So far I can use my 26" bandsaw with a temporary table.
But I want to add a tilt-able table, and the best way to do that is with trunnions. Trunnions put the axis of tilt at the top of the table, which means the opening in the table for the blade won't move side-to-side as the table is tilted. Also, by tightening down on the trunnions, the table's angle is conveniently locked in place.
I printed out 1:1 templates of the parts on some card stock (thick paper), and cut them out with about a 3 mm margin around them. I then traced these shapes onto some 18 mm baltic birch plywood and rough cut from a large sheet with a jigsaw.
Then cutting to the lines on my unfinished bandsaw.
A layer of hardwood goes between two layers of the baltic birch plywood.
I glued this middle layer on, let the glue dry, then glued on the second layer of plywood so I wouldn't have to worry about lining up all three layers at the same time.
The top part of the trunnion needs to have a slot so it can swivel around the mounting bolt. I made the spacer out of two parts with a big gap in between to leave a slot.. The spacer layer also has a notch cut out near the edge, which is where the mounting screw will later go.
Second layer glued onto the trunnion pieces. You can see the slot here.
The middle layer of the piece with the slot is slightly thinner than the other part. This will help this part not rub against the trunnion support beam once everything is put together.
Then gluing the paper template onto the parts and cutting up to the line on the bandsaw.
Then doing the final trimming on the belt sander, right up to the line.
Where the top part of the trunnion has a slot, the bottom part just has a hole for a carriage bolt to go through. On my previous bandsaw, I made the middle layer as two parts to leave a gap to make the hole, but this was difficult to line up while gluing, so for this one I made the middle layer one piece and drilled out the hole afterwards.
Fitting the pieces together. I'm always amazed not just that the pieces slide together nicely, but that they slide well and continue to fit well as they are rotated.
The bottom part of the trunnion attaches to the end of the trunnion support beam with dowels. I attached a complementing paper template to the support beam, which also has the dowel positions marked.
I used an awl to punch through the templates to mark all the hole centers.
Then with a forstner bit in the drill press I carefully drilled the dowel holes. I picked a piece with fine even grain for the beam so the drill would not wander as it entered the wood. The coarse grain in oak or ash, for example could pull the point of the drill bit to the side as it enters the wood.
I tapped just a few dowels into the trunnion piece for a dry fit. The more dowels, the harder it will be to pry the dry fit apart again once I'm ready to glue it up.
I had also scored where the edge of the trunnion piece is supposed to go through the template on the end of the beam, and after fitting it, I could see that it matched the location exactly.
Then cutting out a notch on the bottom front left to make room for the lower wheel, and another notch to make room for the blade guides.
And fitting the other trunnion on the back side. I only used two dowels for this one for the time being.
I traced a line back from where the blade is, and a second line 22 mm to the left of that one (behind it from this vantage point) to work out the trunnion beam position. The edge of the trunnion beam needs to line up with the second line.
With the rear trunnion pulled off again, I worked out where it's safe to put screw holes. If you are using the plans, those are already worked out for you, but I hadn't worked out this detail in my CAD model yet when I built this bandsaw.
Then drilling 20 mm (3/4") holes for washers, then a 1/4" (6 mm) hole in the middle of those holes for some big 1/4" wide screws to go through.
With the trunnion beam positioned back on the saw, I placed a drill bit in each hole and tapped it with a hammer to mark where the pilot hoes need to go.
I only drilled very small pilot holes initially because for the time being I'm only using some 4" long #10 wood screws to hold down the beam down because I still need to go buy those bigger screws. But using smaller screws before final assembly also helps to not wear out the screw holes in the wood.
A carriage bolt locks the trunnions in place, but I needed a pad to go around the head of the bolt so as not to dig into the inside of the trunnion that mounts to the table.
I started with a piece of wood with two 3/8" holes in it, sized for the carriage bolt. But the head of the bolt has a square part, so I had to carve the hole up to square on one side.
Then using a hand plane to make the bottom side of this piece curved to match the inside curve of the trunnion.
And finalizing that shape on the belt sander so it matched the curvature of the inside of the trunnion.
After that I cut the block in half lengthwise to make two pads for the two trunnions.
A washer and coupler nut goes on the bottom end of the bolt to pull the upper part of the trunnion tight against the lower part. Tightening this will lock the table angle in place.
I still need to make a nice knob to go onto this coupler nut.
With the trunnion support beam in place (but not screwed down yet) I positioned the lower blade guide and marking where the mounting screws for those will go.
I'm adding some threaded inserts for attaching the lower blade guides. If I had made this beam out of hardwood, I could have just tapped machine screw threads straight into the wood, but on this spruce, they would wear out too quickly.
Then attaching the lower blade guide.
Once I was confident that everything was the way it should be, it was time to glue the trunnions onto the trunnion beam. First I glued the seven dowels into the lower part of the trunnion.
Then mating that with the trunnion support beam. I made the mistake of applying glue to the wrong end at first, and the holes did not line up, so I had to apply glue to the other end, glue that on, then work quickly to do the other side before the glue I put on the wrong end dried.
I want to fasten the trunnion beam down with some big 1/4" wood screws, but I still need to buy those. So for the time being, I'm just using some #10 wood screws. The advantage of using undersized screws for now is that I don't wear out the screw holes with putting it on and taking it off while I work on it.
For my 20" bandsaw, I used coupler nuts to make threaded inserts in the bandsaw frame becuase I figured I might remove that beam from time to time to use the bandsaw as a sawmill, and I didn't want to wear out the screw holes in the wood.
But in three years, I haven't removed that trunnion beam once. And I don't plan on using this bandsaw as a sawmill, so big wood screws should be fine.
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