Monday, November 16, 2015

Tooth angle on a Japanese crosscut saw


My sincerest apologies to my friends who have been wondering where I've been for the last 2 months. Popular speculation had me suffering an unlikely and grisly demise, fallen to my death in some hidden lava tube, but no....





Our house on the mainland Oregon coast sold, and there were a few projects that still needed to be finished up before handing off the keys to the new owner. It's an ironic cliche that the carpenter's house is never finished and this is no different. The cobbler's children that suffer from lack of shoes, that sort of thing. You probably know how it is. Anyways, 3 weeks of intensive house type woodworking, flat winter's lighting and rain. Lots of rain. That's at least one thing that Hawaii and the Oregon coast share.



Having been in Hawaii now for just over one year, visiting the mainland again reminded me of numerous things that I seem to have already forgotten, but one of the most notable for me was the light. Daylight that is. There's not much of it, and what there is comes at such a low angle, it seemed as though everything looked just the slightest bit "off" to me. Shadows were long and the colors didn't look as vibrant. My iPad evidently forgot about the relatively northern light too. The pictures that I took are, well, not my best. Yeah, blame the camera, haha.



The stairway to the attic bedroom needed a door and handrail.



I had to get a bit creative, trying to squeeze a manufactured door and jamb into such a narrow opening, but I got lucky. Down the road from our old house is "R. Gray's bargain yard", a wonderful resource for scroungeing unusual building materials. The owner, Bill, came to my rescue yet again and found me an off-size, special order return that fit the opening, needing only a bit more massaging than your typical install.



It was fun to do some plain old carpentry again, so different from the stick and log work that I've been doing in Hawaii. After packing off all my tools to bring home to the Big Island, it felt funny to be packing them back to Oregon again, but at least I got to plane some wood. Electricity came in handy. I still miss my old tablesaw at times.



Ahhhhh, my old workbench......didn't ever get that project completed either, but at least the new owner is an eager woodworker. She'll finish it up nicely. She was psyched to keep my old saw and I'm glad that it found a good new owner.



I brought along a minimal assortment of tools, nothing fancy.


The TSA always gets a treat, looking through my baggage. They generally do a better job packing my bags than I do, and never skimp on the tape that holds the lids on he boxes, haha. A tough and thankless job, to be sure.



I was so happy to be planing wood again, I maybe went a little above and beyond on some of the tasks that needed completion. The attic railing (Port Orford cedar....such a great wood!) posts and balusters received a winding chamferred edge and a simple bridle joint attachment, draw-bored and pegged using bamboo skewers.





And finally, capped with some nice ribbon figured African mahogany that I was saving for a special place. The light was so bad, I couldn't get a picture. It definitely made the colors in the attic look off. Ewww, yuck!



If I ever figure out how to plane that curly, interlocked crap with a kanna and NOT get any tear-out, I'll share the knowledge. It's good to have goals, right? The 47 degree kanna that Dave gifted me would've been just the thing, had it been here – sigh.



So where was I?


Before I left, I had started on this post, some thoughts regarding an optimized tooth pattern for a Japanese saw I've been using for working green wood, but maybe this should be a WIP thing instead. Get this thing going before I forget what I've already done. An aspect of blogging that I love......I can show my mistakes. Maybe we both learn that way, hmmmmm?


So, spoiler alert. I'm not satisfied with this saw, so you might not want to jump right in and copy what I'm doing here. Not quite ready for prime time...... yet.



I need a general purpose saw that works well on green, sticky wood.



I've had this old bugger kicking around for a while, but haven't really felt the need to use it very often.....'till now. This was 1/3rd of a lot that I bought for $15 on eBay nearly four years ago and I guess it's time I put this thing into circulation. They sell even cheaper on Yahoo Japan, so have Murakami get you a bunch.






Felling trees, even the relatively small ones, using a pruning saw (much less using a trusted ryoba) is good meditative work, but when a tree is in danger of dropping onto my head, I want to get done with the task as quickly as possible, you know?

It's time to pull out the big(ger) guns.






The toothed length of this crosscut saw is a respectable 20" (about 510 mm) and the handle is nice and fat, perfect for two handed sawing. There are a few slight bumps to the blade that I still need to remove, as you can see from the slightly brighter spots on the body where it has been rubbing in the cut. Contact with the walls of the cut = friction, so hammering out the dents is a short list priority. You can also see a couple of lines of fairly severe corrosion that run diagonally across the blade. Bummer, but not the end of the world.


The farthest end of the saw where the teeth are largest has a vertical tooth angle. 0* rake angle.



90* and pointy, these teeth are similar to a rip tooth, but still have a front, back, and top bevel/facet.



I'm holding the file to show the approximate angle of the cutting face, around 75* or so. That would be 15* away from being a purely perpendicular rip tooth.


Not being the purely perpendicular face that you would see with a proper rip tooth, it's more of a hybrid, but this is a general purpose saw, I suppose. You might notice that I've already jointed the saw, the tops of the teeth are showing little flat surfaces.





As we approach the handle end of the saw, the teeth gradually assume a more relaxed slope.



These teeth are the familiar shape that you see on any crosscut blade, although the rake angle is more shallow than you'd see on a ryoba for instance, about a -10* rake angle. These teeth at the heel of the saw are probably shaped differently to make it easier to start the cut. The relaxed tooth angle gives a nicer shearing action.



The tooth pattern must have originally looked more like this example from a pruning saw manufacturer.



My saw is similar, but the saw in the photo above has both leading and trailing edges at much shallower angles, closer to 45* from the looks of it.



When I check my saw, the file shows a cutting angle of nearly 60*, so a 30* angle to the leading edge.



It's pretty much a standard crosscut tooth shape, although I'm going to try reducing the height of the teeth a bit, in orders to lend extra durability for cutting these dense Hawaiian hardwoods.




Rust is bad! Here is a closeup of the rusted area.



The tooth in the center has been polished using a hard novaculite oilstone and is tilted towards the viewer. Skip a tooth either direction and the two teeth at the edges of the photo are the rusty ones. The pitted rust on these teeth will prevent them from ever being truly sharp. Worse, the little pits will tend to hold onto little threads of wood fiber, increasing drag and tending to pull the cut to one side. Unfortunate.





So, this is all fine and dandy, but so far I am really just copying the tooth pattern as it is. The interesting points are that this saw has both a progressive tooth size AND shape. And of course, it has a hand forge-welded tang, the saw blade tapered in both length and height....all that good Japanese craftsman stuff.

What am I doing differently, you ask?


Every 5th tooth I mark with a pen, prior to filing the top facet of the teeth. The fifth tooth I will turn into a raker, to better clear away the wood waste.





I use the 5th tooth raker through most of the length, but leave the teeth closest to the handle alone.






In the interest of experimenting with saw tooth shape, I'm going to alter the shape of the teeth in stages, beginning with the rakers. The upper slope I'm going to start with is.....oh, maybe 12*, probably too shallow, although it's similar to the clearance angle you want for a plane blade.



Other than filing the raker tooth to a flat/chisel tooth, I leave the forward and trailing edges alone. It will be an admittedly crappy rip tooth shape, but I'm experimenting here, OK?


I give ALL the teeth a top slope of about 12*, but otherwise the other teeth are just copied as they were. Looking at the photos, I see that I need to work more on keeping my angles even from one side to the other. Everyone has a "strong" side, so it's just one more thing to give some thought to.




How did it work?


It cut. This is 8" of hard Ohia. felt crappy, haha. Both slow AND grabby, the worst of both worlds! The saw was dull and slow before, but sharp(ish) and slow?!



How about something softer? A low quality fir 4x.



Awful. Those big ol' teeth grabbed those growth rings and tried to rip that stick out of my hands on nearly every stroke. The cut surface quality is terrible as well (at least for a Japanese saw). And slow. Or perhaps my standards are just too high. Nawww. It sucked.



So there ya go. Universal Japanese saw v2.0......epic fail. There are some obvious things that can be improved, tip slope angle being the principle suspect, but we'll have to see. It's rare that sharpening a tool will lead to a decrease in performance and this was pretty lousy, so something interesting must be going on. It sure gets me thinking.