johnsmachines

Almost finished.

When turning the big end journals the supporting block for each crank had to be heated to release the Loctite and remove the block, then re-glued in place after the journal was finished.

Then the mainshaft itself was turned.

But first the centres for the big ends were cut off, after making sure that the journals were totally finished!

In this instance I used the horizontal drop bandsaw, because I have not yet replaced the damaged blade on the vertical bandsaw. There is a piece of steel clamped in the vice, and the weight of the workpiece is sufficient to keep it in place during the sawing.

As you can see I used a flood coolant-lubricant. Here getting the dimensions close to final using a tungsten insert tool, at 235 RPM. At that speed balance weights were not required. Depth of cut was 0.5mm, and frequent stops for measurements, so it was a time consuming process. And to disassemble and clean the cross slide DRO glass scale. I reversed the workpiece where required to cut towards the headstock. I still do not know exactly what the steel grade is, but whatever, I had several changes of inserts as they lost their edge.

The final machining step (I hope), was to mill the keyway grooves. That took another 6 hours.

The CNC rotary table was very useful for setting the angles, and locking the shaft in position, on the mill. Two 6mm carbide endmills were required to cut the 10 keyways. Here I used a spray coolant, powered with compressed air. A little less messy than the flood coolant.

The crankshaft is almost ready to be installed in the traction engine. The support blocks to be removed finally. The shaft ends to be chamfered. And the crank weights to be drilled, tapped and bolted in place.

I had marked the eccentrics positions before the original disassembly, and here I have installed them approximately in the same positions on the new crankshaft. Of course they will require small adjustments later. The gears slide smoothly on their splines.

Doubtless there will be installation issues. The old crankshaft deviated from the plans in quite a few respects, and sometimes I was unsure whether to copy the old crankshaft, or to follow the plans. “Copy the old crankshaft” was the general advice, but there were some obvious discrepancies which had to be addressed. I can only hope that I have made correct decisions.

Not a lot more to show after today’s 5 hour workshop session, but the debulking with the bandsaw and mill is complete. The 26.5kg bar now weighs just over 7kg.

I started to bandsaw the remaining 2 blocks, and was just finishing a long cut when the sawing sound abruptly changed and the cutting stopped. WTF? Examination showed that the blade teeth were still sharp, but the teeth set on one side was gone. I think that there must have been a hard inclusion in the steel which stripped the side set. Whatever, that blade is stuffed. To make matters worse, I did not have a replacement on hand.

So, I had to revert to milling to remove the waste blocks. Just to reiterate, the blocks are 38.1mm x 38.1mm x 180mm so it was a lot of swarf again. But I am now using flood coolant, so the swarf was not red hot, and the 12.7mm carbide cutter survived intact. I was reminded why I normally avoid coolant however. It is VERY messy.

The remainder of the session was occupied by measuring and marking for the crank cut-outs.

Almost every surface of that solid bar will disappear when the turning in the lathe is done. The only surfaces which remain will be the bar ends, and the square surfaces where the counterweights will be attached, and they will not be visible.

The next step.

Do I cut out the crank slots, or do I rough turn the mainshaft? If I cut out the crank slots then I would install some packing blocks, then turn the mainshaft. I cannot see a significant advantage in either next step. Any thoughts?