Hand saws, how straight does the plate need to be?

[Mike Holbrook]

So I have been acquiring vintage hand saws over the last couple years. I enjoy restoring nice saws to their original glory. One aspect of restoring saws continues to elude my understanding though. I am just not sure how much: curve, bend, kink.... is enough to start causing a functional problem with a saw. Many of the saws I have won on auction arrive with less than a perfectly straight plate and I am just not sure what I should and should not consider a functional issue. I have saws that appear to have significant physical issues that seem to still saw fairly straight, at least within the parameters of my less than perfect skill set. I think I sometimes feel the irregularity in the plate while sawing but may not see an issue in the kerf the saw is making.

I also confess that although I have read posts/articles on straightening saw plates, I am not confident enough with the suggested techniques to actually attempt to use them on a nice saw. I actually won two saws that were professionally sharpened. I had a few typed conversations with the person who did the restores. He offered to sharpen and or straighten a few saw plates for a very reasonable rate. Both of the saws I have from this person are quite old, a Disston #9 and a Disston #12. The plates on both the saws are incredibly straight. He indicated that it was not a big deal for him to straighten plates. Maybe the job is not as hard as I think it is? I just can't fathom how one could get plates as straight as the #9 + # 12's are?

[Mike Allen1010]

[QUOTE=Mike Holbrook;2100407]One aspect of restoring saws continues to elude my understanding though. I am just not sure how much: curve, bend, kink.... is enough to start causing a functional problem with a saw. Many of the saws I have won on auction arrive with less than a perfectly straight plate and I am just not sure what I should and should not consider a functional issue.

Hi Mike,

Great question and IMHO, the answer like with so many other woodworking questions is "it depends". From my perspective, a consistent "bend", is less problematic than a "kink/dent" for two reasons; a gradual bend presents the cutting edges to the work surface in a consistent, manageable way and a bend is a lot easier to fix (boiling water, the edge of your bench, re-tension as needed).

The fewer teeth you have engaged in the kerf at any one time in the stroke, the less important it is the saw plate is straight. The rationale is the only part of the saw plate/tooth line that affects the straightness of the kerf are the teeth that are actually cutting at any given time.

For example, if you are crosscutting an 8/4 board (regardless of the width), you only have ~ 3" of the tooth line engaging the work it any point (assuming your using the tooth line at a 45° angle to the workpiece). It is only any curvature of the saw plate across this 3" length that would affect the "straightness" of the kerf.

All that said, a bend is pretty easy to fix with little risk of further damage and unless you're working in 4" or thicker stock, I think a bend of <1/2" across the entire length of the tooth line of a 26"-28" saw has no negative effect on performance (regrettably not so for a smaller backsaw were straight is critical).

Depending on size, a dent or kink is more problematic than a bend because a kink/dent presents a more abrupt deviation from the rest of the plate and a deviation in two dimensions - both along and perpendicular to the long axis of the plate (unless you can hammer it out).

When the kink enters the kerf, it effectively makes the entire saw plate "wider" because the saw plate is now contacting the work piece at two places -- the tooth line and at the kink/bulge. This creates additional friction/heat/resistance in the cut - which means more work for the sawyer and a greater likelihood the teeth will catch at the kink again bending the plate even more. In addition, an abrupt change in direction of the tooth line that occurs at the kink makes it harder to keep the cutting teeth aligned with the layout line.

That said, a kink or bulge that deviates 1/16" from the plane of an otherwise straight saw plate is virtually unnoticeable in a coarser pitch (and typically thicker plate) ripsaw or crosscut saw IMHO -- the set of the saw teeth will minimize the degree of contact between the dent and the work piece. For a finer pitch crosscut saw (which can have a narrower blade and less set), a straight plate makes a very high degree of accuracy a lot easier. The plate doesn't have to be perfect (there are not many of those saws out there after 100 years of use), but any kinks or dents should be of a size that is only apparent on close inspection.

I'm not a blacksmith or a metallurgist (far from it!), but I have smithed lots of saw plates and I think there are some kinks/dents that can't be made more than 95% straight. Maybe there are those who can completely straighten all kinks/dents, but I know I can't.

It is worth learning how to straighten a saw plate and there is lots of good information about how to do that here on SMC (Bob Smaler's tutorial is an excellent start). I would strongly encourage you to start with an inexpensive/non-collectible saw that is so badly kinked/dented that he can't be effectively used in its current state. Saw smithing is an acquired skill and you can definitely make things worse! However, with a little practice, you will significantly increase the likelihood you will make your flawed saw plate very usable, as compared to turning it into "scraper material".

All the best, Mike

[george wilson]

If there is a mild curve in a blade in a crosscut type saw,pour boiling hot water on the blade and instantly bend it in a straightening direction. Don't worry about temper. S saw is tempered at about 750º to be a spring temper. The water is 212º,of course.

To straighten a back type saw,if there is an "S" curve,clamp the front edge of the saw in a smooth jawed vise,and tap the front end of the back to jerk it straight. If there is a mild curve,clamp the saw's back by 1 end,preferably with the handle taken off. The blade is clamped teeth upwards. Take a Crescent wrench,and use it to twist the back a little as if you are trying to twist the blade into a drill bit(except just a LITTLE twisting).:) The back will not appear distorted like it would if you actually bent the back lengthwise to straighten the toothed edge. We made many saws in Wmsburg.,and adjusted them third way if necessary. It works just fine.

Only if the saw has a creased kink in it would it become necessary to try to hammer it flat. I'd avoid trying that if at all possible since it takes experience. I just don't buy kinked saws.

[Charlie Stanford]

So I have been acquiring vintage hand saws over the last couple years. I enjoy restoring nice saws to their original glory. One aspect of restoring saws continues to elude my understanding though. I am just not sure how much: curve, bend, kink.... is enough to start causing a functional problem with a saw. Many of the saws I have won on auction arrive with less than a perfectly straight plate and I am just not sure what I should and should not consider a functional issue. I have saws that appear to have significant physical issues that seem to still saw fairly straight, at least within the parameters of my less than perfect skill set. I think I sometimes feel the irregularity in the plate while sawing but may not see an issue in the kerf the saw is making.

I also confess that although I have read posts/articles on straightening saw plates, I am not confident enough with the suggested techniques to actually attempt to use them on a nice saw. I actually won two saws that were professionally sharpened. I had a few typed conversations with the person who did the restores. He offered to sharpen and or straighten a few saw plates for a very reasonable rate. Both of the saws I have from this person are quite old, a Disston #9 and a Disston #12. The plates on both the saws are incredibly straight. He indicated that it was not a big deal for him to straighten plates. Maybe the job is not as hard as I think it is? I just can't fathom how one could get plates as straight as the #9 + # 12's are?

They need to be straight. Joinery saws must be straight. Try resawing with a kinked or bowed saw (even mild deformities) and you will quickly be disabused of the notion that anything but pin straight will do.

[peter gagliardi]

In my experience over the last 25 years, it seems a slight even bow the entire length of up to 1/4 " or so on a panel saw is of no consequence whatsoever. Kinks, or twists are another matter altogether.
Peter

[David Weaver]

i agree with peter. A gradual bow that occurs uniformly over the length of a saw, and not in a large amount, is just fine.

Anything with a back, though, as straight as you can make it.

[Mike Holbrook]

Thanks for the excellent thought on saw plates guys. Mike Allan summarizes my philosophy regarding saw plates in good detail, thanks Allan. I think I have been fortunate in my "on-line" purchases to date. I always try to make sure plates are straight before buying a saw and thus the plates I have are generally relatively straight. All my backsaws have straight plates. I believe my hand saws, with some curve in them, have maybe 1/8" curve or less over the length of the blade. I find thinner "sway back" plates on my longer saws to be harder to judge, sighting down those already curvy blades. These blades seem to be more flexible thus bending naturally depending on how they are held, even sighting down the teeth.

I have a couple saws that may have what I would term a small dent 1/4-3/4" area at the teeth that appears to not quite be on the exact same plane as the rest of the blade. I find these areas to be quite hard to see sometimes, small more or less polished areas near the edge seem to trick my eyes (has nothing to do with my vision getting worse as I get older). The saws I have like this feel a little rougher moving through the kerf than dead straight saws. The other reason I am having a little problem figuring out if the "dents" I think I see are significant or not is both saws also arrived with too much set in the teeth. It may even be that the extra set was intentionally introduced to counter small dents. One saw is a Disston D8, 24", 7 PPI, with a rough sharpening job made with too large a file, leaving ragged tooth edges. The other saw is a Disston #12, 24", 8 PPI, which has a similarly rough sharpening job. The teeth on both saws look like they were filed for rip cuts but it is hard to tell for sure. I plan to refile both saws for cross cutting. The # 12 I think will be good once I redo the teeth, as the major problem just seems to be rough teeth and too much set. The dent in the D8 is clearer and may need to be dealt with.

The saw I have been most concerned about is a sweet little 22" Atkins, 8 PPI that I like a great deal. 1/3 of the way from the tip, the plate has a visually clear change in the plane of the plate at a specific point. On the positive side the blade appears to have less than 1/8" of total bend and the saw makes a fairly straight cross cut in a 2x4. I have a Bridge Tool Co. 22" saw with "extra thin back" that has/had a very similar bend that I have experimented a little on. The bend in this saw was "fixed" by a previous owner. There are clear hammer marks in the plate near the bend.

So the reason for my post other than general improvement of my saw knowledge is I have been trying to decide whether or not to try to improve these plates myself or ship them off to a professional. I have not resharpened them as I imagine this would be part of the service provided by a professional.

[Charlie Stanford]

You don't need all that many saws quite frankly -- sounds like you already have a decent stable. Unload the ones that aren't straight. Keep the ones that are. If there is a functionality that just cannot be satisfied without a new [to you] saw then get one, only with a straight plate. Unload the saw with visible hammer marks -- that's evidence of a hack. A 2mph crosswind will make that saw kink in the cut if its tension is ruined which it probably is.

[Mike Holbrook]

I hear you Charlie. I have a business on the same property I live on. I plan to have a few hand saws at the work location. I have need of rough chairs, cabinets....for the business. I built the building and have added on to it several times. The house and business are far enough apart that I do not want to carry basic tools back & forth. The tools at the business may get handled, used...by employees/clients who may not show nice tools proper respect. The nicer saws will stay up at the house in my workshop. All my backsaws will stay in my shop.

I bought some higher risk less serviceable saws early on when I was learning. I have had the opportunity to try out a fairly large range of vintage saws which has given me a good idea of what seems to be comfortable and work well for me.

[Michael Ray Smith]

If there is a mild curve in a blade in a crosscut type saw,pour boiling hot water on the blade and instantly bend it in a straightening direction. Don't worry about temper. S saw is tempered at about 750º to be a spring temper. The water is 212º,of course.

A while back I asked George about using steam instead of boiling water to heat the blade. Since then, I've tried it, and that works, too. I heated the blade by holding it in the steam rising from a pot of boiling water. The downside is that you can heat only a few inches of the blade at a time. If you need to heat more than that, take the pot of boiling water and pour it over the blade. Or, if you have a vessel large enough to immerse the blade in the boiling water, you're really in business.

[Mike Holbrook]

I read that too Michael. I just have not screwed up the courage to try it yet. The assurance that 212 water want mess with the temper may be just what I needed to hear, although there is this tensioning concept I read about that seems unique to saw blades. I still do not understand exactly what tensioning is nor how I might adversely change it. Since I now have specific saws that I like and intend to use I am a little slow to risk damaging them in an attempt to improve what may be minor issues. At the same time I don't like the idea of entrusting them to USPS (going & returning), if I were to send them to a professional.

The "bend" in my Atkins 22", 8 PPI saw is along a discernible small area, maybe an inch wide , so steam might actually work. Maybe I will try the steam first.

[David Weaver]

If you just hit the plate with 200+ degree water, you won't affect the tensioning. The tensioning is applied to the saw by compacting the metal either with a hammer, or maybe disston and others may have used rollers to speed up the process (someone other than me might know that). If the tensioning isn't done evenly, the saw won't be straight, if it isn't done at all, the saw will be floppy.

[Mike Holbrook]

Hmm, I have this Atkins 26", 8 PPI saw that despite my attraction to Atkins saws leaves me cold. It always feels like I am sawing with a wet noodle. I thought it might be the fact that the plate has been worn down but maybe it is a tensioning issue.

[Jessica Pierce-LaRose]

Could very well be both - I believe the majority of the tensioning work is in the first few inches of the blade above the toothline - if it's worn down enough, you start to lose that.

[Mike Holbrook]

I am clueless about the tensioning, but that makes sense. It is not always easy to know how wide the original plate was though. I believe there may have been a trend towards lighter saws which ended up producing models with smaller plates. I think Atkins plates were just smaller vs Disstons anyway. I am still confident the plate on that 26" Atkins is worn down.