Building a model Drag Saw

[CHIPWELDER]

I've spent 6 hours today in "geometry world", coming up with a set of linkages that will work for the drag saw. I know of no set of equations that will let you calculate this stuff. It is more "try it and see" engineering. What I have here is a set of linkages that go through all of the required motions without binding or going into a "lock" position. Now I have to take the time to do a visual comparison between what I have and what a real drag-saw looks like. This is fun stuff, but it isn't easy. Before I cut any metal, I will build these linkages full scale in cardboard and using "stick pins" work it through all of the required motions.

Mechanism Design vol 1 Arthur G. Erdman et al. Ibuprofin can be sourced locally. Isn't there a clutch showing in your photo? Possibly a small cone type?

 

[Brian Rupnow]

Goody--believe it or not, the new blade is exactly the same size as the previous blade. The only difference is in the tooth profile.

 

[goody]

But the tooth profile is more closely in scale with the tooth profile of a full size blade.

Pat

 

[nel2lar]

Brian
One of your more interesting builds and enjoyed it all the way. The only thing it needs is a stop so the saw does not try to go to China.
Beautiful bild.
Nelson

 

[Brian Rupnow]

Nelson--If you look really really close you can see a vertically oriented 1/4" bolt setting behind the top swing arm with the hex head on top. The swing arm can only go down that far. That is what prevents the saw from coming out in Peking.

 

[SteveM]

Hello Brian
your drag drag saw is - like all your builds - interesting, beautifully engineered and innovative. I have (like I guess the silent majority) been watching with great interest and wouldn't normally comment.
Now I love your saw as it is, but I cannot help but think that it could be so much better with a different blade. I've been cutting timber using handsaws in one guise or another for about 40 years, and I agree the modern saws usually have a cheap and cheerful look about them. But they are things of astonishing beauty when it comes to cutting timber! They outperform and outlast plain steel saws by miles. And they can be resharpened quite simply when eventually they fade. I'd be amazed if your machine couldn't slice through that log in less than a minute by using a weighted hardpoint toothed blade designed to cut on both push and pull strokes. Something like this (picture hopefully below).
I'd leave it as broad as could be accommodated to help with stiffness (), and in trimming it to length I would also make it long enough to add a weight to the tip; perhaps a pound or two of lead loosely secured so that it'll break free should it ever foul on the wood.
I hope that helps and it hasn't offended!
Best regards
Steve