# Thread: Spiral tool path from two circular motions

1. ## Spiral tool path from two circular motions

Dear MASTER CAM wizzards,

I have a rotary displacement Patent which is being machined for prototype.
Unfortunatly our shop partners who know MC like the back of thier hand, cannot set up the cuts needed for our displacement chambers.

The attached files illustrate that we need to describe a simple circular tool path in the X,Y plane.

At the same time and in ratio, we want the table holding our part to rotate 180 degrees.

I think this could also be done by combining both motions into one tool path of combined rotation.

Either way is fine, and a Master Cam rep told me this was possible. I do not have the language of MC to set this up for our shop guys.

Do they have a chance? We know the geometry is correct since a rapid prototype was done and I made a lathe attachment mechanically reproducing what we need.

Any help is appreciated! sj

2. is the cutter rotating as it helical mill down? who is the Mastercam rep? it looks to me like it can be done if the cutter stays stationary and just follows the arc. Is there a pitch for the shape?
Steve

3. ## Pitch=60mm

Steve, by the way that is my name too,

Yes there is a pitch=60mm between crests. So quite coarse. This is necessary to have wide chamber walls defining a closed space which the blue thing (drive plate sweeps through).

It is hard to get your meaning of the tool remaining stationary while following an arc. But I think you get the idea. It really needs to follow a full circle in the X,Z plane. There will only be chips flying for 120 deg. so you are right about the arc.

Question is: how does one program a circular tool path and its axis?

While this takes place would we rotate the table by degrees or cutting speed?

The rep I spoke to was Brian at Mac Dac.

-steve

4. you will need to draw a helical shape exactly like you see it and drive the curve with a 3-d contour. draw the one for the bottom of the tool to follow the side cut will form with the bottom cut. if the insert is stationary.
Steve

• Does this invention fulfill a special niche? It looks like it will be a bear to make the drive plate seal, unless the path is perfectly smooth (probably have to be hardened and ground) and even then the sliding component of friction looks to be substantial. Reminds me of tip seal problems in the Wankel engine.

• Steve,
That is helpfull. I was defining the path of a ball end cutter by it's center. So instead, I should draw the bottom points in a contour path.

It is a 3d model but I can make a series of x,y,z points with values. The model was actually lofted from a series of 2d circles at each 20 deg. position.

That is what I gather from your instruction 'to draw the helix'.

Thanks

• Huflung,

Yes, the displacement will be used for hydraulic pumping initially. It will move a very large volume per rotation.

After that we will be trying pneumatic motor/compressor operation that will lead to engine configurations.

The seals are an issue. A couple things are helpfull though: The direction dosent reverse, so one way sealing is easier. Also, there is going to be oil ahead of each Drive Plate backing up the seal.

For pumps, the sweep of a single drive plate acomplishes both the intake and exhaust stroke. As an engine, two cycles are completed simultaneously.

Friction will depend on how tight we try to keep the seals. At high speed this is less important. Think of the chambers as guides that duct the blades of a turbine. The air flow will be mechanical rather than aerodynamic.

• Have you researched a machining concept called thread whirling? I'm not dead certain how it works even today but it might be an avenue to look at from a production viewpoint.

http://www.productionmachining.com/a...s-in-town.aspx

Some videos available on Youtube as well.

• Well if you fail to make any money with your pump/motor you will not be lonely.

You do have one of the more interesting and challenging means of gating the piston from one section to the next.
But the twin screw is hard to beat.

A long line of positive displacement rotary engines.
http://www.dself.dsl.pipex.com/MUSEU.../rotaryeng.htm