After I built my multi-slot mortising machine, I didn't need my old home-made slot mortising machine anymore. But the XY sliding table that it was based on was too useful a part to be left unused. I originally got the table from a surplus sale. It's totally pre-CNC technology. I found it as a "new product" in a 1968 issue of Popular Mechanics via a Google book search. I also had this fixed drill chuck assembly that I had come across at some point, and between the drill chuck and the XY table, I figured I should be able to build a pretty decent horizontal boring machine.
I wasn't sure if my method for extending the shaft would work, so I temporarily rigged up the chuck assembly and drive before gluing anything together for a test. I used a piece of 1/2" drill to extend the shaft. Drill rod is much too hard for setscrews to grip, so I used an angle grinder to grind a keyway into the drill rod. It's always fun to see the sparks flying! Strangely, they don't set sawdust on fire, even if I deliberately shoot them into the sawdust. Though to be cautious, I always make sure that making sparks is not the last thing I do before leaving the workshop. That said, angle grinder sparks most definitely can set stuff on fire at close enough range.
The drill chuck assembly has a 3/4" shaft, and I made a wooden coupling to connect it to the 1/2" drill rod. I figured I might need to make this coupling more robust and maybe line it with rubber to give it more flexibility, but this first try at a coupling is still holding up. So I'll wait for it to break before I make a better one.
The shaft goes through a ball bearing next to the pulley. I didn't have a ball bearing with a 1/2" hole kicking around, but I had one with a 3/4" hole, and I used a bronze sleeve bearing that I had lying around to bring the shaft up to the size of the bearing. I had to sand the sleeve bearing just a little bit to make it fit inside the ball bearing. I found that the bronze sleeve would slowly wander along the shaft towards the coupling, and out of the ball bearing while it was running. So I wrapped some electrical tape around the shaft to keep it in place. The larger ball bearing is also just held in the wood by friction. The hole wasn't exactly the right size, so I wrapped two turns of electrical tape around it to make it fit tight. I was however very careful to ensure that the center of the ball bearing lined up precisely with the axis of rotation of the drill chuck assembly.
The drill chuck slides up and down along two 5/8" steel shafts on bronze sleeve bearings. The 5/8" steel shafts in turn are attached to a vertical "post" which is attached to the base. Boring can involve substantial forces, and all these forces are transferred through this vertical post. So the post's connection to the base is very critical.
Maybe I went a little overboard making it a septuple (seven) mortise and tenon joint. I cut the multiple mortises with my slot mortiser, and the tenons with my screw advance box joint jig. Once it was set up, making seven mortises didn't add much effort.
As long as the drill head is only moved up and down within a normal range, the belt doesn't need to be adjusted. But if the head is raised all the way up, the belt tension adjustment needs to be moved to prevent the belt from getting overly tight.
I have about 15 cm of vertical adjustment range on this machine. Not quite as much as on my slot mortising machine, but enough.
With a stepped pulley on the motor and just a single pulley on the drill head, the motor does need to move forwards and back to make use of the different sized pulleys. The motor mount is held parallel by a protrusion in the base and a slot on the bottom of the motor mount.
I cut multiple slots in the bottom of the motor mount, so that the motor can be slid side to side in different forward / aft positions. That way, the motor can be aligned so that the various steps of its pulley align with the single pulley on the drill head assembly. This approach worked quite well, and I re-used a simlar scheme for the gear mount on my screw advance box joint jig.
I checked the alignment by mounting a long piece of 1/2" drill rod in the chuck, and checking that it was square and level with the table. Initially, it wasn't quite level. When something doesn't line up right, it's always a matter of figuring out which part most leads to the misalignment and correcting that part. Interestingly, the main source of vertical misalignment was that the holes in the chuck assembly were not drilled precisely. I hadn't drilled those, but had just assumed that they were done accurately in a machine shop. Not so, it turned out. I ended up filing the holes out a little with a chainsaw file to allow me to mount it level.
To clamp my drill chuck and motor assembly to the machine, I ended up clamping it to the ends of the rods that the table slides on. This cut down on how much forwards and back motion the table has, but I still have about 15 cm worth of stroke, which is more than enough for my purposes. I came up with this wedging idea to clamp to the steel rods. The trapezoid shaped blocks have t-nuts in them, and screws through the base pull them up against the shaft. The shaft nearest the motor mount only has a wedge on one side. The other "wedge" is part of the base, and serves as a reference.
Continue to part 2 of this article