Which would be the strongest

[Bill Huber]

Ok, I know that is a dumb title for the thread but I didn't know what else to put.

I have steel patio doors, they have the big wood blinds on then and have little plastic things at the bottom to hole them. Well they get broke all the time so now I decided to make some from wood with magnets in them. The test ones are working really well so I am now making the final ones.

I am using hard maple, I had some 4/4 scraps.

They are 2 1/2 x 1 7/16 x 7/8 and have 2, 1/2" rare earth magnets in the end to attach to the door. There is a hole 1" from the magnet end that the blinds are screwed to so they can pivot when you one then or close them.

Now the question which way is the strongest or is there a difference.

The longer part up or the longer part down, I can not feel any difference but I do not have a way to measure it.
The pull would be up at the pivot point.

one.jpg two.jpg

[Bruce Page]

Bill, I read your post 3 times and I still don’t understand what yer trying to say (it has been a long day). Which way are you pulling and from where?
If you are pulling up from the small hole then the left model would have a stronger magnetic strength.

[Bill Huber]

Bill, I read your post 3 times and I still don’t understand what yer trying to say (it has been a long day). Which way are you pulling and from where?
If you are pulling up from the small hole then the left model would have a stronger magnetic strength.

Yes I would be pulling up for the pivot hole in the unit.

I was thinking the left one but I keep looking at it and changing my mind back a forth all the time.

[Wes Grass]

In 'theory', it doesn't matter. It's a torque moment about the top edge of the block, countered by the pull of the magnets.

[Jason Roehl]

If those drawings are proportional, I'd say the one on the right for the reason that Wes said it didn't matter--the torque moment. The difference is that if you picture a line between the pivot point and the top edge of the bracket, that line is longer in the image on the left, meaning for the same vertical force, there is more leverage (torque) since the distance between the force and the pivot is greater. The image on the right gives the magnets more leverage to act against that force.

I can't back all that up with numbers, though--I'm too far removed from my glory days in AP Calculus-based Physics classes...

[Ken Fitzgerald]

Bill,

If this is the piece that keeps breaking, I'd say the left one would be stronger and resist breaking at the 90º angle.

[Van Huskey]

If those drawings are proportional, I'd say the one on the right for the reason that Wes said it didn't matter--the torque moment. The difference is that if you picture a line between the pivot point and the top edge of the bracket, that line is longer in the image on the left, meaning for the same vertical force, there is more leverage (torque) since the distance between the force and the pivot is greater. The image on the right gives the magnets more leverage to act against that force.

I can't back all that up with numbers, though--I'm too far removed from my glory days in AP Calculus-based Physics classes...

More gut than engineering BUT I agree.

[Mark Woodmark]

Why dont you make them so the longer part goes both up and down?

[Bill Huber]

If those drawings are proportional, I'd say the one on the right for the reason that Wes said it didn't matter--the torque moment. The difference is that if you picture a line between the pivot point and the top edge of the bracket, that line is longer in the image on the left, meaning for the same vertical force, there is more leverage (torque) since the distance between the force and the pivot is greater. The image on the right gives the magnets more leverage to act against that force.

I can't back all that up with numbers, though--I'm too far removed from my glory days in AP Calculus-based Physics classes...

It is the same drawing just flipped over in SkitchUp.

[Bill Huber]

Now that I drew it up in Visio it looks like it is the same no matter which way I put them.


Drawing1.jpg

[Bruce Page]

The one on the right in this picture.

[Jason Roehl]

It is the same drawing just flipped over in SkitchUp.

I understand that. What I'm talking about is the difference in length between the base of the arrow and the top point between the two Visio pictures. One is the hypotenuse of the triangle (longer), the other is a base of a right triangle (shorter). Since the upward force would be constant, the torque is greater where the distance is longer (t = F x d). The topmost point is the fulcrum on both drawings, but the lever changes from a base of the triangle to the hypotenuse.

[PeterTorresani]

Now that I drew it up in Visio it looks like it is the same no matter which way I put them.


Drawing1.jpg

My first impression was that you are correct in that they are same. I always have the best luck proving something right, by trying to prove it wrong, so I took a crack at it.

If you are pulling straight up as drawn, then each configuration will provide the same magnetic strength. However, if the direction of pull is slightly away from the window then the left picture (in visio) will withstand more force. If the force is towards the window, then the right will be stronger. The reason (from statics class 20+ years ago) is due to the normal distance from the fulcrum to the force vector . My head hurt just typing that.

Nitpicking I know, but what's the fun in a simple answer