Thanks Carl and Bill
I need to convince my bosses I need a holiday...
Had a five hour shop session today. The connecting rod looked like a good candidate to start work on, so I dug around for stock to make it from. A while ago I was given a piece of 20mm mystery steel bar. It was lying amongst some printer shafting, and while the printer shafting had started to rust slightly, this bar didn't have a single spot of rust on it. And compared to some shined-up silver steel, it has that little "extra whitish shine" that indicates high chromium content... So, it's stainless, but I don't know exactly what grade. It was cut both ends with an abrasive cut-off saw, and the discolouring on the ends would be something to stay away from, so I used the band saw to saw off a 4mm slice from one end to get rid of that.
I've worked a bit with free-cutting stainless, so when I tested the sawn off end with a file, I could immediately feel that this stuff was tougher than free-cutting stainless... This was going to be a challenge to machine. I took a couple of minutes to think trough all I've learned about machining stainless. Lower speed. Use very sharp tools. Lubricant/cutting fluid helps. Use a steady feed rate and never let the cutting tool rub. Heat is the enemy. Look and listen to what the machine is doing. And last - not a machining rule, but one that seems to have helped me a lot - be positive; that's half the war won.
So, I decided to take on the "difficult" steel, and thought through all the machining operations. Then I sawed a suitable length off the parent stock:
That was center drilled in the lathe at one end for later turning operations.
Off to the mill, and with a sharp 16mm HSS 4 flute cutter at just 80rpm spindle speed, I started by milling off a 2mm deep flat on the round bar. At the start of the cut I just plunged in, feeding the X axis at about half the speed I would normally for mild steel, and checking that chips were coming off. Once the cutter was about half-way onto the workpiece it sounded like and felt like I should increase the feed rate a bit, which I did, and all of a sudden some nice equal-sized chips started coming off, the mill's gearbox quietened down, and the sound of the cutter shaving off bits of metal went from a raggedy gdgdgdgdgd to a nice even swish-swish-swish sound. The surface finish was far from perfect, but the cutter didn't break, the workpiece didn't work-harden, and I was a very happy chappy
:
I milled some more off the one end - this will become the crank end:
The holes for the crank pin and cross head pin were also drilled and reamed to 6mm. LOTS of cutting fluid while drilling and reaming...:
While milling the other (still round) sides down to size, the "feel" for machining this stuff started improving, and the surface finish got a bit better:
I milled out the slot for the cross-head guide next with an 8mm cutter and a slightly higher speed. The slot should be square in the inside end, but at this point there was no way I could mount the workpiece to do that on the mill, so the inside end is still round. I'll file it square, or - perhaps - there might be a way to mill it square later on... :
On to the lathe, and some clocking up needed in the 4-jaw chuck. When I started in model engineering, I disliked setting up jobs in the 4-jaw. But it's one of the most versatile and accurate ways of doing work on the lathe, so I've been playing a mental game with myself which has turned into it's own bit of workshop fun: How close can I get it by eye, and then how quickly can I get the job centered to within the needed accuracy. The rings on the chuck face and the jaw positions all help. I got within 0.5mm all round on this bit according to the dial indicator. The last couple of adjustments were easy - find the "low" measurement on each opposing flat edge, total them up and divide by two. Ease off on the chuck jaw with the highest reading, and tighten up the opposite jaw. Difficult to explain in words... There's some good video explanations available though. Here I was busy with that process:
A bit of turning started to make the workpiece think it should be round again - just 200rpm on the lathe and steady - but positive - feeds with a sharply honed HSS toolbit:
Then I turned off more stock - starting from approximately half-way along the workpiece toward the tailstock with a sharp right-hand turning tool:
I free-hand turned the beginnings of the
fish-tail fish belly rod finish on it:
Then I did the same on the chuck side - turned everything down and added the
fish-tail Fish belly section:
Some work with files and emery followed. This stock was not the easiest to file - I had to go stroke-stroke-clean each time - with a personal bad habit of running the file in reverse against the palm of my left hand for each clean operation. That can put some "metallic thorns" in the flesh... A couple of grades of emery cleaned up the file marks:
There's still a bit of work left on the workpiece, but my shop time ran out
- So this is where I left off:
Kind regards, Arnold
