Kerf Compensation, CNC Router.

[Chris J Anderson]

Hi to All,

Sorry in advance if this is a dumb question...

When cutting out some mdf with say a 3mm tool, I'll need to obviously move the tool path out 1.5mm.

So what is the best method...
1- Compensate for the tool width at the drawing stage (for me in Corel, only doing 2D), or...
2- Compensate in my Planet-cnc USB Controller Software.

Also, are there any others on here using this software ?

Cheers,
Chris

[Art Mann]

I haven't tried the program you are using but any commercial product will provide a way of cutting inside the line, outside the line or in the center of the line in your drawing. My opinion is that if your design software doesn't have that feature, you need different (or maybe additional) software. I just read up on the software a little bit and it appears to be something like Mach 3 or WinCNC, which is primarily machine control software. There are low cost software products out there that will go between your graphics software and Planet-CNC. It might be possible to use only Corel and Planet-CNC, but I predict you will get very frustrated very quickly.

[Ted Reischl]

Cutter comp is really designed to allow the operator to make small adjustments for tool size/wear. The reason is that geometry can disappear when offset. An example is a notch in the edge. If it is .375 wide and you use a .5 cutter, the cutter comp may cause "undefined" behavior when it gets to that notch. It may ignore the notch altogether or do something bizarre. In any case, you don't want to be finding your "oops" at the machine. In this case the "oops" would be trying to use a .5 cutter to make a .375 notch.

[John McClanahan]

If the Planet-cnc software is creating the G-code from the Coral Draw file, you may get unpredictable results with offset. This is where CAM software helps you out. It allows you to choose cutter diameter and shape, set the offset, cut direction, depth of cut per pass among other things before the G-code is created.


John

[Chris J Anderson]

Thanks to all above for your responses, I do appreciate your time..

I've loaded / licensed / updated the CNC software, which was a breeze, and imported a dxf which then simulates routing nicely on the screen.
This USB CNC Controller software looks to be pretty simple to use.

I use Coreldraw for design, and can easily create the tool / kerf offset using the contour tool, then export the dxf.
I'm only doing 2d designs at this stage so it should be fine (I am happy to be told / warned otherwise).

In the CNC software, when you import a dxf, you are prompted for the number of passes and plunge depth at each pass, then it goes on and creates the Gcode.
So I think this pretty much covers what I want to do with simple trophy bases and shapes in MDF.

Having read the above, would you have any further concerns ?

Thanks again,
Chris

[Art Mann]

Before you dismiss more capable software as being unnecessary, you really need to familiarize yourself with what you will be missing.

[Ted Reischl]

Eventually you will want to pocket something. . . . .doing that with Corel would be a royal PITA. I love Corel, use it for all my design work. . .but use it to create toolpaths? Nahhhh.

[Chris J Anderson]

@ Art,
Yes, I'm aware of that mate. I'm a newbie with this router stuff, and once I start using it I'll become aware of whats lacking in my simplicity I'm sure.

@ Ted,
I'm sure I'll agree with you later, once I learn what a pocket is (going to search now), presuming is a shape cutout thats not all the way through the material.

Thank you both for your comments.

[Chris J Anderson]

Hey Ted,
I've looked at pocketing, for dowels etc.

I'm presuming you are mostly concerned with the ability to do multiple plunges to drill / raise to eject swarf / repeat at increasing depths ?

Cheers,
Chris

[Bruce Page]

Chris, here's a little coat rack I recently finished for a friends grandson. The black areas of the wolf head and paw prints are pocketed .075 deep. I'm sure it is possible, but using cutter comp or offsets to generate the inside and the outside profiles would be an exercise in frustration, at least for me.

[Chris J Anderson]

Thanks Bruce,
Yes I can see that would be a pain to try and do with manually coding after generating a dxf.

However my files will be simple cutouts of say a horse head, outline only on mdf.
The only addition to that would be a chamfered edge which would be simple.

I now understand how pocketing would be complex, and if I ever need that ability, I'll look at vcarve etc.

Thank you all for the answers above, I'm learning the limitations of my setup thanks to your feedback...

[William Adams]

There's a glossary on CNC terms here: http://www.shapeoko.com/wiki/index.php/Glossary

Corrections, suggestions or additional terms would be welcome.