I'm going to post the last piece early in the event that someone has the week off and might want to
try to make one over the holidays.
I changed up the design so the entire cylinder can be made CNC except the cylinder hole. It will still need
to be drilled and reamed. I also wanted a more modern look to go along with the more modern looking base
and standards. Glue up 3 pieces 1-1/4 X 2-1/2 long in the vise and let them set for 30 minutes. This code
will handle a 2-3/4 X 1-1/2 stack. I also tried to cut the entire stack away in the roughing stage so cutting
slots like the flywheel to control the scrap wont be nessessary. When ready, mill the stack to a thickness
of 1.188 inches.
Load the CylinderBottom program. Center of the stack is X0,Y0 and top surface is Z0. The program will center
drill and drill 2 holes. The hole closest to center should be tapped #8-32 before moving on. Use a bottom tap
and get as much thread as you can in there.
After threading the 1/8 inch endmill is loaded and the bottom of the part is cut to completion. Make sure your
endmill measures .125. I have purchased cheaper endmills that were as small as .122. Not a big deal when
milling in manual mode but when in a CNC machine you can see where a circle will be .006 to big.
Now check the diameter of the 1/2 inch long shaft sticking out of the bottom of the cylinder. If it will not fit
into the hole in the standard, there are a few things you can do. You can get into cutter compinsation using
Mach3 but this is supposed to get the newer folks cutting. Mine were to big to sand or file so I went to the
next size drill and redrilled my standards.
The shaft is then cut to a length that equals the thickness of the standard. If you miss, make it a bit shorter
rather than longer. Dont want the shaft sticking out the other end.
This part is made using a fixture like the flywheel. I forgot to get a shot of the fixture but it a simple corian
fixture with a hole in it. When making the fixture I had to use the same drill bit that I used to redrill the
standards. Things like under sized cutters and backlast can have an effect on how the part will fixture so
be aware. The part is set into the fixture and secured with a single screw from the bottom.
The ball end mill is the only tool needed to cut the top. Load the CylinderTop program and touch off the top
of stock to zero Z. Like the flywheel, do not change or zero X and Y axis. I made the code for this side less
agressive because the part will be held in the fixture by only one screw. It will take longer to cut but
increase the odds of nothing bad happening while cutting.
After all the cylinders you are making are cut, use the fixture to hold the cylinders to drill and ream the 1/2
inch hole for the piston.
That's all you need to build the engine. When you assemble the engine be sure not to over tighten the screws
that hold the cylinders onto the standard. Use a real light oil to lube everything. The only 3/16 ID tubing I
could find was 5/16 OD but it doesn't look to bad. Make sure the engine turns freely and put a little air to it!
Hopefully this exercise has taken the mystery out of setting up to cut a piece and was of doing simple setups
to speed up making multiple pieces. If you have a CNC mill but have not run it in automatic, download the
code, get a few pieces of corian, go out in the shop and break some bits! Once you get going the errors become
few and far between and it keeps getting easier.
Here is a video running slow on less than 1 pound of air.
[ame]http://www.youtube.com/watch?v=f2uGxEHwLsI[/ame]
This thing flies on just 4 pounds of air.
[ame]http://www.youtube.com/watch?v=99_zorw5Zjg[/ame]
Cheers!!
Steve!
View attachment CylinderBottom.tap
View attachment CylinderFixture.tap
View attachment Cylinder.pdf
View attachment DoubleCylinder2impTop.tap
