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Cox Engine of The Month
October-2017
MauricioB's

"Cox Medallion .049 R/C"



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redneck reeds

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redneck reeds

Post  roddie on Sat Aug 05, 2017 8:19 pm

Before I go into detail.. The measurements I took were from an oval/oblong-shaped "steel" reed being rigid enough to get a fairly accurate measurement with my caliper. Getting these measurements in the "ballpark" is all you really need to do.

I found some plastic sheet; not sure what type of plastic.. but measuring with a vernier-caliper measured .005" thick. This is the thickness of the Mylar reeds used in the later Cox engines.

The oval-shaped reeds measure .270" x .450" so I cut a length of the plastic into a strip slightly-wider than 1/4" (1/4"=.250") an inch or two long.

There's been threads on using the Mylar from "floppy-discs".. so there's a source for reed-stock that you don't need a caliper to measure. The floppy-disc material is slightly "thinner" but is said to work fine.

I then grabbed a short piece of 7/16" OD (.437") alloy tubing.. because this size fits pretty nicely into the reed-housing on a Cox .049 engine. I proceeded to center it on the strip and mark around the tubing with a pen to establish the oval-shape. Then with "short-snips" using sharp scissors, I made the two radius-cuts. These radius-cuts will be far from perfect.. and if cut on the pen-line or "outside it" will likely end-up oversize. You can trim little bits off when fitting.



My first one was a bit too long (tight) on the reed's long-side.. so I snipped a little off one end. The reed should lay-across the seat without "bowing" inside the housing. It's not real difficult to get it to fit. Better to make it a little "long" and trim it.. than have it too short. The length/radius is probably more critical when using a circlip retainer.. than when using the plastic cap-style retainer.

I haven't ran these yet.. but I'm pretty sure they'll work fine.
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Re: redneck reeds

Post  balogh on Sun Aug 06, 2017 12:25 am

Roddie try a nail clipper of a manicure set that has a radius cutting edge.
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Re: redneck reeds

Post  Admin on Sun Aug 06, 2017 12:38 am

This reminds me that I need to get a new cutting mat for my die-cut machine. I need to cut a bunch of those experimental reeds, I believe you wanted some to test out.

I've had success by tracing a factory reed on the material with a felt tip marker and then cutting it out by hand with some small sharp scissors. Sticking the factory reed to the material with a small piece of two sided tape helps keep it from moving while tracing it.

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Re: redneck reeds

Post  roddie on Sun Aug 06, 2017 9:42 am

balogh wrote:Roddie try a nail clipper of a manicure set that has a radius cutting edge.

That was a great thought Andras.. and I just tried it.. but I see that the radius is much too big. Even my smallest clippers have approx. a 7/8" (22mm) radius.. as confirmed by matching-up to my circle-drawing template. That's almost double the size of the .049's reed-housing's diameter. The clippers could still be used to "nibble-off" the edges easier than cutting a radius with scissors I suppose.

I know that there's people shaking their heads thinking; why not just buy some extra reeds? Laughing Well they're right.. and I do have a supply of different types..

Just an FYI on thicknesses of the different materials..

Copper-star (Cox old type)= .001"
Steel-oval= .002"
Mylar-oval= .005"
Teflon-oval= .010"

I've haven't tried the Teflon reeds yet. At .010" thickness.. they'll likely be "pinched" by a circlip-type retainer. I think the Teflon reeds were meant to work with the later "cap-style" retainers. Those retainers are probably the best for testing alternate reed-materials thicker than the .005" Mylar.
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Re: redneck reeds

Post  andrew on Sun Aug 06, 2017 11:47 am

Should you have some old 3.5" floppy diskettes on hand, there are two sources of mylar in the diskette. The diskette itself has a thickness of .003". I've cut reeds from these, but have had an instance where the reed was sucked out of the seat. These seats were those without the circlip.

OTH, the diskette casing has a cleaning fabric on both sides of the case. Under the fabric is a small piece of mylar which was used to provide wiping pressure to ensure the diskette remained clean. This piece is large enough for a single reed and usually has a thickness of .005" . It is also slightly stiff.

Just another source.

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Re: redneck reeds

Post  roddie on Sun Aug 06, 2017 6:57 pm

andrew wrote:Should you have some old 3.5" floppy diskettes on hand, there are two sources of mylar in the diskette.  The diskette itself has a thickness of .003".  I've cut reeds from these, but have had an instance where the reed was sucked out of the seat.  These seats were those without the circlip.

OTH, the diskette casing has a cleaning fabric on both sides of the case.  Under the fabric is a small piece of mylar which was used to provide wiping pressure to ensure the diskette remained clean.  This piece is large enough for a single reed and usually has a thickness of .005" .  It is also slightly stiff.  

Just another source.

andrew

I'd read about your mentioning the small thicker Mylar strip found in some floppy-discs in Jacob's thread. Good to reiterate that here. There's probably lots of sheet-goods suitable for making reeds. The purpose-made reeds that we can easily source "now".... might not be so easy to find in the future. When our "Grandkids-kids" find one of our old Cox reed-valve engines in a box someday.. hopefully the reed and glowhead will still be good.. and we'd provided some documentation on the care and running of the engine for them to enjoy as we did.
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