I'm a wannabe miniature internal-combustion engine builder. To further
the task of taking the 'wannabe' out of the description, I'm considering
taking an old Cox Medallion .15 and machining a new cylinder and piston
set for it (the original was allowed to run too lean, overheated, and
now cylinder and piston are slightly oval; since the piston is free to
rotate on the rod you can run it for just a little bit before it binds up).

This cylinder has an extra-thick wall up to the exhaust ports, and
rather than transfer ports going through to the crankshaft, it has
transfer slots that come up from the crankshaft to between the exhaust port.

So from the bottom of the cylinder it looks kind of like this (slots
exaggerated, and I hope I can make it more round than the drawing!):

-------
/ ----- \
/_/ \_\
|(_ _)|
\ \ / /
\ ----- /
-------

The normal operations that must be performed on a part of this type by
amateur builders is to bore the inside of the cylinder to size, then lap
it to final finished size, then fit the piston.

My problem is that I am trying to decide when I should cut the transfer
slots. Should I build the whole cylinder, get it lapped and fit to the
piston all nice and pretty, and then take a mill and hack out the slots?
Or should I make the slots, bore the cylinder, finish it off and lap
it? Or should I finish machine it, make the slots and then lap?

Each one of these carries interesting possibilities for making a
cylinder that isn't quite round at the bottom.

Making the slots first of all would let me use a plain old drill bit,
but would make for a lot of interrupted cutting while I'm making the
bore, and possibly machining in some not-quite-roundness, and would
force the lap to work in an oddball cylinder, possibly softening the
transition from cylinder wall to slot.

Making the slots after boring but before lapping would save me from
machining in the not-quite-roundness, but would create the possibility
of the cylinder warping from the stress of milling or from relaxation of
internal stresses. It still leaves me with the odd lapping problem.
Finally, it means that I have to use my 3-in-1 Smithy as a milling
machine, and it is neither convenient to use nor terrifically rigid in
this role.

Making the slots after lapping leaves me with the stress-relief and
milling issues, and it may well raise honking big burrs. It just
doesn't strike as the clean way to go -- ripping into a nice, lapped
surface with a milling cutter just seems _wrong_.

So how would you do this? And why?

Thanks.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

On Fri, 04 Jul 2008 14:15:47 -0700, Tim Wescott
wrote:

I'm a wannabe miniature internal-combustion engine builder. To further
the task of taking the 'wannabe' out of the description, I'm considering
taking an old Cox Medallion .15 and machining a new cylinder and piston
set for it (the original was allowed to run too lean, overheated, and
now cylinder and piston are slightly oval; since the piston is free to
rotate on the rod you can run it for just a little bit before it binds up).

This cylinder has an extra-thick wall up to the exhaust ports, and
rather than transfer ports going through to the crankshaft, it has
transfer slots that come up from the crankshaft to between the exhaust port.

So from the bottom of the cylinder it looks kind of like this (slots
exaggerated, and I hope I can make it more round than the drawing!):

-------
/ ----- \
/_/ \_\
|(_ _)|
\ \ / /
\ ----- /
-------

The normal operations that must be performed on a part of this type by
amateur builders is to bore the inside of the cylinder to size, then lap
it to final finished size, then fit the piston.

My problem is that I am trying to decide when I should cut the transfer
slots. Should I build the whole cylinder, get it lapped and fit to the
piston all nice and pretty, and then take a mill and hack out the slots?
Or should I make the slots, bore the cylinder, finish it off and lap
it? Or should I finish machine it, make the slots and then lap?

Each one of these carries interesting possibilities for making a
cylinder that isn't quite round at the bottom.

Making the slots first of all would let me use a plain old drill bit,
but would make for a lot of interrupted cutting while I'm making the
bore, and possibly machining in some not-quite-roundness, and would
force the lap to work in an oddball cylinder, possibly softening the
transition from cylinder wall to slot.

Making the slots after boring but before lapping would save me from
machining in the not-quite-roundness, but would create the possibility
of the cylinder warping from the stress of milling or from relaxation of
internal stresses. It still leaves me with the odd lapping problem.
Finally, it means that I have to use my 3-in-1 Smithy as a milling
machine, and it is neither convenient to use nor terrifically rigid in
this role.

Making the slots after lapping leaves me with the stress-relief and
milling issues, and it may well raise honking big burrs. It just
doesn't strike as the clean way to go -- ripping into a nice, lapped
surface with a milling cutter just seems _wrong_.

So how would you do this? And why?

Thanks.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html
Greetings Tim,
I would lap last. Because a properly made and used lap will keep the
bore round despite the port cutouts. This means that you can mill the
ports and then file if need be to final shape. Care must be taken when
deburring the cylinder side of the ports because the boring and
lapping will only be removing a small amount of metal. The interrupted
cut when boring may seem to be a bit of a pain but when filing the
ports to get them to shape and smooth inside it will be easier if you
don't need to worry so much about the edges being rounded over where
the port intersects the bore. The lapping operation of course needs to
leave the ports with sharp edges.
Eric

I'm a wannabe miniature internal-combustion engine builder. To further
the task of taking the 'wannabe' out of the description, I'm considering
taking an old Cox Medallion .15 and machining a new cylinder and piston
set for it (the original was allowed to run too lean, overheated, and now
cylinder and piston are slightly oval; since the piston is free to rotate
on the rod you can run it for just a little bit before it binds up).

This cylinder has an extra-thick wall up to the exhaust ports, and rather
than transfer ports going through to the crankshaft, it has transfer slots
that come up from the crankshaft to between the exhaust port.

So from the bottom of the cylinder it looks kind of like this (slots
exaggerated, and I hope I can make it more round than the drawing!):

-------
/ ----- \
/_/ \_\
|(_ _)|
\ \ / /
\ ----- /
-------

The normal operations that must be performed on a part of this type by
amateur builders is to bore the inside of the cylinder to size, then lap
it to final finished size, then fit the piston.

My problem is that I am trying to decide when I should cut the transfer
slots. Should I build the whole cylinder, get it lapped and fit to the
piston all nice and pretty, and then take a mill and hack out the slots?
Or should I make the slots, bore the cylinder, finish it off and lap it?
Or should I finish machine it, make the slots and then lap?

Each one of these carries interesting possibilities for making a cylinder
that isn't quite round at the bottom.

Making the slots first of all would let me use a plain old drill bit, but
would make for a lot of interrupted cutting while I'm making the bore, and
possibly machining in some not-quite-roundness, and would force the lap to
work in an oddball cylinder, possibly softening the transition from
cylinder wall to slot.

Making the slots after boring but before lapping would save me from
machining in the not-quite-roundness, but would create the possibility of
the cylinder warping from the stress of milling or from relaxation of
internal stresses. It still leaves me with the odd lapping problem.
Finally, it means that I have to use my 3-in-1 Smithy as a milling
machine, and it is neither convenient to use nor terrifically rigid in
this role.

Making the slots after lapping leaves me with the stress-relief and
milling issues, and it may well raise honking big burrs. It just doesn't
strike as the clean way to go -- ripping into a nice, lapped surface with
a milling cutter just seems _wrong_.

So how would you do this? And why?

Thanks.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

What Eric says would work and does work for most people...But I'm not most
people...Try this on for size for machining order...

1) machine bore
2) lap/hone bore to "rough" size...something on the order of .0015-.002
under final size
3) machine side ports/slots to completion
4) the VERY last step before fitting the piston is to finish hone/lap
the bore

This order lets you have a little leeway in "damage" caused by cutting and
deburring your side ports, allows you to true the bore back to round after
cutting your ports, and allows you to leave pretty close to sharp corners
where the ports meet the bore with a minimum of fuss.

Just a thought or three.

Mike

wrote:
On Fri, 04 Jul 2008 14:15:47 -0700, Tim Wescott
wrote:

I'm a wannabe miniature internal-combustion engine builder. To further
the task of taking the 'wannabe' out of the description, I'm considering
taking an old Cox Medallion .15 and machining a new cylinder and piston
set for it (the original was allowed to run too lean, overheated, and
now cylinder and piston are slightly oval; since the piston is free to
rotate on the rod you can run it for just a little bit before it binds up).

This cylinder has an extra-thick wall up to the exhaust ports, and
rather than transfer ports going through to the crankshaft, it has
transfer slots that come up from the crankshaft to between the exhaust port.

So from the bottom of the cylinder it looks kind of like this (slots
exaggerated, and I hope I can make it more round than the drawing!):

-------
/ ----- \
/_/ \_\
|(_ _)|
\ \ / /
\ ----- /
-------

The normal operations that must be performed on a part of this type by
amateur builders is to bore the inside of the cylinder to size, then lap
it to final finished size, then fit the piston.

My problem is that I am trying to decide when I should cut the transfer
slots. Should I build the whole cylinder, get it lapped and fit to the
piston all nice and pretty, and then take a mill and hack out the slots?
Or should I make the slots, bore the cylinder, finish it off and lap
it? Or should I finish machine it, make the slots and then lap?

Each one of these carries interesting possibilities for making a
cylinder that isn't quite round at the bottom.

Making the slots first of all would let me use a plain old drill bit,
but would make for a lot of interrupted cutting while I'm making the
bore, and possibly machining in some not-quite-roundness, and would
force the lap to work in an oddball cylinder, possibly softening the
transition from cylinder wall to slot.

Making the slots after boring but before lapping would save me from
machining in the not-quite-roundness, but would create the possibility
of the cylinder warping from the stress of milling or from relaxation of
internal stresses. It still leaves me with the odd lapping problem.
Finally, it means that I have to use my 3-in-1 Smithy as a milling
machine, and it is neither convenient to use nor terrifically rigid in
this role.

Making the slots after lapping leaves me with the stress-relief and
milling issues, and it may well raise honking big burrs. It just
doesn't strike as the clean way to go -- ripping into a nice, lapped
surface with a milling cutter just seems _wrong_.

So how would you do this? And why?

Thanks.

Greetings Tim,
I would lap last. Because a properly made and used lap will keep the
bore round despite the port cutouts. This means that you can mill the
ports and then file if need be to final shape. Care must be taken when
deburring the cylinder side of the ports because the boring and
lapping will only be removing a small amount of metal. The interrupted
cut when boring may seem to be a bit of a pain but when filing the
ports to get them to shape and smooth inside it will be easier if you
don't need to worry so much about the edges being rounded over where
the port intersects the bore. The lapping operation of course needs to
leave the ports with sharp edges.
Eric

Yea, I think lapping last makes the most sense. I think drilling the
slots first, then boring the cylinder, then lapping is probably the way
to go -- but I've never done it before (or I wouldn't be a wannabe!).

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

"Tim Wescott" wrote in message
...

the original was allowed to run too lean, overheated, and
now cylinder and piston are slightly oval; since the piston is free to
rotate on the rod you can run it for just a little bit before it binds
up).

Not to stop you from making a new cylinder, but I am curious, what would
happen if one were to get a ball bearing the right diameter and press it
through the cylinder? (Kind of like when they re-size brass cartrages prior
to reloading.)

--

Roger Shoaf

About the time I had mastered getting the toothpaste back in the tube, then
they come up with this striped stuff.

Roger Shoaf wrote:
"Tim Wescott" wrote in message
...

the original was allowed to run too lean, overheated, and
now cylinder and piston are slightly oval; since the piston is free to
rotate on the rod you can run it for just a little bit before it binds
up).

Not to stop you from making a new cylinder, but I am curious, what would
happen if one were to get a ball bearing the right diameter and press it
through the cylinder? (Kind of like when they re-size brass cartrages prior
to reloading.)

With the equipment I have in the shop right now? Probably a stuck ball
bearing, possibly covered blood and lonely while I take a trip to the
emergency room. I'm not sure that it wouldn't mangle the push end of
the cylinder, even with the 'right' equipment.

I hadn't thought of ball-forming the old cylinder. If I were seriously
interested in getting the engine working with the least work I'd be
searching out a NOS COX cylinder/piston set. Or I'd be asking just how
to go about honing, lapping or otherwise cutting the cylinder back to
roundness so I could build a slightly oversized piston.

The truth of the matter is, however, that before I go cutting out the
dozen or so different parts of a from-scratch working engine, I'd rather
just try making the five needed for a cylinder/piston set.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

On Sat, 05 Jul 2008 09:34:26 -0700, Tim Wescott
wrote:

Roger Shoaf wrote:
"Tim Wescott" wrote in message
...

the original was allowed to run too lean, overheated, and
now cylinder and piston are slightly oval; since the piston is free to
rotate on the rod you can run it for just a little bit before it binds
up).

Not to stop you from making a new cylinder, but I am curious, what would
happen if one were to get a ball bearing the right diameter and press it
through the cylinder? (Kind of like when they re-size brass cartrages prior
to reloading.)

With the equipment I have in the shop right now? Probably a stuck ball
bearing, possibly covered blood and lonely while I take a trip to the
emergency room. I'm not sure that it wouldn't mangle the push end of
the cylinder, even with the 'right' equipment.

I hadn't thought of ball-forming the old cylinder. If I were seriously
interested in getting the engine working with the least work I'd be
searching out a NOS COX cylinder/piston set. Or I'd be asking just how
to go about honing, lapping or otherwise cutting the cylinder back to
roundness so I could build a slightly oversized piston.

The truth of the matter is, however, that before I go cutting out the
dozen or so different parts of a from-scratch working engine, I'd rather
just try making the five needed for a cylinder/piston set.


The normal way to machine a cylinder such as you describe would be to
rough machine the bore; finish machine the bypass areas and then
finish machine the bore.

For finish machining you might look into adapting a Demril tool as a
tool post grinder which would make it easy to grind the bore to
finished size.


Bruce-in-Bangkok
(correct Address is bpaige125atgmaildotcom)

"Tim Wescott" wrote in message
...
With the equipment I have in the shop right now? Probably a stuck ball
bearing, possibly covered blood and lonely while I take a trip to the
emergency room. I'm not sure that it wouldn't mangle the push end of
the cylinder, even with the 'right' equipment.


If I were to try, I think I would remove the crank shaft and piston fron the
block and leave the cylinder attached.to the block. A chunk of pipe in the
drill press to apply pressure top the ball and all the stuck ball and
bleeding could probably be avoided.



I hadn't thought of ball-forming the old cylinder. If I were seriously
interested in getting the engine working with the least work I'd be
searching out a NOS COX cylinder/piston set. Or I'd be asking just how
to go about honing, lapping or otherwise cutting the cylinder back to
roundness so I could build a slightly oversized piston.

The truth of the matter is, however, that before I go cutting out the
dozen or so different parts of a from-scratch working engine, I'd rather
just try making the five needed for a cylinder/piston set.


Why not do both?

--

Roger Shoaf

About the time I had mastered getting the toothpaste back in the tube, then
they come up with this striped stuff.

On Jul 6, 2:31*am, Bruce in Bangkok
wrote:

For finish machining you might look into adapting a Demril tool as a
tool post grinder which would make it easy to grind the bore to
finished size.
Bruce-in-Bangkok

Some older Dremels fit snugly into a copper pipe cap or reducer that
you can solder to a base.

My new Dremel mount is an upright rectangle of aluminum morticed into
the compound slot and bored in the lathe to fit the nose of the tool.
The tee slot clamp is a lawnmower wheel axle bolt which has a low-
profile hex head. A carriage bolt with a washer pounded onto the
square and cut flat on the sides works for larger tee slots.

Roger Shoaf wrote:
"Tim Wescott" wrote in message
...
With the equipment I have in the shop right now? Probably a stuck ball
bearing, possibly covered blood and lonely while I take a trip to the
emergency room. I'm not sure that it wouldn't mangle the push end of
the cylinder, even with the 'right' equipment.


If I were to try, I think I would remove the crank shaft and piston fron the
block and leave the cylinder attached.to the block. A chunk of pipe in the
drill press to apply pressure top the ball and all the stuck ball and
bleeding could probably be avoided.


I hadn't thought of ball-forming the old cylinder. If I were seriously
interested in getting the engine working with the least work I'd be
searching out a NOS COX cylinder/piston set. Or I'd be asking just how
to go about honing, lapping or otherwise cutting the cylinder back to
roundness so I could build a slightly oversized piston.

The truth of the matter is, however, that before I go cutting out the
dozen or so different parts of a from-scratch working engine, I'd rather
just try making the five needed for a cylinder/piston set.


Why not do both?

The new Cox cylinder is for practice. Once I get this one working, and
possibly the TD 09, then I'm planning on building an Owens Mate (see
http://www.modelenginenews.org, look under "projects").

Eventually I want to build a 1/6 scale model A engine, to fly a 1/6
scale Pietenpol Air Camper. This may not happen until I retire, but
it's an excuse to keep buying stuff for the machine shop. In the mean
time I intend to have fun building engines.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

"Tim Wescott" wrote in message
...

The new Cox cylinder is for practice. Once I get this one working, and
possibly the TD 09, then I'm planning on building an Owens Mate (see
http://www.modelenginenews.org, look under "projects").

An interesting site. However, I have to comment on something that I keep
seeing in print that has been driving me nuts -- in the first article on
building EDMs, they say it was a Russian invention.

It was not a Russian invention. That baloney was perpetuated by Charmilles
EDM in the early '50s. It actually was invented by the predecessor to the US
company Elox, who sold two of their servo-type
tap-buster/square-hole-cutting eroders to the Soviet government two years
before we entered WWII. The Soviets claim they invented it in the early
years of the war.

Back in '77, when I wrote a lengthy article on EDMs for _American
Machinist_, I studied the history in great detail, and read the translated
papers by the Lazarenkos, who claimed the invention. They added some minor
twists but it was basically the proto-Elox machine.

Just setting the record straight. d8-)

--
Ed Huntress

Ed Huntress wrote:
"Tim Wescott" wrote in message
...

The new Cox cylinder is for practice. Once I get this one working, and
possibly the TD 09, then I'm planning on building an Owens Mate (see
http://www.modelenginenews.org, look under "projects").

An interesting site. However, I have to comment on something that I keep
seeing in print that has been driving me nuts -- in the first article on
building EDMs, they say it was a Russian invention.

It was not a Russian invention. That baloney was perpetuated by Charmilles
EDM in the early '50s. It actually was invented by the predecessor to the US
company Elox, who sold two of their servo-type
tap-buster/square-hole-cutting eroders to the Soviet government two years
before we entered WWII. The Soviets claim they invented it in the early
years of the war.

Back in '77, when I wrote a lengthy article on EDMs for _American
Machinist_, I studied the history in great detail, and read the translated
papers by the Lazarenkos, who claimed the invention. They added some minor
twists but it was basically the proto-Elox machine.

Just setting the record straight. d8-)

--
Ed Huntress

Send him an email. He's a good guy, and enough of an academic that an
opposing view (particularly if you can back it with citations) will be
meat and drink to him.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

"Tim Wescott" wrote in message
...
Ed Huntress wrote:
"Tim Wescott" wrote in message
...

The new Cox cylinder is for practice. Once I get this one working, and
possibly the TD 09, then I'm planning on building an Owens Mate (see
http://www.modelenginenews.org, look under "projects").

An interesting site. However, I have to comment on something that I keep
seeing in print that has been driving me nuts -- in the first article on
building EDMs, they say it was a Russian invention.

It was not a Russian invention. That baloney was perpetuated by
Charmilles EDM in the early '50s. It actually was invented by the
predecessor to the US company Elox, who sold two of their servo-type
tap-buster/square-hole-cutting eroders to the Soviet government two years
before we entered WWII. The Soviets claim they invented it in the early
years of the war.

Back in '77, when I wrote a lengthy article on EDMs for _American
Machinist_, I studied the history in great detail, and read the
translated papers by the Lazarenkos, who claimed the invention. They
added some minor twists but it was basically the proto-Elox machine.

Just setting the record straight. d8-)

--
Ed Huntress

Send him an email. He's a good guy, and enough of an academic that an
opposing view (particularly if you can back it with citations) will be
meat and drink to him.

Well, that would be very tough. I could give him leads but my guess is
they'd come up dry at this late date. I had access then to the McGraw-Hill
library, which was full of historical metalworking books and the entire
_American Machinist_ archives. I doubt if there is a complete set of those
anywhere now, except, possibly, in the Library of Congress.

I'll take a look at my old article and see what it says. We didn't use
references on those Special Reports, so I'd have to do it from memory.

--
Ed Huntress