IanW
11th December 2014, 06:33 PM
A couple of years ago I made myself a saw for cutting the sides of dado or sliding dovetail trenches (http://www.woodworkforums.com/showthread.php?t=156575&highlight=sliding+dovetail). It provoked quite a discussion, and a few very reasonable questions, like "Why would you want to build a saw like this when an ordinary backsaw will do the job?" I have a couple of answers to that, the flippant one was "Because I can", but the serious answers are that a saw like this has a low centre of gravity which makes it easier for me to keep against the guide when sawing. The wooden 'back' to this saw also acts as a depth stop, so the saw cut ends up an even & repeatable depth all along (except for the last 40mm or so in a stopped trench - see later). The amount of blade exposure is easily adjustable by loosening the 3 retaining bolts.
That saw was a prototype, but I have this habit of not getting around to making the 'production' model for some considerable time (or never, in some cases!). Well, I decided to move quickly this time, so in just a shade over two years (:;), here is its successor (which could be a record for me): 333909
I made some 'improvements' on this saw. It is a teeny bit longer, and I set the hang angle of the grip a little higher (i.e. closer to the horizontal). If you are wondering why the blade has that funny sticky-out bit at the front, it's because I wanted to see if a bit more crowning on the end would be helpful in clearing sawdust. I wasn't sure it was going to work as I envisaged, so I added the bit extra, reasoning I could cut it off and reshape the end, if it did what I hoped. It doesn't seem to add any value, so it's coming off. Here is the original compared with the new: 333910
The original handle was set at about 25 deg. from vertical, the new one is set closer to 40 deg. I took that angle off a very comfy backsaw I use a lot on a bench hook. As it turns out (just a few trial cuts so far), it's actually a bit high. There is a slight difference in the way I lean to make these trenching cuts, and the handle could benefit from being a trifle lower, somewhere around 35 would be the Goldilocks angle, I think. It's still pretty good, and works fine as-is, I'm just being a persnickerty old goat - I will almost certainly not make another, but if I do.... Just goes to show, I can theorise all I like about how to establish the perfect hang angles (see the long discussion here (http://www.woodworkforums.com/showthread.php?t=190583)!), but it still boils down to some trial & error for a specific saw in a specific application.
And about cutting a stopped trench. I found with my old saw that I could cut all but the last 20-30mm to full depth if I just made a short hole at the 'stop' end: 333912
The bit that the saw couldn't cut because of the slight crowning of the end was easily fixed by cutting down on the sides with a wide chisel, registering it against the sides. However, the extra crowning on the new saw means the cut is a bit shallower still, & leaves a longer length to remove: 333913
So, as it doesn't seem to be of any material help in any other way, it's going to be removed & I will go back to the slight crowning of the original, which did a perfectly good job after all!
Was it worth the effort? Not really, the old saw works nearly as well, & certainly well enough to do the job. My newer saw is a bit smoother (I'm better at forming teeth & sharpening), a bit more comfortable to hold, but that's it. BTW, the cuts look a bit ragged in the pic, that's because I was using some very soft & crumbly old Hoop scrap, and also because I was being lazy, and only clamped the guide with a single hold-down, so the guide moved a bit on a couple of cuts. I wouldn't do that if I was trenching some expensive cabinet part.... :no:
Cheers
That saw was a prototype, but I have this habit of not getting around to making the 'production' model for some considerable time (or never, in some cases!). Well, I decided to move quickly this time, so in just a shade over two years (:;), here is its successor (which could be a record for me): 333909
I made some 'improvements' on this saw. It is a teeny bit longer, and I set the hang angle of the grip a little higher (i.e. closer to the horizontal). If you are wondering why the blade has that funny sticky-out bit at the front, it's because I wanted to see if a bit more crowning on the end would be helpful in clearing sawdust. I wasn't sure it was going to work as I envisaged, so I added the bit extra, reasoning I could cut it off and reshape the end, if it did what I hoped. It doesn't seem to add any value, so it's coming off. Here is the original compared with the new: 333910
The original handle was set at about 25 deg. from vertical, the new one is set closer to 40 deg. I took that angle off a very comfy backsaw I use a lot on a bench hook. As it turns out (just a few trial cuts so far), it's actually a bit high. There is a slight difference in the way I lean to make these trenching cuts, and the handle could benefit from being a trifle lower, somewhere around 35 would be the Goldilocks angle, I think. It's still pretty good, and works fine as-is, I'm just being a persnickerty old goat - I will almost certainly not make another, but if I do.... Just goes to show, I can theorise all I like about how to establish the perfect hang angles (see the long discussion here (http://www.woodworkforums.com/showthread.php?t=190583)!), but it still boils down to some trial & error for a specific saw in a specific application.
And about cutting a stopped trench. I found with my old saw that I could cut all but the last 20-30mm to full depth if I just made a short hole at the 'stop' end: 333912
The bit that the saw couldn't cut because of the slight crowning of the end was easily fixed by cutting down on the sides with a wide chisel, registering it against the sides. However, the extra crowning on the new saw means the cut is a bit shallower still, & leaves a longer length to remove: 333913
So, as it doesn't seem to be of any material help in any other way, it's going to be removed & I will go back to the slight crowning of the original, which did a perfectly good job after all!
Was it worth the effort? Not really, the old saw works nearly as well, & certainly well enough to do the job. My newer saw is a bit smoother (I'm better at forming teeth & sharpening), a bit more comfortable to hold, but that's it. BTW, the cuts look a bit ragged in the pic, that's because I was using some very soft & crumbly old Hoop scrap, and also because I was being lazy, and only clamped the guide with a single hold-down, so the guide moved a bit on a couple of cuts. I wouldn't do that if I was trenching some expensive cabinet part.... :no:
Cheers