Scotsman,
I make my own tools too... generally quite badly, but I'm the only one who uses them, so no worries. I've built both a planer and a wire loaf-cutter, like below.
Here's the planer I made some time back. It's over-engineered, which makes it sturdy and easy to use. The blade is cut from some aluminum I had lying around, and "sharpened" by hand. It's not very sharp at all, but it's adequate to cut new soap. It's removable too, for re-sharpening. I've been considering replacing it with steel, but it's not a priority so I haven't gotten around to it yet. My only dissatisfaction with this tool is that the cut-depth isn't adjustable. It's set based on the difference in height from one side of the top surface to the other side.
Then I just (almost) finished my first wire loaf-cutter. It's based on some pics I found via Google. The frame is 3/4" plywood. The dark green loaf-cradle is cut from a recycled plastic beam I had lying around (nasty stuff to work with. Makes the whole basement smell like burning plastic when you cut it on the table saw.) It's sized to my silicon loaf mold, and will give me 11 1" bars from each loaf. I'm using 18 gauge guitar strings and normal guitar tuning machines for the wires and tensioners.
Things I wasn't aware of:
1. guitar tuning machines are not all the same post-length. They're sold in sets of six, and some sets come in 3 pairs; each pair of a distinct length. Apparently, this is useful when you're building a guitar. I didn't notice until after I'd been fitting them for a couple days. It's not a big deal, but it was a surprise. Other sets-of-six come all the same post-length. They're marked on the packaging, if one knows to look.
2. locking tuning machines (which these are) don't lock the string to a specific tension. Rather, they lock the string into the turning-post... so it doesn't slip out. I had hoped the 'locking' would help me keep a consistent tension, but I misunderstood.
Here's the same thing from the hinge-end.
And, from the inside.
I used each sting twice, because the tuning machines are expensive, and sold in sets of six, and I needed twelve wires. I anchored them and turned them around 3/8" pivot pins I got from a place called Fastenal. Very convenient. I set the pivot pins into hardwood inserts, because I didn't trust the plywood to stand up under the load. If the guitar strings don't work out, my next step is either piano wire, or something called 'music wire' that I can get for cheap from an industrial supply place called Grainger (who knew?).
Most of my construction agonizing was around two things:
1. assuring that the grooves in the plastic loaf-cradle would line up with the cutting wires. I cut the grooves first, then mounted the cradle, then mounted the wires to line up with the grooves. It would have been smarter (easier) to mount the wires first, then groove the plastic wherever the wires ended up....
2. making sure the cutting wires would cut sufficiently deep to assure they would completely cut through the loaf. I've been wire-cutting my last couple of soap batches using wire wrapped around wooden toggles (the classic garotte), and it was tough to pull the wire tight enough to force it to cut. And - that's the other reason I added the hardwood inserts... they raise the cutting wires (actually, when the top is closed down, they lower the cutting wires) further, to assure a complete cut.
It's not pretty, but it might give you some ideas. If you'd like more pics, just let me know.
Best luck!
Todd