I've built a working Mendel out of 25mm Plywood. Everything non wood is compatible with a plastic Mendel. I started without a drill press, but realized it's not going to work without one.
I've simplified the axis design greatly by using slide bearings instead of ball-bearings. I couldn't get iron bars, so i took aluminum ones. They work great and friction with wood is pretty low.
I wasn't able to make the big gears for the z-axis out of wood. After several failed tries I capitulated and bought some gears from maedler.ch.
Making a more or less reliable extruder was by far the biggest challange. With the original mendel design direct drive extruder, I wasn't able to extrude at all. So I pretty soon decided to build a worm drive extruder inspired by Hydraraptor. Now the PTFE barrel was no match for the worm drive, so I had to switch to a PEEK barrel. Actually a PEEK mod (PEEK with 10% PTFE, 10% Graphite, 10% Carbon Fiber) one. PEEK mod is twice as strong, has three times less friction and has half the heat expansion than normal PEEK.
With a warm thermal barrier restarting the extruder required a lot of force. So I cooled it by driiling 6 4mm holes through it, and attaching a heat sink with short alluminium bars. Looks pretty cool, and I've never had any restarting problems again.
With the wood gears for the X ad Y axis (top right), the precision was a little unreliable. In some positions the error was around 1-2mm. I printed some new ones at a high precision spot:). I also changed the design a little, to a center hole with 4.5mm. After drilling them out to 4.8mm I simply pressed them onto the 5mm stepper motor shaft.
Left bottom you see my failed z driven pully attempts.