# A walk-along circular saw plywood ripper.

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• posted on April 14, 2008, 10:49 pm
wrote:

I'm not seeing the advantage, unless you're using two hands or have Superman's wrist. Can you post a picture?
Based on the pivot points, a long arm fixed to the saw, held my a short hand, I would see the saw enjoying the mechanical leverage gain.
Think of where the pivot point for a shovel or a wrecking bar is. It's at the opposite end of the stick from your hand

You still don't want to ruin it! <G>
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• posted on April 15, 2008, 12:08 am

Imagine a short handled wheelbarrow,
Compared to a longer one, less torque at the wheel applied by the operator.
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• posted on April 15, 2008, 1:01 pm
"BoyntonStu" wrote in message

Easy to disprove:
Grab an eight pound sledge hammer by the handle, 4" from the head, and hold it straight out at arm's length.
Now grab it by the handle 3' from the head and try again.
Can you say: "mechanical disadvantage"? ;)
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• posted on April 15, 2008, 1:04 pm

Imagine a long flimsy handle on that wheelbarrow. One single long flimsy handle...
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• posted on April 15, 2008, 10:10 pm

Why imagine long and flimsy?
A 4 foot 2x4 is not long or flimsy.
Imagine 2 crowbars: one 4" long, the other 4 feet long.
Which one applies the most torque?
The hold-down torque is applied about the handle fulcrum point located at the rear of the saw plate.
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• posted on April 15, 2008, 10:23 pm

No, the torque is applied at your wrist. You rotate your wrist to rotate the 2x4, supplying the downward force on the saw which is at the end of the 2x4.
Look at it the other way around. If, for whatever reason, the saw wants to jump up, it has the mechanical advantage due to the length of the 2x4 to twist your wrist about its pivot point at the end of your arm.
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• posted on April 15, 2008, 10:59 pm

No, the torque is applied at your wrist. You rotate your wrist to rotate the 2x4, supplying the downward force on the saw which is at the end of the 2x4.
Look at it the other way around. If, for whatever reason, the saw wants to jump up, it has the mechanical advantage due to the length of the 2x4 to twist your wrist about its pivot point at the end of your arm.
Have a friend come over. Take a 6" long stick in your hand and have your buddy try lever it back and forth in your hand. Now take a 4 foot long stick, hold the end of it, and your buddy on the other end, and have him lever it back and forth, then get back with us on which one takes less effort for you buddy! (in this example your buddy equals the saw!) Greg
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• posted on April 16, 2008, 2:13 am

I think we're arguing the same side of the argument here, only differing in ascribing where the torque happens and where the resultant force occurs.
Torque occurs about a center of rotation. Torque varies directly with the length of the lever arm. A saw on a stick is asking for trouble.
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• posted on April 16, 2008, 2:23 am

Agreeing with you, just to lazy to go back the the OP's post and respond there! Greg
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• posted on April 16, 2008, 3:12 am

The stick in my hand is the saw in the slot.
You have it backwards.
Consider a shovel with a short handle to dig a hole? No way.
YOU use the long handle to increase YOUR torque on the shovel head.
In a like manner you use a long handle to keep the saw in the groove.
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• posted on April 16, 2008, 4:42 am

No, you use the shovel like a lever, with the fulcrum being the edge or side of the hole you're digging. Mechanical advantage then is given by the ratio of the handle length to the length of the shovel face.
When you pick up a load with the shovel, you move one hand down closer to the shovel face to decrease the torque required (the lower hand providing a new fulcrum).
There is no fulcrum to provide a pivot point for the saw on the end of a stick, just what force you can muster by torquing the other end of the stick where you're holding it.
Put a weight on a shovel face and try to lift it while gripping only the shovel handle. Repeat sliding one hand down near the business end. Compare efforts.
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• posted on April 16, 2008, 11:22 am
On Wed, 16 Apr 2008 00:42:56 -0400, "Greg Neill"

I tried that example 15 messages ago, with the bonus of a wrecking bar added for good measure. <G>
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• posted on April 16, 2008, 12:20 pm

Place the tip of the shovel face on the ground.
Is it easier to tip the load upwards with a short handle or with a long handle?
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• posted on April 16, 2008, 1:00 pm

Without a fulcrum obviously the short handle is preferred, as I intimated above.
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• posted on April 16, 2008, 4:13 pm

The fulcrum is offset from the lever handle by the length of the plywood plate.
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• posted on April 16, 2008, 5:33 pm

What fulcrum would that be, and how does it result in a downward directed force on the saw and plate? The saw is fixed to the plate, right? Torquing the handle about the fulcrum would lift the rear end of the plate, and wouldn't do much to prevent the whole saw + plate assembly from lifting out of the cut.
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• posted on April 16, 2008, 8:59 pm

If you push the angled handle to make a cut, the effort will resolve into 2 components: (1) forward and (2) downwards.
I never feel any lifting feedback.
Have you ever experienced a kickback or a lift using a circular saw?
I have worn out several in my lifetime and I have yet to see any difficulty in this arena.
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• posted on April 16, 2008, 9:29 pm

True.
I've had cases where binding caused some pretty radical saw motions that required firm hand control.

Well, good luck with that.
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• posted on April 17, 2008, 1:55 am

Kickback or "lift" from a circular saw? More times than I could possibly count! A couple times just the other day! Greg
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• posted on April 17, 2008, 2:33 am

Greg,