UHMWPE Rail Buttons

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dhbarr

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I've found the Rattworks Delrin AF, but if I'm reading my coefficients of friction correctly UHMWPE should be both stronger and slicker.

Anybody out there making them? Or have vendor listings for appropriate washers / standoffs to roll your own?

Alternately, more information that tells me I'm wrong and to just buy the Rattworks Browns?
 

Steve Shannon

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Keep in mind that the coefficient of friction is but a small portion of friction. That's multiplied by the normal force, which is usually quite small because launch rails are nearly vertical. A clean and smooth rail is more important than the difference between Deleon and uhmwpe.
 

thequick

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Where I work UHMWPE has a bad reputation because it is difficult yo de-burr. Expect high machining costs.
 

nh4clo4

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The difference is negligible compared to the drag of the button itself during the flight.
 

heada

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Have you considered PTFE (Teflon)? You can get PTFE in tube form in various ID/OD combinations. Slice off 2 wider sections and 1 thinner section and assemble your own button. No need to turn anything and never run out.

Another option would be to make your own pop-off rail guide. These could be made from whatever material you want to get the desired rail friction but also detach from the rocket once cleared of the rail to lower in-flight drag.

-Aaron
 

dhbarr

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The buttons I have in mind would be explicitly for flyaway railguides.

It's an interesting point that I hadn't considered, using pure PTFE tubing. I'll go look at strength figures there.
 

AlphaHybrids

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I agree with Steve. Cleaning the rail and making sure it is free of exhaust and gunk will benefit you more. Also making sure your rail buttons are aligned so they slide freely instead of bind when loading the rocket.

Alternately you could use a bigger igniter - you'll probably make up for the lost altitude from rail buttons. I feel like you have a case of analysis paralysis.

Edward
 

dhbarr

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I agree with Steve. Cleaning the rail and making sure it is free of exhaust and gunk will benefit you more. Also making sure your rail buttons are aligned so they slide freely instead of bind when loading the rocket.

Alternately you could use a bigger igniter - you'll probably make up for the lost altitude from rail buttons. I feel like you have a case of analysis paralysis.
Inspecting & maintaining the rail is already on the list. Making absolutely certain the buttons are aligned is already there. Affixing the NC to the fore tube so there's no airflow delamination up front is on the list. Odd number of air sampling holes not inline with any protuberances fore or aft is too. Correct shape & position of fillet leading edge is there.

Are all of these going to be done on every bird? Nope. I just -really- dislike not knowing why we do certain things in particular ways, or if we've tried another way & it didn't work because Reason X. So I read until I run out of things to read, then I ask :)
 
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