Stair saw tooth geometry

[Paul Incognito]

Ok, so I'm making a stair saw. Through the research I've done, I've learned that most stair saws are filed rip, 8-11 ppi. Any sugestions on specific geometry? I tried filing a blade crosscut and it doesn't work so well. I filed it 8 degrees rake and 20 degrees fleam, 10 tpi because that's what I had. It doesn't cut well accross the grain. It rips ok, but not great.
I should mention that I'm pretty new to saw sharpening. What I know I learned from here and vintagesaws.com.
Thanks,
PI

[Jim Koepke]

I could be totally wrong here, my understanding was that a stair saw was for cutting the slot in the bottom of a tread for the riser.

If that is the case, then the saw should be filed for a rip cut.

Maybe others know better.

Also, pictures with some close ups of the teeth's profile might help.

jim

[Paul Incognito]

to take some pics, but can't get a clear shot. Attached is the best I could do.
I thought the saw was for housing the treads in the stringers.
Am I way off base with 8* rake and 20* fleam for a crosscut saw? I'm going to re-file it rip anyway, but it would ge nice to know why it doesn't cross cut well.
Edit: It was filed 14* rake. I re-filed it 8* rip and it rips much better.
Thanks,
PI

[Jim Koepke]

The photos appear as if your camera can not focus on things close up.

If your camera has a button with something that looks like a flower that may enable closer shots than the normal view.

jim

[Paul Incognito]

Thanks Jim.
No flower on the camera.
I think I got it sorted out. I re-filed the teeth rip with 8* rake and it cuts much better with the grain. Still not so much across the grain, but I'll mostly be using it to rip, so it'll work.
Here's a pic of the completed saw. Oak finished with danish oil.
PI

[John A. Callaway]

I did not know such a tool even existed. Wouldn't a regular sash saw or carcass saw filed rip serve the same purpose?

[Jeff Burks]

A stair saw is made to cut the housings (http://www.woodworkinghistory.com/images/kelley_router_stair_stringers.jpg) in a stringer. This is also referred to as gaining a stinger. The "gains" being the open sided mortises made for housing the tread, riser, and wedges. The sides of the saw act as a depth stop (usually around 3/8") and the body of the saw stiffen the blade across its entire length. Both riser and tread cuts are on a diagonal to the edge of the board, so they are cross cuts. The nosing portion of the cut is made with a bit & brace. Since this is a stopped cut, and the carpenter often uses the pitch block as a saw guide to start the cut, then the saw needs little or no set on the teeth. Saw away from the nosing so that the teeth can eject chips. The stair saw makes the perimeter cuts and the waste is removed with a chisel and router plane.

Almost all stair saws are designed to allow for a quick blade change, or a depth (http://www.greatplanestrading.com/HUM1/Hum088.jpg) adjustment. Some of the saws have a deeper blade and a side fence. The blade usually has 2 or more slots or notches cut into the top to allow for the saw nuts. You can still sometimes find really old (http://www.antiquetools.co.uk/product_images/23.jpg) saws kicking around, but not all of them were made specifically for stairs. Some of them are made for starting dados and sliding dovetails. Some of the odd versions appear to cut on the pull (http://www.gilai.com/product_1166/6-Inch-Stair-Saw.-German) stroke (http://www.gilai.com/product_1167/Stair-Saw--5-Inch-Made-in-England). This guy appears to have set his blade to cut on the pull (http://insidetheworkshop.blogspot.com/2010/02/stair-saw-to-heaven.html) as well (bottom picture).

The grooves and rabbets made in the treads and risers are better made with rabbet planes, plows, and moving filister etc.

148,136 (http://www.google.com/patents?id=dX9aAAAAEBAJ&zoom=4&dq=%22stair%20saw%22&pg=PA1#v=onepage&q&f=false) is and example of a stair saw design.

This saw (http://www.oldtools.com/FW11001.jpg) has been setup with a curved blade to help make a plunge cut (like a flooring saw - #34 (http://www.greatplanestrading.com/HUM1/Hum011.jpg) is this photo). Normally you don't need the curved blade because the carpenter would cut a series of stopped holes at the nosing with a brace and chisel out the waste first. There are lots (http://images.google.com/images?as_q=stair+saw&hl=en&btnG=Google+Search&as_epq=&as_oq=&as_eq=&as_sitesearch=&safe=images&as_st=y&tbs=isch:1,isz:lt,islt:qsvga) of different designs, and most carpenters and joiners made their own stair saw out of an old broken saw (http://www.norsewoodsmith.com/content/recycling-old-hand-saw). A few companies like Disston (http://www.disstonianinstitute.com/gallery2.html) made them for retail.

[Pedro Reyes]

Now if one wanted to cut dadoes, wouldn't you file x-cut?

/p

[Paul Incognito]

Geez Jeff. Everything you wanted to know about stair saws but were afraid to ask.
Thanks for all the info.
Now...on to my question, if I wanted to use a stair saw for cutting accross the grain, how would I file it? I've used the tooth geometry I stated below for back saws and they cut fine, but for the stair saw, I can't even get the cut started. Maybe a curved blade like the one in your link? Maybe with no set in the teeth?
It cuts well with the grain regardless of tooth profile.

[Jeff Burks]

I don't think I can give you a definitive tooth geometry. Suffice to say that the stair saws I have handled were filed crosscut with lots of fleam, but I didn't actually compare the teeth to anything nor try out different configurations.

It could be that you have poorly sharpened teeth, and it could be that you are using a bad sawing technique. For example, it is never easy to start a cut with the entire saw engaging the work piece. If you are actually cutting a stair housing than this is how I would set it up:


The stairs get a pencil layout with help from the pitch block. If you don't know the pitch block is a triangle of wood cut to the rise and run of the stair, often with a fence attached to ride the edge of the stringer. It looks kind of like a wooden Swanson Speed square.

The nosing gets a series of touching or overlapping holes equal to the diameter of the nosing profile (say 1"). The waste points left between the bored holes get removed with a chisel and router plane. The pitch block is placed in position to guide the saw blade and held with a clamp.

You are standing on the "show" edge of the stringer with the nosing pointing at your belt buckle (for normal push cut). You place the saw against the pitch block with only the rear inch or so of teeth on the stringer. The rest of the saw is off the work piece. You push forward to start the cut using both hands on the saw. After every stroke you pull the saw back father to lengthen the cut until you are sawing from the nosing area all the way out the back of the stringer (might take 10-15 strokes). Once you have the kerf started all the way you remove the pitch block. Keep sawing until the sides of the saw bottom out on the stringer (assuming you are using the saw as a depth stop).

With this type of sawing the blade actually fully exits the work piece each stroke and and you have to be careful to place the blade back into the kerf without making a mess of the work piece. Make sure you shake the chips out of the blade and maybe blow out the kerf a bit as you work. Zero set on the blade keeps the teeth from wrecking your pitch block. The direction of cut is "nosing to exit", and you start cutting near the exit if that makes sense. The exit (for lack of a better word) is the point where the tread and riser housings exit the lower edge of the stinger.

I hope that is clear... it's been a long day at work.

[Paul Incognito]

Thanks Jeff.
I think I found the problem: there's a loose nut holding on to the handle. :)
I'll file another blade cross cut and play around with the geometry. But it probably comes down to tecnique, I've been trying to start the saw with the blade flat on the workpiece. That doesn't work so well.
PI

[Jeff Burks]

Yeah it's a common misunderstanding about starting that kind of cut. Bear in mind that each additional tooth engaging the workpiece multiplies the force required to push the saw (or something like that). So it takes a lot more effort to saw a 16/4 billet than a 4/4 board because there are so many more teeth in the work at once, and a lot more friction in the kerf. A stair saw has 2 handles for a reason!

Starting a stair cut with all the teeth on the wood is going to cause 2 problems.
The teeth are likely to clog before they exit.
The saw is liable to jump off the line.

Not to mention turning your arm into silly putty...

[greg Forster]

As Jeff noted, some stair saws were made to cut on the pull . I see this alot on early, craftsman -made stair saws and on "dovetail saws" (for cutting sliding dovetails).

Since I use a r***** to dado skirt boards when trimming out stairs,I don't have any on-hands experience with stair saws; why cut on the pull stroke?

One reason may be that since the entire length of the sawblade is engaged in the cut almost 100% of the time, a pull stroke might decrease the chance of kinking the blade, or maybe (brainstorming here) this allows the saw to pull the sawdust back out of the cut rather than pushing it into a "deadend"? I know table(ing) saws work on the pull stroke, although not quite the same situation. Maybe cutting on the pull would influence how the teeth are sharpened? And maybe this (pull stroke) would improve the sawing process?




edt. thought about the tooth direction a little more and yup the saw needs to cut on a pull stroke to clear the sawdust out of the kerf. Checked in some of my books showing this type of saw and both English and Continental saws cut on the pull stroke

[Jeff Burks]

There are many stair saws designed to cut on the pull stroke, but that is not a requirement of the cut, nor the tool. You simply need to point the teeth toward the exit point of the cut. Whether you use a push saw or pull saw is entirely up to the preference of the carpenter. Does it really matter what side of the board you stand on? It's just important to understand that you can't saw wood if the teeth get clogged with chips. A curved flooring saw is designed to plunge cut. The teeth ramp themselves out of the kerf to expel the saw dust. A straight bladed saw can't expel dust if sawing into a stopped cut, but it can expel chips if sawing away from a stopped cut. And as far as the blade goes, I don't think there is any possibility of kinking a stair saw under normal use.

1,607,403 (http://www.google.com/patents?id=pNZgAAAAEBAJ&zoom=4&dq=stair%20saw&pg=PA1#v=onepage&q&f=false) is an example of a Stair Saw designed to cut on the pull. There is very little if any difference between push and pull saw handles, and often the blades are symmetrical and reversible for either direction.

The ABC of Stair Building (http://books.google.com/books?id=XicDAAAAMBAJ&lpg=PA165&dq=%22stair%20builder%20saw%22&lr&as_drrb_is=q&as_minm_is=0&as_miny_is&as_maxm_is=0&as_maxy_is&as_brr=1&pg=PA164#v=onepage&q&f=false) article shows a carpenter using a pull style Stair Saw against a straight edge to start his housing. He has used a combination of drill and gouge to cut the nosing section.

I should also point out that all of the Disston catalogs show their Stair Saw set up to cut on the push stroke. They used a somewhat standard 8TPI 6" Long x 1 5/8" blade that could be adjusted to cut as deep as 3/4".