Mery Explosive Engine - page 3
The connecting rod isn't too difficult except that it's slightly tapered
(.008/inch). To cut the taper, I shifted the tailstock over.
The length of the part is just over 7 inches so 7 * .008 = .056.
You only shift the tailstock half of the taper so .028". Take
a skim cut and adjust from there. I didn't get any shots of
the rod boxing in process but that's pretty straight forward.
Turning for the gears isn't any big deal so I didn't get any shots.
The tooth cutting is cake if you know what you are doing. Get
the right cutters and setup the indexing head correctly. I
know it's a pain but take a scratch cut on each tooth. The
first time you'll see if you if you made a mistake is when you cut
your LAST TOOTH. Then you might have a choice of 2 small ones
or one big one. Hint: Neither!!
Have a look at the broach pictures. Rather than make a new bushing, I had a 1/4" bushing from my set so I turned a collar to make up the difference. I had to cut it upside down so the collar was pressed against the bushing head and wouldn't come off. Let the broach cut the keyway through the collar then into the bore. It sure beats making a new bushing!!
Now that I'm pretty much done with the big stuff it's coming down to
the nitty gritty. Starting with the explosion chambers.
I struggled with leaving them together thinking there must be a way
to take advantage of that but I couldn't find any. I cut them
apart first and it all fell together from there. The next
thing I did was file the top and sides to an 'average', meaning,
take off the high spots. Then holding it like picture one, I
squared to the side 'ridge' and took a skim cut on the flange face.
Next cut was on the top. Setup putting the previous cut on the
back jaw, and leveling left - right with an indicator on the filed
parts. Close is good enough. I was about .005"ish.
Now a skim cut but don't cut the back face. Now you can flip
it over and set the top down on parallels and skim the bottom of the
flange face. Keep in mind, if you are careful, there is about
.015 on the back and each of the side ridges. Not a huge
amount but you can get a cleanup. You'll need them to get
things squared up for cutting. Once you have skim cuts and
it's all squared, you can go for sizes. Cut the overall width
(ridges) and the sides of the flange faces. You should be able
to handle the rest from here.
The valve hole needs a little explanation. I started after I
had all of the milling finished. Then I set it on a parallel
under the flange face. Mill the bottom of the pocket to a
depth of 1/2" from the top face. Next I drilled the small .113
hole first. It calls for it to be reamed but I didn't want to
buy an off size reamer for 2 holes. I drilled it 2 number
drill sizes smaller then used the .113 drill to ream it with.
Slow RPM so the sides of the drill cut and it's close enough.
The guide is the important size. Next came the .218 reamed
hole. Drill it to depth then ream. Now for that tapered
hole. 3deg taper? Really? This doesn't need to be tapered and
nobody will ever know unless they read this. Start by using a
3/8 milling cutter and plunge to the 3/4" depth (1/2" from the
bottom of the pocket). Remember these depths are all from the
intake hole CL but if you milled the pocket bottom carefully,
subtract 1/4" from the depths on the print and go off the bottom
face. Back to the 3deg taper hole. Take a 13/32 drill and
gently drill the hole almost half way down the 3/8" section and ream
it to 27/64". The ream gives a nice sharp concentric edge.
Now I took a piece of 1/2" steel and cut a 45deg point on it.
I used that in the drill chuck with some lapping compound to cut the
45deg seat. Don't press too hard! Up and down.
After getting the cut close to size, I recut the 1/2 pin because the
lapping compound cuts both the cast and the pin so going back for a
second cut cleaned it up. It takes a bit of time and patience
using this method but anything else wouldn't be concentric or might
dig a bigger cut. All you really want is to break the corner
for a valve seat. You'll see later how it gets finally
lapped. Now go drill those 3-48 holes for the cover.
When you drill the intake hole on the flange face, pay attention! The inside is step. If you try to use a 1/4 drill, it will walk once it hits the inside step, been there. First find the hole, then center drill it. Use a small drill like 1/8 to drill a pilot through. Next use a 1/4 end mill to cut the rest. Even if you use a 2 flute end mill, you should pilot it so you don't get any walk. You can go all the way into the chamber with the mill since you want as much hole as you can get.
I had the same struggle with the exhaust chamber castings as I did
with the explosion chambers; do I cut them or machine them
together? I decided to cut them apart. The first pic is
setting up for the first cut. I'm chucking on the cylinder end
and indicating roughly true, the round section. I'm moving the
4 jaw to true it up then I went to the round section on the other
end and tapped on the end to get that true. I rechecked the
first section to be sure I didn't knock it out. Then I cut the
round 'outside' section (pic2). I drilled the 1/2 hole and
also took a cleanup cut on the outside. It came to 1.300" for
almost 100% cleanup. I'll probably need that as a reference
later. Pic3 is after I flipped the piece around and am cutting
the face of the cylinder end flange. Again I drilled the 1/2
hole and took a skim cut on the OD to the same 1.300" on the high
points.
I knew turning the outside of the exhaust flange would come in handy.
I used that to locate the center of the cross bore. Without
something on the outside, turned true to the inside, I would have
had a hard time locating for the valve bores. In this
operation I did all of the holes for the valve chamber and the
tapping for the cap. The end mill is to flatten the bottom of
the hole for the valve seat. I also lapped the 45deg seat.
I missed that the valve heads were supposed to be cast iron.
Fortunately they are small enough that I can harvest them from
cutoffs from other pieces. This should stand as a reminder not
to throw those little nubs in the trash just yet. Also, don't
be too overzelous with machining extra material. I had one
cast nub that could have given me extra valve heads but for some
reason, I drilled the hole for the piece all the way through the
scrap too. So after finding enough to make exactly 4 valve
heads, I turned them to a bit larger than finish diameter in a
collet then parted off 4 heads. I drilled and reamed the first
2 for exhaust. Then I took the 5/32 drill rod and turned the
end for the heads. NOTE: I bought the drill rod on size for the
valves. It's not that expensive and it a LOT easier than
turning that tiny drill rod down. Using a #1 center drill, I
drilled the end to give me something to peen. With the head
.001" smaller than the shaft, it's a nice press fit. I used
the nose of the drill chuck to push it onto the shaft. At this
point the head is only about 1/8 from the chuck. I don't want
too much sticking out so it won't bend. Now I took a 1/8"
punch and a small peen hammer and gently tapped around the center
drill hole to peen the shaft into the chamfer of the head.
LOTS of small taps are better than a few good hits! Just keep
walking the punch around the end and you'll see it peening over.
DON'T hit the head itself or you'll break the cast or push it
crooked on the shaft. Next, re-touch the center drilled hole
with the drill to clean it up. Pull the shaft out far enough
to get your tool behind to cut the 46deg slope and use a center.
Cut the OD to size and cut the valve slope. Yes, I said 46deg.
The seat is 45 but the best valve seals are small faces. The
.032 wide face called for in the print is too big so we'll adjust
the angle here and lap to a nice fine ring. I probably should
have made it 47deg but it should be OK.
I drilled the intersecting holes from the flanges into the bores
using an angle vise and held them the same way I am in the pictured
operation. I used a protractor to set the angle and a 1/4" end
mill to cut a small flat. I then used a #2 center drill to
pilot and used it to go all the way through to poke into the bore.
I then chucked the end mill again and used that to finish the hole.
Using a drill for this invites a walk. If you do it all
correct, you'll poke into the bore about 1/32 from the seat.
That's not much room for the error of a drill walk. The
pictured operation is simply drilling the flange holes themselves.
I have a piece of aluminum between the top and the jaw since the
flanges extend above the top of the cap end. I also drilled
the .063 hole for the governor pivot.
12/4/2012 - For those watching these pages, things have been busy over the summer so there hasn't been too much progress. I have got more pictures and am pretty much down to the 'fit and finish' stage. However, now that winter is approaching, I'm sure I'll find myself in the shop more often. I'll update the photos soon hopefully. Keep checking back!