Netters, Since I've been making and selling chromoly aircraft parts for a number of years, I'd like to weigh in on this discussion:
My experience with laser cut chromoly parts is that the cutting process leaves an area of hardness near the cut that can only be cut with carbide tools. (I learned this by destroying a new HSS "F" reamer on the 1st hole). The thickness of the material affects the depth of the heat affected zone: the thicker the steel, the further the hardness extends from the edge of the cut. (On 1/4" plate, about .040 from the edge of the cut will be hard). On a batch of axle base plates I had laser cut, I found the heat affected zone so difficult a problem that I sent the plates out for heat treatment before I continued with the machine work. (The center hole in the base plates has to be bored for a press fit with the axle tube and the laser cut surface was so hard my carbide boring bar was bouncing off!) I have gone back to fabricating my axle base plates in-house. I rough them out on a 7" x 12" metal cutting band saw that has flood cooling, then mill them square. The bolt pattern holes are drilled using a drill fixture and the large center holes are bored on the lathe. The axle tubes (7/8" x .190 wall chromoly) are pressed in and then TIG welded. The axle blanks are heat treated to RC 30-34 prior to machining the bearing journals and threading the ends. The threading is done on the lathe. If I was going to make up a set of WAF's one-off, I would have them water jet cut with the bolt holes about .010 undersize and then ream the holes to size. If I were to do a production run of WAF's and wanted to have them laser cut, I'd have all the holes cut .010 under, heat treat the blanks to RC 30-34, ream all the holes to size (including the lightening holes), dress the long edges on my stationary belt sander, and then tumble them! Note: at RC 30-34, you can use HSS reamers and counter sinks, carbide tools are not required. 4130 in the "N" condition has a tensile strength of about 90,000 psi; at RC 30-34 it will have a tensile of 130,000 to 140,000 psi and still be ductile enough to be bent to shape. (That's a 50% increase in strength!) Regards, Tracy O'Brien www.tracyobrien.com
