Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

I started the crank shaft quite some time ago. This is as far as I got it.



I decided at the time that I would be better off making the base first, so that the crankshaft could be turned to fit the bearing journals, and that was a good decision.

I swapped over to my collet chuck to proceed. It bums me out that I have to true up my collet chuck every time I refit it - but I suppose expecting to rely on the large threads on the lathe to accurately locate a chuck in terms of concentricity was naive at best. It actually only takes me about 10 mins to align it now in any case. The collet chuck has a set of 4 adjustment screws for fine tuning.





I can get it set up and running true enough that I can't detect run out on this DTI, and the ER collets are a lot better to work with than the 3 jaw on diameters 1" and down.

So - bit of clean up on the face:



Drill center hole:



And clean the diameter.





Then I cleaned up the outer faces of the cranks a bit:



It is necessary now to turn the larger diameters next to the crank to an exact length, to locate the crank shaft centrally in the base casting. It was at this point I decided that it would really nice to have a fine adjustment carriage stop - or any carriage stop come to that. So I have paused work on the crankshaft to make one.

The plan is to get the larger diameters turned to length using the collet chuck to hold each side, then I will turn the 3/8" diameter shafts to size between centers to get best concentricity.

My 1/4" reamer arrived, so I decided to finish up the cross slide. Got it all set up, found the edges and positioned the center of the pin. Did a quick visual with a drill blank to make sure it looked centered in the casting boss.





Then spot and drill. I drilled to about .015" undersize, but drilled out half way to that first.





Then reamed to 1/4"



Checked with a pin gauge - got it spot on this time!



Then set up and milled the slot.



Finding hole center by using pin gauge and a feeler gauge.



I plunged the slot to get most of the material out.



Then cleaned up the sides and bottom of the slot. The end mill was just long enough. Worked well though.



Finished!



And it even fits and slides easily up and down the rails. Will wonders never cease?





Decided to finish off the valve. I had faced and pocketed this some time ago, but was not happy with the amount of error I was getting milling depths. I now have that resolved, and so......





I tickled out the slot until the material to be used for the nut just fit in.



And then the same for the other slot. Again - plunged most material out, leaving 0.01" on depth, then cleaned up.



Finished part - still needs some deburring.





Then I started thinking about some other components. I was enjoying milling so I moved on to making a collet to hold square bar stock, which will be used to make linkage components for the valve drive rod.



The overhang of this aluminum rod did cause some chattering at the end, but by making a finish pass it cleaned up fine.



After taking the shaft about 0.01" past centerline, I rotated the part 45°, positioned the cutter and milled a slot.





Chopped into two pieces, and being used to hold the sqaure stock in the lathe.



That's as far as I got today. Next stage is either the linkage components or go back to the crankshaft.

OK - I made a new holder. Same idea as before, but turned the body down to 3/8", leaving a stock 1/2" lip to stop the adapter disappearing inside the collet, per Marv's recommendation. This has indeed turned out to be a good move.

New holder:



And using it to start making the linkage.



The little holder is not perfect - it is not quite centered. Off by about 0.002 I think, which is really not acceptable - I could center much better than that in a 4 jaw, but my 4 jaw is a bit big for this job. I may attempt another holder. It's actually quite a good exercise for tuning in my milling techniques.