On Tuesday 30 March 2021 13:04:30 Chris Albertson wrote:
> Here is another common bearing design and these folks do supply
> editable 3D CAD files.
> https://www.skf.com/us/products/rolling-bearings/roller-bearings/taper
>ed-roller-bearings/single-row-tapered-roller-bearings/productid-30302 I
> like tapered bearings because the "play" can be adjusted. They are
> used in pairs with some kind of threaded tension device (screw
> threads) pushing them together. Even if printed the pair have
> such a wide base they don't wobble.
>
> If you plan to use printed bearings you design the machine differently
> with MUCH larger bearing race diameter and much large ball/roller
> size. Perhaps 3X larger. The entire machine needs to be designed
> around the bearings. What I do is FIRST look on eBay to find the
> best deal on sealed bearing units. then step #2 is design the machine
> parts they go into. Many times you find skate bearings and make
> those work. Other times you find there is a common tapered roller
> bearing that sells at a low price.
>
> If you print the bearing you really must make it oversized compared to
> a metal one. You can't swap metal and printed plastic interchangeably
> as if they had the same strength and tolerances
>
I am fairly well aware of that which is why I am concentrating on putting
a very large bearing around the internal spline printing that moves
which is 119.2mm in OD. I have 140mm of alu to hide this in, so there is
plenty of room for a bearing with 5mm balls.
I can adjust it to use the airsoft bb's, around 170 of them.
But I've done a cross section that will, it rotated enough times to make
the races, come very close to making printable races. which I think my
nearly $2000 printer can do once I gedt the PIE sheet and a better
liquid glue that McMaster3d sells. This must be a different glass in
this Dremel, occasionally you can make the rub on glue stick work but
even then its 3 or 6 times start to get past the 2nd layer before it
comes loose and I wind up with an ounce of filament welded to the bottom
of the head.
But the rotation eludes me. I can // the for(ang=[0:1:360]) out and get a
perfect cross section of the two races faceing each other, offset to the
radius, wihe ball groove centered between them, but the instant I
uncomment the for statement and add the terminating } by uncommenting it
too, then openscad is stuck forever at the 999/1000 point of the render.
Forever being about an hour of wall time now.
Here is what I've hacked up in about 2 hours so far:
==================================================
// my feeble attempt at generating a ball bearing.
// my alu block is 140.9mm square
dmtr=119.24; // in mm's squeeze it a hair.
height=9.25; // in mm's
ctr_ht=(height * .50000); // center of ball
echo(5, dmtr, ctr_ht);
halfd=(dmtr * 0.50000); //multiply's are faster
echo(7, halfd); // center of ball radius
innr=(halfd-ctr_ht); // inner ring ID
echo(9, innr);
outr=(halfd+ctr_ht); // outer ring radius
echo(11, outr);
outd=(outr*2); // copy to lathe, outer ring OD, machine alu to fit
echo(13, outd);
ang=0; // must be rezeroed each time
for(ang=[1: 1: 360]) {
rotate(ang) translate([innr,0,0]) difference(){
rotate([90,0,0]) rotate(45) cylinder(h=1,r=4.75,center=true,$fn=4);
rotate([90,0,0]) rotate(45) cylinder( h=1, r=2.5,center=true,
$fn=360);
rotate([90,0,0]) scale([.4,1,1]) rotate(45) cylinder(h=1,
r=4.75,center=true, $fn=4);
}
}
=============================================
What I would like to do but openscad can't, is render the [( )] pattern
once and then rotate it into a 2nd buffer with that for loop. That
would, or should render a heck of a lot faster than this as it finally
got done while I was typing this. But I'm not going to try printing it
till I get to wally's and get a jar of the airsoft bb's so I can measure
them myself. By then maybe I'll have the other stuff from amazon and
gizmodorks, starting with a new, hardened steel nozzle. I had to burn
out a blockage and it hasn't been the same since. But its saved and
openscad quit as it was going fubar according to gkrellm and my keyboard
response. Its not the most stable single threaded app even as an
AppImage. Just leave it running for 8 hours and it gradually uses more
and more cpu.
And I couldn't find any airsoft plastic bb's at Wallies. So I threw a
2500 bottle of crosman copper plated steel bb's in my cart, the went
over to the grocery side and bought about 70 bucks worth of freezer
stuffers, and I lost my cool and got loud at the self checkout. Some
ignoramous at corporate has decreed I must be 16 years old to buy bb's
so the register yelled for help. Since I'm 16 + another 70, I blew up.
As far as I was concerned, I was buying ball bearings, loose in a small
plastic jar.
Thanks Chris.
Cheers, Gene Heskett
--
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
If we desire respect for the law, we must first make the law respectable.
- Louis D. Brandeis
Genes Web page <http://geneslinuxbox.net:6309/gene>
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