A totaly differnt (Inverse) method of filing

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A totaly differnt (Inverse) method of filing

Postby Jim_Thode » April 28th, 2016, 7:53 pm

What if you could sharpen a crosscut saw in a special way, then for several future tune up sharpenings it would only take a few minutes to keep the saw cutting well?

I’ll call it inverse filing for three reasons; one, it is completely reversed from traditional filing instructions; two, only the back side if the cutter tooth is filed for tune up sharpening and three, the cutter is filed toward the cutting edge rather then the normal filing away from the cutting edge.

The basic idea is to file a saw so that the cutter teeth set is a little more then ideal and the rakers are a little shorter then ideal with the ideal that the tune up filings will bring the settings into the “ideal” range and maybe a little beyond. At the same time the settings at any time are still within an acceptable range for a good cutting saw.

Start with a saw with the whole cutter teeth set as needed, that is the tooth is bent out near the body of the saw and not just the tip of the tooth. A well tapered saw would work fine with 0.008” of set and the rakers at 0.008” lower then the cutters. So when the saw is set up (full joint and sharpening) the set is set at 0.014” and the rakers are set at 0.014”. The saw should cut fine with these settings. Then when the saw gets dull, only the back sides of the cutters are filed to remove any dull surface on the cutter tips/edges. On the saw I’ve used this method I measured that about 0.0005” needs to be removed to sharpen up the cutters. At this rate the saw could be tuned up about twelve times before a full sharpening was needed.

I’ve did this on my broken, welded, patched falling saw and other then one hitch it has worked fine. The problem I had was after three or four cords of firewood cutting the saw would start to bind up in the cut after 5 to 10 inches into the cut. It acted like there was not enough set, but there plenty of set when I checked it. It did cut fine up to that point. Then I figured out that most files are twisted and that when I flat filed the cutters I was not filing the cutters in line with the saw. This caused problems, especially when the saw started to get dull. The last time I used the saw, last fall; it would only cut about 6” and start to bind. So recently I spent about 15 minutes to tune up the saw, making sure to use a flat file. Then just to test the saw I went out and cut about half a cord of firewood today. It cut well with no noticeable dulling or binding. If my past experience holds, it should be good for another four plus cords of cutting before I will need to tune it up again.

On the saw I have filed like this the rakers have not needed any attention. They are quite hard and hold an edge well. They may need a little touch up at some time before fill filing is required.

With the setting on this saw now at about 0.013” of set and rakers about the same I figure that saw will be good for probably six to eight tune ups before it needs a full sharpening. That works out to something like 24 to 30 cords of firewood with just a short time in the filing shack. It is going to take several years to fully run the course of confirming my idea.

There seems to be several advantages when using inverse filing. Less wear of cutter length, IE the saw will last longer. You can get more tune ups then the normal filing method before full jointing and sharpening are required. It is easier to file, no angles to worry about. Much faster to tune up a dull saw just a few strokes per tooth, less then 15 minutes per saw. No burr or wire edge because the filing is into cutting edge. Filing the back side cleans up any pitted surface on the back side of the cutters.

I don’t think I’d recommend that everyone run out and convert their saws to this method but it may be interesting to consider or try on a limited trial basis. It is a major deviation from how we were taught to sharpen a saw.

Comments, questions and suggestions are always welcome.

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Testing

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Testing

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Re: A totaly differnt (Inverse) method of filing

Postby Gavin Longrain » April 28th, 2016, 10:57 pm

Jim,
The idea of mini-tune ups seems good to this largely armchair filer. I really appreciate your thought-leadership here. Well done!

Was your idea used in the past?
If so, has anyone noticed references to it?
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Re: A totaly differnt (Inverse) method of filing

Postby dayle1960 » April 29th, 2016, 4:40 am

Good idea. I like your "thinking outside of the box".

While I was reading this thread the one thing that kept passing through my mind was the file. Did you use a course file or a fine file? I wonder if one would be more beneficial over the other. Also, maybe, instead of using a file the backside of the cutters could be hit with a diamond stone instead of a file.

Would a mirror finish on the back side of the cutter be better than a filed appearance?
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Re: A totaly differnt (Inverse) method of filing

Postby PATCsawyer » April 29th, 2016, 6:08 am

I've been doing this with my personal saws for a couple of years, only I use an EZE-Lap hone instead of a file. I find that it doesn't take much of a stroke to skim off a little metal on the back of the teeth. Using a dial gauge, I can also be ultra accurate on how much set I remove. This probably changes the jointing of individual teeth very slightly, but not enough to matter and worth the trouble in exchange for a sharper saw.

Alan Boyko mentioned this method to me a few years ago and said it was an old technique used to tune up saws in the field. I think it has been downplayed due to the risk of inexperienced filers mucking up their saws by overfiling. This is definitely a technique requiring finesse.

I back hone all my teeth just slightly after jointing to insure clean metal for the point-up. That small shiny spot on the tooth tip in the last photo is from that process.

The set of the tooth and the thickness of the actual hone plate puts a slightly negative angle on the stroke, though not the 2° recommended by John S. Perhaps if I'd had more set on these teeth or a shorter hone the angle would've been greater.

P1014165.jpg

P1014164.jpg

P1014170.jpg
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Re: A totaly differnt (Inverse) method of filing

Postby Jim_Thode » April 29th, 2016, 7:11 pm

Gavin Longrain wrote:Jim,
The idea of mini-tune ups seems good to this largely armchair filer. I really appreciate your thought-leadership here. Well done!

Was your idea used in the past?
If so, has anyone noticed references to it?


No, I have not seen any references to this method in the past.
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Re: A totaly differnt (Inverse) method of filing

Postby Jim_Thode » April 29th, 2016, 7:32 pm

dayle1960 wrote:Good idea. I like your "thinking outside of the box".

While I was reading this thread the one thing that kept passing through my mind was the file. Did you use a course file or a fine file? I wonder if one would be more beneficial over the other. Also, maybe, instead of using a file the backside of the cutters could be hit with a diamond stone instead of a file.

Would a mirror finish on the back side of the cutter be better than a filed appearance?


I use an 8" mill file that is relatively fine. In my case the area filed is about 3/8" across and removing even a little metal over that size of area would be difficult with a fine hone and with a plastic handled hone there would be no support to keep the surface in line with the saw. If just a little spot on the tip of the tooth needed honed like PATCsawyer shows, then maybe a hone may be the way to go.

There is an option and some do suggest touching up the cutters with a hone on the normally filed surfaces. I think that is a good option for some folks. The disadvantage is that two surfaces need to be honed, it would take longer, it may be harder to maintain the angles and more material needs to be removed from the length of the tooth to remove the rounded worn cutting edge. The advantage is that even a non-filer should be able to make the saw cut better and as long as a fine hone is used there is little chance of damaging the saw.

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Re: A totaly differnt (Inverse) method of filing

Postby Jim_Thode » April 29th, 2016, 7:49 pm

Here is a photo with a straight edge across the the saw. The tooth points out from the saw at the point, maybe about 2°. This angle is caused because the file is flexed some when filing the back surface of the cutter.

Z99A3274a.jpg


I don't understand how a "negative" angle at the tip would be good thing. It would likely cut fine when the cutters were very sharp but once they started to dull a little I would think it would start to bind up. The kerf would get smaller and smaller as the saw preceded in the cut.

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Re: A totaly differnt (Inverse) method of filing

Postby soli » April 30th, 2016, 3:45 pm

FWIW, with my idiosyncratic cutter geometry, subsequent tuneups are much simpler than with conventional teeth, plus the tuneup filing does not nibble away at the cutter set, or the raker depth(the "ideal" set/depth are maintained), plus the tip of the cutter is more robust, plus there is less drag in the kerf when sawing than with conventional cutters. Here is Diablo's drawing of my method:

Image

Tuneups involve filing/honing the two flank bevels of each cutter. The slope bevel is left alone. I first explained my method in this post viewtopic.php?f=21&t=930#p4523 in Diablo's 'thread on 'Saw Aggressiveness':

For what it is worth regarding filing lance teeth, I've started filing the tips a bit different. Traditionally, the tip is a point, the apex of three ridges. Two of the ridges are the cutting edges. The third ridge is the shoulder. In the last stages of filing a lance, there is a tiny flat spot on the tip. I used to continue traditional file work until it just disappears. This spring I changed. I now hold the file flat to the shoulder ridge in order to file down the shoulder. This creates an additional bevel and a tip that is no longer a point. The tip ends up being a tiny, maybe 1/32" long knife edge that will be parallel to the bottom of the kerf. My thinking is that the tip is significantly more robust to wear and damage, and the tip profile is more streamline.
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Re: A totaly differnt (Inverse) method of filing

Postby Jim_Thode » May 1st, 2016, 10:14 pm

Soli,
The flat top cutters seem like a reasonable idea. I've never seen a saw filed like that except my wife picked up a saw at a craft bazaar recently with kind of flat/rounded tips. At least is looks like someone had did something like it in the day but for some reason it did not catch on. This same saw had some very strange rakers and I don't know what the idea was there.

I cleaned up the saw and cleaned up the back side of the cutters to remove the pitting at the tips. I also filed a few of the cutters with a flat top just the see how that works. The saw is set up so I can file the back side of the tooth to tune up the saw and/or file the sides of the flat toothed cutters if the tip is not worm or rounded too much.


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48" cut off falling saw with Sells Handle

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Note flats on tips. I also see some bent over tips, maybe because of the thinner metal at the point

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Strange raker

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The flat top on these is almost 3/23" wide so that is wider then yours. I'll see how it works.

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Re: A totaly differnt (Inverse) method of filing

Postby chancwj » March 1st, 2018, 9:23 am

Jim,
What's your opinion of the three-faceted cutters with flat knife edges? Do they have more or less drag than traditionally sharpened two facet cutters? Do they wear slower in use?
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