studysession

Hi -

I am new to CAD programs and need some help. I draw a part in my CAD program. Now I want to cut it on my CNC Mill. Attached is a pic of my mill and a pic of what I want to cut out.

The milling bit I want to use is 3mm in diameter. When it goes to cut a line it will now cut 1.5mm extra material off each cut. How do you compensate for this? I know there has to be away to do it without making the drawing bigger. I would appreciate any advice to help.

Many thanks!!! Keith H

CoosBayLumber

My Feedback: (1)

I had been using a bit of freeware software obtained from CADALOG a few years ago. The mill I work with operates using G-code. The freeware was called DWG2G. You have to set up your drawing such that the lines run the proper direction.

(For those not too familiar with Autocad or the such, the lines shown DO have a direction)

I then went through the conversion process. Afterwhich it asks for EXACT cutter diameter, for which it will offset. You can reverse the direction of all of the lines in the file, not a few.

Then, you have to add in by hand the cutting depth, tool speeds etc. If you know G-code, this ought not to be a problem. About only thing nice with the abbreviated program, is that it calculates all the curves, but you have to set the BASE point and slip over the figure in CAD before going into the conversion, or it will begin cutting off some place away from your metal.

Wm.

Highflight

My Feedback: (4)

True, but on parts where there's only a single outline, I find it easier to draw the entire outline of the part as a single PolyLine, and then simply OFFSET the line to accomodate the cutting tool (by exactly 1/2 the diameter of the tool).
Either way works.

Highflight

studysession

I think there should be a way to do it in the CAD program. Just not sure how.

I do also own a copy of AutoCAD. Do you know how to tell it to compensate for the diameter of the tool?

Thanks!!

Highflight

My Feedback: (4)

Nope.
You have to understand that you don't go directly from CAD to your CNC machine.
You have to churn an outputted .dxf file from your CAD program into software that converts the entities from the .dxf file into G-Code. Then, you run the G-Code file with the software that drives your CNC mill.

I "sort of" do what you are asking in AutoCad by offsetting my Polyline by half the diameter of the tool, but that's sort of cheating (although it works). But I then still have to do what I described in the preceding paragraph.

Highflight

studysession

offsetting my Polyline -- What do you mean by this?

As for the dxf to GCode - that is what the software that controls my mill does. I take a dxf file and load it into Mach2 which is the software that controls my mill and it converts to GCode then. I can do a lot there. But need help with this area.

There is way to much to learn.

Highflight

My Feedback: (4)

Mach2 is simply a program that does both, convert to G-Code AND run your CNC machine. There are some programs that are more specialized that may only do one or the other so you're good to go.

OFFSET is the actual command used for offsetting the polyline. In AutoCad, you just invoke the OFFSET command, you are then prompted how much you want to offset, then you are asked to pick the line (polyline) you want offsetted, and then you click again on whichever side of the line you want the direction of offset to be.

If, for example, my cutting tool is .125, I would OFFSET my polyline by .0625 to the OUTSIDE of the outline of my part. That way when you run your .dxf export and run it through Mach2, you don't have to worry at all about tool diameter (set it to "0" if prompted) because what's going to happen is that your CNC machine will track ACTUAL line at it's center, and since your line is already offset by 1/2 the diameter of the tool, your accuracy will be maintained.

I cut quite a few templates each week (for work) and by doing it that way, it's quick and easy as long as I don't forget what cutter I'm using. Of course, if I want to cut the same template but with a different size cutter, I'm screwed, but for me, that's not a problem.

Highflight

studysession

OK - this makes a lot of sense. Now is OFFSET something I type in and how does it know which line I am refering to when I use it?

studysession

OK found the OFFSET command. Now it shows 2 lines. How will the mill know which to cut? I am going to now export it out of AutCAD as a DXF file and see what happens on Mach2.

Thanks!

studysession

OK - I have some questions again - I think I answered all the above questions and found the OFFSET - just need to know something.

Do I delete the original lines or do I assign the new lines to new layers so the mill will ONLY cut out the new lines? Hope that makes sense.

Now another question since you seem to be a lot more familiar with AutoCAD than I. I bought the AutoCAD for Dummies book and been going through the help files. How in the world do I turn on a grid that shows every mm apart. The items that I am going to mill are very small and need to easily measure 1mm and 1.5.. etc

Many thanks for all the help.

studysession

OK - I have a bigger grid now. WOW! AutoCAD is not as easy as SolidWorks for getting the simple things done. If I knew how to do the OFFSET thing in SolidWorks I would just use that. But have no clue how to do it in SolidWorks.

Now just have to figure out how to tell Mach2 which set of lines to cut when i use the OFFSET command???? Thanks for the help!

Highflight

My Feedback: (4)

All you do after you've done the OFFSET and have your newer outline is to erase the original inside line. That's it, go cut just the remaining OFFSET line.

Highflight

studysession

Cool thanks!

studysession

Thanks for all the help - Everything was right on except for center hole. I was off just a tad. I could not of done it without your help THANKS!!!

As for the hole I dremeled it out a bit. I now need to figure out how I will mount the batteries. Tell me what you think.

Highflight

My Feedback: (4)

I would think that velcro would do the trick for the battery packs. Make the area of the velcro patches large enough to hold them secure but small enough to be able to remove and replace them without tearing the packs apart.

Highflight