Bow/Frame Saw Details

[Phil Starcovic]

So, Michael Faurot (http://www.sawmillcreek.org/member.php?u=30540)and I will have talked about making this bow/frame saw. During our brainstorming process, we have come up with two concerns so far (and i'm sure we'll have many more down the road). Hope you can help shed some light on these:

1) Is there a certain length that we should make the cheeks? It seems that there will probably be a "sweet spot" such that if we make them longer, the cheeks will snap (regardless of the strength/species of wood) in trying to tension the blade. And if we make them too short, we won't be able to tension the blade enough.

2) If we choose to make turned handles to hold the blade (as shown by the "The Disston saw with Jute tension cord" post #3 of http://www.sawmillcreek.org/showthread.php?t=107681), what can we do to prevent the blade from turning while sawing. Michael has had some problems with this while using other saws.

Thanks for the help.

[Brian Kent]

In the link you provided I really like Harry Strasil's 2nd and 3rd pics where the blade was not just pinned but embedded in the ends of the handles. This looks pretty solid to resist blade twists and turns.

[Eric Hartunian]

I've been playing with this for a long time. I've made a couple, and can't seem to get them right. Here is my problem, and I don't think the length of the cheeks is the issue. I can't get the saw to "work" with out excessive twisting of the blade. Tighter tension doesn't help, either. I've used the Gramercy blades, and an old bandsaw blade with the same results. It is as if the frame wants to move around and twist, but the blade just gets hung up in the kerf.
Anyone have better luck???

Eric

[Robert Rozaieski]

Put leather washers between the handles and the frame to provide some resistance to the blade/handles twisting when you don't want them to but still allow you to turn the blade when you do want to.

Bugbear had a good design on his web site that might help you with dimensions http://www.geocities.com/plybench/bowsaw.html.

You might also consult the Grammercy plans. Joel and his crew did a lot of research when designing their saw and kindly made it available for everyone http://www.toolsforworkingwood.com/Merchant/merchant.mvc?Screen=NEXT&StoreCode=toolstore&nextpage=/extra/bowsawdesign.html.

[Eric Hartunian]

I probably didn't explain well. The handles turning in the frame isn't the problem. They don't twist. The blade itself twists. So lets say I want to cut a gentle curve...I begin sawing, and as I try to turn the saw, the blade stays in the kerf, the whole saw turns, and the saw blade twists. Maybe I am putting too much pressure on the saw? I can cut smooth curves with a coping saw, but that blade is only about 6" long, and in a very ridgid frame.
Who knows...

[Robert Rozaieski]

Eric,

It could be your technique, it could be the blade. How wide is the blade? The Grammercy blades (what I use in my antique saw) are very thin, thinner even than coping saw blades so they turn very well. Wider blades are more difficult to turn but it was definately done with wider blades historically (my saw originally came with a 1/4" wide blade).

More likely though it is your technique. What is likely happening is that you are using the full length of the blade with the shorter coping saw but not with the longer turning saw. I had this problem when I first started using my 12" saw and still do if I find myself trying to go too fast. The solution is to take it slow, not pressure the saw into the cut (let its weight do the work) and use long, smooth, full length strokes employing the entire 12" of the blade with each stroke. It can be hard to get used to the longer stroke of the bow saw after using short coping saws for so long (it was for me) but try taking it slow and using the full length of the blade and see if that doesn't help some.

The secret for me was to get my coping saw out of the shop and put it in the garage, dedicated to house trim duty. Once I was forced to use the bow saw and couldn't simply reach for the coping saw instead, it made me be more careful and slow down.

Also, make sure you're using the correct amount of teeth for the thickness of stock you are sawing. Joel sells several different blades with different PPI for different thickness of stock. I use the 10 point for stock 3/4" and thicker and the 18 point for anything less than 3/4" thick. Having two different blades does make a world of difference in the speed and smoothness of the cut.

[george wilson]

Bandsaw blades aren't really correct for these saw blades. Are there any sources for bow saw blades? We used to make them for the museum,so didn't buy them. We made them .042" thick at the cutting edge,and ground them to a taper from cutting edge to back.The back edge was about .030" thick. This is how the old ones were made,by the way.The teeth were 8 t.p.i.. The blades were also tapered for their length,starting at 3/8" wide,going to about 3/16" wide at the other end. We filed the teeth sharp,but didn't set them due to the rapid taper in thickness. The rapid thickness taper also helped the blades to negotiate turns better.

Early on,I had tried bandsaw blades,in 1971,but they just weren't sharp enough. Can you go over your blades and file the teeth sharper?

[Joel Moskowitz]

Single biggest problem people have is not sawing though a curve. as you turn the saw continue the long stroke so it cuts - otherwise you are just twisting the blade and it will jam.

[Daniel Kennedy]

. We made them .042" thick at the cutting edge,and ground them to a taper from cutting edge to back.The back edge was about .030" thick. This is how the old ones were made,by the way.The teeth were 8 t.p.i..


Could you please explain how you tapered the blades in more detail? What did you use to grind them?

[harry strasil]

with wider blades in a turning bowsaw you need more set which makes a wider kerf so the blade will turn. I very seldom use a turning saw except for the one with a coping saw blade. The double turning saw works pretty well tho, one blade is rip, the other is crosscut.

Coping saw.

http://img.photobucket.com/albums/v81/irnsrgn/wood/copingsaw.jpg


Double Turning saw.

http://img.photobucket.com/albums/v81/irnsrgn/wood/doublebowturningsaw.jpg

[harry strasil]

If you look closely at the Disston Turning Bow Saw, you will see a stove bolt under where the handle goes thru. Disston drilled for the turning handle then cut a kerf up past the hole and used the stove bolt to tension the handle.

http://img.photobucket.com/albums/v81/irnsrgn/wood/disstonbowsaw1.jpg


I used the same procedure when I made my Deep Throat Turning Saw.

http://img.photobucket.com/albums/v81/irnsrgn/wood/bowsaw3.jpg


And I make my own blades by buying old warranteed hand saws for a buck or two and toothing and sharpening to what I want, then cutting the teeth and however wide a blade I want off with my plasma torch and then dressing the back where the cut is. FWIW

[george wilson]

Harry,does your torch ruin the temper in the blade? I'd rather shear it. Shearing spring steel is o.k.as the steel cracks off ahead of the cutting edge.

I just cut the teeth on the edge of a sheet of .042" spring gteel,and chomped off the tapered blade. Then,I freehand ground the taper on the blades on the Wilton square wheel grinder 1 side only. I used a block of wood behind the blade to hold it against the wheel,and rested the blade's back on the horizontal tool rest. Takes grinding skill to do it,and also to not burn the blade,which is not much mass,and easy to overheat. A sharp 36 grit,then 80 grit blue zirconia belt is best for the coolest grinding. If you do it on a wheel,the grind will,of course,be hollow. I used the flat platen. You could even do it on a water cooled grinding wheel,like a Tormek,and draw file it flat afterwards.

I suppose you could also do it on a 6"X48" woodworking belt sander,but urge you to use the blue belts,not brown,which are not as sharp,and overheat easily. I haven't tried to buy blue belts for my 6X48,as it is for wood. You could do it on a disc sander,if you flex the blade,but it would be trickier.I'd make the blaed 4" too long,and hold it at the ends,cutting the ends off later. You could rig up a wooden back rest to support the blade.

I might mention that the original 18th.C. blade we copied was just about 1/16" wide at the cutting edge,.062",but the steel we had was .042" max. Our blades worked fine,though. The cabinet shop used them to contour thick legs,and the gunsmith used them to saw out 2 1/2" thick maple stock blanks.

We did the sharpening after the grinding.

[harry strasil]

no it doesn't get hot at all, I have cut thru paper labels on the other side of different metals and it doesn't even burn the paper. A plasma cutter makes the 4th state of matter a super heated gas (plasma) that comes out of the little tip at 120 MPH + and is 28,000 degrees approx. it happens so fast on thin stuff you can grab it with your fingers immediately after you cut. Only about a 5th of the air comes out of the tip, the rest is used to cool the tip and the metal being cut. It doesn't leave quite as smooth an edge as a laser or a waterjet cut tho.

[george wilson]

Sounds great!!