BUILD A
1/2 A
Engine
Page 1
First of all, you must love machining, model airplanes, or you're a sick puppy to be attempting this project, either way sometimes, we go to the extremes for our obsessions and I guess this is one of those times so, get out the mic's and lets make some chips.
Some machining experiance is required. A cnc mill is helpful,a lathe and a manual mill. You'll have to figure out how your going to do the exterior contouring if using a manual mill. There are twelve setups involved without having to add a few more so, I will only discuss the methods used for machining on a CNC except for the crank and bearing bores which was done on a manual lathe. Bearings are 1810zz and 166zz with shields removed.
The processes and setups used were established based on the machines I use and the time constrants. I do the work at a vocational school during the evenings so I'm limited to three hours per sesson, three days aweek. The CNC mill is a Bridgeport retrofit with Boss XT controler with no tool changer or spindle orientation.
Steps will simplified until I finish the whole project and see how much is left on the web page then I may add more detail.
Step 1: Obtain a block of 2024 and qualify to 1.740" tall x 1.250" wide x 3.750" long, keep those tolerances tight.
Step 2: Take the block and mill a 1" shank on one end. This is how I'm going to hold the part for some of the machining. In a CNC vise the part on end, 1.740" relative to the x-axis, set right edge to +.460", y to the center .625".Make sure to run an indicator, on the quill, to insure it is parallel, this is the bottom reference for fixturing and we want the shank concentric. Use a 3/4" end mill, shank is machined to 1" +.000/-.001 X 1.500" deep. This opp will also produce three flats for fixturing.
Step 3: To the lathe for turning the crank and bearing bores. You'll need a " M " porabolic drill, carbide boring bar .280 min X 3", 5/16 reamer, 3/32 full radius I.D. groover, single point threader or 5/8-40 tap.
Drill 2 " deep and size the hole by boring to about .305 x 1 3/4". Start boring for the rear bearing with the same, or larger bar, .4998 +.0001/-.0000 x .9695 deep, use the best hole gage you can get. I test the fit with the bearing, it's more of a feel because if too tight you'll crush the bearing outter race if you have to heat the case to install.
Bore the crank step .601 +.001/-.001 x .815" deep, the undercut for rod clearance with the internal groover, the backplate sealing surface .2185 deep x .800 , ream hole, and thread with min of 10 threads, 5/8-40.
