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-   -   a couple printed ideas (https://vansairforce.net/community/showthread.php?t=147771)

Planecrazy232 03-31-2017 06:48 AM

I have a buddy with a printer. If you are sharing the file it would be appreciated!! agrecojr at comcast dot net

AAflyer 03-31-2017 04:23 PM

WoW!
 
Those HAVE to be about 5 knots, RIGHT?!! ;)
JK, I'm jealous of your capabilities.
Some day, the entire 'Quick-build" fuselage will be printed, I guess.:D

Weasel 03-31-2017 07:27 PM

Idea
 
Quote:

Originally Posted by Steve Melton (Post 1162100)
:), and maybe here for this draggy thing. looking at the photo, maybe use an access panel screw behind to secure? it may not be in-line but if is then maybe slide the plastic fairing over the ball then move it aft to lock on the ball and secure with a panel access screw? and BTW, the tie down ball is also a good jacking point, I always leave it on.



http://www.vansairforce.com/communit...=139792&page=3

Just a thought
Quote:

Originally Posted by Weasel (Post 1094881)
Aluminum Angle is your friend

You could also use a round head bolt



Steve Melton 04-01-2017 09:12 PM

fuel test
 
fuel test after 6 days soaking. texture is the same as original. no particles in the fuel jar after several minutes of shaking. pull test the insert to the point where the .032 wire stretched and failed. placed the fairing back in the fuel. so far the fuel does not appear to be affecting the fairing. plan to conduct another pull test after more soaking.





this one was not soaked and also failed the wire. I am planning for a creep test on the insert by applying a constant weight over time.

Steve Melton 04-01-2017 09:20 PM

thread lock test
 
I applied several thread lock types to the fairing and found that MXlock affected the ABS. So far the others did not.

failed test


I will pull these this one after soaking but I don't expect good results.



these seem OK after several hours but will have better results after several weeks. I also tested RTV but don't have photo. Initially it didn't appear to have any reaction.



Steve Melton 04-01-2017 09:30 PM

set screw
 
I used the nylon tipped set screw but I was able to twist the fairing on the drain boss with some effort. The friction coefficient is low with the nylon tip and ABS to the alum. I don't believe the nylon tip set screw is a viable option. there is minimal force on the fairing to lift it off but over time it may. I believe it is better to use the set screw without the nylon tip to the alum boss. there is not much land on the boss and the fairing set screw is moved upwards as far as possible to allow for the plastic insert nut. for added attachment strength, some RTV or other adhesive on the fairing may be beneficial.




Steve Melton 04-01-2017 09:46 PM

stress analysis
 
this model does not accurately represent the printed part because I cannot model the internal hollow-hatch print but it is close for the areas where the set screw and boss are located because those are mostly solid.

a quarter turn on the 32 pitch thread set screw = .008 inch deflection and allows the fairing to maintain enough clamp thru 130F temperature delta. say you install at -30F and fly to 100F. the plastic will expand 5x the aluminum but you will still have .004 inch deflection clamp on the fairing. ABS is quoted as being creep resistant so I believe it will not relax and will maintain the clamp over time but some additional adhesive may be beneficial.

for installing, one quarter turn of the set screw after contact is the optimal value for clamp and minimizing stress in the plastic part.

some pretty pictures from my Mecway home analysis.

axial displacement


vertical displacement


overall displacement magnitude


von Mises stress


axial Principle stress


reaction force magnitude

Steve Melton 04-01-2017 10:00 PM

printing
 
a print photo


Steve Melton 04-02-2017 08:36 PM

more pull test
 
as expected the MxLock 42 does not play well with ABS but the other thread lock was fine from a strength point.

MxLock 42 coated insert failed at 10 lb pull


the penetrating Locktite 290 and RTV were fine and broke the .032 wire upon pull testing.



I didn't pull the VC-3 yet but it appeared to have the best adhesion and did not damage the ABS surface nor did it become hard. this is the same thread lock I use for plexiglass and if the pull test is successful it will be my thread lock of choice for ABS.

VC-3 appears to be very good for ABS. a series of pull tests still pending.


the avgas soaked fairing pull test was repeated with success determined by failing the .032 wire. no deterioration of the fairing was evident. I returned it to the avgas for another week.

Steve Melton 04-02-2017 08:50 PM

build method
 
parts:
- ABS printed fairing, mine are printed as such: layer thickness = .2mm, 5 bottom layers, 4 side layers, 4 top layers, 35% infill
- 8-32 heat set insert for plastic, mcmaster carr
- 8-32 x 5/16 set screw, mcmaster carr or Ace hardware






remove support material


clean inner hole with #4 drill bit


clean outer hole with 1/4 inch drill bit, take caution to only clean to shoulder of the inner hole


heat the brass insert for 10-15 seconds (I used a small butane torch) and push it in as straightly as possible. ABS will become soft at 340F (170C) so the brass inserted does not require too much heat. If the insert is too hot it will damage the plastic.


you may have some plastic extrude from the end. use a pick and it will easily be removed.


you may have a slight bulge from on the upper surface because on the insert. cut that away with a knife.


file the top smooth to remove an remaining support material


finished, ready for install. one quarter turn of the set screw is recommended after contact.


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