Backsaw saw back mortises: Tight or loose, which is better?

[rob streeper]

In my collection of saws I have noted a very wide range of closeness of fit of the saw back to the mortise in the saw handle. Thus I have a question: Which is better, loose and sloppy or tight? I can see arguments both ways. Sloppy looks messy but it may have the very useful characteristic of allowing the saw back to move about while the saw is in use without placing stress on the sides of the mortise thus reducing the risk of breaking out the upper cheeks of the handle. Tight may also be of utility, particularly with thinner saw plates, in that it holds the back more rigidly in line with the cut preventing wandering. Most of the makers on the Forum cut tight mortises. What's better and why?

Here are some examples. First a series of Disston backsaws of varying era.

This is an old Disston #4. Nice and tight and the blade slot does not project back into the handle.

332638


Old miter box saw. Again the back is fitted nicely.

332637


A newer miter saw. Mortise is tight but the blade slot cuts deeply into the face of the handle.

332635


And what looks like the newest Disston, terrible fit of the back in my opinion.

332636


Now for maker #1. Saw 1 perfect fit.

332631


Likewise for saw 2.

332633


And for saw 3.

332628


Maker #2 saw 1 perfect fit.

332632


Saw 2 is also perfect.

332630


Saw 3 however has a slight over-run of the blade slot into the handle, back fit is excellent.

332634


Maker 3, sloppy fit of the back to the mortise and a deep cut into the face of the handle. This is also the saw with the soft blade I discussed in my thread on hardening saw plates (http://www.woodworkforums.com/showthread.php?t=182165).

332629

So what do you think? Tight or loose? Why?

[rob streeper]

What? Nobody cares? Why am I spending so much time trying to get a close fit if it doesn't matter?

[burraboy]

What? Nobody cares? Why am I spending so much time trying to get a close fit if it doesn't matter?


Nobody knows? Probably to get a valid indication you would need access to quite a large number of saws and be able to try them all to see if there is indeed any variation in their performance. From an aesthetic viewpoint the tight ones look better to me anyway.

[rob streeper]

Nobody knows? Probably to get a valid indication you would need access to quite a large number of saws and be able to try them all to see if there is indeed any variation in their performance. From an aesthetic viewpoint the tight ones look better to me anyway.

I like the tight slots too. In my experience with the saws pictured I can't really tell any functional difference. The older saws with the sloppier mortises feel pretty much the same, perhaps because they all have plates that are thicker than is usually seen on the modern boutique saws.
In making my own saws however I find that the thin tall plates absolutely require a tight fit of the back to the plate and of the back to the mortise in the handle. If everything is not tight the plates will flex in use causing the kerf to wander unpredictably or to bow causing an outboard drift.
More generally I wonder about the relative importance of aesthetics and function in the boutique tools market. Is appearance more important than function or the converse? Maybe a subject for a poll on the site?

[burraboy]

More generally I wonder about the relative importance of aesthetics and function in the boutique tools market. Is appearance more important than function or the converse? Maybe a subject for a poll on the site?

Can of worms there Rob, I'll excuse myself now.

[rob streeper]

Can of worms there Rob, I'll excuse myself now.

I appreciate your concerns. I however am generally not squeamish about bringing up such subjects and would genuinely like to hear the views of others on the forum.

[planemaker]

Hi Rob. I prefer a slide fit. Yes aesthetics is an important element to consider when building a backsaw. But it should always be considered a secondary priority over performance. Good saw makers through ongoing experience reach a level where they are able to include both these elements within their work.

Stewie;

[rob streeper]

Hi Rob. I prefer a slide fit. Yes aesthetics is an important element to consider when building a backsaw. But it should always be considered a secondary priority over performance. Good saw makers through ongoing experience reach a level where they are able to include both these elements within their work.

Stewie;

I agree. I've always admired Bridge City Toolworks products for their fine appearance but I'm much more impressed by their functional excellence despite the eye-watering prices they command.
I think a closer fit, unless a loose one is technically justified, is a mark of high craftsmanship. My mortices are particularly difficult to make because the profile of my folded backs is somewhat like a teardrop. Takes lots of test fitting to get it right.

333019

[Simplicity]

I think Rob
You have just answered your own question
It's a sign off Quilty.
I personally think a saw with a lose back is only going to get loser over time due to parts moving wobbling a bit.
Tho one with a back stuffed in the mortise is going to put undue stress on the mortise possibly breaking out at a week spot in the grain.
I think a buyer of bespoke saws is going to look for things such as the fit of the back to the mortise.
I know I would.
Partly because I understand from doing it
It is a fine line from in my opinion from looking truly great to looking like it was hacked out with blunt chisel the back to mortise fit that is and Ye I know it's hard thing to do well.
I also think it may be hard to explain to the novice saw buyer the reason for the loose fit of the back even if we add a feasible reason.
It may be seemed to be sloppy workmanship considering the price a handmade saw will sell for compared to the hardware chain stores $9.99 do all saw.

[Ron Bontz]

From my perspective, the saw back has a 3d function. Please forgive my lack of eloquence in my attempt to explain this.
1) The primary purpose/ importance of any saw back is to support the saw plate horizontally, ( x axis ), keeping it straight under compression from the toe end. The thinner the plate the more important. As the cut proceeds forward the forces shift from compression to tension along the plate. ie: if you are half way through the stroke, the front half is in tension and the heel half compression. Hence Japanese saws do not need backs always being in tension. This is also why the toe end of the spine should be as tight if not more so than the rest of the spine. To prevent distortion/ wrinkling of the plate. ( A down side to folded backs not made with enough spring force on the plate. Or slotted backs being too loose in the slot. ) I have considered placing a steel pin through the toe of the spine just to see how much difference it would make. But then there would be the problem of removing the pin for what ever reason.
2) The saw back folded or slotted, does very little in the way of vertical support of the plate.( z axis ) The plate thickness and tote slot are responsible for much of that. However, the back adds to that rigidity binding the plate in the center of the tote/ plate slot. ( if that makes any sense ) Hence if the spine is not centered on the plate/ tote mortise you get that nasty bow in your plate. Some may compensate for this misalignment by having the spine fit loosely ( float ). This may also help compensate for a plate slot not being parallel with the tote sides. But then the plate will not be parallel with the tote, vertically or horizontally, when all is said and done. Straight plate but at an angle to the handle.
3) A parallel spine will assist in maintaining a plate parallel with the tote as mentioned but with a loose fit the plate/ spine will move from side to side along the y axis during use. Just as the plate moves from side to side if you only put the spine on the plate up to the cheek and stop. Sooner or later you will kink the plate right at that spot or damage the tote.
Once the tote is tightened down onto the plate, there should be the same amount of pressure on both components. All components should be parallel with the tote vertically and horizontally as well as center alignment. Plate and spine. To loose and the plate may move along the y axis as well as the z axis during the stroke and your cut may not be so easy to keep straight. http://d1r5wj36adg1sk.cloudfront.net/images/smilies/smile.gif
Also one should note, a slotted spine will often make contact with the plate 1/4" to 3/8" depending on how deep the slot is cut. So if the slot is not parallel with the sides of the spine, the plate will be skewed, adding to the problem of alignment between the plate slot, mortise and spine, vertically. Laying it on an inspection plate, or other nice flat surface, and pressing down on the spine will show this clearly with the plate being higher on one side than the other.
On the other hand a folded back may not make as much contact with the plate, perhaps 1/8" or less, depending on the shape of the folded back. This allows for some slop to some extent with the contact point being able to rotate slightly, one way or the other. But now you have the problem of getting that tote mortise fitting properly. If you are using a mill/ CNC machine you can angle the cutter to match the folded back. This is assuming every folded back is exactly the same shape/ size. Some of the vintage makers seem to have just preferred to just mill the top of the slot to fit snug, leaving a gap along the bottom. ie: a vertical mortise only. This would allow for a certain amount of misalignment of the plate/ spine mortise. That would also allow for different plate thicknesses. ( Bonus )
Lastly, by having the plate slot cut deeply ( beyond the spine ) it adds some flexibility to the tote itself. Same principle as the folded back but at an adjacent angle. Clothes pin effect, for lack of a better description. So I hope this rambling, at least, makes some sense. So now I have done gone and muddied the waters. AGAIN. http://d1r5wj36adg1sk.cloudfront.net/images/smilies/smile.gif

[rob streeper]

Ron,

Agree with your comments. I've found that the thin plates need a very tight back, especially when taper ground. So tight in fact that the first couple times I fit some up I was afraid that the plate might tear or wrinkle. Never happened so I guess the grip isn't that high. Another observation I've made is that it is good to leave a slight gap, no more than a millimeter or so between the bottom of the back and the mortise. This gap allows for post assembly tensioning of the plate without the risk of splitting or compressing the fibers of the tote.

So that's four votes for nice-and-tight and zero for big-and-sloppy. Anybody else?

Cheers,
Rob

[Ron Bontz]

I think I like the tern "slide fit" or snug better. :) Lie Nielsen is a good example of an excellent fit. Oh, I could only wish I had all his toys. :):)

[RayG]

I always try for a nice neat fit, no gaps.. sometimes I manage to fluke it and get one that fits perfectly.. Never loose..

Ray

[planemaker]

As a follow up from Ron's excellent comments, with slotted backs, my preference is to use loc-tite to fully adhere the hardback in position. With the backsaw fully assembled, apply a thin bead of loc-tite to both sides of the slot, and wipe away the excess with a rag before its hardens. Then remove the handle so that the remaining area of the slot can be treated with loc-tite. Wipe away the excess; job done.

Stewie;

[rob streeper]

As a follow up from Ron's excellent comments, with slotted backs, my preference is to use loc-tite to fully adhere the hardback in position. With the backsaw fully assembled, apply a thin bead of loc-tite to both sides of the slot, and wipe away the excess with a rag before its hardens. Then remove the handle so that the remaining area of the slot can be treated with loc-tite. Wipe away the excess; job done.

Stewie;

Sounds like your saws are permanently assembled. That would open some options on saw bolts/screws because they become essentially non-functional in the sense that there's no further need to remove them once the Loctite hardens. For instance, you could use tapered pins secured with Loctite or compression rivets as used in knife handles. Your design creates a lot of options...

[planemaker]

Hi Rob. That's not how its meant to work. I am only using the loc-tite to permanently adhere the slotted hardback to the top edge of the saw plate. Which means the saw bolt assemblies are still a requirement for the backsaw handle. One of the benefits a slotted hardback has over a folded version is how easy it can be removed up until the decision is made to permanently secure it in position. They are generally machine slotted to a slide fit tolerance. My personal preference, is to wait until the backsaw is ready for the final task of filing and setting the saw teeth before I permanently secure the hardback.

regards Stewie;

[rob streeper]

Hi Rob. That's not how its meant to work. I am only using the loc-tite to permanently adhere the slotted hardback to the top edge of the saw plate. Which means the saw bolt assemblies are still a requirement for the backsaw handle. One of the benefits a slotted hardback has over a folded version is how easy it can be removed up until the decision is made to permanently secure it in position. They are generally machine slotted to a slide fit tolerance. My personal preference, is to wait until the backsaw is ready for the final task of filing and setting the saw teeth before I permanently secure the hardback.

regards Stewie;

Given the theme of the thread I misunderstood your post as implying that you glued your backs to your handles in addition to gluing the blades to the backs.

[DSEL74]

I like the tight slots too.

Don't we all!!:D

I gotta say I agree with pretty much all the comments above, although it did take some concentration to digest all of Rons detailed post.

When considering the fit on old saws you have to allow for wear, compression, rust binding, misuses etc. All these things may give false readings in tight or loose fitting scenarios. To me anything that doesn't look deliberate or meant to be always feels a lower quality. So if it looks over cut mortice or blade slot then I get the impression of sloppy workmanship. If the blade slot is going to extend then it should finish inline with some other detail or element so it looks deliberate not just some random distance.

My own saws bug me for some of these points:doh:

[IanW]

For some reason I missed this thread 'til today - must need better specs! :doh:

I don't think it makes a lot of difference to function if the spline slot in the handle is loose or tight, for saws using plate of about 20 thou or thicker. As has been mentioned, many old saws are decidedly sloppy, but seem to work just fine if all else is up to scratch. However, pride dictates I do my darndest to get a neat fit when making a saw. Like RayG, occasionally I get it close to perfect. :U However, my penchant for working with some pretty unforgiving woods means there are nearly always a few tiny blemishes (fiddleback figure is usually the worst, it loves to shed little bits from those curls, along an otherwise perfect edge!). Probably very few people other than the maker would notice, but they bug me! :~

I think a firm, and even fit of spline to plate is important, otherwise you may have a lot of trouble getting a straight saw blade. Too loose and much of the stiffening function will be lost. As an amateur, slotting my backs is the easiest & safest route, I don't think I could ever manage the skill required to bend a truly straight back that would grip evenly along its whole length. :no: My preferred fitting method is to cut the slot to a sliding fit & pinch it a little in a vise to get the desired firmness. Using loctite seems like an admission of failure, to me, but it's probably a very sensible & pragmatic way to go, in truth. Pinching in the vise is a bit fraught, and it's easy to overdo it & end up too tight.

One of the problems I've had, a few times, is a slightly bellied blade slot in the handle. The area where the bolts tighten down has to be planar, or when you tighten up the bolts on final assembly, you find there's a small bow at the end of the blade. Took me a while to figure out what was causing it, but eventually the light dawned that there was a slight belly in the blade slot (the bow went away when I loosened the bolts). I've had a couple of handles with this defect, so I now take great pains to saw a dead-straight kerf for that blade slot! It's not unique to me, I've noticed - a few old commercial saws that have the same problem. It doesn't really affect function, as it is only the very heel of the saw that bends a bit, but it doesn't look good!

Cheers,

[MarvW]

Hi guys,

I have been repairing and refurbishing backsaws for a number of years. I've done a lot of them. I've come to the conclusion that the mortise part of the saw design is a flaw and a weak point.

I'm one of those guys who likes to jump outside that proverbial box and try something totally different. I have made an attempt at changing the design to solve the problems surrounding the mortise.

I'll try to post a few pictures to show what I've done. Now, don't go crazy on me. Try to focus on the reason for the way I did what I did, not necessarily how it might look to you. It's meant to look and be different. This was my first attempt with a bottom side mortise. I've since done others with some modifications.

https://lh6.googleusercontent.com/-0UpaGl54Ebw/TL3FH7RE5gI/AAAAAAAAGQU/Au1HTDQ8-Aw/w800-h600-no/IMG_2328.JPG

This shows how the back extends into the handle so as to eliminate the need for a slot in the handle for the blade. And also eliminates screwing the handle to only the blade. Instead it is attached to the back.
https://lh5.googleusercontent.com/-pjBqMob11Uc/TL3FGj2IEJI/AAAAAAAAGQE/-8kfib-45FI/w800-h600-no/IMG_2324.JPG

Here is what it looks like fully assembled. You can make a handle most any shape you want.
https://lh3.googleusercontent.com/-d_CYAs6lMPU/TL3FJoRarZI/AAAAAAAAGQs/15gZCg4ITU8/w800-h600-no/IMG_2338.JPG

Most people seem to prefer the traditional look of a backsaw even though, over the years, it's been plagued with the fit of the mortise and screwing the handle to a flexible saw plate.

Here's another attempt at using this design. With this one, I took it a step farther and made the back out of wood and epoxied it to the blade. I know this is way off in left field, but the idea was to simplify the whole thing and still end up with a saw that cuts just as well as the traditional designs. I put these ideas out there for you to contemplate and perhaps spark some additional ideas for improving the handle to blade situation.
https://lh3.googleusercontent.com/-5R7w4D2TKHw/VEalpku53KI/AAAAAAAAI84/rRVDQ1BjMBg/w800-h600-no/IMG_3418.JPG

Here's another one. This one I started with a $10 cheapo Bucks Bros. saw that I bought new at Home Depot.
https://lh6.googleusercontent.com/-hNaLIOH--ok/VGo1YARaqsI/AAAAAAAAJCQ/r5LZCZ4YGIE/w800-h600-no/IMG_3442.JPG

This is the Home Depot thing..
https://lh6.googleusercontent.com/-fjmOo3FDKI0/VGo2wK9COII/AAAAAAAAJDs/pBnUTkD-wvA/w800-h600-no/IMG_3053.JPG

I apologize if these pictures are shocking to you. The thoughts kind of rattle around in my mind until I'm driven to turn them into reality. :D

[burraboy]

Thanks for the post Marv, there's plenty to think about in that. I'm not sure if I can get my head around largely unsupported blades of those depths though. Perhaps there will be comments!

I was also impressed with your marquetry oak table top! I have some oak boards that might be best used in that fashion. Any chance on a thread to show us some construction details there?

[rob streeper]

Hi Marv,

I like your willingness to question ingrained patterns of design. How do the saws work?

Cheers,
Rob

[DSEL74]

Design aside Marv they look well made. What you haven't mentioned is the thickness of the blade and how well you found them to work or not.

[IanW]

Whether or not you've 'improved' saw function is only part of the story, Marv, at least you are thinking about it & trying to address what you see as shortcomings in traditional design. Mucking about & having some fun is the main game for an amateur saw maker, imo.

I can't see why building a saw like you've done wouldn't work, though as burraboy suggests, the blade depth might be a factor to consider, a little moreso than with a traditional handle, but that's just a guess. You should conduct a few tests with blindfolded users, & see if any can tell whether they are using a conventional handle, or one of yours. :U (I suspect few will...)

My thinking is that part of the reason for attaching backsaw handles in the 'traditional' style would be simply convenience, and partly to get the handle in the 'right' position for comfortable & ergonomic use. As long as your handles are well-positioned, the stresses on the saw plate should be similar. One of the problems I've had with traditional attachments, is that if the kerf and/or spine slots aren't done very accurately, tightening down the saw bolts can put a small curve in the heel of the saw plate (I sometimes wonder if this is why spline rebates are so loose on many manufactured saws). Attaching via the spine alone should solve that.

Cheers,

[rob streeper]

I'm glad that the conversation on this thread has become more technical.

I can see both advantages and disadvantages to seating the saw back rigidly in the handle, some of which have been mentioned already but that bear summary.

1) Rigid or close fit mounting makes for better directional control of the tooth line, particularly with thin blades.

2) Rigid mounting helps support the saw blade, particularly thin blades reducing their tendency to flex in use.

3) Rigid mounting may reduce wear to the blade slot of the handle and the screws by limiting the movement of the blade in the blade slot.

4) Rigid mounting allows the handle to be cast right or left relative to the tooth line.

5) Rigid mounting looks better and is considered to represent a higher level of craftsmanship.

And some disadvantages such as.

1) Rigid mounting increases the likelihood of breaking out the sides of the back mortise in the event that the saw is severely flexed.

2) Rigid mounting is somewhat more difficult to do well. Mistakes in mortising stand out.

3) Rigid mounting causes deflection of the tooth line when the back mortise and blade slot are not perfectly aligned. Aside from manufacturing mistakes such an effect may be induced by warping of the handle due to age or changes in moisture levels.

Overall, I think that the benefits outweigh the disadvantages. I have never seen a backsaw with a broken mortise and I have never broken the mortise of any of the saws I have made despite using the saws with deliberate aggression to test their robustness.
I have purposely mounted a backed blade in a handle with too large a mortise and found that the flexibility of the blade and the mass of the back tend to cause the blade to run off-line.

[MarvW]

Thanks for the post Marv, there's plenty to think about in that. I'm not sure if I can get my head around largely unsupported blades of those depths though. Perhaps there will be comments!

I was also impressed with your marquetry oak table top! I have some oak boards that might be best used in that fashion. Any chance on a thread to show us some construction details there?

The blade thickness is .025. What we think of as a "supported" blade is only supported at the heel end and usually not the full depth of the blade. The toe end is always unsupported in that sense. When using the saw, I do not detect any deflection of the blade due to not being screwed to the handle.

The marquetry oak table is not my work. We bought the table at a furniture store many years ago. It sometimes works well for a background for taking pictures of wood.

[MarvW]

Hi Marv,

I like your willingness to question ingrained patterns of design. How do the saws work?

Cheers,
Rob

Hi Rob,

In my hands, the saws function as well as any other well fitted handle to a back. However, I can clamp any backsaw with a top mortise in a vise by clamping only on the back and be able to move the handle side to side at least to some degree depending on how tight the back fits the mortise. With my bottom mortise design and the handle bolted only to the back, I can do the same test and not have any side to side flexing. The back I have on the first saw is 1/4" x 3/4" steel with a milled slot and pressed onto the blade.

The second saw has a wood back that is 1/4" x 1" well seasoned black walnut with the blade epoxied in the slot and into a slot in the handle. The stiffness of the blade using the wood back and epoxied to the blade is surprisingly stiff and inflexible. With the blade attached in that manner, I was quite surprised to be able to thimp the blade and get a ring from it. I have never been able to do that with any other backsaw. Not that, that is important. It's was just unexpected.

[MarvW]

Whether or not you've 'improved' saw function is only part of the story, Marv, at least you are thinking about it & trying to address what you see as shortcomings in traditional design. Mucking about & having some fun is the main game for an amateur saw maker, imo.

I can't see why building a saw like you've done wouldn't work, though as burraboy suggests, the blade depth might be a factor to consider, a little moreso than with a traditional handle, but that's just a guess. You should conduct a few tests with blindfolded users, & see if any can tell whether they are using a conventional handle, or one of yours. :U (I suspect few will...)

My thinking is that part of the reason for attaching backsaw handles in the 'traditional' style would be simply convenience, and partly to get the handle in the 'right' position for comfortable & ergonomic use. As long as your handles are well-positioned, the stresses on the saw plate should be similar. One of the problems I've had with traditional attachments, is that if the kerf and/or spine slots aren't done very accurately, tightening down the saw bolts can put a small curve in the heel of the saw plate (I sometimes wonder if this is why spline rebates are so loose on many manufactured saws). Attaching via the spine alone should solve that.

Cheers,

Hi Ian,

The thickness versus the amount of blade below the back is always a serious consideration. The handle design and the method of attaching it to the blade is mainly what the experiment was for with these saws. Over the years I have repaired many old backsaws for customers that were either cracked or pieces broken off. The title of this thread pertains to how tight should a top mortise be, tight, snug, or loose. With my design, all of these concerns become moot. My thinking was, the back is kind of the backbone of the saw, so why not allow it to also support the handle as well. At the same time, simplify the making of the saw by eliminating drilling the blade and matching the holes to the handle and slotting the handle. With the wood back saw, even the screws are eliminated. And the back can be done by most any woodworker. I made the back and the handle two pieces, but it could be done with only one piece if the wood is stable enough.

It is apparent, from the lack of interest I get from people I show these ideas to, most people are stuck on the traditional look of a backsaw. Drastic change is difficult for a lot of people. I fully understand that. After all, we are all individuals with our own preferences. Sometimes though, it can be interesting to at least ponder something new, especially if it is an improvement. Lee Valley has been quite successful with their New Concept backsaws. However, the average woodworker can't make backsaws like theirs. But they can do what I did. :)

[rob streeper]

Hi Rob,

In my hands, the saws function as well as any other well fitted handle to a back. However, I can clamp any backsaw with a top mortise in a vise by clamping only on the back and be able to move the handle side to side at least to some degree depending on how tight the back fits the mortise. With my bottom mortise design and the handle bolted only to the back, I can do the same test and not have any side to side flexing. The back I have on the first saw is 1/4" x 3/4" steel with a milled slot and pressed onto the blade.

The second saw has a wood back that is 1/4" x 1" well seasoned black walnut with the blade epoxied in the slot and into a slot in the handle. The stiffness of the blade using the wood back and epoxied to the blade is surprisingly stiff and inflexible. With the blade attached in that manner, I was quite surprised to be able to thimp the blade and get a ring from it. I have never been able to do that with any other backsaw. Not that, that is important. It's was just unexpected.

The lesson I'm taking from this is that supporting the back well is the key issue. Unless the blade is tall and or thin supporting the blade doesn't matter as much. Witness gentleman's saws and the ancient cane handled saws http://www.wkfinetools.com/hUS-saws/z_UnusualSaws/18thCentSaw/18thCentSaw.asp.

Leaves a lot of design latitude...

[MarvW]

The lesson I'm taking from this is that supporting the back well is the key issue. Unless the blade is tall and or thin supporting the blade doesn't matter as much. Witness gentleman's saws and the ancient cane handled saws http://www.wkfinetools.com/hUS-saws/z_UnusualSaws/18thCentSaw/18thCentSaw.asp.

Leaves a lot of design latitude...

Rob,

Using the Gents saw for comparison does a good job of putting it in perspective. Change the handle from a broom stick to a handle with a grip hole and you have something that closely resembles my bottom mortised design. :)

[hiroller]

Gents saws attach a handle to the spine and work on a push stroke just fine. I spent many an hour chopping small bits of wood in half at my Dad's bench as a kid with a saw that looked a lot like this any didn't notice any problems.:q