Milling vs Cutting

[buddym]

Time for me to revist this topic.... I use mach3 to run my DIY machine... I draw 2-D parts to cut in cad program xxxxx and then convert dxf to g-code. It works for my limited purposes so far but it seems to me I am cutting parts, not milling parts My g-code looks like line plots to cut 1 or more tool paths to match the line art I draw in cad. This brings me two problems: first, I can find no way to tell the machine to "cut away" material to leave my part as drawn, where the tool is moved to remove material and leave my part in the desired dimensions. Instead, what I get is a simple x-y path that cuts along the center of that path. This results in a part that has tom be scaled prior to cutting in order to have the part come out the right size. If my tool path could be generated to cut the material away from the part, it would seem then that the part would be the correct size when finished, without regard to the tool diameter other than the offset required to avoid letting a 1/4" tool cut into the material.

The second problem is that this style of cutting limits me to 2-D so I can't cut different depths, (like screw pockets that are only 1/2 as deep as the material) without manually editing the z in the g-code. This would seem to more a limit of my experience and skill level with CAD and g-code conversion than a problem with the programs or machine.


All of this does get to a point, which is this question... with cad, say bobcad, turbocad, etc, mach3, and my x-y-z mill, how do I draw and cut parts that are 3-D and don't need manual scaling to keep the parts from being affected by a toolpath that cuts the "center" of a line?

Thanks,
Buddy

[mc-motorsports]

You need a better CAD/CAM package. I use RhinoCad and RhinoCam, costs between $1800 and $5000 depending on your CAM options. MasterCam is the only other CAM package I would concider, but it starts at $6k and as of right now, Rhino does everything that I need. The only thing that MasterCam has that I could use right now would be high speed milling opps of 2d profiling paths. I can program high speed milling opps for 2d and 3d pocketing or 3d horizonal roughing, but I'm stuck with the simple 2d profiling opps.

[mc-motorsports]

Just to add to this, sounds like the CAM program your using now is freeware or shareware and just programing a tool path based on the curves that are drawn? It probably expects you to draw the tool path and not the part.

Try downloading FreeMill from MecSoft.
http://www.mecsoft.com/freemill.shtml

[ger21]

Originally Posted by buddym This brings me two problems: first, I can find no way to tell the machine to "cut away" material to leave my part as drawn, where the tool is moved to remove material and leave my part in the desired dimensions. Instead, what I get is a simple x-y path that cuts along the center of that path. This results in a part that has tom be scaled prior to cutting in order to have the part come out the right size. If my tool path could be generated to cut the material away from the part, it would seem then that the part would be the correct size when finished, without regard to the tool diameter other than the offset required to avoid letting a 1/4" tool cut into the material.

What you should be doing is offsetting your lines in your CAD program by the tool radius, which would allow you to get correctly sized parts. Your next option would be a good 2D CAM program, that'll do the offsets for you. Vectric's Cut2D and SheetCAM are two good ones, both under $200

The second problem is that this style of cutting limits me to 2-D so I can't cut different depths, (like screw pockets that are only 1/2 as deep as the material) without manually editing the z in the g-code. This would seem to more a limit of my experience and skill level with CAD and g-code conversion than a problem with the programs or machine.

Cutting to different depths is typically done by drawing on different layers in the CAD program, with the different layers being assigned different depths. It depends on what you're using for g-code conversion, but even the free ACE converter let's you use multiple depths of cut from a single 2D .dxf file. It's all in the layers.


If you put some thought into it, it's actually possible to do some really complex parts with a 2D .dxf drawing.

All of this does get to a point, which is this question... with cad, say bobcad, turbocad, etc, mach3, and my x-y-z mill, how do I draw and cut parts that are 3-D and don't need manual scaling to keep the parts from being affected by a toolpath that cuts the "center" of a line? Thanks, Buddy

As was mentioned, the cheapest way is Freemill. Also look at www.Meshcam.com and Vectric's Cut3D.

[Riceburner98]

Originally Posted by ger21 What you should be doing is offsetting your lines in your CAD program by the tool radius, which would allow you to get correctly sized parts. Your next option would be a good 2D CAM program, that'll do the offsets for you. Vectric's Cut2D and SheetCAM are two good ones, both under $200

^^- what he said! I've been doing it this way for years now. Just do a "contour" / offset line around the line where you want to cut. I have BobCad but never bothered learning how to fully use it; I still draw my parts in the free "emachineshop.com" software then just use BobCad to generate the G-code from the lines I drew. Draw the part, then "contour" say .125" for the toolpath, then just export only that toolpath as a DXF and convert it to G-code. I'll usually throw in another .01" contour outside as a rough pass, then use the .125" as a finish pass. I do some pretty complex parts that way. I always go over the G-code by hand to clean it up and optimize it, so that's where I adjust my depths as well..

[buddym]

Tha sounds great, thanks very much for all of the help. I had one other question: Does the contour only apply to the outer perimeter of a part? What I mean is if I draw a part with cutouts in it, does the CAD automatically know not to cut away material it's not supposed to? Say if I had a 4" x 4" square part, with a 1" x 1" hole in the center...and I configure that CAD to do outside contour, will the CAD generate code that will contour the perimeter of the part but still cut the 1" hole the correct size?

Thanks again,
Buddy

[Riceburner98]

It will only cut away what you tell it to with your toolpath. If the toolpath is only the outside contour, it would only cut that. (making sure you lift up your Z axis before moving anywhere else of course, so you don't plow through material when you do a rapid to move away) To cut the inside hole, you'd just do a "contour" on the *inside* of the line that makes that hole. So then you'd tell the G-code program to cut that toolpath also. I guess it really depends on what you're using to generate your G-code, and how automatic it is. The way I use BobCad I select one toolpath (say, the outside of the part), then hit "convert" then go down a few blank lines, select another toolpath (that inside 1"x1" square) and hit "convert" again so it does little chunks of code for each toolpath. Then I go in and manually add in my Z up and down's and change speeds and such. I'll usually put those chunks into a subroutine that I can call a few times dropping the Z .02" or so each time. (M98 P100, etc..) I started out doing all my G-code by hand before I was suckered into buying BobCad, so I wrote a lot of G-code by hand for 2D and 3D parts.

[buddym]

So my current method....draw part in simple cad, import into mach with lazycam, generate g-code is less than ideal you would say? Seems I need a bit more HP on the cad side of things to get toolpaths correct and not use lazycam to generate the g-code at all, but rather let the CAD program do it?

Buddy

[Riceburner98]

Actually, that sounds about the same as I do it.. I haven't personally used lazycam so I can't say how it works, but it sounds like that's basically the same as what I do with BobCad for "CAM" / G-code and the free Emachineshop program for my CAD. Does your CAD program allow you to do "contours" where it pops a line out .125" (or whatever) distance from the line you pick? If so, then it sounds like you should be OK.. Just generate that line (which will now be your toolpath) then import that into lazycam and use that line to generate the G-code instead of the line that's your actual part drawing... I'd post a picture but I'm not sure how..