saw sharpening critique/input

[Phil Mueller]

Pete gave me some good technique pointers in the saw file thread, so I went after a garage sale 10 pt rip saw to see what I could do. The teeth were in fairly bad shape with quite a few "low" and mishapend teeth. I ended up jointing it pretty agressively, then shaping as best I could. I aimed for 5 degree rake/zero fleam.

Used a Bahco 6 Xslim. It was a new file. I used one edge to shape, and a fresh edge for final sharpening.

Bottom line, I guess, is it cuts nice and straight.

But "tooth beauty" as I call it, is a far cry from the saws I have from Pete and Mike Allen.

My self critique is I need to work on shaping. I'm still trying to get better at knowing how much pressure to use to "push" or "pull" a tooth forward or back. Rake angle is also a bit inconsistent which has to be bacause I'm not holding the file angle (rake) consistent enough. Agree?

My other question most related to the saw file thread, is that the Bahco file left good size "flats" at the bottom of the gullet. My benchmark saws (from Pete and Mike Allen) have pretty sharp angled gullets. Is this a result of the file, my technique, too large a file...? I was really careful not to go beyond removing the jointed flats...but?

So, here it is...let the critiques begin. And thanks!

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[Luke Dupont]

Looks very consistent. Excellent work. My bow saw blade that I cut the teeth for myself are not that consistent, and yet it still performs excellently. As long as all of the teeth are jointed and on the same plane so that they're all cutting at once, you're fine.

The difference in geometry of the gullet is just due to the characteristic of the file (rounded corners vs sharp corners). I have never used a sharp cornered file so I can't comment, but it seems that it would make being accurate (especially in cutting teeth yourself) much easier. I wouldn't worry about which one to use that much if you don't mind widening the gullets. That said, if you think you'd like to try out a sharp-cornered file, why not acquire one and compare for yourself?

[Patrick Chase]

My other question most related to the saw file thread, is that the Bahco file left good size "flats" at the bottom of the gullet. My benchmark saws (from Pete and Mike Allen) have pretty sharp angled gullets. Is this a result of the file, my technique, too large a file...? I was really careful not to go beyond removing the jointed flats...but?

In my experience Bahcos run "blunt", meaning that the corners tend to be less sharp at any given size than some other brands. Assuming "10 pt" means 10 ppi (9 tpi) the file size is about right based on the traditional rule of thumb that the file's face should be twice as tall as the length of the back of a tooth. Some people like Isaac at Blackburn Tools for example recommend smaller files than that, though.

The practical downside of a rounded gullet bottom is that you lose some ability to clear sawdust, and therefore some speed. IMO the amount of rounding you show is perfectly fine, though, because it looks to me as though you've only lost a few percent of the potential gullet volume. Most of the gullet's volume (and therefore dust-clearance ability) is up close to the tip, and you really have to round the bottom pretty badly to put a significant dent in it.

[Kees Heiden]

I have the idea that a more rounded gullets makes the plate less sensitive for stress cracking between the teeth. A good quality steel is not very suspect in this regard, but some old saws can be very brittle. And a very sharp corner might lead to s stress concentration spot.

That said, I don't really beliefe in the neccesity of using a file that has flats > twice as wide as the tooth height. Sawfiles dull on the corners, especially the modern ones. Using large files so you always have a completely fresh face when you turn the file to a new corner, are usually prety huge!

The teeth you show there looks pretty perfect to me.

[lowell holmes]

Get Lee Valleys saw filing kit and watch Ron Herman's video about saw sharpening.

You will be able to sharpen saws that are incredibly sharp and track properly.

[Pat Barry]

Overall not bad. Some rounding / faceting on the trailing edges of the tooth (yellow) points but the leading edge angles (red) look pretty consistent.

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[Phil Mueller]

Thanks folks! I have watched the Ron Herman video a number of times...just working through the learning curve. I am also using the LV file holder/guide. I appreciate the highlights, Pat. Does help to see what is going on. I don't expect after a hand full of saws to be perfect. Sometimes it feels like learning to swing a golf club...posture, muscle memory, file angle, stroke pressure, right light angle. Come to think of it, I am a lousy golfer, so I at least feel I'm making better progress at this.

[Patrick Chase]

I have the idea that a more rounded gullets makes the plate less sensitive for stress cracking between the teeth. A good quality steel is not very suspect in this regard, but some old saws can be very brittle. And a very sharp corner might lead to s stress concentration spot.

It's certainly true that sharper corners concentrate stress, though as you say the plate should be strong and/or ductile enough to render that a nonissue.

My engineering intuition is that if a saw were brittle enough for sharp gullets to be a problem, then you wouldn't be able to set it (which requires plastic deformation of the teeth).

[Chris Fournier]

It's certainly true that sharper corners concentrate stress, though as you say the plate should be strong and/or ductile enough to render that a nonissue.

My engineering intuition is that if a saw were brittle enough for sharp gullets to be a problem, then you wouldn't be able to set it (which requires plastic deformation of the teeth).

I think that it would have to be a very messed up saw plate to see any cracks propagating at stress risers and yes the teeth would likely break when set not while in a cut.

[Luke Dupont]

I learned to sharpen saws by watching Ron Herman's video. I still have the video.

There are no rounded teeth in his video. If a saw is in bad shape, I file it smooth and then file new teeth. Rounding of the teeth is unacceptable. The sharpened tooth line should "grab" your palm if you just put your hand on the toothline.

Ron Herman really addresses all of this.

You need a filing system. I explained in another post how I do it and I have been successful. My saws are sharp, cut smoothly, and cut fast. If you need a tooth pattern, down load it, there are sites that will provide them. Or if you will send a private message to me, I will send you a pdf showing whatever spacing you want. You print the pdf and cut 1/2" strips, tape the strips together end to end so they will have the length . I attach the strips to the saw plate on the upper side, not on top. A single file cut at each line will locate the teeth. These marks become the gullet and the teeth develop when adjacent gullets meet each other.

We're talking about rounded gullets, not teeth. The teeth are still sharp.

[Stewie Simpson]

More critical as you work your way through 10 tpi/ppi spacing's and above, the rounded gullet formed between 2 teeth will have an effect on those tooths end height. The provided example is not of my work.

https://i1.wp.com/paulsellers.woodworkingmasterclasses.com/wp-content/uploads/sites/2/2014/05/DSC_0009.jpg?zoom=3&resize=600%2C398&ssl=1

[lowell holmes]

I didn't understand that rounded gullets were desirable. They might work on larger teeth, but never on a dovetail saw. :)

[Stewie Simpson]

Lowell; it saddens me to tell you those teeth were filed by Paul Sellers.

[lowell holmes]

I attended classes at Homestead Heritage in Waco Classes while Paul was there.
I know Paul has reasons for what he does. I may have to try one to see why he would do that.
Maybe I should have said that would never work on one of my saws.

I never saw him leave space between gullets twenty years ago.
He filed his saws all rip cut at that time. Like Tage Frid, he cut crosscut with fine rip filing.
I do file crosscut on crosscut saws.

It is 8:45 on Sunday Morning here in Texas. What time is there in Australia. I understand time zones, but I do get confused with the time differential in New Zealand and Austrailia. You not only are in a different time zone, but also different hemispheres. I know hemispheres have no bearing on time.

[Stewie Simpson]

Lowell; I am on Australian Eastern Standard Time. https://www.timeanddate.com/time/zones/aest

Stewie;

[lowell holmes]

Thanks! Now I will know if it's day or night, today or tomorrow when I read a message from our Australian friends.

You are 15 hours ahead of Houston. Dickinson is in the Houston Metropolitan area.

[Patrick Chase]

More critical as you work your way through 10 tpi/ppi spacing's and above, the rounded gullet formed between 2 teeth will have an effect on those tooths end height. The provided example is not of my work.

https://i1.wp.com/paulsellers.woodworkingmasterclasses.com/wp-content/uploads/sites/2/2014/05/DSC_0009.jpg?zoom=3&resize=600%2C398&ssl=1

Why would a rounded gullet impact tooth height if the tooth are all uniformly spaced and properly jointed? I'm not arguing that they should be rounded, but I don't see the connection to this specific problem?

The teeth are clearly not ideal in the picture you posted, but it looks to me as though they're simply unevenly spaced. For example the 5th tooth from the left is shifted to the right, leading to a deep gullet between 4-5 and a shallow one between 5-6. Ditto for the 3rd from the right. Both of those could have been avoided by taking more care to keep the spacing uniform during cutting. There are other, similar examples.

Similarly, the "land" on the second tooth to the right of the file is larger than any of the others, and the gullet between it and the 3rd is a touch small. That one is easier to fix than the others, since you can address both issues at the same time by filing the back of that tooth.

Note that the fact that the picture is taken from above and to the side makes the teeth that are set in the direction of the camera look at bit smaller than they really are. You have to look directly from the side to accurately judge tooth shape, though you can accurately judge tooth-to-tooth spacings. In this case the errors are big enough that I don't need to see the side-on shot to know that this saw has problems. I remember seeing that picture on Paul's blog and being... surprised. I wouldn't show something like that in public :-).

[Pete Taran]

Patrick,

It's just geometry.

Please review the attached training aid, and if it's not clear, please say so and we can delve into it further.

Regards,

Pete

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[Pat Barry]

Patrick,

It's just geometry.

Please review the attached training aid, and if it's not clear, please say so and we can delve into it further.

Regards,

Pete

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Why would you use a rounded file for some of the filing and a sharp file for the others?

[Phil Mueller]

Hi Pat, I don't think that that is a conscience decision. It's just what files you happen to own and use. The Bahco files, from what has been said here and from my experience, have a more "rounded" edge. Pete is saying the Nicholson files he's getting have a sharper edge, and would be prefered as the illustration shows.

[Patrick Chase]

Patrick,

It's just geometry.

Please review the attached training aid, and if it's not clear, please say so and we can delve into it further.

Regards,

Pete

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Ah, I think I misunderstood Stewie's post. I thought he was saying that the rounding of the file somehow caused the tooth spacing/height variation that's evident in that picture of Paul Sellars' toothline, and was struggling to understand how those were connected.

Upon reading again I now think that he was making the same point you did, i.e. simply that rounding the gullet reduces the height. I agree (as you say it's 9th-grade geometry), and I already acknowledged as much in #3 when I remarked that the gullet volume would be reduced.

Never look for complexity where a simple interpretation will do... :-)

[Pete Taran]

Yes indeed. I think it is called Occam's Razor. :)

As a side note, I used the Rounded Corner syndrome as an early indicator of declining quality. Grobet used to make most files perfect, but the 6" Extra Slim size had about 30% that didn't have filled out corners. I used to cull them out and ship them back. At some point I realized that they were just reboxing them and sending them right back. That was shortly before they had a falling out with Vallorbe.

Back when Simonds used to make their files in the US, they had the sharpest corners ever. They were a first class file. The Bachos were always square in the corner in the smaller sizes. Nicholsons aren't perfect, but I think they are the best out there at the moment.

Happy Sawing,

Pete

[Stewie Simpson]

The NOS Nicholson USA Taper Files are still in high demand from ebay buyers for a good reason. For 12 tpi and above I prefer to use the 180mm Vallorbe 3 Square Needle Files. (The higher the no. the finer the cut.) http://jewellerssupplies.com.au/needle-file-vallorbe-three-square-160mm-p-635.html

I am not alone in recognising the benefits of the Vallorbe Needle Files for high tpi backsaws. There are a number of well known boutique backsaw makers who also use the same product.

What's driven Vallorbe to maintain the highest quality specs within their merchandise has been the strong demand from the jewellery trade.

[Patrick Chase]

Since it didn't happen without pictures, here are 4 new-in-box 6" 2XS files. I've focussed on the start of the toothing near the tang, since that allows you to see how sharp the blank's edges are. From top to bottom: Bahco, Grobet, Nicholson, Simonds.

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Note the squared-off edge in Bahco's blank, and also the weird waviness thing in the edge toothing. It's hard to see, but the (Indian-made) Simonds also has a pretty blunt edge. The Bahco 5" 2XS isn't any better. I posted images of 6" files because I have a wider selection of those for comparison. FWIW that was taken handheld using ceiling-bounced flash with a 90 mm macro lens at 1:1.5 magnification or so, so my apologies for the hinky focus. I was too lazy to break out the tripod and macro rail.

Stewie's posts convinced me a while back to switch to needle files for everything above 14 tpi or so. As he says they tend to be a lot better made. As far as I can tell Nicholson, Glardon-Vallorbe, and Grobet Swiss all come from the same factory in Switzerland (they're all marked "Made in Switzerland" and have identical toothing, knurling, and taper profile. The only thing that's different is the engraving of the brand name). Bahco needle files are also Swiss-made, and have the same taper profile (to within a couple mils) and toothing as the preceding trio but with slightly different knurling and the brand name printed on. "Grobet USA" needle files are made in Italy, appear to be identical to Corradis, and are also decent.

[Stewie Simpson]

The following video up to 1.40min will help buyers identify Swiss Made Files.

https://www.youtube.com/watch?v=gZ2K6OOA53I

[Patrick Chase]

The following video up to 1.40min will help buyers identify Swiss Made Files.

https://www.youtube.com/watch?v=gZ2K6OOA53I

Thanks!

She's explicit in that video that "Grobet Swiss" and "Glardon Vallorbe" files are the same thing. Taking what she says at face value that would indicate that the Swiss-made Bahcos and Nicholsons are indeed from the UMV factory as well.

For some reason I thought Otto Frei's prices were fairly eye-watering for needle files, but you prompted me to look again and they're extremely competitive. 3-square 200 mm cut-2 files are $7.60 each in box quantity. Isaac at Blackburn wants $15 for that file. Hmm... (digs for credit card)

[Patrick Chase]

Yes indeed. I think it is called Occam's Razor. :)

As an engineer I've seen "Occam's Razor" used to justify some mind-blowingly bad interpretations of data, but yeah, in this case the shoe fits :).

I view Rounded Corner Syndrome as an important attribute (which is why I brought it up in #3) but one of several to be weighed. The Bahcos in particular have crisply formed toothing (you can see the difference relative to the others in the full-res version of the image I posted in #24) that's long lasting by current taper-file standards. The rounded corners make them less than ideal for fine-pitch saws, but on balance I think they'e competitive with any other currently available product.

EDIT: The Bahcos also have noticeably deeper toothing than some others. While I personally don't see that as a determining factor either way, I sometimes wonder if the folks who claim "5X greater life!" with Bahcos simply aren't carding enough...

[Normand Leblanc]

The major disadvantage that I can see to a rounded corner file is that it's much easier for the file to rotate and, at one point, the file "float" in the gullet. When I use a crisp edge file, it's almost impossible to get the rake wrong. The file really sit well.

Normand

[brian zawatsky]

The thing I like about the Bahco files is they seem to stay sharp considerably longer than Grobet or the newer Nicholsons. I've not tried any of the Indian made Simonds files though.

In crosscut saws I combat the flat that the Bahco leaves in the bottom of the gullet by adding slope to the gullet. It doesn't get rid of the flat, but it does produce a taller tooth by virtue of changing the tooth geometry a bit, so it lessens the impact of the flat-bottomed gullet.

On rip saws, I don't slope the gullets because it adds some fleam to the front of the tooth. The workaround here is to use a smaller size file than typical on saws beyond 7ppi where gullet size really matters. I've noticed that if the gullets get too small on fine-toothed joinery saws, for example, the saw will choke and bind in the kerf.

As someone else mentioned, the corners of the file wear out well before the faces do, so I pretty much always disregard the "rule" of file size should be twice the tooth height.

I'm of the opinion that there isn't a saw file made today that can compare to a NOS made-in-the-USA Nicholson. Or at least I haven't used one yet, anyway.

[Patrick Chase]

The major disadvantage that I can see to a rounded corner file is that it's much easier for the file to rotate and, at one point, the file "float" in the gullet. When I use a crisp edge file, it's almost impossible to get the rake wrong. The file really sit well.

Normand

Err, exactly the opposite is true. There are 3 cases to consider:


If the file corner is exactly the same radius as the gullet bottom then the file registers on both faces (the front and back of the adjacent teeth) and the gullet bottom. This is good in the sense that there's no play in rake or fleam (i.e. there's only one set of angles in which the file can register).
If the file corner is more rounded than the gullet bottom then the file "wedges" against the tooth faces without contacting the bottom. This is also good, again because there's no play in either rake or fleam.
If the file corner is sharper than the gullet bottom then the file only registers against the gullet bottom. There is play (what you call "float") in both rake and fleam, and you have to rely on muscle memory or a guide to preserve your angles.

I found the float/play in the 3rd case to be fairly noticeable when I switched from taper files to needle files for my 14-15 tpi dovetail saws. When I was exclusively using taper files it wasn't a problem, and now that I'm consistently using needle files on those files it hasn't recurred.

[Luke Dupont]

Yes indeed. I think it is called Occam's Razor. :)

A bit off-topic, but:

Have you ever learned of something semi-obscure, and then seen/heard reference to it everywhere for the following week? I know there's a name for this, most likely, and that the theory goes that you just didn't know to look for it before, but geez. This is about the third or fourth time this week, and I only just learned of the theory.

Anyway.

In regards to Paul Seller's example, I'm curious; just how much is your (Patrick Chase / Stewy / Other People who commented) judgement of that saw just a reflection of human desire for perfect geometry, and how much does it actually indicate problems in performance? I can't help but feel there is more to it than that. I've also heard Roy Underhill comment that slight variance in saw teeth is not necessarily a bad thing, as it makes the saw cut smoother/vibrate less/what have you, sort of in the same manner as hand-cut rasps. As long as the tooth (/teeth) before it is taking off an amount of material equal to any variance in height, one should be good, and in the grand scheme of things, a few teeth here and there isn't a huge issue for performance.

I'd also like to point out that varying depth and uneven teeth do not indicate uneven height, and can trick the eyes. The saw blade that I made is somewhat unevenly spaced, and I have quite a variance in spacing and even angle with the teeth. But they are all jointed fairly accurately and contacting during the cut. There's also variance in the set, which I accomplished by hand with a screw driver. Yet, it cuts much faster than any other saw that I've experienced from a factory or antique shop/flea market. In the end, I think a wild and visually ugly amount of variance can still be well within parameters for an efficient tool, and that insistence that one must go above and beyond to achieve utter precision or consistency usually is exaggerated.

Anyway. I personally would prefer evenly cut teeth for the aesthetics and ease of sharpening, of course, but I'm not going to throw out or recut a saw just because it appears ugly. You can usually fudge the teeth such that they're on the same plane, even if they're somewhat wildly spaced, and that variance doesn't always seem to be a bad thing.

All that said: The reason my teeth are unevenly cut is, I think, because I used a rounded-corner file which makes for a pretty sloppy registration surface, so do keep that in mind ;)

[Stewie Simpson]

In the later stages of shaping the teeth by hand, its rare that you will end up with all the flats being of equal size. That's part and parcel of hand filing, versus punching the teeth out by machine. Its what you do next to resolve that discrepancy that many less experienced saw filers will battle to resolve successfully. If you add some extra filing strokes to those odd teeth, you end up promoting a variation in the gullet depth. If you change the file angle slightly so your only making contact with the front of the tooth, you end up promoting a variation in the critical area of rake angle. The answer is to change the file angle slightly, so your only making contact with the less critical area at the back of the tooth. The 3 main areas to focus on in order to improve your saw filing skills (without discussing file quality, fleam angles, and tooth set), are a consistent rake angle, a consistent gullet depth, and a consistent height line across the tops of all the saw teeth. IMO. The need to joint the teeth on more than 1 occasion to meet those values mentioned, should be considered as an essential requirement to refining your saw sharpening technique.

Stewie;

[Phil Mueller]

Appreciate that input, Stewie. As I move through this learning curve, I often find it necessary to joint 2-3 times (sometimes more) to get the things you mentioned consistent. Of course, many of my practice saws are a train wreck from a previous owner and I'm still figuring out the shaping thing...so a few jointings can be chalked up to inexperience. I expect jointings to reduce once saws are in decent shape.

[Patrick Chase]

In regards to Paul Seller's example, I'm curious; just how much is your (Patrick Chase / Stewy / Other People who commented) judgement of that saw just a reflection of human desire for perfect geometry, and how much does it actually indicate problems in performance? I can't help but feel there is more to it than that. I've also heard Roy Underhill comment that slight variance in saw teeth is not necessarily a bad thing, as it makes the saw cut smoother/vibrate less/what have you, sort of in the same manner as hand-cut rasps. As long as the tooth (/teeth) before it is taking off an amount of material equal to any variance in height, one should be good, and in the grand scheme of things, a few teeth here and there isn't a huge issue for performance.

IMO the problems with that toothline are more cosmetic than functional. It probably cuts reasonably well. The one tooth that has a noticeable land on top may may not cut as well as others because it effectively has zero clearance, but other than that I don't see anything terribly concerning. With that said, if you look at work that Stewie and Ron have posted, or if you look at saws filed by Pete Taran or Mark Harrell, the Real Pros (tm) don't make mistakes like the ones I nit-picked or at least don't allow them to see the light of day. That's mostly what I was remarking about.

The bottoms of saw kerfs aren't cosmetic surfaces the way rasp-shaped surfaces often are, so I don't think that analogy holds. With saw kerfs you're more worried about speed and the cleanliness of the exit than about the bottom of the kerf, and I don't think that nonuniform spacing helps either. It may help with starting the cut *if* you have bad technique. Also with rasps you have multiple rows of teeth cutting simultaneously, so the problem of "chugging" is a lot more noticeable and harder to avoid.



I'd also like to point out that varying depth and uneven teeth do not indicate uneven height, and can trick the eyes.

Indeed. That's why I was careful to say that you can only judge height from a side-on shot, which that was not.

I suspect those teeth are indeed all at the same height, because you can see at least a teeny sliver of land (from jointing) on top of most of them.

[Luke Dupont]

Its what you do next to resolve that discrepancy that many less experienced saw filers will battle to resolve successfully. If you add some extra filing strokes to those odd teeth, you end up promoting a variation in the gullet depth. If you change the file angle slightly so your only making contact with the front of the tooth, you end up promoting a variation in the critical area of rake angle. The answer is to change the file angle slightly, so your only making contact with the less critical area at the back of the tooth.

That's my understanding as well.

On my first try (the hand-made blade I did), I have intentionally varying rake angle from heel to toe, but I intuited what you're espousing and attempted to keep a consistent rake angle while getting everything down to the same height. That said, I did make a few mistakes on rake angle with a few teeth here and there -- perhaps as much from my kind of poor ability to gauge the precise angle of the saw file as anything else.

The first thing I do before modifying the angle of the file is to see if I can't get the tooth to the right height by taking a few filings on either side of it without disturbing the end height of the neighboring teeth too much. Then I proceed to work on the back/widen the gullet without disturbing the face of the neighboring tooth, if I have to. So, I guess I use a mix of method #1 and #3, but I try to avoid #2.

[Luke Dupont]

The bottoms of saw kerfs aren't cosmetic surfaces the way rasp-shaped surfaces often are, so I don't think that analogy holds. With saw kerfs you're more worried about speed and the cleanliness of the exit than about the bottom of the kerf, and I don't think that nonuniform spacing helps either. It may help with starting the cut *if* you have bad technique. Also with rasps you have multiple rows of teeth cutting simultaneously, so the problem of "chugging" is a lot more noticeable and harder to avoid.


Yeah, I had a similar intuition/doubts that such variation is of any benefit with a saw, but thought I would throw it out there to see if anyone had better insight.

I guess I was taken aback by, I think it was your comment that, while recognizing that the it's tough to tell from the angle, stated "it's easy to see that the saw has problems."

Are there any major downsides to such inconsistency that I'm missing, assuming all teeth are contacting in the cut and that rake angle is more or less consistent?

[Edit - Off-topic side thoughts again]
Hm. Apparently it isn't just me. There's a significant spike in google search results for Occam's Razor, particularly in the US.
I'm wondering if this term came up in a political debate or something. Though, the overall sample of searches appears surprisingly low regardless.
https://www.google.com/trends/explore?q=Occam%27s%20Razor

[Patrick Chase]

The following video up to 1.40min will help buyers identify Swiss Made Files.

https://www.youtube.com/watch?v=gZ2K6OOA53I

On a related tangent: As I noted in another post the company that produced the video Stewie linked, Otto Frei, offers very good pricing on the Glardon files. Three-square 200 mm cut-2 needle files are $7.60/ea when ordered by the box. I ordered a box on Sunday night and they showed up this morning, exactly as advertised (I live very close to their West Coast distribution center).

Highly recommended.

[Patrick Chase]

Less-related tangent this time...



The bottoms of saw kerfs aren't cosmetic surfaces the way rasp-shaped surfaces often are, so I don't think that analogy holds. With saw kerfs you're more worried about speed and the cleanliness of the exit than about the bottom of the kerf, and I don't think that nonuniform spacing helps either. It may help with starting the cut *if* you have bad technique. Also with rasps you have multiple rows of teeth cutting simultaneously, so the problem of "chugging" is a lot more noticeable and harder to avoid.

Speaking of chugging, back when I had cheap rasps I had OK luck twisting or pivoting the rasp during the cut, such that the teeth in a given row don't all follow the same path. You can't always do it, but it's a nice "get out of jail" card sometimes.