Cuting a round edge in z axis

[curtesy]

newbie here!

I am trying to cut a round edge on a 2X4. The desired arc of the curve is one inch and I am using a 1/2 inch cove cutter. Plotting the travel in the Y and Z plane in 1 degree increments, I use a spreadsheet to calculate the sine and cosine of the bottom point of the cutter position in one degree increments. I create the sbp file and submit it to the SB. In preview mode, the round edge appears perfect, however, when the cut finishes, I wind up with a vertical (into the Z plane) drop of the edge. The finished product appears as if someone made a perfect round edge using a 2 inch rounding cutter and then cutting off about one inch, leaving a truncated arc.

The cutter position formulae (for the bottom point of the cutter) are:

Y = R*Sine(Theta)
Z = -RR-CR+R*Cosine(Theta)
where:
RR= the rounding radius;
CR= the cutter radius;
R= RR+CR.

Using the values of CR= 0.25 inch, RR= 1.0 inch and R= 1.25 inch, the position of the bottom point of the cutter at 30 degrees of travel for example is Y=0.625 and Z=-0.167.

I have tried different cutters, different values for the radii to no avail. Worse yet, when I transpose the formula to the X Y plane, the round curve is cut correctly. Only when cutting in the Y-Z (or X-Z) plane does this problem occur. Almost as if the robot modifies the horizontal or vertical movement when simultaneously cutting in Y(X) and Z.

Any ideas??

The attachment is the sbp file.
sbp file for rounding edge

4587 (7.2 k)

[curtesy]

An extra note, The SBP file reflects the original project, to wit, cut a fish hook groove in a drawer front to serve as a handle. I ran into the edge problem in the original cutting and am simplifying the problem.

ciao
Curt

[widgetworks_unlimited]

I don't see anything out of the ordinary - the cut file progresses smoothly without the 1" jump that you're seeing.

When you start the file you're safe Z height is 1". When you finish your cut, you're jogging to Z = 3". Is it possible that you don't have that much Z travel? (Or that you're hitting a software travel limit?)

[dana_swift]

Curt- there are only a few of us that regularly compute our own SBP files from mathematical models.

I cut rounded Z curves all the time based on my implementation of functions just like what you have proposed. It works great, so something else is wrong.

The only trick for doing what you are wanting is to be sure your plunge move rate is the same as the XY move rate. The way you are cutting the corner should not be concerned with that as Z plunges slowly anyway.

If you command Z axis to move 1" and it moves 1", and X and Y are likewise correct. You should get what you want.

Another thing I do is generate DXF "shape" files as a program output, import the DXF into Aspire and generate tool paths there. Writing a general purpose DXF generation library is non-trivial tho.

I have plotted your YZ profile as:


4588

For what its worth, discussions like this are usually found in the "Let's Talk ShopBot » Developers" section. But this will work just fine..

Sorry I cant be of more help- it looks like you are doing it correctly.

D

[curtesy]

Dana

Thanks for the response. I am going to rework the prog to cut a complete curve at one X and then move to a new X.

See if that works.

ciao
Curt