Case for Roots Blower

[Mooselake]

Not asking for any new development (yet) with all the other wonders in the works.  Seems like I asked something like this a while back for routing, but couldn't find it.

I looked at making a 3D printed roots blower this weekend (testing a new extruder on my PB Plus), but couldn't see how to print the enclosure for it.  Plating just makes a rectangular case.  Good for the top and bottom plates but doesn't create the inside geometry to make the blower work.  How would I go about doing this?

Kirk

[ArtF]

Hi Kirk:

The case for a roots blower is a circle, cut in half and extended in each direction then joined top and bottom. Theres really
many different shapes people use. Good point though, it'd benioce to have the case for it when you generate it.. Ill bump
that up my list..

Art

[Mooselake]

Here's a pair of blower wheels, 20T mod 2.5 to make them a 75mm diameter.  I plan to make a case like Art recommended; good excuse to use openSCAD's hull function.

They're printed at 0.13mm layers, 20% hex infill every 3 layers, of 1.75mm red mystery PLA using Printrbot's beta dual-geared extruder and their new all metal extruder (sort of an E3D clone with a 0.4mm nozzle, setup reviewed here).  I've been playing with extrusion widths, and the 1.2mm I used for the infill was too wide and got some missed steps, which is why there's a couple zits on the top despite 6 top and bottom layers.  Elmer's washable school gluestick on glass.

Kirk

[Mooselake]

The case for a roots blower is a circle, cut in half and extended in each direction then joined top and bottom. Theres really
many different shapes people use. Good point though, it'd benioce to have the case for it when you generate it.. Ill bump
that up my list..

Lawnmower supercharger!

Kirk

[ArtF]

Kirk:

Awesome, they look good.
( Use a circle of a diameter equal to the height of the roots.. should be a "just fits" situation, but
too tight and it will jam, from there the looser it gets the less the efficiency..though even a loose one will work. :)

Art

[Headsmess]

probably much the same as ill be doing for making a gear pump..

you know the CD.

you know the major dia.

draw two circles on whatever (sketchup for moi), extrude to depth, erase all the bits that make the drawing messy, and the appropriate bits to make the inlet/outlets, bearings, etc... remember to add some clearance but keep it tight as possible.

easier for you, youre only printing it!

[Mooselake]

easier for you, youre only printing it!

You must not have a 3D printer :)

Kirk

[Mooselake]

Here it is!  I had to do some fitting, plus the white box mystery filament jammed and shifted the case a few steps right where the sides join the base.  The gears aren't my best print, didn't try to optimize the slic3r settings (google richrap's blog for how to do that...)

I've attached the configurable openSCAD file for anybody who wants to try it.  Set the height to zero to make a cover, how to fasten them is left as an exercise for the reader.  If I was really good I'd have made an indent, or perhaps we could call it a future enhancement.

I found a spoke funny.  I thought that the "2" spoke would be cool (then "3" for a 3 lobe version), but the base of the two attaches with a little line, and slic3r skipped them at my settings, leaving the 2 detached from the hub.  I couldn't find a way to fix it.  No biggy.

It'd be nice to be able to have screw holes in the shaft collars (and in the roots blower, too).  I could have drilled (or added) them, but decided to try wicking loctite and a press fit.  Didn't really work, probably because I had to take it apart for the fitting, I'll just epoxy them at some point.  It took a small arbor press the first time I put them together, not so hard after prying them apart.  A future enhancement (about 2022 after you catch up with that list, Art) could be to add a twist to the Roots lobes, then it'd look just like the car version.

All in all a fun project; I'll try another one after my T-Glase order arrives, then maybe go for one big enough to supercharge my Vibe :) .

Kirk

[ArtF]

EXCELLENT job Kirk.

  Yours I think are the first Ive seen printed so well. Do you find they rotate OK?

Art

[Mooselake]

Uh, er, no, well almost.  They're pretty close, but have just enough drag at one spot on the outside of the case that they slip on the drill rod shaft and don't stay lined up.  I'm going to try CA glue on them after a little more scraping on the case, then I'll probably have to bite the bullet and try small setscrews.  Or use it as an excuse get some hex or square shaft...

One reason they're only 10mm high was to sort out issues like this.  The OpenSCAD case program I uploaded has 0.1mm more clearance preset in it, so it should be OK (if not, the numbers are easy to change)- it was originally printed with an extra 0.1mm, which was a bit too small.  If the print (darn cheap filament) hadn't shifted that little bit it might have been fine, but 0.05 on each side was stretching it.  It would probably have been easier to just reprint, but I'm stubborn.

I used 6.35mm for the shaft size, and the holes were a tight press fit on 1/4" drill rod - I used a small arbor press to push them in.  Taking it apart again for fitting was their downfall.  They're still tight, but not enough.  Too tight to get green loctite to wick in, though.

It's been interesting to make, and a handy demo of a roots blower, although without a top it won't move much air.  I wanted something to test out the new extruder hot end, and use Gearotic and learn something new at the same time.  I would have used helical gears, but didn't want to take the time to figure out how to get the center-center distance right; with spur gears the same mod and tooth count as the roots just plugged in.

Didn't there used to be a handcrank in the indicator list?  I couldn't find one.

GM's still near the top of my all time good investment list!  Thanks again, Art.

Kirk

[ArtF]

Kirk:

  Cranks will return.. :)

  You coudl always export a shaft AND a roots both as a monolithic STL.. Gearotic has no trouble mashing them into one in output..

SO if you design a  shaft and have it just an inch long or so , and export them in one file..t will print all as one...?

Art

[Mooselake]

While you supposedly can't put a round peg in a square hole, you can put a square peg in it :)

Stopped at the local hardware store and picked up an assortment of square keystock (this was before I read Art's post above), plan to reprint the gears and blower with square shafts since Art added them a while back.  I've got an assortment of different filament types for my geared extruder review on the other forum (t-glase, filaflex, pctpe (plasticized copolyamide tpe, almost sounds like one of those drugs of abuse but it's nylon and other goodies), and color changing ABS).  Once that's done I'll get back to rooting around.  Maybe that pctpe stuff would make a good bearing, two tests in one.

Wonder if filaflex or pcpte would make a tip gasket?  Hmm...

Kirk

[ArtF]

Sounds like your well on your way. :)

Art

[Mooselake]

Art, do you have any plans to let bearings have different types of shafts?

This gadget is just a toy/demo/challenge project, but I thought it would be interesting to put a printed bearing into the case (just add a hole and print separately, not part of the case).  Like most real bearings the ones in GT only have round shaft holes (although I have some on my farm equipment that have square holes, so they do exist).  No big deal, just something to consider for about entry 9000 on your list of 10,000 things to add to Gearotic.

I'll see if I can make a bushing, or just ignore the problem and put the square peg in the round hole, for now.  If the MBE was closer I'd ask about using the Blidgeport, but it's too far.

I haven't tried printed bearings, maybe I'll just make a couple for fun.

Kirk

[ArtF]

Kirk:

Hadnt planned on it... but Ill list it. I added bearings for fun, I dont many will ever use them, though they do print and run, your printer has to
be pretty good to make one work. I think its a real test of a 3d printers abilities..

Art