Rake and TPI
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- This topic has 7 replies, 4 voices, and was last updated 1 year, 4 months ago by Sven-Olof Jansson.
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I’m reading a general consensus online that says less rake to 0° for softwoods and around 10° rake for hardwoords, I’m only talking RIP saws.
I have a 13 tpi rip tenon saw where I filed the first inch or two very passively and the others teeth very aggressively at 0° rake , at that moment I didn’t know much about rake but it works excellent in pine and softwoods.
I also filed another 13 tpi rip saw very passively with a LOT of rake by accident when first learning to sharpen and crosscut through white oak with a LOT of ease and cleanliness, not the fastest though.
Both done on 13 tpi rip saws.
How much does rake matter in comparison between a 13 TPI saw vs a 20 TPI saw.
Do you want a 20 TPI saw to cut more aggressively using less rake or doesn’t that matter much compared to more rake? Is it purely a softwood vs hardwood kind of thing?
I will have to file some of my 20 tpi and 15 tpi saws soon and am not sure what to go for in terms of rake with these higher TPI saws. I tend towards filing with 10° rake for an all-rounder.My tenon saw is sharpened like the first saw you mentioned: relaxed for the first inch and then aggressive. I use it for everything and wouldn’t bother having a different saw for different woods. This saw is 13 tpi. For my style of work, what is most important is set and uniformity. By uniformity, I mean giving a clean cut line without any jaggedness in the cut. By jaggedness, I don’t mean blowing out fibers during a cross cut. On some saws, depending upon the sharpening, if you rip (like cutting a dovetail) and examine the cut, it might swerve to one side or the other if the set isn’t even and / or it might show jaggedness along the ripped kerf…little steps on either side of the kerf. That is what I am talking about. I keep my set very small, small enough that I may sometimes be at the limit of binding and will then lubricate the plate. The net result of all of this is a saw with an aggressive filing, but which leaves a kerf like a dovetail saw even though it is 13 tpi. My fancy LN dovetail saw its on the shelf and I probably should sell it. It is too slow for my taste and too short. Meanwhile, this old Disston 14″ tenon saw does all of my work.
So, I would explore using your aggressive sharpening in everything and see if it actually produces a problem that isn’t solved with a good knife line. In some cases, you may need a pair of knife lines, sawing in between.
What reason was given for having a ore relaxed rake in hardwoods?
Thanks!
It was said that the higher rake in hardwoods would give less resistance compared to a lower rake which would stick more into the wood and makes it a little more difficult to push the saw.
This basically sums up the consensus on some internet forums: [img]https://www.blackburntools.com/articles/saw-tooth-geometry/images/rake-guidelines.gif[/img]
What also seems to influence your cut is the angle of your saw handle.
- This reply was modified 1 year, 4 months ago by Jasper.
When developing sawing skills, especially at the start, there’s a tendency to have the saw get stuck. This happens when starting the cut when the teeth make little divots in the wood and then dig into them. Those divots can form when you start the cut by placing the full weight of the saw onto the work and then draw back. The saw cannot cut when drawn back, so it just bounces on the points of the teeth, which forms the divots. Then, when you push forward, the saw binds into those divots and seems to jam.
One fix for this is to learn to do what Paul describes as “just brush the saw on the surface.” To do this, you unweight the saw, bearing most of the weight via the handle. You can then move the saw back and forth along the start of the cut. It is like making light lines when sketching or like rehearsing the cut. With such a light touch, the saw doesn’t make divots to get stuck in yet can still sort of scratch out the start of the cut. For me, it feels like I am also getting my arm moving in the proper line. This all happens in a few seconds and as things feel right and the saw is engaging the wood, you let more of the saw’s weight fall onto the work until you are fully engaged in the cut. My guess is that this when you see Paul give a final, definitive push forward and then clear the teeth. You don’t need to do that last step, really, but it might help you get a sense of how quickly and progressively this happens in the first moments of getting started with a cut.
There’s a good chance that this is the essence of “More experience required” in the left hand column of your chart. You can probably develop this in an afternoon by just starting a bunch of cuts working across a piece of scrap. If you get stuck, look and see if you’ve formed the divots. If so, just move over and try again. Later, when you have a feel for things, come back and see if you can overcome those divots. You’ll be surprised to find that the secret is to float the saw (unweight it) and gently work into, through, and past those divots.
There, now you just need one tenon saw. 🙂
Jasper, before I (sort of) got the hang of sharpening saws, I studied with great care charts like the one you provided above, which seemed to require different saws for hardwoods and softwoods. (I also noticed saw dealers advertise ever so precise numbers for the amount of set in their saws, numbers I would never be able to reproduce when sharpening.) I also noticed that Paul did not seem much worried about such things. My sharpening, and my sawing, improved greatly when I pretty much followed what Paul does. I use the same saws for hard and soft woods. I file my joinery saws pretty aggressive (accept for the first few inches, which seems common) just as you talk about. I do not like a straight 90 degrees, and usually go just a bit off of that. Personal preference? Focusing on unweighting the saw, again as Ed mentions, solved the problem of teeth catching: one day i realized it almost never happens any more, even with a pretty aggressively filed saw.
Also, as Ed talks about, the biggest problem I have is if I have too much set in the saw. It creates ragged cuts. Yah, I do always end up with too much and have to take some out. For some reason, I have never had uneven set which causes the saw to wander off course.
I do like the Lie Nielsen dovetail saw. I had to change how it was sharpened a lot: it was not nearly aggressive enough. Hm . . . maybe they had optimized it for softwoods! I don’t know. I also have a Veritas medium tenon saw. It came with so little rake that it almost wouldn’t cut. At first I thought it was me since I was a beginner. But I finally sharpened it following more or less Paul’s suggestions and it cuts well.
One thought: if you have several saws, it makes perfect sense to try different things on different saws. I have several tenon saws I bought here and there at reasonable prices and have played around a good bit with rake, set etc. That is how I learned to sharpen. I did settle in on a rather simple formula, but it seems others differ.
For yuks, I pulled out the LN dovetail saw, got it started and then took 10 strokes. Then, I did the same with my “do it all” 14″ saw. Then I repeated both. The latter cuts roughly twice as fast. The kerf on the LN saw is slightly more refined, but not by much. The extra speed means you can make bigger mistakes faster. On the other hand, I sometimes think that one gets in trouble by trying to make course corrections while sawing a dovetail rather than accepting what is happening, so being done in a few strokes rather than having a dozen strokes to change my mind and oversteer might be an advantage. I confess to not being the best dovetailer, though.
I think the real reason I dislike dovetail saws is that I have long arms and tend to pull the dovetail saws back too far, even pulling them out of the work or jamming the toe into the work. That’s just clumsiness, but cutting with a short saw feels like walking up stairs that have risers that aren’t tall enough or pedaling a bicycle with too-short cranks, like a kids bike.
- This reply was modified 1 year, 4 months ago by Ed.
- This reply was modified 1 year, 4 months ago by Ed.
Attachments:
You must be logged in to view attached files.Yes, I am sure that a 14 inch tenon saw will cut much faster than a short dovetail saw when using full strokes. And I suppose that can make mistakes happen very fast. On the other hand, in my limited experience, and at least up to a point, I have found the faster cutting saw far more accurate than the slower cutting saw — though I doubt my Lie Nielsen cuts as fast as Ed’s saw. After struggling with cutting dovetails and tenons accurately, I found three things that helped a lot, a sort of trifecta of discoveries. First, a more aggressively sharpened, faster cutting saw. As Ed mentions, all those extra strokes of a slower cutting saw seem to increase the chances for messing up, or even to guarantee messing up, I at least in my case. Second, trying to control the way my hand naturally wants to twist in each stroke of the saw. Oddly, my hand wants to twist in different direction on either side of the dovetail. Third, I made a Moxon vise which raises the wood to a more comfortable height for dovetails. (Has anyone else found that planning, cutting dovetails, mortising, etc., all seem to want different height benches?)
Anyway, just a few thought from someone who still finds it amazing that my own hand cut dovetails actually come together pretty well most of the time.
1 December 2022 at 6:57 pm #782170My suspicion is that being comfortable with the tool is what’s most important for a good result. To test that I used seven different rip-cut backsaws aiming at a 1:7 angle, without marking it out, over the edge of 21 mm thick white oak.
The saws (from left to right in picture below) and their cut lines were:
Lie-Nielsen tapered dovetail saw: 10″, 15 ppi
Bad Axe Tool Works dovetail saw: 12″, 15 ppi
Pax 1776 dovetail saw: 12″, 15 ppi
Bad Axe Tool Works carcass saw: 14″, 14 ppi
Veritas carcass saw: 14″, 12 tpi, rake angle 10°
Lie-Nielsen tapered tenon saw: 16″, 11 ppi
Veritas tenon saw: 16″, 9 tpi, rake angle 14°
(rake angles, where not mentioned, were 0°)The LN dovetail saw is the one I use for cutting dovetails, and I could immediately sense where I should go (though a little adjustment was required).
The Bad Axe dovetail saw was faster and had a very narrow kerf, while feeling different. The Pax dovetail saw I haven’t used for a long time and didn’t do well with.I immediately lost control over the very aggressive Bad Axe carcass saw, while the Veritas one, and old friend, worked better albeit much more tardy.
Of the tenon saws, the LN is the one for everyday use, and though not small, it felt comfortable enough. The Veritas Tenon saw was the slowest of the lot. I suppose it must be because of the rake angle.
All in all: kerf and rake angle are probably very relevant to speed of cutting, and by definition blade length.
[attachment file=”Back_saws_rip_Compr.jpg”]
Wouldn’t the consequences of going astray also be a factor when weighing what saw to prefer? This picture below shows cuts for concealed mitred dovetails, and how too deep cuts would be quite visible along the joint line – which by definition always will leave room for improvements.
[attachment file=”Mitred_Dovetails.jpg”]
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