bsa crankshaft nut mikes-models

1 How I got the job.
2 The defective part arrives.
3 Stock material and choice.
4 Machining process

How I got the job...

Whilst working on the Mills diesel engine there was a shout from outside the
garage. The gentleman concerned came into the workshop he started to talk
about his collection of vintage motorcycles. He explained that he was working
on a friends vintage bike and after a longish chat, explained they had a
problem with a crankshaft nut. I asked if he wanted me to try and make one
for them. No guarantees of course...... so there we are..............now I have to
deliver!!!! It will be great if I can do it, not just for them but for my own
confidence. Likewise if it doesn't work...well I will carry on until I do get it
made!

There was a bonus though, the possibility of some bar stock in return for the
nut. So now I will wait to see the pattern............

The defective part arrives

My contact, Jeff arrived with the nut and I was given the dimensions that they
wanted for the inside threaded bore. I have considered making a shaft to that
size to test the nut on.

The nut doesn't have any flats as I expected, rather it has a round outside edge
and 4 slots cut in it. The photos to the right give a better description than any
of my words.

What to use?

The ONLY stock I have that is large enough is a large lump of stainless steel
picked up from my local scrap yard, so its no choice really. I hope that
stainless steel will be satisfactory, I can't see why not, but if you know better
please email me and soon!

The other potential difficulty is if it will even machine! Hmmmmmmm

Proposed machining order

Subject to the bar stock being ok this is my first thoughts on a machining
order.

1 Turn to the thin flange's outside diameter.

2 Machine the main body to diameter.

3 Face down with the small face.

4 Centre drill then drill through, increasing drills until suitable size for boring
bar.

5 Cut threads at 20tpi

6 Make the internal radius by grinding a special tool profile

7 Take to the milling machine and mill the four indentations

8 Reverse the set to correct angle and mill the two slots show in photo 1

Polish and pray!

------------------------------------------------------------------------------

Session 1 - 8th March 2008

Took bar to the band saw to cut a suitable piece to old in the chuck. It took
about 20 minutes even with constant cutting oil added. However, the bar was
then taken to the large lathe, I am sure I will need its umph.... and was very
pleasantly surprised to find that whilst it is certainly hard, it is possible to turn
it. and that's as far as I have gotten this session. Its been more of a testing out
day really.

Time spent 30 minutes.

Session 2 - 9th March 2008

Having given it some thought overnight, I decided that I would make a
11/16th threaded shaft to help me when boring the nut and checking the
threaded size.I feel it is important to have some method of checking my work
as I do not have access to the shaft it will fit on.

I used some steel bar to make the blank and remembered to cut a relief for
the tool to pass into. I also remembered to set the top slide to the required
29.5° (on the x axis!). Having remembered all my lessons, including setting the
tool at right angle, I started the cut, and for once everything went well. Just to
make sure I had set the right gears on the Myford, and the correct depth, I
tried out my thread gauge [photo opposite] and it was a nice fit. So the
finished stud will now sit until the nut itself is ready for threading.

Having made the stud, I started by cleaning up the stainless steel bar. It does
turn but you can tell it is hard, the tool needs constant re grinding. Hopefully
the next session will complete the nut although I always seem to underestimate
the time to complete tasks. It seems to me that 90% of the time is for setting
up and the turning or milling is only 10%. All together a reasonable session.

Time spent 2 hours. Total time now 2 hours 30 minutes.

Session 3 - 14th March 2008

Today I completed collecting all the measurements and started to turn the
blank to shape [see photo opposite right]. I then opened out the central hole
to near the final diameter and cut the threads. One advantage of working with
this bar stock is that as long as I kept regrinding my tools, the threads cut
were strong. The critical test though was would the stud fit?

Well the answer was a pleasing yes! The fit was snug, but not to tight. [photo
left]. What I now had to do is turn a tool to give the required profile in the
centreand I used the old nut to act as a template to give the right radius, the
only thinng now was would it cut the stainless steel? I decided that the best
thing to do would be to remove as much metal as possible so the tool would
have less work to do. The results are shown in the photo with the stub fitted
on the right hand side of this page.

Once the turning was completed I needed to cut the four indentations on the
rim. To do this I set the nut up on the Vertex dividing head on the Mill and
once I located the centre, milled the four at the 90 degrees required [photo to
the right] You will also see I proteced the threads by inserting the stub
threaded shaft.

The final machining job left was to cut two slots on the reverse side of the nut
so after reversing it in the chuck I set the Vertex at the right angle and milled
the two slots to the correct depth.

That completed the machining and I must admit I was quite pleased with how
the session went. I have added a series of photo's below so you can make
your own judgement. The shaft was machined to 0.0005" of an inch measured
by both digital calipers and a digital micrometer (can't trust my eyes!)

Time taken 3hours 45 minutes. Total time 6hours 15 minutes.