mikes-models

Session 3 24th July 2008

I guess Ron must be on holiday, as I have not recieved a reply to my request for clarification of the
methods for turning the crankshaft, as detailed in his article (issue 1 Model Engine Builder). So I
decided to have another go at making the fixture to hold the crankshaft, for turning the big end.

I tried several diffierent methods of getting the offset of 0.625" and followed Ron's directions. After
the first fixture was completed you can imagine my dissapointment when I only had 0.3125" from the
centre to the centre of the hole drilled to secure the crankshaft to. I secured the crankshaft in place
and took the fixture to the ML10 lathe with the 3 jaw chuck and took a light cut to see where the big
end would fall. It was 1/2 the distance it should have been!

I therefore re-read again(!) Ron's directions and spent nearly 1 hour getting the off set in the 4 jaw
chuck and finally drilled the holding hole. When removing the fixture and comparing it with my first
failed attempt I was most dissapointed (being VERY polite here!) to find it was exactly as the first.

I think this was the most dissapointing aspect of the whole build to date and I admit I pushed through
too long before stopping for rest. It was time for a cup of tea and a review of the problems. I
re-read again (about the 15th time) and I still can't see where I was going wrong. So I thought that I
would forget about Ron's desription and look at the task afresh.

All I needed was a fixture, that when secured in a 3 jaw chuck, held the crankshaft so the big end
gave a 0.6125" throw, or 0.3125" from centre of the big end to the centre of the crank. So why not
just turn up a piece of aluminum with a diameter of 1.5" (looking at Ron's instructions I think
something is wrong because the crank holding hole would be close the the outer edge of the fixture)
and instead of using the 4 jaw chuck, with all its positional problems, use the milling machine instead
to drill the hole in the correct position.

So thats what I did. It was then a simple task to cd drill the piece on the 3 jaw ML10 before taking
it to the milling machine. Here the centre was found and then the table of the milling machine was
moved 0.625", then centre drilled and correct hole drilled. All in all a 10 minute job at the outside!!

After fitting the crankshaft into the larger fixture, it was a case of changing the 4 jaw chuck back the
the 3 jaw and mounting the crank blank. A light cut was taken again and the big end position
measured and this time its in the right position! So it was time to finish before I make a mistake, and
rest.

When I start again it should now be a hopefully simpler task to turn the big end, although I know that
the whole piece can be made into scrap by not making the crank web to thickness and the big end
undersize (I hope I don't regret writing this!)

time taken 5 hours 10 minutes total time for crank so far 8 hours 30 minutes

Session 4 28/08/2008

Unfortunately I haven't been well enough to get into the workshop until today but managed to nearly
finish the crankshaft.

I decided that I would use the Myford ML10 to finish the crankshaft as there is a better 'feel' for
smaller work. The disadvantage is not having any DRO's but my recent work using the lathe got me
back into dials again. My habit of measure, measure cut measure again........seems also to go well with
the Myford.

After cleaning up the back face of the crankshaft from the previous session, and using a freshly
sharpened HSS tool managed to make the delicate cuts leaving the crank pin proud and a couple of
thou oversized. After some 800 grade wet and dry paper and 3 in 1 oil the pin was fiished to size.

I must admit that when trying to form the undersize cut iit coulld have gone better as I should have
changed tooling from the cutter I had to a boring tool. Once changed I could tidy up the work but it
was a nervous time as I was working close to the finished crank pin!

However because I still had to 'adjust' the position of the taper on the front of the shaft I now had a
problem to hold the work. I could have put some shim around it but I was so pleased with its finish
running in the bushes I didn't want to risk damage. I came up with the thought of making an aluminum
fixture with a close fitting central hole and cut across its diameter 3/4 of the way through. Then turning
over another deep cut at 90 degrees to the first. Something like a ER collet. When trying it first it didn't
grip it very tight so I made the saw cuts deeper and it then worked a treat.

The next task was to make a 10 degree taper on tool steel for a D bit. Once completed this was used
to cut the taper in the prop driver, held in a ER25 collet mounted on the ML10.

Now I had both the taper on the shaft and the prop driver in the right place, the crankshaft was placed
in the crank case and the prop driver tried to see what if any end float was there. Ron's plans show
between 10 and 15 thou to be in place. I didn't have any so it was back to the lathe a shave a little off
the back of the prop driver as per Ron's instructions.

Now all that is left to do is mill some of the flanks of the crankshaft and that will be that!

Time spent 2 hours (mainly making fixtures and tooling) total 10 hours 30 minutes