paper and needle files were used to get the slot wide enough to fit the blade. Care was taken when testing the fit to only slide them over the ends that would be covered once fitted anyway so as to avoid any visible scratches.
Step 4: Fitting the Handles
I decided to add one handle before grinding an edge on the blade so that I had something to hold it with. This was removed later for sanding the blade, but I have put the step in now so you know how to do it.
Fitting the handles to the adaptors made in the previous step is relatively straightforward as long as you sized the spike correctly. Placing the point of the spike in the handle hole and pushing it in gets it most of the way, but to get it to stay there I recommend hitting it a few times with a soft mallet.
Attaching the adaptor to the blade is a little harder. First you need to make some pins. We used 3mm stainless rod to fit our 3mm holes. As you might expect, once aligned these weren't going to stay put. Flexing of the joint would gradually walk them out of the hole. So in order to keep them in tightly we gave the pins a bit of a mullering to make them less circular. We whacked one end with a hammer and over tightened it in a vice to make it less circular. We also slightly bent the pin such that it could be pressed in but was held by the force of the adapter straightening it. Before fitting, the pins were filed round to the approximate curvature of the adaptor so they fit nicely once pressed in.
Press the more circular end part way into the hole, with the end curvature aligned with the surface of the adaptor. Avoid pressing it too far, as the blade still needs to be slid into position.
Carefully slide the blade into position, look through the holes in the back of the adaptor to align the blade holes. Once in position press the pins through further until they are flush with the surface.
Step 5: Grind an Edge on the Blade
To grind a sharp edge onto the blade, I mounted a Dremel on a work bench to sit through a cut out in some scrap wood. I adjusted the height to meet the blade at a shallow angle when placed on the wood. After making sure the Dremel was secure I spun it up and carefully ran the edge of the blade over the grinding bit one serration at a time. To keep everything even across the length of the blade I ground evenly across with multiple passes. The grinding stone will wear down during the process so the height may need adjusting.
On the final pass, look out for the ground edge breaking through to the surface and try to keep the amount the edge recedes constant across the blade.
There may be some burrs that need knocking off, but the blade should now be sharp. A standard sharpening steel can improve the edge further but I found this wasn't required.
NOTE: From now on more care is needed handling the blade!
Step 6: Take the Handle Off and Sand and Polish the Blade
Unfortunately, despite carefully cleaning the wood and blade before grinding, grit from the grinding bit got trapped under the blade as I moved it tracing multiple copies of the serration shape in the surface. In order to remove the marks I decided to remove the handle I had fitted to get better access for sanding. I used an M3 screw to press the pins out in order to remove the handle.
I went through the grits from 80 to 1200 and then 40um 20um and 9um finishing film. This left a matt satin finish that was in keeping with the rustic saw look.
When happy it is time to fit both handles again, the same way as before.
Step 7: Forming a Leather Sheath
I thought it would be nice to make a sheath for the cake saw, not least because it was big and sharp!
I bought some thick tan leather. This is the first time I have worked with leather but I found it straightforward. I soaked it in a bucket of warm water for a couple of hours. I then folded it in half to get the main crease in, placed it wrapped in a bin liner under a bucket of water with a plank of wood to spread the load, and left it overnight.
By the next day water had stopped dripping out so I relocated the leather from my bath to my garage and inserted the saw to form the leather around. I pressed the leather around the handle adaptors and used an old car battery on a plank with some absorbent padding to apply weight to the middle to get good creases around the ends of the saw, as well as to help dry it out. I left it for a couple more days; the leather took the form of the saw beautifully.
Step 8: Sewing the Sheath
Once the sheath is formed to the shape of the saw it holds on quite well, but opens up at the ends. I did a neat line of stitches down either end to make it more secure.
To do this I used a leather pin wheel to make some holes through the leather evenly along a line for stitching through. I found that any needle that would take my extra thick thread didn't fit through the holes so I widened them with a 0.9mm micro drill bit. After that stitching was much easier.
Once stitched the saw fit was nice and secure.
Step 9: Cut Cake!
Now the cake saw is finished, give it a good clean, bring it to a fancy venue and marry someone. Then you get to work with them to cut a cake with a saw!