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Every Wonder How a Part is Made? Well Here is Just One Way...
This is a total “What I looked for as a beginner but never found page”
Step 1- Think About Your 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? 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?
Step 2- Draw the Part in CAD
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.
Step 3- Offset the Part
NOTE MOST CAM PROGRAMS HAVE TOOL COMPENSATION
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)
Step 4- Convert to G-Code
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.
Step 5- Check the G-code
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.
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, and not in the way, use it.
Step 6- Setup the Machine
You will need to tell the machine where to begin. Remember,
your part will get cut out exactly as it looked on the CAD program so know where
your "origin" is. For our little machines, put the cutter at 0,0,0 and start from
there. One easy way to do this is to loosen the cutter, bring it to the work piece,
move Z down just a bit more and THEN tighten the endmill in place. Don't forget to
"zero" out the machine before running your program.
NOTE: I sometimes run a few lines
of the program above the piece to make sure the machine will not crash into anything.
This also gives me the opportunity to make sure the part seems right and I did not
do something wrong.
Remember, once its begun it's all over :)
Step 7- Watch and Check the Machine
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.
Step 8- Deburr and look at final piece!
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
Step 1- Think About Your 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).
Step 2- Draw the Part in CAD
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.
Step 3- Bring into your CAM program
Here you can see the part in the once free version of Visual Mill.
Step 4- Setup Roughing Toolpath
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.
Step 5- Setup Finishing Path
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.
Making of a 2D (really 2.5) Part
Making of a 3D Part
