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Offline Bill_O

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oscillating tangential knife
« on: October 26, 2009, 02:45:58 PM »
Has anyone made a oscillating tangential knife? I have made the tangential knife but now I need to make an oscillating one.

Bill

Offline Dan13

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Re: oscillating tangential knife
« Reply #1 on: October 26, 2009, 03:37:25 PM »
Bill,

What is the oscillation frequency required? There are two ways you can do it depending on the frequency required. Either mechanically, by rotating an offset weight - good for low frequencies and very easy to make, or electrically, by putting a ferromagnetic iron core inside a coil through which an alternating current of a desired frequency is flowing. The AC current causes minor dimensional changes in the iron core as it reverses polarity which makes the oscillation. It is good for high frequencies, but requires a cooling system, as it rapidly gets hot as it oscillates.

Daniel

Offline Bill_O

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Re: oscillating tangential knife
« Reply #2 on: October 26, 2009, 04:32:09 PM »
I do not know the exact frequency but if you look at the link below you can see what I am talking about. It is moving up and down very fast. I would not be surprised if it was 50 or 60hz.

http://www.comagrav.com/oscillating_tangential_knife.html

The travel only needs to be 1/16 to 1/18 inch.


Bill

Offline Dan13

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Re: oscillating tangential knife
« Reply #3 on: October 27, 2009, 03:39:08 AM »
Well, can't really see it oscillating ;)

By the sound it makes I'd say it oscillates at a frequency around what you suggested. I think it should be very easy to make. Just use a cam wheel and calculate the required offset to give the desired travel. A small DC motor with speed control drive the cam wheel. Since you don't know the exact  frequency, you can use the speed control to change frequencies and adjust it till you get good results.

Daniel

Offline Bill_O

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Re: oscillating tangential knife
« Reply #4 on: October 27, 2009, 09:31:41 AM »
Daniel,

It is kind of hard to count. ;D I was just taking a guess. I can design a mechanical system but I am worried about longevity. I like the idea you had about using a coil and magnet. How would I go about figuring out what I need to do that?

Bill
Re: oscillating tangential knife
« Reply #5 on: October 27, 2009, 11:03:20 AM »
Says in the description....3000 per minute for the electric model.....if I'm reading it right.
The pneumatic model is proboably like a handheld air chisel, where you can regulate the speed with air flow and pressure.
Just a guess though.
RC

Offline Bill_O

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Re: oscillating tangential knife
« Reply #6 on: October 27, 2009, 11:19:32 AM »
I did not think about something like an air chisel. I was still thinking in terms or an air motor. I will have to do some looking for things like air chisels.

Thanks for everyones input.
Bill

Offline Dan13

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Re: oscillating tangential knife
« Reply #7 on: October 28, 2009, 08:16:33 AM »
Bill,

The other idea i mentioned it not suitable for this application, since its movement amplitude is very small - in the range of microns, and it usually used for ultrasonic frequencies.

There is another, very simple way to achieve what you want though. You can build a simple device based on a solenoid principle. Use an electromagnet powered by an alternating current to alternately pull and push a small permanent magnet located in a tube of some kind. You could even use two electromagnets with 180 degrees offset phase on both ends of the tube to enhance the power.

Another variation of this would be using a simple electronic circuit (that can be achieved even with merely the mechanical parts of the design, without a single electronic component) to alternately power on and off an electromagnet that would pull a piece of steel loaded with a spring - as soon as the magnetic field disappears the spring will pull the steel piece back. I would go with this design. It is very easy to design to achieve the required amplitude.

Daniel

Offline Bill_O

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Re: oscillating tangential knife
« Reply #8 on: October 28, 2009, 09:38:05 AM »
Daniel,

Thanks for the help. I have a guy here that is good with the electronics side of things and will talk to him about making our own solenoid. I will go ahead and look at the mechanical side sense that is my strong side.

Bill

Offline Dan13

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Re: oscillating tangential knife
« Reply #9 on: October 28, 2009, 12:17:09 PM »
Bill,

The simple version I mentioned doesn't really have any electronics. The mechanics takes care of the electronics. See the picture: when you close the circuit with S1, the electromagnet pulls the steel strip which immediately opens the electric circuit (S2) and disables the electromagnet, allowing the steel strip to spring back and close the circuit again, and so on...

It hard to predict the frequency with this design though, depends on the coil inductance and the core iron bar, as well as the steel strip. But it's easy enough to make and experiment.

Then, as I said, you can use a simple electronic circuit (based on a 555 IC or the like) to control the ON and OFF time intervals and frequency of the electromagnet power.

Daniel