Thread: Dimensioning backsaw plate.

I like the analysis Stewie, but then I like (and did) analytical work! Could we extend this to ppi? As I understand it we want at least 5 teeth in the cut at any one time for effective cutting. Also we generally want smooth cuts for back saw ripping (this is meant to be a finished surface for dovetails and tenons). This suggest something more than > 5 teeth in the cut. How many extra teeth do we need for a smooth cut?

8 inch plate; timber to rip = 0.25 inch, assuming we want at least 5 teeth in the cut >= 20 ppi
10 inch plate; timber to rip = 0.375 inch, assuming we want at least 6 teeth in the cut >= 16 ppi
11 inch plate; timber to rip = 0.50 inch, assuming we want at least 7 teeth in the cut >= 14 ppi
12 inch plate; timber to rip = 0.75 inch, assuming we want at least 8 teeth in the cut >= 11 ppi
13 inch plate; timber to rip = 0.75 inch, assuming we want at least 8 teeth in the cut >= 11 ppi
14 inch plate; timber to rip = 1 inch, assuming we want at least 10 teeth in the cut >= 10 ppi
15 inch plate; timber to rip = 1.50 inch, assuming we want at least 12 teeth in the cut >= 8 ppi
16 inch plate; timber to rip = 2 inch, assuming we want at least 15 teeth in the cut >= 8 ppi

As even long back saws, > 20", typically have 11 ppi, the above breaks down somewhat. However if a panel saw is used for large tenons, that saw probably is 8 ppi, or less.

Keep the analysis coming Stewie.

Cheers
Peter

Hi Peter. Some great analytical work.

At this stage the same post content has also been forwarded to other hand tool forum sites requesting feedback. Can I suggest the right thing to do at present is allow a reasonable period of time to lapse so others can raise their points of view on whats been suggested so far.

regards Stewie;

After discussions with Isaac Smith the following is a revision of my previous recommendations.

Stewie;


IMO. Where length is given a value; depth could be calculated using a predetermined ratio. For example; if a saw plate of a starting blank size of 12 inch in length x 3 inch in depth is deemed an ideal ratio to work from, this can then be transposed to give us a base value of 4 to 1.

Formula: D=L X 0.25.

(pre-spine depth of plate)

8 inch plate; D = 8 X 0.25 ( 2 inches)

10 inch plate; D = 10 X 0.25 ( 2.5 inches)

11 inch plate; D = 11 X 0.25 (2.75 inches)

12 inch plate; D = 12 X 0.25 ( 3 inches)

13 inch plate; D = 13 X 0.25 (3.25 inches)

14 inch plate; D = 14 X 0.25 ( 3.5 inches)

15 inch plate; D = 15 X 0.25 (3.75 inches)

16 inch plate; D = 16 X 0.25 ( 4 inches)


Saw Plate Gauge. (pre-spine depth of plate)

Up to 1 1/2 inch (0.015 / 0.018)

1 1/2 to 2 inch (0.018 / 0.020)

2 1/4 to 3 inch (0.020 / 0.025)

3 1/4 to 4 inch (0.025 / 0.032)

4 1/4 to 5 inch (0.032)

Using the traditional descriptive here is a listing of the different types of backsaws as well as their common features.

Tenon Saw, was the largest of the back saws and was made in lengths from 18 to 20 inches. As the name suggests, it was used for cutting tenon cheeks, and was most commonly found in a 10 ppi rip configuration. This particular name has "stuck" and is commonly used to refer to any back saw.

Sash Saw, commonly found in a 14 inch length and offered in 13 ppi, both crosscut and rip. This was the general purpose back saw.

Carcass saw, commonly found in 11 to 12 inch lengths and was primarily made in a 14 ppi crosscut configuration. It was used to cut very precise joinery across the grain.

Dovetail saw, commonly found in 8 to 10 inch lengths with rip teeth in pitches from 14-17 ppi. Since most dovetail saws were used on 7/8 inch dressed lumber, most will have a very narrow blade for greater control and stiffness. Many people confuse short back saws with dovetail saws. It is often difficult to tell then apart, but dovetail saws almost always have a much thinner blade and more graceful handle than the ordinary back saw. Dovetail saws are unique in that they were offered with three different types of handles: open, closed, and also with a turned handle.

Information source: http://www.vintagesaws.com/library/f...97/fall97.html

Stewie.

Dovetail Saw: Rip Tooth. Traditional lengths of 8 - 10 inch.

Carcass Saw: Crosscut Tooth. Traditional lengths of 11 - 12 inch.

Sash Saw: Rip Tooth or Crosscut Tooth.Traditional lengths if 14 inch.

Tenon Saw. Rip Tooth.Traditional lengths of 18 - 20 inch.

Stewie;

Originally Posted by planemaker

Dovetail Saw: Rip Tooth. Traditional lengths of 8 - 10 inch.

Carcass Saw: Crosscut Tooth. Traditional lengths of 11 - 12 inch.

Sash Saw: Rip Tooth or Crosscut Tooth.Traditional lengths if 14 inch.

Tenon Saw. Rip Tooth.Traditional lengths of 18 - 20 inch.

Stewie;

On another forum site Pedder raised an important point. If you go back and review early Disston catalogues, fleam was filed not on their backsaws. Comparative to rip saws of the same dimensions , a higher tpi were chosen for crosscut work. My apologies for the confusion.

Stewie;

When you make a backsaw, the person doing the work will presumably have made a pre determined decision to the general makeup of the saws features.

Such as its length, its depth, its saw plate thickness, whether its to be dedicated for just crosscut work, for rip grain work, or a combination of both that may class it more in a general purpose category. He will also consider what is the best choice of tpi/ppi and tooth configuration that will best serve the backsaws intended function

Lets revisit the list of tradition descriptive's that were in common use many years ago for backsaws, to gauge a better understanding of there relevance to todays modern world.

Tenon Saw, was the largest of the back saws and was made in lengths from 18 to 20 inches. As the name suggests, it was used for cutting tenon cheeks, and was most commonly found in a 10 ppi rip configuration. This particular name has "stuck" and is commonly used to refer to any back saw.

Sash Saw, commonly found in a 14 inch length and offered in 13 ppi, both crosscut and rip. This was the general purpose back saw.

Carcass saw, commonly found in 11 to 12 inch lengths and was primarily made in a 14 ppi crosscut configuration. It was used to cut very precise joinery across the grain.

Dovetail saw, commonly found in 8 to 10 inch lengths with rip teeth in pitches from 14-17 ppi. Since most dovetail saws were used on 7/8 inch dressed lumber, most will have a very narrow blade for greater control and stiffness.

As you can see from the traditional terms of reference, dedicated backsaws of that period still retain an important relevance that could be still retained used in today's modern saw making. General purpose backsaws are also covered within the descriptive of a Sash Saw. That could be retained also.

What would seem be of major conjecture to our modern day thoughts of backsaw is the lengths referenced back then. But we also need to keep in mind that within each of these descriptive's we have the mention "commonly found". That would suggest to me that there existed some general flexibility within the lengths of the backsaws and the terms used to best fit its general description.

But I would also like to conclude that in defence of the typical lengths mentioned, I agree with the principal practice of increasing the length of the saw plate to better accommodate a deepened depth of plate. The premise being you require a longer saw stroke to best deal with deeper cuts.

I would like to make special mention to the question Isaac raised.

Given that there are legitimate uses for a 12" saw filed rip, what would we call that saw? Some use it for cutting larger dovetails or smaller tenons cheeks. The terms dovetail and tenon are already taken for different saws, so carcase seems like the best fit.

Its a very pertinent question to raise, as I myself enjoy working with 12" saw plates.

We no from what Pedder uncovered when studying early Disston Saw Catalogues, that fleam was never used to differentiate the saw tooth from crosscut or rip grain work. That an increase in the tpi/ppi was relied upon to make the backsaw function better on crosscut grain.

That being the case, I see no obvious reason why a backsaw of more modern era build could not retain the class of a Carcass Saw because it has a rip tooth. But I would suggest there would also need to be some additional features within to the saws make up to make it more compatible to its traditional use.

Lets review again the traditional descriptive; Carcass saw, commonly found in 11 to 12 inch lengths and was primarily made in a 14 ppi crosscut configuration. It was used to cut very precise joinery across the grain.

To cut very precise joinery across the grain, you would also need to include the following features. The saw plate would need to be of a relatively finer gauge. Such as 0.020. The tpi/ppi would need to be on the higher end of the mid range. Such as 14 - 16. The rake of the teeth would need to be backed off slightly to best cut through the crosscut grain. Such as 10* or slightly above. That the set on the teeth would need to be kept minimal to keep the sawn kerf quite narrow. And lastly, the depth of plate would also need to be contained within a defined range to best complete the precision crosscut work.

As a good example of what I would still class as a Carcass Saw. Length in the range of 11 to 12"; of 0.020 gauge; depth of usable saw plate in the range of 2 to 2 1/2"; rip tooth with a rake angle 10 to 12*, tpi /ppi of 14 - 16, tooth set with minimal clearance.

An interesting topic of discussion.

Stewie;