Bandsaw trunnions and table

Up to this point I used my 20" bandsaw with a temporary table clamped to it, but my goal all along was to make a table that tilts on trunnions for this saw. Trunnions allow the table's axis of tilt to be aligned with the surface of the table so that the top of the table doesn't move side-to-side with respect to the blade as it's tilted.

But if you are building this bandsaw, a temporary table is necessary so you can use the bandsaw to cut the trunnions for the actual table.


Making the trunnions

I printed out the 1:1 templates for the trunnion parts from my cad model using my bigprint program. In the plans, I'll include 1:1 PDFs for thsese parts. I cut them out roughly and pasted them on some 18 mm Baltic birch plywood. I have to buy this plywood new and it isn't cheap, so I always try to make best use of whatever shape of scraps that I have.

If you don't have any Baltic birch or similar quality of plywood (one that is hardwood throughout), I'd recommend using a hardwood such as maple instead.


The trunnions need a hole at an angle. I'm adding a middle layer with a gap in it to make this hole.


I glued the middle layer to the top layer, let that dry, then glued on the bottom layer. That way I only had to align one layer at a time.


The top part is glued together much the same way, but there is a much larger gap in the middle layer to allow it to swivel around the bolt that holds it in place.


With the glue dried, I cut the parts right to the line. The most critical part is the curved part of the trunnions.


Drilling out the dowel holes for the lower trunnion part. I used an awl to make a divot at each dowel hole center, then used a brad point bit to drill out these holes. Once the glue dried on the other part of the trunnions, I cut those out.


Checking how the two halves fit. Even with a light hand sanding, they rotated against each other very nicely.


But having a nice belt sander, I used that to tweak the shape some more.


The trunnion halves will be clamped together by a carriage bolt. The bolt head needs to have something to allow it to push against the inside curve of the trunnion while still allowing them to rotate.

I glued the templates from my plans on the end grain on a piece of maple hardwood.


Before cutting them out, I drilled the hole for the carriage bolt.


I then filed the hole square for the head of the carriage bolt, and checked the fit with the trunnions. So far so good.


Trunnion beam

The beam that holds the trunnions is over 7 cm thick. I glued two pieces of hardwood together to form this, then squared it up on the jointer, planed it to the right thickness, and cut it to width and length on the table saw.


The beam has a notch on one side of it to make room for part of the lower blade guide. I made a cut on either side of this notch with a table saw, then cut out the middle part on my still unfinished bandsaw.


Marking the layout for the dowels in the end of the beam with callipers. I then punched center divots and drilled the holes on the drill press.


A slight indent needs to be cut on either end of this beam to give a bit of clearance for the upper half of the trunnions. I placed the trunnions on the end, marked the line, then cut part-way with the table saw to hog it out. If this is too complicated, you could also use a hammer and chisel to cut it away (this cut-out just provides a bit of clearance, so accuracy is not important)


Gluing in five dowels. These were quite a tight fit.


Checking to make sure the dowels line up. With the dowels fitting as tightly as they did, I would have a hard time getting it apart again after a dry fit. So I took my chances and went straight to the glue up.


Getting those joints together was less elegant than I had hoped, and I ended up with a very slight gap on either end, despite lots of clamping pressure and pounding. This would have been easier if my dowels had been a looser fit.

If you build this bandsaw, I recommend gluing the trunnions on the end of the beam without any dowels, letting the glue dry, then drilling through the trunnion and into the beam and adding the dowels one at a time. This means the dowels will be visible, but that's still better than what I did.


Checking how the beam fits on the bandsaw. I then realized, I forgot to cut the notch for clearing the lower wheel.


I marked the shape of the notch on a piece of hardwood, which I used to set the saw height and determine which angle the beam had to be on the table saw sled for cutting.

Then making a series of cuts to hog out the notch.


I broke away the rest of the wood, then used a chisel to finish up the cut.


Positioning the blade guides against the beam to establish where the mounting holes need to go.

If you are building this bandsaw from my plans, you can just use the measurements from the plans. But when I built this, I hadn't put that much detail in the drawings yet.


I drilled 1/4" holes, then used a 5/16" machine screw tap to make threads right in the wood. Based on my tests when I made the blade guides, this should hold up well enough. If not, I could always drill the holes larger and add threaded inserts later


Mounting the trunnion beam

Locating where the beam needs to go. The left-right position (as seen from the bandsaw's front) is determined by the blade guides.

In terms of forward and back, the notch for the lower wheel should be centered in the notch cut on the bottom of the beam.


My recommendation is to attach this beam with four large wood screws like the one shown, about 5" (12 cm) long. Or you could use eight #12 wood screws. Either option would be *much* easier than what I did.


I decided to use four 3/8" bolts. I drilled and counterbored the holes to make room for the heads.


With the beam positioned and clamped in place, I inserted the bolt and hit each one with a mallet to leave divots where the holes needed to go.


I then drilled large holes with a Forstner bit. The first two with a hand drill, but these ended up slightly crooked. I used a drill with a drill guide for the rest, but these also ended up slightly crooked. I should have clamped the drill guide to the bandsaw frame while drilling. I ended up drilling into the holes again at a slightly different angle so I had a space large enough to get the inserts in straight.

This drilling contraption is called a "drill guide" (I'm often asked), so if you want to buy one, search for "drill guide" on Amazon or Rockler or wherever.


I couldn't find any beefy enough threaded inserts, so I took some coupler nuts and cut lots of notches into the sides of them with an angle grinder. The holes are large enough for the coupler nuts to fit loosely, so next I used some construction adhesive to glue the nuts in. Construction adhesive is good at gap filling.


I made small wooden plugs for the ends of the coupler nuts to keep the adhesive out of the threads. I also put the bolts in the coupler nuts, with some electrical tape to keep the adhesive from gluing the bolts into the nuts.

With a fairly loose fit, I stuck some small pieces of wood next to some of the nuts to get them to line up straight while the glue dried. This whole procedure was very inelegant, so I really don't recommend doing it this way. The reason I'm doing it this way is I want to experiment with milling logs with the bandsaw later, and that will require removing the bandsaw table from time to time.


Sub-table

The table consists of two layers. The lower layer, which I call the sub-table, needs a cut-out in the middle for the blade and to add clearance for the blade guides.

Rather than making a six-page printout, I'm just transferring the layout manually with a tape measure.

You can see a row of holes on the right edge. This reclaimed plywood used to be part of a shelf, and these are the shelf pin holes.


I cut the slot (for inserting the blade) on the table saw.


Then cut out the hole in the middle on the unfinished bandsaw.


I had to cut some pockets for the screws to mount to the bottom of the table. I'm using a 3/8" Forstner bit in the drill press, which works well for cutting into the angled surface.

If you don't have any Forstner bits, I'd recommend cutting a similar pocket with a 3/8" or 10 mm wide chisel.

After that, I drilled the hole for the screw shank, and used the tip of a 3/8" metal cutting bit to add a countersink to the holes.


Mounting the trunnions. The trunnion is centered along the line which marks the lateral position of the blade.

In terms of forward and back position, I placed the trunnion beam on the sub-table so that the notch (for the blade guide) lined up with the forward-and-back center of the blade, then marked where the trunnions ended up on the table.


Adding the trunnion beam to the sub table, then making sure it can tilt the full 45° range of motion.

The heads of the carriage bolt ended up hitting the table, so I had to chisel out about one mm to make more room for them.


I then attached the trunnion beam to the bandsaw frame, and the lower blade guide to the trunnion beam.


I then adjusted the blade guides. With two screws to loosen and tighten for each guide block, these are more awkward to adjust than my previous guide block design.


I added the sub-table to see how everything lined up and fit.


Here you can see how the extra hole in the sub-table provides clearance for the blade guides. But I still had some interference.


I cut a chamfer along the body of the lower blade guide to clear the sub-table. and chipped away a few parts of the sub-table where the guides were still hitting.


With the table at 45 degrees, you can see how parts of the blade guides protrude above the sub-table. So the main table will also need to have some notches cut out of it.


Cutting out the hole in the middle of the main table. I'm cutting this with a jigsaw because I didn't want to cut a slot to the edge of the table before gluing it together. That way I don't have to make sure both sides of the slot are aligned flat while gluing up.

You can see a few smaller holes in this piece of wood. This is because it's a reclaimed piece of wood that used to be the side of a night stand. The wood is a hardwood panel with two layers of veneer on either side to stabilize it. I used the same type of material for the tables on my first and second bandsaws, and it has held up well.


I added lots of glue to the top of the sub-table...


...then clamped on the table's top layer. I used four small clamps through the hole in the table to clamp the middle of it, plus lots of clamps around the outside edge (I hadn't added all the clamps yet at this point)


I then chiselled out the extra clearance for the blade guides for when the table is tilted to 45°.


Next I routed a ledge around the hole in the table. I used a square, clamped to the table to guide the router along one edge, then moved the square to guide it for the next edge, doing this for each edge.

After that, I chiseled the corners square.


A piece of 6 mm thick Baltic birch plywood fits into the hole to act as an insert. I just slide it in place while the saw is running to make a zero clearance insert for the blade. Though, if you want to tilt the table, you have to slightly widen the slot and add clearance on the bottom side.

Testing the table by cutting a large piece of hardwood. The temporary table had some flex to it, so I occasionally encountered chatter when cutting thicker material, but with the rigidity and mass of this table, this wasn't a problem anymore.


I then cut out two more star knobs like the one I made earlier. I drilled out the hole in the middle, filed out the hole roughly hexagonal, and pressed a coupler nut in the hole.


The knobs I just cut out are for the trunnions.


The basic bandsawing functionality of this saw is now complete.

If you dream of restoring some big old 100-year old cast iron bandsaw, well, so far, this bandsaw is about as complete as these 100-year old saws were, because enclosures, guard, and a motor were not included with these saws.

Next: Bandsaw enclosure


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