Jump to content

Banner.jpg.b89429c566825f6ab32bcafbada449c9.jpg

Truss scope using 3D printed parts

Dave_D

By Dave_D
in DIY Astronomer

Recommended Posts

Dave_D

Dave_D

Posted
Posted

After looking at, and nearly fainting at the cost of moonlight truss brackets, i've been toying with the idea of 3D printing truss ends using 100% infill PET-G... wondering what are peoples opinions about using 3D printed parts in load-bearing parts of scopes and is it practical/possible

I did a test print of one of these blocks and it was damn near indestructible... even went as far as running over it in my car lol

The ball-ends will have a steel M5 cap head bolts running through them for extra strength.

balljoint_zps7jfb4csw.png

Link to comment
Share on other sites
saac

saac

Posted
Posted

Dave the connectors will be very much subjected to static loads  so I'd hazard a guess that if your test print held up under the load of your car then they should be fine.  Just a thought, do you need to print the block in two halfs as shown in your diagram, could you not print it in a single component as per the mooonlite connectors?  Perhaps the weakest point might be the threaded portion where the screw reacts as it holds down on the ball. I'd give it a go, set up a proper test, I think you could be onto something.

 

Jim 

Link to comment
Share on other sites
Gina

Gina

Posted
Posted

PETG is immensely strong though slightly flexible.  Also, be aware that all plastics deform under constant pressure.  But my advice is to try it - nothing to loose other than a few pence worth of filament and your time in designing the parts.

Link to comment
Share on other sites
Bagnaj97

Bagnaj97

Posted
Posted
12 hours ago, Dave_D said:

wondering what are peoples opinions about using 3D printed parts in load-bearing parts of scopes and is it practical/possible

My 3d printed piggyback tube rings (https://www.thingiverse.com/thing:2181161) are still holding up. I printed in PLA rather than PETG because I was worried about flexure with PETG. I should imagine the load on a truss would be far less.

Link to comment
Share on other sites
Dave_D

Dave_D

Posted
  • Author
Posted

well it didn't work. the neck section of the ball joint, even with a 5mm bolt just doesn't have enough strength to stop layer separaton and the part splitting under load... would probably be better if the filament was put down lengthwise but then i'd have to use supports which wouldn't give a decent enough quality ball.. ho-hum back to the drawing board (or dig REAL deep in my pockets for 16 moonlite brackets). The two blocks housing the ball on the other hand, would probably survive a direct nuclear strike.

Annoyingly though, there's a local firm who's website says they can make carbon fibre tubes up to 350mm diameter. e-mailed them 2 weeks ago about this and had no reply. not the first time i've had not even a 'not interested' reply. i really hate pig-ignorant companies. you'd think with the economy in the mess it's in, these small places would be up for making a few quid.

Link to comment
Share on other sites
Dave_D

Dave_D

Posted
  • Author
Posted

i might try upping the ball diameter to 25mm and printing the ball and the tube plug as separate pieces and using a metal bush to replace the neck section. it's a natural weak point in the design that would probably still fail. it was 100% infill at 0.1mm layer height. 

Link to comment
Share on other sites
saac

saac

Posted
Posted

Dave,

 

If you do eventually go down the route of the Moonlite connectors all I can say is that you won't be disappointed. They are made from delrin and the quality is excellent.

Here is a bit of a wild-card - what about moulding the blocks rather than printing.  In the past I've used mouldable plastic material called polymorph (trade name). It's a thermoplastic that can be moulded for small prototyping projects. When it sets it is remarkably hard  and (like delrin) can undergo some basic machining - tapped threads etc.  The trick of course is to make the moulded shapes true rather than the usual organic form that they take.  Dimensional conformity is also a bit of a problem as is repeatability but if you were to use a mould made from say wood of a half block then maybe you could make it work. 

Jim

Polymorph

Link to comment
Share on other sites
PeterW

PeterW

Posted
Posted

Polymorph (polycaprolactone) is not going to be strong enough. I am part way designing my own scope truss clamps.. basically like the Obsession split block, with the tilts built in, printed solid I can't see they'd get damaged, just need a small amount of flex to lock the pole in place.  Got other things to design first though.

Keep us posted, good luck

 

peter

Link to comment
Share on other sites
Dave_D

Dave_D

Posted
  • Author
Posted

Iv'e done them in both PLA and PET-G (the PLA gives a slightly smoother finish for some reason) and to be honest, at 100% infill there seems to be practically no difference. I've tried twisting, bending and dropping (out of my 1st floor flat window)and neither type showed any problems lol. The parts were designed in OpenSCAD so once i've finished making the scripts fully parametric i'll post them in here, they're quite short.

Link to comment
Share on other sites
PeterW

PeterW

Posted
Posted

Are you using these on BOTH ends of the truss? My concern would be accuracy of positioning the blocks and the exact equal length of the poles. 3 points defines a plane... 4 legged tables always wobble.. you got 8 legs... are you going to tweak the lengths when you assemble to remove any small variances?

PEterW

Link to comment
Share on other sites
Dave_D

Dave_D

Posted
  • Author
Posted

couldn't be bothered making it any nicer than this lol

// define the block size
block = [25,70,20];
// define the ball size
ball_dia = 10;
// define the printing tolerence for the balls
tolerence = 0.05;
// define the block mid points
x_middle = block[0]/2;
y_middle = block[1]/2;
z_middle = block[2]/2;
// define the ball offset from centre
sphereoffset=14;
// define the object smoothness
$fn = 100;
// distance of M5 Cap head bolts from edge
M5_offsets = 7;
M5_shank = 2.5;
M5_head = 4.5;
// locking bolt
locking_bolt = 2.5;

difference()
{
    cube(block);
    translate([block[0]-7,y_middle-sphereoffset,block[2]])
    sphere(ball_dia+tolerence);
    translate([block[0]-7,y_middle+sphereoffset,block[2]])
    sphere(ball_dia+tolerence);

    // centre locking bolt
    translate([x_middle,y_middle,-30])
    cylinder(h=100, r1=locking_bolt, r2=locking_bolt);

    // M5 holes
    translate([0,block[1]-M5_offsets,M5_offsets])
    rotate([0,90,0])
    cylinder(h=block[1], r1=M5_shank, r2=M5_shank);
    translate([0,M5_offsets,M5_offsets])
    rotate([0,90,0])
    cylinder(h=block[1], r1=M5_shank, r2=M5_shank);

    translate([block[0]-5,block[1]-M5_offsets,M5_offsets])
    rotate([0,90,0])
    cylinder(h=10, r1=M5_head, r2=M5_head);
    translate([block[0]-5,M5_offsets,M5_offsets])
    rotate([0,90,0])
    cylinder(h=10, r1=M5_head, r2=M5_head);
}

Link to comment
Share on other sites
Dave_D

Dave_D

Posted
  • Author
Posted
3 hours ago, PeterW said:

Are you using these on BOTH ends of the truss? My concern would be accuracy of positioning the blocks and the exact equal length of the poles. 3 points defines a plane... 4 legged tables always wobble.. you got 8 legs... are you going to tweak the lengths when you assemble to remove any small variances?

PEterW

positioning will be fine... had a bit of a windfall so i'll soon be getting myself a 750x500mm OX Metal CNC  router (http://www.openbuilds.com/threads/ox-metal-cnc-router-mill.7218/) to build all my toys with :D

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

Go to topic listing

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.