instrument sizes

[Bill Chernoff]

Can anyone provide a diagram of a 2 1/4 inch instrument cutout? I found one
for the 3 1/8, but not the smaller size.

I've googled and googled again...

Thanks in advance.

Bill

[Jim Carriere]

Bill Chernoff wrote:
> Can anyone provide a diagram of a 2 1/4 inch instrument cutout? I found one
> for the 3 1/8, but not the smaller size.

Bill, in the last chapter of my Kitfox build manual, there is a diagram
for that:

A big 2 5/16" (58mm) hole, and four small #18 (0.1695, just a shade
smaller than 11/64") screw holes with centers spaced 2 5/8" (67mm) apart
(ie, the little hole centers are 1 5/16" from the center of the big
hole). For comparison, the equivalent numbers on the next diagram for 3
1/8 instruments are 3 1/8" and 3 1/2" respectively.

Hope this helps. I have everything for my panel and none of it is 2
1/4, so I can't say either way if the diagram is accurate. I haven't
got to building up the panel yet anyway. FWIW, I have so far found very
few (count on one hand) errors in the manual.


Jim

PS-
Not trying to talk down to you in my description either :) Just playing
it safe so someone with the same question can archive this thread down
the road. Speaking of, the manual instructs to measure all of the holes
first before drilling, otherwise it's too easy to get the screw holes to
not quite line up (!).

[Bill Chernoff]

>
> A big 2 5/16" (58mm) hole, and four small #18 (0.1695, just a shade
> smaller than 11/64") screw holes with centers spaced 2 5/8" (67mm) apart
> (ie, the little hole centers are 1 5/16" from the center of the big
> hole). For comparison, the equivalent numbers on the next diagram for 3
> 1/8 instruments are 3 1/8" and 3 1/2" respectively.


Thanks for the quick reply!

When you say #18 screw holes I ssume you mean #18 drill. Are the screw
threads 6-32?
4-40?


> PS-
> Not trying to talk down to you in my description either :)

Not at all. I appreciate the clarity.

[Jim Carriere]

Bill Chernoff wrote:

> When you say #18 screw holes I ssume you mean #18 drill. Are the screw
> threads 6-32?
> 4-40?

Yep, #18 drill, which is a little larger than even a 10-32 thread. Here
is a very very handy reference of drill sizes, including which size you
drill before tapping which thread, that I bookmarked long ago:

http://bobmay.astronomy.net/misc/drillchart.htm

Google is my friend.

By the way, the numbers Bingelis recommends are 2 9/32" (vs 2 5/16") for
the instrument, 0.169 (vs #18, 0.1695) for the screws, and the same
spacing.

I think you can drill the screw holes any size you wish (which is
probably what I will do), #18 is what is specified in my build manual.
I think it's well oversize and leaves A LOT of room for error. It's
almost (not quite) big enough for the head of a 6-32 screw to fall through.

I'm not sure where a regular person finds a #18 bit. Aircraft Spruce
doesn't list them. Ace Hardware lists them for about three bucks, I
don't know if the stores normally stock them. Home Depot Aerospace does
not. I might use the next smallest size, and after cleaning up the
burrs with a countersink it will probably turn out close enough.

For screw sizes, umm, well, the 3 1/8 turn needle kit I got from
Aircraft Spruce came with brass 6-32 screws. Specifically, MS35214-29,
which are 6-32 x 3/4. I just checked the fit, and I don't think they'll
be quite long enough, so I'll probably order several -31 (1" long) when
I order hardware for all my other instruments.

Bingelis recommends 6-32 brass screws, adding that 8-32 while acceptable
are unnecessary.

The only instruments I have that came tapped are Westach EGT/CHT gauges,
and these are tapped for 6-32 (definitely not 8-32 or 4-40).

Last random thought, I wonder what they do in parts of the world that
have left the dark ages and embraced metric :)

[John Kunkel]

"Jim Carriere" > wrote in message
...
> Bill Chernoff wrote:
>
>>
> I'm not sure where a regular person finds a #18 bit. Aircraft Spruce
> doesn't list them. Ace Hardware lists them for about three bucks, I don't
> know if the stores normally stock them. Home Depot Aerospace does not. I
> might use the next smallest size, and after cleaning up the burrs with a
> countersink it will probably turn out close enough.

Places like Harbor Freight sell drill sets that cover the common fractional,
number and letter sizes for around $40. At that price everybody can have
just about every drill size they'll ever need.


>
> For screw sizes, umm, well, the 3 1/8 turn needle kit I got from Aircraft
> Spruce came with brass 6-32 screws. Specifically, MS35214-29, which are
> 6-32 x 3/4. I just checked the fit, and I don't think they'll be quite
> long enough, so I'll probably order several -31 (1" long) when I order
> hardware for all my other instruments.

6-32 has been the standard size for instrument screws, brass screws limit
the amount of magnetic material in the vicinity of the compass.
Instruments that aren't threaded or have a captive nut usually have a hole
somewhat larger than the body of a #6 screw, this is to allow for the "legs"
of the commonly used NAS 487 instrument nut.

[karel]

"Jim Carriere" > wrote in message
...

> Last random thought, I wonder what they do in parts of the world that have
> left the dark ages and embraced metric :)

}:-)
that's the easy part:
-) if it's just a plain hole, find the proper length & diameter & fit
-) it it's threaded and needs to be,
run the next larger reamer (?) in metric, then proceed as above

for those unaware: metric screws, bolts &C only have a diameter and a length
M4*40 means it is 40 mm long and will pass a 4mm hole,
now isn't that all there is to say?

[Bob Kuykendall]

Earlier, karel wrote:
> ...for those unaware: metric screws, bolts &C only have a diameter and a length
> M4*40 means it is 40 mm long and will pass a 4mm hole,
> now isn't that all there is to say?

Um, no, not quite. Like inch-size fasteners, metric fasteners will
often have more than one thread pitch available. I know I've spent more
than a little time sorting M10 nuts into 1.25mm and 1.5mm thread
pitches.

[karel]

"Bob Kuykendall" > wrote in message
oups.com...
> Earlier, karel wrote:
>> ...for those unaware: metric screws, bolts &C only have a diameter and a
>> length
>> M4*40 means it is 40 mm long and will pass a 4mm hole,
>> now isn't that all there is to say?
>
> Um, no, not quite. Like inch-size fasteners, metric fasteners will
> often have more than one thread pitch available. I know I've spent more
> than a little time sorting M10 nuts into 1.25mm and 1.5mm thread
> pitches.

Um, well, err, scratch...

In 30 years of shade-tree mechanics I never came across such a thing...
And I'm quite sure the thread pitch will be defined somewhere in DIN
for the various diameters
though I'd have to search for the reference text.

There's some creativity available across the pond!
Now to find some more useful application for it...
KA

[Jim Carriere]

Just a followup to this thread (timing is everything...), I had some
success using 2-1/4" and 3-1/8" holesaws and match-drilling the
screwholes. This is pretty long...

I started the screwholes with a long 1/8" bit, and with these you want
to be very very very particular about getting it centered, then slightly
enlarged them (9/64 or 5/32 as necessary... depending on how far
off-center my match-drilling was), and finally countersunk the cockpit
side of the hole.

Minor "gotchas" and notes:

Westach 2-1/4" EGT/CHT gauges come with their screw holes pre-tapped,
and a 1/8" bit is a bit too large (it will chew up 6-32 threads).

I just about wore out my fly cutter making one very ugly 2-5/8" hole
(probably too much rpm), hence I decided to try holesaws. The hardware
store holesaws made holes slightly undersize. I had to enlarge some of
my 2-1/4" and 3-1/8" holes using a Dremel sanding drum and about ten
minutes of patience per hole. The 2" automotive instruments required
more minutes of patience.

You can trim/debur/countersink big holes in 0.063" aluminum using a
utility knife and file.

Here are the important points of how I made the big holes:

1) clamp the workpiece to plywood (the plywood will stabilize the 1/4"
bit in the middle of the holesaw, otherwise the holesaw will try to
wander ALL OVER THE PLACE!)
2) drill a 1/8" pilot hole where the center of the instrument will be.
3) use the hole saw at low speed (I have a large two-handed variable
speed/max 850rpm drill but used about half that speed... only had a few
very minor kickbacks)

(I don't have a drill press)

[Ernest Christley]

Jim Carriere wrote:
> Just a followup to this thread (timing is everything...), I had some
> success using 2-1/4" and 3-1/8" holesaws and match-drilling the
> screwholes. This is pretty long...
>
> I started the screwholes with a long 1/8" bit, and with these you want
> to be very very very particular about getting it centered, then slightly
> enlarged them (9/64 or 5/32 as necessary... depending on how far
> off-center my match-drilling was), and finally countersunk the cockpit
> side of the hole.
>
> Minor "gotchas" and notes:
>
> Westach 2-1/4" EGT/CHT gauges come with their screw holes pre-tapped,
> and a 1/8" bit is a bit too large (it will chew up 6-32 threads).
>
> I just about wore out my fly cutter making one very ugly 2-5/8" hole
> (probably too much rpm), hence I decided to try holesaws. The hardware
> store holesaws made holes slightly undersize. I had to enlarge some of
> my 2-1/4" and 3-1/8" holes using a Dremel sanding drum and about ten
> minutes of patience per hole. The 2" automotive instruments required
> more minutes of patience.
>
> You can trim/debur/countersink big holes in 0.063" aluminum using a
> utility knife and file.
>
> Here are the important points of how I made the big holes:
>
> 1) clamp the workpiece to plywood (the plywood will stabilize the 1/4"
> bit in the middle of the holesaw, otherwise the holesaw will try to
> wander ALL OVER THE PLACE!)
> 2) drill a 1/8" pilot hole where the center of the instrument will be.
> 3) use the hole saw at low speed (I have a large two-handed variable
> speed/max 850rpm drill but used about half that speed... only had a few
> very minor kickbacks)
>
> (I don't have a drill press)

Good advice, Jim. I do have drill press, and it helps to get things
straight. If you can do a composite panel...

Start with 2" thick foam. Cut the hole 1/8" larger than necessary. Use
3 1/4" and 2 3/8" hole saws. Cut the back side of the hole square to
about 1/2" deep.

Coil 2" wide, tape covered strips of aluminum flashing and wrap one end
with pieces of wetted 1" tape. The tapes should be long enough to make
one circle of the instrument. It will take about 6 layers of 8oz tapes,
but you want to build up enough to "close the hole up to the proper
size. You may need to do 3 layers, let it partially cure and do 3 more,
because the coil will only 'push-out' so may wraps at once.

Stick the coil into the hole so that the tape is against the back side
of the panel, help it expand to completely fill the hole by running a
screw driver around the perimeter, and pack the corners that you dug out
with flox.

Glass the back of the panel and let the unit cure.

Pull the coil out from the front, and cut the glass for the instrument
holes (real easy with the cured tapes as a guide). Heat the glass with
a hair dryer if you find it difficult to cut.

Match drill holes into the flox for mounting screws.

Sculpt and glass the front of the foam for a beautiful contoured look
with eyebrow shades for each instrument. Drill a 3/16" hole at a 45
degree angle into the back toward the cured tape, without penetrating
it. You are just trying to clear the foam out of the way. Sink an LED
into the hole for instrument lighting. Sand the coiled tape for more
diffusion of the light.

I'm about halfway done.