Posted: 6/24/2025 10:30:22 PM EDT
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What has everyone screwed up machining lately? I spent 2 hours this evening machining a little disconnector for a DPM FCG I'm making. It's supposed to be a little V shape piece at a 22° angle. Some machining, some fitting and .... It's no longer bent! Or usable! 
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Many years ago, I bought a Smithy combo lathe/mill. It was neither. That said we set about learning to use the thing. Our goal? Gunsmithing. Specifically building/customizing pistols. Mostly 1911s We obtained some brass plumb bobs, used in the local oil field to gauge tanks. They are about 1" diameter and 6" long. Perfect for our needs. Easy to cut and easy on equipment. After some learning on scraps, we actually mounted a set of adjustable sights on a plumb bob. Complete with rear and front sights, including dovetails. I had purchased a Norinco 1911 at a nearby gunshow. It was to be our first victim. We mounted it in the vice and measured not twice but several times. We spun up the 1/2" HSS 4 flute endmill for our first cut across the back of the slide. We chose 10 thousandths as depth for our first cut. I turned the cross feed dial and made contact. Nothing happened. I turned some more. The pressure became quite firm. Still nothing. Keep in mind, we had never actually cut steel, so I was unsure how much pressure was appropriate on the crossfeed. I pressed on, putting quite a bit of pressure on the tool and feeling it in the wheel. There was an EXPLOSION!. My friend and I both instinctively dropped to our knees. We were on opposite sides of the machine. The machine was still turning. I reached up and turned it off. I had put enough pressure on the cutter that it had failed catastrophically. 2 flutes were fractured off the cutter. Turns out that 1911 was made of AL2 tool steel and tougher than a pig's nose. The endmill was destroyed. There was the slightest scratch on the slide. So began out journey into gunsmithing After lots more study, we obtained carbide cutters and proceeded apace. We have built many guns since the ill-fated start to our hobby. |
Some face palms are forever
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My latest screw-up was an overload on steady rest bearings with a heavy electric generator rotor which did not have a center in the end of the shaft. Instead, the wound rotor lead wires protruded through the end of the shaft. The 5202 double row deep groove ball bearings failed rather spectacularly and scored the shaft bearing fit on which they were riding. Some repairs were then required on the rotor bearing fit and I had to resort to using a spider with bronze steady rest bearing pads on the spider. Other features on the shaft were not true enough to the bearing fit to allow direct contact of the bronze pads. Needless to say, the set-up to make the repair took longer than the repair itself. The rotor in question weighs about 3700 pounds. |
If I were a hedonist, I'd be a hermit.
You need a good airgun if you don't have one already.
You need a good airgun if you don't have one already.
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Not quite a machining screw up but I did ram an endmill through the fleshy part of my thumb next to the thumbnail by pinching it between an endmill and an MG42. Blood. Everywhere. The day before I managed to try to remove the pad of a finger with an MG42 bolt and receiver. This thing is out for blood! |
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D2 is pretty tough stuff even in annealed condition. Carbide cutter or HSS? Even annealed, it will chew up either one, but carbide sure lasts a lot longer. I was proofing a program on my CNC mill out in the garage and rapid'ed down into my part the other day... Editing program lines at the control... Luckily it was sitting in the vise with no parallels underneath and just pushed down, cushioning the blow a bit and avoiding any damage to the cutter. Part was even salvageable! Lucked out on that one. |
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I use both carbide and HSS depending on what cutter I need. I prefer carbide for most things. Fing fusion 360. Been trying to do a pretty simple path on the CAM side. I've done this path before. Well, it was using 40GB out of 32GB (overflow uses the herd drive as a cache) and had somehow written 370GB of data to the hard drive and still not managed to make a simple path in 8 hours. Ended up having to flush f360 and reinstall. Still won't make that CAM path. Was back up to 40GB used. Managed to kill it before it wrote more than a few GB more to the HDD. |
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Originally Posted By sneaker: Wow! How long of a program? Sounds like it might be better to break it up into a couple of separate programs. Or are you saying that Fusion is glitching out and making things way too big? It's fusion being a POS as usual. I've made paths of an essentially identical part in under 5 minutes. Hell, just a few days ago I made a path of that exact part. Fusion updated and as usual is crappier than before. I was very surprised to see it had eaten 400GB of hard drive with cache it refused to clean up. The part is maybe a few MB as a step on the flash drive I brought it over from solidworks on. Not a complex or large part. 17"x6"x0.375" with some slots and hole features. Takes about a day to machine one manually so I was hoping to make the CNC do the work and I'll just come back and tap the threaded holes when it's done. |
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Don't you hate it when you grab a tap, run it through a piece then thread a matching piece to find out the tap you thought you grabbed isn't the one you actually grabbed? Grabbed a tap, threaded the round center, set up the lathe, threaded one rivet support 1/4-20 to find out I used a 1/4-28 tap. So, I have one piece that works great and one that won't at all. I am an idiot. I get to make another. Rivet support for riveting MG42 rails. 
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Member
Joined:
Aug 2026
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MO, USA
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A few years ago. Showing off to my friend my new face mill and its delightful finish as I was making a set of 5 small parts. I needed to remove the base stock from them so with my new face mill why not just get it done in a few passes? Invert the parts in the vise, snug up and tap a bit to seat them. Get to talking, and I don't go at all past snug. Kick off the program and first two passes are great. Then the third pass we are talking and I step over to show him something on the screen which is thankfully off to the side. Suddenly there is a very loud buzzing noise and then a almighty "THWACK" and then just the sound of motors moving, no cutting. It had launched that part right out the front, into the insulation at my shop roof and then against and into the wall behind it. So had we been standing there a few seconds longer one of us might not be as pretty anymore. After that I'll use the facemill to get down to maybe 1/8" of bottom stock but I prefer endmills to clean up the last of it. That was one of those spooky moments when you remember its perfectly capable of maiming you if you get complacent. |