Re: I'm back, with more senseless ramble on engine building!!

On Jun 19, 3:53 pm, payments...@xxxxxxxxx wrote:

Does anyone know how to precisely mount a scat boring tool to a case??
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Maybe not a Scat tool. But the following method(s) worked okay for
the tools made by Gene Berg, BMG and a couple of others.

But you probably won't like it :-) Because the first step has nothing
to do with the tool. It has to do with the drill press.

Is it bolted to the floor? If not, make it so. Then make a pair of
diagonal braces in the form of struts. Most buys used sections of
straight exhaust tubing but some used solid bars. You weld a tang on
each end to accept a bolt then drill I tap the table of the drill
press. The table is positioned at the correct height for the tool &
the crankcase half -- and of whatever fixture you're using to support
the left-hand case-half (ie, the one with the studs). Some guys used
plywood, other drilled & tapped aluminum plate, some welded up a steel
fixture... then spend several years truing it up :-) But there you
are, finally, with the table at the proper height and a collar or
other stop to re-position the table in the future. The struts are
bolted to the table and the tang on the floor-end of the strut is used
to mark the concrete. Then you remove the struts, whip out your
hammer-drill and shoot a couple of holes in the concrete to accept
steel inserts threaded for 3/8" or 1/2" bolts... whatever diameter
matches your struts.

NOW you get to bolt everything together and with a bit of luck, your
cutter will produce a hole that is not only round but square, which
one of those Machinist Jokes, which means you don't have to smile
unless you wanna.

As for positioning the cutter on the case... Didja notice that the
case ALREADY has some holes for pistons? Well, most of them anyway.
Didja figger out that the REAL job is simply making the EXISITING
holes bigger? Okay then, because the next step is plain old-fashioned
Common Sense. You make up a plug out of aluminum plate that is a
light press fit in the hole in the crankcase. You do that on a lathe
and you want to hold to +/- a thou OR LESS, which means you've got to
take the temperature into account. It gets tricky because it isn't a
CIRCULAR plug, it's rectangular, having one dimension narrow enough to
fit between the legs of the tool, the other being long enough to span
the diameter of the spigot-bore in the case. The tricky-bit comes
from this being an 'interrupted cut' during turning, meaning it's
going 'thumpity thumpity thumptiy virbrating the hell out of the lathe
and knocking your tool bit out of alignment while you're trying to
hold to plus or minus a thou and not even coming close, but there it
is.

Did I mention that the center of your plug is drilled & tapped to
match the thread of your tool? No? Well, never mind... Make sure
the threaded bore is perfectly SQUARE with our plug. In fact, you may
wanna do the one before the other. Even to machining a threaded spud
for the nose of your lathe's spindle and screwing the plug to that.
(It's a MACHINE TOOL fer crysakes! It's SUPPOSED to be rigid,
accurate, expensive and a pain in the ass to make.)

To align the tool to the case you simply install the plug in the hole
and torque down the fasteners in an easy-X pattern, rotating the tool
by hand to ensure it doesn't bind at any point. Now you can remove
the plug, install the cutter and make your FIRST CUT of the THREE you
must make.

Easy, eh? In fact, if you DON'T do all that stuff the odds are you'll
simply ruin the crankcase. Oh, it'll be good enough for the Kiddie
Trade -- that's why they made the things! But if you don't have a
RIGID fixture to support the crankcase half, and don't have a RIGID
surface under the fixture, and don't a method of aligning the cutter
to the true center of the existing spigot-bore -- you really don't
have much of a tool.

Which isn't to say the engine won't run. Slap some chrome on it,
noisy exhaust system, you're an Instant Expert. The Bad News is what
happens a couple years down the road. But by then the Kiddies will
have gotten through their Volkswagen Phase and nobody really cares if
the engine was a total piece of *** because the NEXT Kiddie is
already planning to build himself a new engine that will be like
totally awesome. And kewl, too. Or some damn thing.

Now, I'm sure a few folks will detect a hint of negativity in this
message but to give credit where due I DID tell you how to do it. And
if you wanna do it RIGHT I'll even tell you that too: Use a milling
machine.

-Bob Hoover

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