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Author Topic: Matching music wire and aluminium tubing size for shaft-bearing  (Read 698 times)
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lincoln
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« Reply #25 on: September 12, 2019, 12:07:33 AM »

I'm not a mettalurgist, but I'm guessing that some relatively weak steel wire can be work hardened by stretching. Would take a fair amount of force and it probably depends on tbe alloy.
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Ashu
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« Reply #26 on: September 15, 2019, 09:17:55 AM »

I have made the modified Squirrel (rectangular stab and a framed trapezium for fin where I can put rudder tab). I have made the prop hub by gluing two popsicle sticks, 25 x 3 x 2mm each, which is quite strong. I have put a 3mm long piece of the #18 needle tube at its centre and glued with epoxy. The hub now spins freely on the shaft...I'll make a freewheeling mechanism later.

I am now making the propeller. I've made a pitch gauge for 1.3 P/D for the 5.5" prop that wills set the angle at 75% radius. I will use cone frustum shaped yogurt cups for the blades and toothpicks for prop spars. I found this very nice article and excel sheet by Fred Rash on "Bucket Formed Props" for cutting prop blades out of a conical cup: http://www.dcmaxecuter.org/building_tips.shtml The Solver add-in optimised the parameters for close-fit to helical shape.

I now want to make the prop blades as per the method by John Barker where he uses elliptical arcs on 2 circles (attached pic). It mentions that there is a "design cord" (smaller circle) and "max cord" (bigger circle). My conventional commercial plastic prop with square tips has a cord of 18mm from about 50-100% radius. So that should be my 'design cord' at 75% radius or the 'max cord' at 45% radius? What cord length should I choose for 75% radius location?
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Re: Matching music wire and aluminium tubing size for shaft-bearing
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Glidiator
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« Reply #27 on: September 17, 2019, 08:47:20 AM »

Hi Ashu,

Check out this thread I posted 3 years ago.

https://www.hippocketaeronautics.com/hpa_forum/index.php?topic=20755.0

Good to connect to another indoor enthusiast in India - it is a rare breed.

Anant
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raggedflyer
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« Reply #28 on: September 17, 2019, 03:27:17 PM »

I used to work at a medical instrument manufacturer that had 20 technicians fabricating medical tools continuously using thin wall, small diameter stainless steel hypodermic tubing. Standard practice was to cut it by rolling the tube beneath a sturdy craft knife blade (Stanley knife type). A fine ring is impressed into the tube wall and it will either cut through or weaken to snap off. Seems strange until you try it. Cut end can be cleaned up with emery paper or nowadays a Dremel type tool.

Stainless hypo tube can also be crimped in a 3 jaw check - we did this to set gas flow rate or to fit tightly onto another smaller internal tube. So you could crimp down onto a slightly undersize wire to achieve a good bearing fit.
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Ashu
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« Reply #29 on: September 19, 2019, 02:38:54 AM »

I used to work at a medical instrument manufacturer that had 20 technicians fabricating medical tools continuously using thin wall, small diameter stainless steel hypodermic tubing. Standard practice was to cut it by rolling the tube beneath a sturdy craft knife blade (Stanley knife type). A fine ring is impressed into the tube wall and it will either cut through or weaken to snap off. Seems strange until you try it.

Thanks. Yes you had mentioned this in your first post. I tried it with the snap-off blade knife I have here, but that method didnt seem to work with this needle. I tried an Xacto knife blade too. I am not sure if it is the knife, but maybe the method works for much thinner needles about 24gauge or more? This 18 gauge needle is strong (chart shows wall thickness as 0.216mm) and I am able to cut the needle after much effort only by using my craft knife like hand-saw.
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RalphS
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« Reply #30 on: September 19, 2019, 04:03:24 AM »

Ashu -  just wrap a small piece of masking tape around the tube where you want the cut.  The blade will easily cut into the masking tape as you roll it and will guide the blade as you increase pressure to cut the tube.
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