Making A Crankshaft -7

by John

Not finished yet, but the end is in sight. Maybe 2 or 3 more workshop sessions.

Today I roughed out one of the crank journals. I had hoped to do both of them, but had some problems to solve.

Normally big end journals are turned on the lathe. With this crankshaft, the lathe tool “stickout” is over 40mm. And the section is initially square, so the turning would be VERY interrupted. So I decided to try a new method (for me), of converting the square section steel to round section on the MILL. This is the setup…

On the left is a rotary table, powered by a stepper motor. On the right is the tailstock. The heights were adjusted using a height gauge. The Y position was determined with a clock gauge. The vertical mill has a 12mm carbide end mill running at 2000prm. Depth of cut initially 0.5mm. Rotary table is set to run for one complete turn. The stickout of the endmill is about 45mm, to just clear the flanges… the weakest link. I broke another endmill, so reduced the rotation speed, and added spray lubricant. Even so, it was not a secure setup. It improved after I replaced the ziptie with soft wire.

The end result, a “roughing in”, was not too bad. Since the end mill was centered over the journal, then moved to the lateral extents. each cut bulges slightly in the middle. In retrospect I could have flattened the cylinder by creating a final spiral. But since it will all be finished with a lathe cutter, that is irrelevant.

Note the Loctited spacer in the other crank space. I started the same process on that big end journal, spotted the difference, and aborted the process just in time.(!).

So I transferred the crankshaft to the lathe…. and discovered that the toolpost was too wide to permit turning due to collision with the shaft end block.

Here is the turning setup. If the toolpost looks a bit odd, I have removed about 10mm from the near side, to allow clearance. This was a damaged toolpost, so I had no hesitation in modifying it. Note the extreme tool stickout. That is why I wanted to NOT have interrupted turning. So I have not yet tried the setup, but I think that it will work. The journal is currently about 38mm diameter. It needs to be reduced to approx 26mm. Stuart Tankard made this tool, and its left hand companion. Thanks for the loan Stuart! I will proceed gently. And use flood coolant-lubricant.

So, again, not much to show for 5 hours in the workshop! But progress is happening. And this is a fascinating job!

Incidentally, the rotary table stepper motor became too hot to touch during the milling. But it did not falter. Very impressed. I think that it would be possible to do the entire journal shaping on the mill. Maybe next time.