Modifying a Thingiverse stl file in Prusa Slicer  

RE:

I don't know about the slicer, but I have often imported STL files into OpenSCAD and modified them in various ways (doesn't always work though, some files seem to confuse it).

Modifying the part as you require will be tricky and it's not really a slicer job - but this is the sort of thing that is so trivial to design that it's quicker to make it from scratch.

I have thrown together an OpenSCAD script that makes this:

It's based on the measurements given in your Amazon reference but not everything was specified there so you will have to measure the part in detail and enter any differences in the User-Settable section.  The Amazon spec was in inches hence the inclusion of a multiplier, you can of course remeasure in metric.

//  OpenSCAD Weber gas control knob

inch=25.4; // Original specified in inches = conversion gain

//  Begin user settable parameters - adjust to suit

outerdia=29/16*inch;
stemwidth=inch/2;
stemcentre=3/8*inch;
stemlength=11/8*inch;

keysize=stemcentre/3;

pinchheight=6/8*inch;
cylheight=4/8*inch;
pinchtaper=inch/8;

//  End user settable parameters

$fn=50;  // Smoothing

hull(){
  intersection(){
    hull(){
      translate([-outerdia/2,-stemwidth/2+pinchtaper/2,0]){
        cube([outerdia,stemwidth-pinchtaper,1]);
      }
      translate([-outerdia/2,-stemwidth/2,pinchheight]){
        cube([outerdia,stemwidth,1]);
      }
    }    
    cylinder(d1=outerdia-4,d2=outerdia,h=pinchheight);
  }
}
difference(){
  translate([0,0,pinchheight]){
    cylinder(d=outerdia,h=cylheight);
  }
  translate([0,0,pinchheight+4]){
    cylinder(d=outerdia-4,h=cylheight);
  }
}
translate([0,0,pinchheight+1]){
  for (a=[0:5]){
    rotate([0,0,a*365/6]){
      translate([0,-1,0]){
        cube([outerdia/2-1,2,cylheight-3]);
      }
    }
  }
}
translate([0,0,pinchheight]){
  difference(){
    cylinder(d=stemwidth,h=cylheight+stemlength);
    cylinder(d=stemcentre,h=cylheight+stemlength);
  }
}

translate([0,0,pinchheight]){
  intersection(){
    cylinder(d=stemwidth-1,h=cylheight+stemlength);
    union(){
      translate([keysize/2,keysize/2,0]){
        cube([keysize,keysize,cylheight+stemlength]);
      }
      mirror([1,0,0]){
        translate([keysize/2,keysize/2,0]){
          cube([keysize,keysize,cylheight+stemlength]);
        }
      }
    }
  }
}

Copy the script, paste into OpenSCAD and compile to STL - or modify to taste.

You will need to enable support from the build-plate.  I suggest you print slowly and perhaps a few degrees hotter than usual to get good interlayer adhesion and thus cope with the twisting forces expected in use.

OpenSCAD is free to install so you lose nothing trying this way.

Cheerio,

RE: Modifying a Thingiverse stl file in Prusa Slicer

In PS, you can "cut" the model at the diameter changes, manipulate the individual pieces, then re-assemble them on a common center. You may run into a problem with the hole in the center of the stem. These are frequently "D" shaped holes, and increasing the diameter of the stem will also increase the size of the hole. You can right click on the stem and "plug" the hole with a cylinder of appropriate diameter and length. In a seperate CAD program, construct a "D" shaped post of appropriate dimensions, save as a STL, right click on the model again and add the post as a negative space in the center of the stem. You will probably have to tweak (scale) this feature and test print a couple of times befire you get it right. Good luck.

RE: Modifying a Thingiverse stl file in Prusa Slicer

Diem,

Thank you ever so much for all your kind help!

I'm still learning which software is the easiest (best?) to use when you need to modify an. stl file found on Thingiverse.

I've done some basic adjustments in Tinkercad but that's not intended to provide you with "machine" specs or the details OpenScad and meshmixer can.

I'm self-taught with little time in our public library Maker Space to play around with various software so I very much  appreciate your and everyone's kind help.

People often think 3D prints is just a matter of finding a file and pressing  the print button when the fact is there can be a lot of work in printing seemingly straight forward objects like a grill knob.

I'm so appreciative.

3D prints is just a matter of finding a file and pressing the print button

It can be - especially when the manufacturer supplies files for specific spare parts.  The problem with Thingiverse, Printables and similar resources is that files are rarely described accurately enough and the search functions are almost useless for finding them.  We really need users to specify Manufacturer, device type, name, version, release year, partname, partnumber; and then it must be possible to search on all of these.

And I'm as guilty as any about not publishing fixes.  I make dozens of odd parts like this for no-longer supported machinery, mostly marine engineering but also some for longshore workshops; most of them are so specific that only a few people worldwide would have any use for them but most of those are well enough connected that they will be referred to me at need and I can email a copy of the file.  I don't charge for copies.

This is a consumer product so let me know if any changes are needed and perhaps I will try to publish the file properly.

Cheerio,

RE: Modifying a Thingiverse stl file in Prusa Slicer

Hi Diem...

This is wonderful of you to create and share this with me. I’ve only used OpenScad once to convert a file to .stl. I’ve never created one. I’m stuck at the beginning as I copied your code into the OpenScad Console and chose Export to .stl but it said the file didn’t exist.

I would so appreciate your help guiding me through this. Thank you so much.

You have not rendered the file - in the view pane click the first icon, with the chevrons, for a preview.  This is a quick view and will not be complete ... then click the second icon, this is a full render and will take a few seconds.  Now you have a structure that can be exported as STL.

Cheerio,

RE: Modifying a Thingiverse stl file in Prusa Slicer

Hi Diem... Again, I'm a novice at OpenScad. I copied all your code from // OpenSCAD Weber gas control knob to the end and imported that in. I then pressed the 1st icon and all your code disappeared, then I pressed the 2nd icon and it wanted me to Open. I've attached 2 screenshot as this is challenging to follow with text. Thank  you.

That's the editor pane - the view pane is the one with the XYZ scales.

Cheerio.