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November-2017
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"Cox Tee Dee .010"



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Prop . Screw for .020 TD Size ?

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Happy Prop . Screw for .020 TD Size ?

Post  getback on Thu Nov 17, 2016 6:24 pm

I got a Pee Wee Prop screw is that the same size ? / I think someone put a too large one in this one to a point it looked Good < the bay> It came with a .049 Alum. Spinner lol! But any way i took the crank out because it was gummed up and now cant get the DEE Prop screw to go in far enough to put the prop plate on >/>?> Very Happy Hep !! Size to tap ? lol!
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Happy Re: Prop . Screw for .020 TD Size ?

Post  roddie on Thu Nov 17, 2016 9:10 pm

Geez... well.. IDK the screw-size of hand Eric.. but I would guess it to be 4-40. Whatever the proper screw-size is.. I would find one (or cut one) that fits deepest before bottoming. The .049 prop-screw is 5-40. I can't see that being easily threaded into a Pee Wee crank. If the threads in the crank are buggered "deep".. you might have a junk crank there. If there's enough material (diameter) to bore the crank larger.. A 5-40 tap requires a #38 drill (.1015"). You'd then need to either drill your .020 prop-hubs to .125".. or cut-down/re-balance some .049 props to run on that engine.

!!CORRECTION!! My records show the Cox .020 Pee Wee/Tee Dee to have a 3-48 prop-screw! If it was necessary (and possible) to enlarge the crank-bore to fit a 4-40 machine screw, the tap-drill would be size #43 (.089"). Your prop-hubs would need to be reamed-out to .116" (#32 drill). This is approx. .012" larger in diameter than the stock .020 prop-hole which is about .104".

Hope this has helped some.. A good hardware store may have a 3-48 tap. It would be a sound investment.. as many old U.S. made small-displacement glow-engines use 3-48 head-screws.
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Happy Re: Prop . Screw for .020 TD Size ?

Post  KariFS on Fri Nov 18, 2016 3:51 am

Eric, Roddie's right, the screw is supposed to be a 3-48:

https://www.coxengineforum.com/t10309-prop-screw-for-020-td-size#130449

If the thread on your crankshaft is partially damaged, maybe you could find a screw or a stud that is longer than necessary, screw it (heh) all the way to the bottom and then use a washer, or a stack of washers and a nut to pull the prop plate back on. This would help to preserve what is left of the thread in the crank. And in any case, lubricate the thread before pulling the plate on.

Also, if the thread is damaged, you might want to use a stud, install it into the crank with thread-lock (Loctite or such) and then mount the propeller with a nut? It will probably require a washer AND a spring washer, or possibly a nyloc nut but in any case the crank would be usable again.

I have wondered about the reason why prop screws are the standard way to mount propellers, as a stud and a nut would be a much better way. Same thing with tools used to pull prop plates back on, a stud and a nut are much easier on the crank thread than using just a screw.
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Happy Re: Prop . Screw for .020 TD Size ?

Post  getback on Sun Nov 20, 2016 9:51 pm

Thanks for the replys guys , i have a 3-48 and 2-56 tap's coming 3.99 each he even gave me a deal on the smaller one from 5.49? I will get it fixed up when they get here . Funny i must have 4-5 4-40 taps lol!
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Happy Re: Prop . Screw for .020 TD Size ?

Post  1/2A Nut on Mon Nov 21, 2016 9:51 am

Pee wee and TD .020 screws are the same thread size.
I like using3-48 X 3/4 hex head bolts.

Cox engines thread chart:

http://www.mh-aerotools.de/airfoils/cox_techinfo.htm
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Happy Re: Prop . Screw for .020 TD Size ?

Post  getback on Mon Nov 21, 2016 3:28 pm

Thanks Brad , i knew i had seen this info some where but couldn't find it at the time i posted and ck'ed with'en also . Eric Small Cox Logo
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