My New Sawing helper at work

[harry strasil]

This is my new frame sawing helper and me at work, he works cheap, doesn't complain or talk and never gets tired.

http://img.photobucket.com/albums/v81/irnsrgn/wood/th_sawing005.jpg (http://smg.photobucket.com/albums/v81/irnsrgn/wood/?action=view&current=sawing005.flv)

[Ken Fitzgerald]

Harry,

No offense. Your helper will age and give out over time. When it happens you don't want to be there to receive his slap!

[David Keller NC]

Harry - I've seen something similar to this done with one of the solid-rubber bungees. As Ken notes, the cord-type bungees do give out over time, though presumably there's a small risk of the metal part flying toward you.

One inventive guy actually had a frame-saw vise on a stand, and the back of the stand was braced with a 2X4 about 3 feet from a wall. On the wall, there was a wooden track with a captured slide, and the slide had a hook that was tied to a bicycle inner tube. As the saw advanced on the work, the captured slide slid down the track, so none of the sawing effort was wasted in a direction other than horizontal - very clever.

[Bill Houghton]

I suppose you could attach a sapling to something, like a spring pole lathe.

[Jim Koepke]

Next thing to try is to mount it all vertically with a treadle. Then you can feed the wood while moving the blade with foot power.

jim

[Bill Houghton]

Next thing to try is to mount it all vertically with a treadle. Then you can feed the wood while moving the blade with foot power.

jim

and then you can put a motor on it and save all that sweating...

No, no, just kidding. The bungee assist is a great idea.

[Garth Keel]

Is that your grandson in the video? How did you get him to do the work while you filmed? :D

[Ken Werner]

But Jr., don't his arms get a little rubbery after you work him so hard?

[James Carmichael]

He seems like a handy "fellow"

[Matthew Dunne]

I guess I don't quite get it. The bungie assists in pulling on your push stroke, but only by releasing energy you've stored in the bungie during your pull stroke. The pull stroke is therefore that much harder. In other words, the bungie doesn't add any energy to the system--you're still doing all the work. Right? Or am I missing something?

[Pedro Reyes]

I guess I don't quite get it. The bungie assists in pulling on your push stroke, but only by releasing energy you've stored in the bungie during your pull stroke. The pull stroke is therefore that much harder. In other words, the bungie doesn't add any energy to the system--you're still doing all the work. Right? Or am I missing something?

The saw offers significantly more resistance on the push stroke.

/p

[harry strasil]

The bungee isn't that strong, and it also acts like another person so the saw saws faster and relieves some of the down pressure on my wrists.

[george wilson]

Harry,if you like it,do it,but I must agree that there is no free lunch. When you pull back on it,you are doing more work.

[Pedro Reyes]

Overall, there is more work done with the bungee, after all no machine is 100% efficient.

But muscles usually work in pairs, and Harry (or anyone else) using a push saw works the muscles involved in pushing the saw a lot more than those involved pulling it back, thus tiring faster. The bungee, altho taking (a very minute amount of) extra energy, helps balance the "load", so probably helps overall.

/p

[Tim Put]

Though there probably is; it is not necessarily the case that more energy is being used with the addition of the bungee. It's true that the bungee is not 100% efficient, but that doesn't matter. What matters is the efficiency of the whole machine, Strasil included. That may very well have gone up, and even if that is not the case the subjective effort may have gone down.

Adding parts that dissipate power doesn't always increase the overall power consumption of a machine, and further, they don't always reduce efficiency. If they did we'd see single cylinder, single speed, motorized unicycles as a major mode of transportation ;)

[harry strasil]

Each to his own I guess, I have rather large wrists, but not as large as they used to be. When I went into the Navy at 17, I had 14 inch circumfrence wrists from grinding and polishing plow lays all day, sometimes 16 hours a day. and not too many years ago I could take 10 5/32 6010 arc welding rods and grasp both ends of them in a bundle and bend them to a 180 in the middle. But, I am older now and have been disabled since January 2006 and I have lost a lot of my upper body strength. When ripping horizontal like in the video with a frame saw you use your wrists to put down pressure on the saw web. Sure it takes a little more exertion to pull the saw back toward you, but what the bungee strap really does is put more down pressure on the blade, so you have a slight bit more effort pulling it back, but when you realize that with the bungee you only need half the push strokes to do the same amount of work, its well worth the little extra effort needed to pull it back.

[Matthew Dunne]

Sure it takes a little more exertion to pull the saw back toward you, but what the bungee strap really does is put more down pressure on the blade, so you have a slight bit more effort pulling it back, but when you realize that with the bungee you only need half the push strokes to do the same amount of work, its well worth the little extra effort needed to pull it back.

That makes a lot of sense. Thanks for the info, Harry.

[george wilson]

How about putting a bungee strap vertically,on each end of the blade. that would put more cutting pressure on the work-maybe too much. Or,you could simply put weights on the saw for vertical sawing.

[Pedro Reyes]

Woodworking forum, but I just can't keep myself from replying, sorry, I don't mean to be rude.


Though there probably is; it is not necessarily the case that more energy is being used with the addition of the bungee. It's true that the bungee is not 100% efficient, but that doesn't matter.
There is more energy being used by adding the bungee, it gets warm, it even makes noise, all that was energy not returned by what is simply a spring. Not being 100% efficient does not matter?


What matters is the efficiency of the whole machine, Strasil included. That may very well have gone up, and even if that is not the case the subjective effort may have gone down.
Leaving subjectivity out, if you measure efficiency as:
how quickly Harry's muscles & wrists tire/lenght cut ----it does go up. Technically he could cut more.
But that's the point I was trying to make on my post.
If you measure it as:
energy used/length cut --------it goes down.



Adding parts that dissipate power doesn't always increase the overall power consumption of a machine, and further, they don't always reduce efficiency. If they did we'd see single cylinder, single speed, motorized unicycles as a major mode of transportation ;)
I can't make sense of the first statement, it seems contradictory when refering to power (which should be energy to avoid time here). Of course adding a second cylinder can help with efficiency (instead of moving a weight you are moving another cylinder which returns energy better than just a spinning weight.)
The last one is trying to simplify so many things it is also impossible to address, but for one, for some applications you just can't get all the energy needed out of a single cylinder engine, size starts to matter in pragmatic ways.


/p

[Tim Put]

Perhaps I wasn't very clear, but at the risk of sounding pompous: what I said is right.

Adding parts that dissipate energy (you're right that we don't need to include time, but I do find thinking in rates can ease understanding and as long as you're consistent time cancels out) does not always increase the total energy dissipation of the whole machine. Parts often dissipate energy while simultaneously reducing the energy dissipation of some other component.
All (practical) bearings dissipate energy, but they dissipate less energy than the plain bearing that would be there if the proper bearing wasn't. Perhaps the forces involved in the push stroke put pressure on Mr. Strasil's joints such as to greatly increase friction losses in them. In that case relieving some of that pressure with the bungee may reduce frictional losses in his body more than losses outside is body are increased.

Energy used/length cut may in fact go up.

P.S. I agree that the last sentence of my previous post didn't do anything to aid understanding. It was a very weak, flawed, reductio ad absurdum; made primarily in jest. Hence the smiley.
I'm fond of using reductio ad absurdum, but couldn't come up with an easy to convey example in this case, so I decided to poke fun at myself.

[harry strasil]

Its really comical to me the direction this thread has taken, one persons simple idea to help him accomplish sawing a piece of wood, is being dissected like a frog in biology class in High School. LOL