Ball bearings you say? 3D printed BB crankcase.

I was wondering how long it was going to take for that new carb fuel inlet to be spotted. I accidentally left it on the carb when it took the picture. I had one crumble when it was installing a carburetor and thought there must be a better solution.

The brass fuel barb is 3-56 threaded one from Clippard. The barb is too small for regular size .049 fuel tubing and only works with the .010/.020 fuel tubing. They are also almost $1 a piece too.
I did approach Matt and he is also working on an alternative solution.



I also tried to do a direct print of the entire part. Being so small I can’t get fine enough detail on the barb fitting. I might be able to change the design of this so the barb comes out round vs oval. This prints as an overhang so I would have to teardrop shape the barb for it to come out round on the 3D print. This would also require a lot of cleanup work where just tapping a hole would be easier with a threaded nipple.

Jason if the problem is only the size of the fitting fuel tubing, then what I would do is attach an 010 or 020 size, short  fuel tube to the nipple so that the barb will hold it, then pull the larger, 049 size fuel tube over the other end of short 010 size tube, and  run it up to the 049 engine...I may also pull a small spring - the one used in Babe Bee tanks - into the 010 size tube to prevent it from collapsing under the external pressure by the 049 tube..or would just add a copper or aluminum tube connector in between the 010 and 049 tubes etc...

My garage-tuning solution, not ultimately professional, but would still be working with your small nipple, and be several orders of magnitude better and more reliable than the all-plastic COX fuel nipple...I would still be interested in buying such a hybrid solution...

These fittings would fit the .049 size fuel tubing but have a painfully slow shipping option.


https://m.aliexpress.com/item/32696220692.html?trace=wwwdetail2mobilesitedetail&spm=2114.12057483.0.0.2d50546d9TXC5Y

They are for pneumatic hose but should work fine. They will be larger than the Clippard 3-56 version.

I made the fuel inlet thicker for more strength. I tried to crush a glass filled Zytel Version with my fingers and could not even get it to deform it’s that strong. I need to test it with fuel to make sure there still isn’t an issue with leaks.

Good to see that you will soon find the solution !!! I believe the small nipple size is just cosmetics, if the larger size is difficult to source, I would still happily compromise on the small one...we are modelers anyway and need our part of innovations when completing our fuel systems on our planes..

Any word on the threaded insert?

They came in today. I need to update the drawing to make the screw boss bigger and enlarge the hole size. Backplate will be updated as well. 5/8-18 Bottom tap came in also but I need to take the first 2 tapered threads off of it on the grinder.

More tweaks but eliminating the potential of stripped screw holes is worth it.

I have set up the 65 deg carb mount with a Killer Bee .049
Will be bench testing the throttle function and peak power
with the APC 4.4x4 labeled as a .049 Free Flight Prop.

Well that makes more since , i was thinking it had something to do with the cly. placement But didn't want to sound stupid and say something about the size of the insert >> guess i missed a line . Looks good Brad why is it U use .020 spinners on .049 engines again ( i am having brain farts i guess )

Less mass out at the end of the driveline for less wobble, reduced heat and increase in rpm.
Helps to center the prop / insets a bit and allows the use of a E starter.

Thanks Brad , makes since to me

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Then you need a mold , right ?

Why do it with epoxy resin if make a mold why not do it with aluminum? Me if I had the chance to have this crankcase I would print with some kind of wax then I would make a mold with I would not waste my time with resin whatever the kind I already have a good result to repair parts of crankcase leaks this kind of thing build parts wit !!!! Other than to make a beautiful art Decorative display engine
I will never use this method for Important piece dont waste mony use aluminium If you seriously want to complete this type of engine crankcase This is my humble opinion I must clarify that I find the prototype valid is should just use aluminum rather than losing $$$$% time is money best made of aluminium Not plastiques reson for that is plastiques wil Not hold for long terme use Yes you will say that the cars of our day use different types of plastic in the engine, it is really no good for intensive use the cars are no longer what they are. Now made cheap al this To save mony $$$ Then it's us the poor customers who are fooled its wy That I keep my old nissan gtr for always

A low viscosity 1 or 2 part methyl hydrate resistant epoxy could be used to infuse the 3d printed parts.  It would prevent leaks and add stiffness.  The use of epoxy is not intended to mold or make a mold, but just to seal the porosity of 3d printed parts.

If the part is made of ABS a quick dip in acetone will sometimes achieve the same result.  It softens the material and is used to improve the finish of ABS parts.

PETG as a 3d printing filament is resistant to Methyl alcohol.

Has anyone tried using an SLS printer for such fine detail parts?  If so what resin was used? SLS is Selective Laser Sintering. A laser scans a layer of powder and cures it or binds it. The bed is lowered and a new layer of powder is spread and the laser process continues. You can have metal parts made this way.

They also have laser cured liquid resin printers. You can buy home ones for less than $1000 with very small build volumes. I am not familiar with the properties of the finished product with respect to chemical resistance etc. In this machine a layer of liquid resin is cured by a scanning laser. Then the print bed is lowered and a film of resin floods the top surface. Then the laser cures the appropriate areas and the process repeats.

A company like Shapeways can make a very high resolution part for evaluation. They have a choice of materials and methodologies of printing to choose from. They are one of many 3D printing service bureaus around the country.