OK. The plans for the (brass) spraybar showed you turning it down to
1/8", drilling a 1/16" hole, then threading it 5-44. I did. It's bent.

Should I have tried tapping it _before_ drilling out most of the meat?
Should I be single-point threading it (with support from a center,
obviously)?

(I think it's straight enough to be useful -- if I jam the needle valve
wire into it it kinda straightens out. But I don't want this to happen
on job #2).

Assuming it works I'm just a needle valve and needle valve carrier away
from a working engine! Too bad all I'm making is the venturi.

--

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

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

On Fri, 17 Sep 2010 23:38:50 -0700, Tim Wescott
wrote:

OK. The plans for the (brass) spraybar showed you turning it down to
1/8", drilling a 1/16" hole, then threading it 5-44. I did. It's bent.

Should I have tried tapping it _before_ drilling out most of the meat?
Should I be single-point threading it (with support from a center,
obviously)?

(I think it's straight enough to be useful -- if I jam the needle valve
wire into it it kinda straightens out. But I don't want this to happen
on job #2).

Assuming it works I'm just a needle valve and needle valve carrier away
from a working engine! Too bad all I'm making is the venturi.


You don't actually need a spray bar. You can use a nut sort of thing,
in a tapped hole on one side of the intake and a and a jet screwed
into the other. The needle screws through the nut, across the intake
and into the jet. I don't know how well they would work at some
intermediate setting but they worked well at full throttle settings. I
believe that the tethered cars originated the idea, at least the first
I saw was a Dooling .29 which came form that sort of environment.

Cheers,

John D. Slocomb
(jdslocombatgmail)

On 09/18/2010 05:24 AM, J. D. Slocomb wrote:
On Fri, 17 Sep 2010 23:38:50 -0700, Tim
wrote:

OK. The plans for the (brass) spraybar showed you turning it down to
1/8", drilling a 1/16" hole, then threading it 5-44. I did. It's bent.

Should I have tried tapping it _before_ drilling out most of the meat?
Should I be single-point threading it (with support from a center,
obviously)?

(I think it's straight enough to be useful -- if I jam the needle valve
wire into it it kinda straightens out. But I don't want this to happen
on job #2).

Assuming it works I'm just a needle valve and needle valve carrier away
from a working engine! Too bad all I'm making is the venturi.


You don't actually need a spray bar. You can use a nut sort of thing,
in a tapped hole on one side of the intake and a and a jet screwed
into the other. The needle screws through the nut, across the intake
and into the jet. I don't know how well they would work at some
intermediate setting but they worked well at full throttle settings. I
believe that the tethered cars originated the idea, at least the first
I saw was a Dooling .29 which came form that sort of environment.

I know -- that's actually the way that most RC carburetors introduce
fuel into the airstream.

But this engine is designed to have the venturi held in by a spraybar
that goes all the way across, so that's how I'm doing it.

--

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

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

On Fri, 17 Sep 2010 23:38:50 -0700, Tim Wescott
wrote:

OK. The plans for the (brass) spraybar showed you turning it down to
1/8", drilling a 1/16" hole, then threading it 5-44. I did. It's bent.

Should I have tried tapping it _before_ drilling out most of the meat?
Should I be single-point threading it (with support from a center,
obviously)?

(I think it's straight enough to be useful -- if I jam the needle valve
wire into it it kinda straightens out. But I don't want this to happen
on job #2).

Assuming it works I'm just a needle valve and needle valve carrier away
from a working engine! Too bad all I'm making is the venturi.

You're in a whole 'nuther size range than I work in. That said, I
often single point 'almost' to size and use the tap just for that last
little shave on something light and tight specs.

karl

On 09/18/2010 11:08 AM, Karl Townsend wrote:
On Fri, 17 Sep 2010 23:38:50 -0700, Tim
wrote:

OK. The plans for the (brass) spraybar showed you turning it down to
1/8", drilling a 1/16" hole, then threading it 5-44. I did. It's bent.

Should I have tried tapping it _before_ drilling out most of the meat?
Should I be single-point threading it (with support from a center,
obviously)?

(I think it's straight enough to be useful -- if I jam the needle valve
wire into it it kinda straightens out. But I don't want this to happen
on job #2).

Assuming it works I'm just a needle valve and needle valve carrier away
from a working engine! Too bad all I'm making is the venturi.

You're in a whole 'nuther size range than I work in. That said, I
often single point 'almost' to size and use the tap just for that last
little shave on something light and tight specs.

karl

Hmm. That may just do. I thought about threading before drilling, but
what if I bend it then? Then I'm totally screwed!

Ah well -- I'm still learning. And what I have _will_ work, if for no
other reason that when you shove a piece of 1/16" music wire into that
bent, threaded section it straightens right up!

--

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

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

On 09/18/2010 09:50 PM, DoN. Nichols wrote:
On 2010-09-18, Tim wrote:
OK. The plans for the (brass) spraybar showed you turning it down to
1/8", drilling a 1/16" hole, then threading it 5-44. I did. It's bent.

More detail needed. I can't properly visualize this.

Should I have tried tapping it _before_ drilling out most of the meat?
Should I be single-point threading it (with support from a center,
obviously)?

You are talking about "tapping" and "single-point threading" in
almost the same sentence. Is this an internal thread (thus to be tapped
given the size) or an external thread (a good candidate for single-point
threading).

You know, I distinctly remember thinking to my self that I didn't know
if there was a word for making an outside thread other than "threading",
and deciding that I would use that. I don't know how the word "tapping"
managed to creep in there any way.

If it is an external thread -- and not the full length -- I
would probably single-point thread it before drilling.

-- snip --

So -- for those of us who don't know your engine and the
instructions for making the parts -- details, please.

There are no instructions for making the parts -- I have some model
engine plans, but no detailed instructions. The engine itself isn't any
of the engines for which I have plans for -- it's an old OS MAX 25S.
But the venturi construction is pretty standard across the model
airplane industry: Someone made it work right in the 1930's, and
everyone has copied it since.

Here's a picture of the thing made and assembled to the engine:
http://www.metalworking.com/dropbox/venturi_done.jpg. The part in
question is the spraybar, which goes through the venturi and venturi
housing on the engine. It retains the venturi (against an O-ring), and
it feeds a metered amount of fuel into the flow as the engine
(hopefully*) runs.

The spraybar construction is:

* Nipple on one end for the fuel tubing (seen on left in picture)
* Hex section, to make it into a "bolt", for tightening and as a
reference to see where the spray hole ends up.
* 1/8" clear section through venturi, this is the 'actual spraybar'
part**.
* 5-44 threaded section, starting about 1/2 inch away from the
flat on the hex section, and extending 1/2 inch out to the end.
* a 1/16" hole that extends about 7/8" into the spraybar from
the threaded end, then a 50 mil section to act as a stop for
the needle valve, then a 1/16" hole from the nipple.

The needle is just a piece of 1/16" music wire (I don't have any drill
rod that size, and needle wire will work), ground to a point, shoved
into the spraybar, and with the carrier soldered onto the end. The
carrier is tapped (really tapped) 5-44 then split across the threads to
provide dependable friction; this provides the adjustment of the needle.

I'm putting a drawing of the spraybar up onto the dropbox, so you can
get an idea of the construction of the thing. If it shows up it'll be
at http://www.metalworking.com/dropbox/...i_spraybar.jpg.

* Actually the engine runs quite well, if a bit down on power. I need
to build one or two more venturis in larger sizes, and experiment.

** Following traditional model engine practice, the venturi throat is
straight; the obstruction of the spraybar creates the necessary choking
down for the venturi effect to happen.

--

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

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

On 09/17/2010 11:38 PM, Tim Wescott wrote:
OK. The plans for the (brass) spraybar showed you turning it down to
1/8", drilling a 1/16" hole, then threading it 5-44. I did. It's bent.

Should I have tried tapping it _before_ drilling out most of the meat?
Should I be single-point threading it (with support from a center,
obviously)?

(I think it's straight enough to be useful -- if I jam the needle valve
wire into it it kinda straightens out. But I don't want this to happen
on job #2).

Assuming it works I'm just a needle valve and needle valve carrier away
from a working engine! Too bad all I'm making is the venturi.

I took Karl's suggestion and single-point threaded it, then finished the
job with the die. It was very slightly bent when I was done -- more, I
think, because I kept at the die-threading until there was _very
definitely_ more resistance, instead of just a hint. If I do another
one, I'll have to remember not to push things.

And the needle goes into the hole very sweetly -- there's some
resistance, but it just slides right in without tools or anything.

(note that this is not the case when I drill the hole with a 1/16" drill
-- in that case, the ever so slightly oversized music wire that I'm
using binds up. So I made a "D" bit reamer with a bit of the same music
wire, and after a pass or two with that the needle goes right in. I
don't know if that's really bad or really clever. Maybe both...)

--

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

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

On 2010-09-19, Tim Wescott wrote:
On 09/18/2010 09:50 PM, DoN. Nichols wrote:
On 2010-09-18, Tim wrote:

[ ... ]

You are talking about "tapping" and "single-point threading" in
almost the same sentence. Is this an internal thread (thus to be tapped
given the size) or an external thread (a good candidate for single-point
threading).

You know, I distinctly remember thinking to my self that I didn't know
if there was a word for making an outside thread other than "threading",
and deciding that I would use that. I don't know how the word "tapping"
managed to creep in there any way.

I think that "threading" is the term -- and perhaps could
include "threading with a die" if you don't single-point it.

So -- for those of us who don't know your engine and the
instructions for making the parts -- details, please.

There are no instructions for making the parts -- I have some model
engine plans, but no detailed instructions. The engine itself isn't any
of the engines for which I have plans for -- it's an old OS MAX 25S.
But the venturi construction is pretty standard across the model
airplane industry: Someone made it work right in the 1930's, and
everyone has copied it since.

O.K.

Here's a picture of the thing made and assembled to the engine:
http://www.metalworking.com/dropbox/venturi_done.jpg. The part in
question is the spraybar, which goes through the venturi and venturi
housing on the engine. It retains the venturi (against an O-ring), and
it feeds a metered amount of fuel into the flow as the engine
(hopefully*) runs.

[ ... ]

Construction is fairly clear from the image -- but the (now
snipped) text gave some additional detail.

The needle is just a piece of 1/16" music wire (I don't have any drill
rod that size, and needle wire will work), ground to a point, shoved
into the spraybar, and with the carrier soldered onto the end. The
carrier is tapped (really tapped) 5-44 then split across the threads to
provide dependable friction; this provides the adjustment of the needle.

O.K.

I'm putting a drawing of the spraybar up onto the dropbox, so you can
get an idea of the construction of the thing. If it shows up it'll be
at http://www.metalworking.com/dropbox/...i_spraybar.jpg.

Hmm .... that turns out to be:

http://www.metalworking.com/dropbox/...i_spraybar.png

(".png", not ".jpg" so my first grap for it with wget failed. I had to
actually use a browser to see what the name really was.

Anyway -- how would *I* make this?

1) Turn down for a little over the first 1/2" and single-point
thread it while solid and reinforced by the hex stock.

2) Turn the rest (beyond the thread) down to the required
diameter.

3) Turn it around and hold it in a collet by the cylindrical part
while turning the Nipple.

4) While held in that position, drill the fuel passage to 0.0625".

5) Still in that position, drill the 0.050" needle valve hole.

6) Reverse it, and hold in a hex collet (if available) or 3-jaw
chuck otherwise, and drill the 0.0625" from that end.

7) Cross-drill the 0.125" fuel outlet.

And, if possible I would look for a finer thread -- so you don't
use up as much of the space between the bottom of the threads and the
bore. Let's see -- tap drill is 0.102" which means that the minor
dimension of the thread will be even smaller. But assuming 0.100" for
the minor (probably even smaller) with 0.0625" bore, that leaves only
0.0188" wall thickness.

A 5-80 (if you can find a matching tap) would have a tap drill
of 0.112", so call it 0.110" minor diameter, and that would take your
minimum wall thickness up to 0.0238" -- a significant improvement.

Good Luck,
DoN.

--
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Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

On 09/19/2010 10:19 PM, DoN. Nichols wrote:
On 2010-09-19, Tim wrote:
On 09/18/2010 09:50 PM, DoN. Nichols wrote:
On 2010-09-18, Tim wrote:

[ ... ]

You are talking about "tapping" and "single-point threading" in
almost the same sentence. Is this an internal thread (thus to be tapped
given the size) or an external thread (a good candidate for single-point
threading).

You know, I distinctly remember thinking to my self that I didn't know
if there was a word for making an outside thread other than "threading",
and deciding that I would use that. I don't know how the word "tapping"
managed to creep in there any way.

I think that "threading" is the term -- and perhaps could
include "threading with a die" if you don't single-point it.

So -- for those of us who don't know your engine and the
instructions for making the parts -- details, please.

There are no instructions for making the parts -- I have some model
engine plans, but no detailed instructions. The engine itself isn't any
of the engines for which I have plans for -- it's an old OS MAX 25S.
But the venturi construction is pretty standard across the model
airplane industry: Someone made it work right in the 1930's, and
everyone has copied it since.

O.K.

Here's a picture of the thing made and assembled to the engine:
http://www.metalworking.com/dropbox/venturi_done.jpg. The part in
question is the spraybar, which goes through the venturi and venturi
housing on the engine. It retains the venturi (against an O-ring), and
it feeds a metered amount of fuel into the flow as the engine
(hopefully*) runs.

[ ... ]

Construction is fairly clear from the image -- but the (now
snipped) text gave some additional detail.

The needle is just a piece of 1/16" music wire (I don't have any drill
rod that size, and needle wire will work), ground to a point, shoved
into the spraybar, and with the carrier soldered onto the end. The
carrier is tapped (really tapped) 5-44 then split across the threads to
provide dependable friction; this provides the adjustment of the needle.

O.K.

I'm putting a drawing of the spraybar up onto the dropbox, so you can
get an idea of the construction of the thing. If it shows up it'll be
at http://www.metalworking.com/dropbox/...i_spraybar.jpg.

Hmm .... that turns out to be:

http://www.metalworking.com/dropbox/...i_spraybar.png

(".png", not ".jpg" so my first grap for it with wget failed. I had to
actually use a browser to see what the name really was.

Anyway -- how would *I* make this?

1) Turn down for a little over the first 1/2" and single-point
thread it while solid and reinforced by the hex stock.

2) Turn the rest (beyond the thread) down to the required
diameter.

3) Turn it around and hold it in a collet by the cylindrical part
while turning the Nipple.

4) While held in that position, drill the fuel passage to 0.0625".

5) Still in that position, drill the 0.050" needle valve hole.

6) Reverse it, and hold in a hex collet (if available) or 3-jaw
chuck otherwise, and drill the 0.0625" from that end.

7) Cross-drill the 0.125" fuel outlet.

And, if possible I would look for a finer thread -- so you don't
use up as much of the space between the bottom of the threads and the
bore. Let's see -- tap drill is 0.102" which means that the minor
dimension of the thread will be even smaller. But assuming 0.100" for
the minor (probably even smaller) with 0.0625" bore, that leaves only
0.0188" wall thickness.

A 5-80 (if you can find a matching tap) would have a tap drill
of 0.112", so call it 0.110" minor diameter, and that would take your
minimum wall thickness up to 0.0238" -- a significant improvement.

There's not a good selection of off-the-shelf taps & dies that I found
for this -- #5-44 was about the best, unless I wanted to spring for M3 x
0.35 (and I didn't check to see what the minor diameter was).

It does, indeed, leave a hideously thin wall.

I keep finding myself fantasizing about making a 5-80 tap from some 1/8"
drill rod and some ingenuity. I'll hold it in...

--

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

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

On 2010-09-20, Tim Wescott wrote:
On 09/19/2010 10:19 PM, DoN. Nichols wrote:

[ ... ]

A 5-80 (if you can find a matching tap) would have a tap drill
of 0.112", so call it 0.110" minor diameter, and that would take your
minimum wall thickness up to 0.0238" -- a significant improvement.

There's not a good selection of off-the-shelf taps & dies that I found
for this -- #5-44 was about the best, unless I wanted to spring for M3 x
0.35 (and I didn't check to see what the minor diameter was).

Hmm ... 44 TPI converted to metric is a pitch of 0.5773 mm, so
the M3 x 0.35 is finer significantly. IIRC, you can use the metric
pitch as the diameter reduction, so that would be 2.65mm minor diameter,
or 0.104" minor diameter -- because you are starting from a smaller
major diameter -- 0.1181" instead of 0.125"

It does, indeed, leave a hideously thin wall.

I keep finding myself fantasizing about making a 5-80 tap from some 1/8"
drill rod and some ingenuity. I'll hold it in...

While you're about it -- how fine a thread will your lathe cut?
Go for 240 TPI. :-)

Enjoy,
DoN.

--
Remove oil spill source from e-mail
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

On 09/20/2010 10:40 PM, DoN. Nichols wrote:
On 2010-09-20, Tim wrote:
On 09/19/2010 10:19 PM, DoN. Nichols wrote:

[ ... ]

A 5-80 (if you can find a matching tap) would have a tap drill
of 0.112", so call it 0.110" minor diameter, and that would take your
minimum wall thickness up to 0.0238" -- a significant improvement.

There's not a good selection of off-the-shelf taps& dies that I found
for this -- #5-44 was about the best, unless I wanted to spring for M3 x
0.35 (and I didn't check to see what the minor diameter was).

Hmm ... 44 TPI converted to metric is a pitch of 0.5773 mm, so
the M3 x 0.35 is finer significantly. IIRC, you can use the metric
pitch as the diameter reduction, so that would be 2.65mm minor diameter,
or 0.104" minor diameter -- because you are starting from a smaller
major diameter -- 0.1181" instead of 0.125"

It does, indeed, leave a hideously thin wall.

I keep finding myself fantasizing about making a 5-80 tap from some 1/8"
drill rod and some ingenuity. I'll hold it in...

While you're about it -- how fine a thread will your lathe cut?
Go for 240 TPI. :-)

It's not the world's best lathe (it's a Smithy). I could probably make
a clean 80TPI cut, but I think I'd have to plan on a reject or three.

Actually, most of the motors I fly with are pretty small: I'm thinking
that I could use a smaller needle to get back some wall thickness if I
really needed it. But these turn out to have plenty of adjustment
range, they're not obtrusively large, and (most important!) they work.
Crash damage isn't an issue, mostly because if you land a plane on the
needle valve you can pretty much assume that it's toast, and hope that
you didn't take the crankcase with it.

--

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

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