Todays Project - What did you do today?

[PixMan]

My day was (as will be obvious) a case of proving out a series of steps to make a tricky little part for a rifle sight assembly. I learned what I can and can't do, so Version 2 will be fine.

I started by lopping off a short piece of some AISI 4142 annealed steel I have been holding onto for some time. I chose this because the part has a lot of material removed and a slot through a bore that could either spring open or collapse if I used the 1018 cold rolled steel I have.



The stock is 1-1/4" x 1-7/8", but I only need a piece big enough to finish at 1.020" x 0.875" x 0.500". I made short work of bringing it down, using a combination of my 3" 45º face mill, my 3/4" 3-insert end mill and a 3/8" solid carbide end mill. I left it a couple thousandths oversize and used my surface grinder to get it (very nearly) perfectly square.



Back onto the CNC Prototrak mill, I first ran the periphery oval shape, noting a slight deviation from full radii at one quadrant where a 120º angle comes off the tangent point to leave a small flat on one side of the oval 1.020" x 0.500" x 0.25" thick section.







After drilling the two holes (one 0.315", one 0.251"), I added the 0.030" radius notch at -21º as noted on the print. I couldn't help but notice how all the chips came off magnetized and stuck everywhere.



I spotted the holes with a 1/4" 90º spot drill and finished the holes as best I could without the benefit of exact size reamers (now on order), I thought I'd just touch the edges of the holes with a countersink. This is where I found a major problem! Either the holes landed out of position, or the countersink did. I think it's actually BOTH. I am worried that after nearly 5 hours of run time something in the DRO portion of the control skipped or mistracked somehow because my readout said I was at X-Y ZERO. The center of the 1/2" bosses served as my X-Y zero datum, so I don't know what went wrong.

I finished the second side and the slot anyhow, to prove out the rest of the process. Would you know it, hindsight is 20-20 because as soon as I finished the slot I realized that I could have and should have simply used a 1/2" collet in the lathe to finish turn the second side and make the Ø0.315 bore. Oh well. The Version 2 will be PERFECT. I should be able to get back into the shop on Friday, because I'm definitely NOT a "black Friday" shopper!