Basic Overview of Making A Part

-Basic Overview of  2.5 D Part-

Will it have curves or straight lines? Will the connections be curved or at some angle? Will it have holes? If so, where? How deep? Will they be tapped, all the way through or just part way? Are there going to be different heights to the part, if so which ones should get cut first? What size cutter are you going to use and will it be able to cut the detail? What material are you planning to use?

Are you going to use only one endmill for the entire process or will there be two? Flat, ball, or other?

How are you planning to machine the part and not hit the mounts that hold the material. If the material that is being held needs to be machined, how are you going to remount the part and not lose its place?

Draw the part in CAD. Try and make sure your lines connect at each joint or the converting program will think of them as "two lines." This will make for 2 extra movements on the Z axis. If possible "join" multiple lines into one. Also, draw the part with one point at "0,0" so you have a reference point when your ready to cut your part. Check to make sure you don't have any extra lines at the joints as these will be converted into movements.  

Remember, you get what you see, so take the time to draw your part right.

The milling machine does not know what size cutter your using until you tell it. It will "trace" the CAD lines and the toolpath must be offset 1/2 of the cutter diameter. You will need to figure out if your converting program will do this for you. If not, which way will the offset be placed so the finished part comes out correct. Notice in the picture, I moved the "offset" path to 0,0 (origin) so I know where to line up the machine for the part later. Also note one of the toolpaths is not offset. 

Again, you get what you see, do it right.
(Note: Your CAM program may do this for you)

Depending on your converting program, it may convert putting in tool path offsets and randomly, shortest path, how your CAD drawing was made, by layers, by the direction of your CAD line, by the way you pick the lines, etc.

You will need to figure this out as well as your cutting speeds and plunge rates. If your program asks for a "min lift" or "min distance between lines" put in the radius of your endmill (again this is where making sure your lines join is helpful) so you don't get extra useless moves.

 This is a good time to add whatever else you need to the G-code such as; name of the part, endmill size used, dimensions of the part, spindle on/off, units, material, etc. 

I always like to check the G-code to make sure it is correct and the part looks correct.

  Make sure there are no extra lines or cuts shown that you did not expect. Again, you get what you see so take the time to do it right.

  If it works, it's secure, and not in the way, use it. 

Make sure things are going right! I have found keeping the chips out of the way of the endmill just as important as using cutting oil. I generally use WD-40 on aluminum and use a straw to blow the chips away (now I have a blower setup :). 

 Change the feedrate as needed and remember it for next time. Make sure the part stays securely mounted and the machine does not hit its endpoints or any of the holding mounts.

In the picture the aluminum is slightly sanded and cleaned with denatured alcohol, then super glued to a wooden block which is held in the milling vise. Worked out great. 

Here are the finished parts. Each is drilled and tapped for  specific screws and the bearing fit is very tight! The parts are slightly buffed to give them a mirror like appearance, a bench grinder with a buffing wheel and proper buffing compound is incredible for this. The edges of the piece are slightly sanded or I use a bit which I run along the side to give it a slight bevel. You could program the machine to use a different endmill (ball endmill) to touch up the edges for that look. (Buffing will also smooth the edges quite a bit).
7-30-02

-Another Example of a 2.5D part-
RC Foamie Airplane

- Basic Overview of 3 D Part - 

You need to figure out what you want to make and its shape. Will it be designed for pure functionality, simplicity, artistry or a little of each? 

3D parts are usually drawn with a file extension of .stl. You will need to see if your CAD program can save in this extension (there are others, just check). Make sure you know what size your part is going to be and remember the smaller the endmill used the more detail you can have (this of course means longer machining time). Also remember not to undercut the part, since the machine will not be able to do that (not these at least).

Draw the part in CAD saving in a 3D format, usually .stl. One thing to make sure is your part is not smaller at the bottom then the top. Remember our little machines cannot cut under that part. Even if you have an undercut the CAM program will not pick this up as it will "drape" a toolpath over the part. 

Remember, you get what you see, so take the time and draw your part precisely.

Here you can see the part in the once free version of Visual Mill. 

3D parts are "rastered." This means parallel lines are put all over the part and the machine follows them. Depending on your program this can be very simple or very sophisticated.

To decrease the time of machining 3D parts are sometimes "rough cut" first and then finished with a finer tool. Above you can see a roughing toolpath using a larger endmill.

If you plan to do this you must make sure the different endmill lengths (mounting) are consistent in the Z axis. You may need a place where the machine goes when you need to change to the other endmill. Or you could use two holders where the endmill are mounted at a predetermined length.  

Here you can see a finer finishing pass. Again the CAM program puts parallel lines over the part and this is called "rastering."

Depending on the part you may need more then rastering, like contouring in 3D. For example, if you want to cut out 3D letters, or letters on a curve, rastering would not be the most efficient way. You would want to cut out the letters then have the machine make parallel lines over them. So again, the process of 3D is can be very complex.

Step 6- Mount the Material

This is probably the hardest part of machining. How exactly should the part be held securely without adding extra nicks and dents from the mounting items. How about making sure the machine does not crash into the mounts, etc. I have found double side tape and superglue to be very helpful in holding many parts. A milling vise is a must, step down blocks a life saver and scrap pieces of wood and metal helpful.
  If it works, it's secure, use it.