Once the pivot pin was turned down to the right size to be tapped M3, I then cut the M3 thread. You probably noticed that the tailstock is removed for this, I ran the lathe at the lowest speed ( I thread at the lowest speed so I dont run into the chuck ) and as I found out when trying to remove the ER32 chuck it was well stuck in there.
Once that was done, I removed the pin and then loctited it into the cylinder. (it was a pretty good press fit)
And that’s as far as I got today. Thanks to Bog’s for reminding me of what I actually had sitting in the corner of the workshop.
I managed to sneak a couple more hours in the workshop this afternoon. I started off by hacking off a little lump of brass for the piston and chucking in the 4jaw, turned down half to diameter.
I then chucked it the other way round in the ER32 collet but made the error of not tightening it enough and it came loose just as I was parting it off to length so I added to my collection of spare “smaller than I wanted” pieces and hacked off another lump of brass, chucked it and turned it down as before. This time I also drilled and tapped M3
I find this to be a good method of tapping on the lathe, to explain; The drill chuck is not jammed in the MT of the tailstock, it has some grip but is free to turn with light pressure. Also the tailstock is also free to move on the ways, and the tap in the chuck is also loose enough to turn if the tap jams in the work. I then run the lathe at a very low speed.
So that’s all I got done today, just 2 pistons made, 1 junked and one that fits ok. If I put a M3 screw in the piston and slide it into the cylinder and turn it upside down the piston gently slides down and stops at the entrance of the cylinder, with out the screw it just falls out. I dont know if it’s too loose, if I pull the piston out rapidly I get a satisfying “pop”.
Things I’ve learnt today;
I learnt that my ER32 chuck has a runout of 0.02mm,
Always start off with a piece of metal that is longer than you need as it makes life easier.
I also tried making a con-rod out of 303 stainless, it didnt go quite as planned but I learnt that it really helps to use sharp carbide tooling and that it doesn’t like my Hss threading tool.(prob was a bit dull, I must resharpen it) I’ll try again the next time with some brass as per the plans.
Also learnt to think a few steps ahead to see what I can do while workpiece is still chucked and true before taking the piece out and then spending 15mins truing it up with the trusty dial indicator.
And finally, always remember to check that whatever chucking device is used it is properly tightened up.
Today’s update.
I started out by sharpening my threading tool and spending 15-20 mins trying to single point 3mm 303 stainless for the con-rod. Deciding that beating my head against that particular spike was not fruitful :bang:, I moved on to machining a new con-rod out of brass. This was much easier.
Then I extended a bit more out of the chuck and turned that down.
Once turned to size it was over onto the mill, I mounted it into the spin indexer thingy, supported the free end with a 3-2-1 block and a little stepped thingy and drilled out the hole for the crank, 2.4mm if I recall correctly.
After a little cleaning up and filing the edges round I have a piston with con-rod
After that I had a little time so I made a start on the crankshaft assembly, specifically on the crank disc which I made out of some unidentified steel, turned some down to 17.5mm, hacksawed it off and remounted it in the ER32 chuck, faced it off and then drilled it 4mm.
Ok, managed to get a couple of hours in the workshop today. Started off by setting up and drilling the offset hole for the crank pin.
The more observant of you will have noticed that the Crank-disc is not properly seated on the 3-2-1 block and so did not drill square. I didnt notice that until I’d finished today and as I’ll explain in a bit I may have to re-bore the pin-hole square. Anyway, after that I found a use for the screwed-up piston, I turned it down to make the crankshaft bush shown below in the middle of the other hacked out bits.
I then chucked up a length of 6mm 303 stainless to turn down for the crankshaft, I turned down to 5mm for the main shaft and a short section 4mm to fit the crank-disc.
Then I did something similar for the Crank-pin, except I started with some 4mm stainless, turned it down to 2.4mm for the press fit into the crankdisc and 2.3mm for the easyfit into the conrod. I also pressed the crankshaft bush into the frame, after I cleaned up the frame,
then did a little assembly just for fun.
Once I did the assembly and tried to turn over the crank I found that it was sticking at TDC and BDC. After a little wondering I checked the squareness of the crank-pin ( it’s amazing how hard it is to use a 4″ engineers square on a part that’s only 17mm wide and the pin’s only 3.5mm high !!) I then realised that the crank-pin is not square and is what is binding up twice per revolution. I’ve not totally decided what to do about this. I could pull the pin out and re-bore the hole wider and square and then make a new pin to fit. Or to just try and bend the pin to square. I’m leaning towards just bending the pin back to square, and that’s what I did.
I managed to make a start on the flywheel, and got one side shaped, to a fashion, and today I bored and reamed the 5mm hole for the crankshaft, then remounted to machine the other side, centred it using the 5mm hole as a reference and then shaped the 2nd side. ( I was so excited about getting so close to completion I forgot to take any pics of these parts )
I then turned a some 6mm brass rod to a close fit for the flywheel, and threaded the end M5, and mounted the flywheel to it to clean up the rim and make sure (hopefully) that I dont have a wobbly flywheel.
After that I drilled and tapped the flywheel for the setscrew I then turned to the air-intake-to-aquarium-type-tubing-adaptor-thingy. I used the same 6mm brass rod and turned some down to 4mm and then threaded it M4 and then bored it through with a 2.2mm bit
Then after some jiggery-pokey with a parting tool,
It was over to the spin-indexer to make a nut-shaped bit.
