mills 1.3cc diesel crankcase model engineering mikes-models

Saturday 12th January 2008 - session 3

Well today’s efforts were a tale of both good news and bad news! I was
pleased with my starting position of an accurate marked out blank. I made
good use of the centre marking tool (photo 5). It really allows you to get
the mark in the right place so that’s the good news, now some of the bad
news. I managed to drill just over half way through from both centre
punched marks, as this time I decided I would drill from both ends, to meet
in the middle. That way the holes should be neater as any run out would at
least be minimised.

The first side went well. I used my magnifying specs to ensure the centre
drill was located correctly, replaced it with the 1/8th drill and drilled to just
over half way, using the digital readout to verify when that was. For some
reason (why do we have the 'for some reason' moments!!) on the last hole I
must have been fractionally out as when checking the scribed lines it was
fractionally out. Fortunately it was on the outside of where it should be so I
will be able to clean it up once before I finish.

The next stage in making the Mills diesel engine crankcase was to position
the blank so the circle, which I squared on marking [see photo 2],was
uppermost, to allow the square shape to be machined. I then used a set of
parallel’s to position the blank sufficiently high to cut the required depth of
ľ” clearance from the vice jaws.

Taking fairly hefty cuts with a 16mm slot drill (with my new collets!) I
machined the surface until the required depth of 11/16th” was met. I took
progressively finer cuts nearer the end position. Other than presenting me
with a lot of aluminium swarf, there wasn’t very much difficulty here. I did
use my digital callipers to get the size of the square correct to 0.001”.

The next stage is to remove the blank and turn it onto its side so the side
can be machined to the required 7 deg angle. To ensure the blank was at
the correct angle I used my digital angle meter (see photo 3 to the right).
Zeroing it on the vice jaws I simply placed it on the blank and adjusted it
until it read 7deg. Whether I marked out wrong, which I don’t think I did,
then there is a slight difference in the marks shown as being parallel to the
top of the vice. I decided that as long as I kept the top of the crankcase to
its correct dimension of ľ” wide, then I could ‘adjust’ the sides where the
lugs would be.

Being careful to keep the rounded curve between the top of the lugs and
the crankcase side (formed by the 1/8th drill) I finished machining one side.
Reversing the piece until the other was done (photo 4). I then removed it
from the vice, de-burred the sides and took it to the bench vice, where
using needle files, I cleaned the worst of the difference between milled side
and intersection of the lug and sides.

One lesson from cleaning the sides up was that needle files are fragile.
That’s a nice way of saying I was too ham fisted in using one! So I now
have a much shortened needle file set.

I did consider using a bull nosed will to create the rounded edge for the join
between the top engine lugs and sides of the crankcase but thought better
of it. However, now seeing the nearly completed (in shaping terms)
crankcase I feel it is another way of achieving the look wanted and would
get rid of the drilling problem.

This nearly completes this session but I though it would be wise to machine
the square nose section of my first blank. The one I drilled the holes in the
wrong place (used the front and not the back to measure and mark out)
and it would then be ready to take over on the machining of the next stage
in the crankcase construction. I did not want to loose all the time put into
the good blank when trying something new, for example the turning of the
internal screw thread in the back of the crankcase! So I will use the
defective blank and machine that first so any lessons learned can be
corrected when using the good one. I have not yet cut many threads and
none internally so this will be an interesting experience. Indeed I may try the
exercise on another piece of scrap before I even try the defective
crankcase.

Well that added another 2 hours to the build. Taking photo’s does add to
the time, and I still include that in my session total.

Time spent today 2 hours. Total to date 6 hours.