No-hob extruder

by profezzorn Aug 13, 2012
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What should the diameter of the large gear be when printed? I'm getting 73.75mm The ID of the small gear is about 4.5. The reason I am asking is I had to print at a scale of 1.1 to get the ID of the small gear to fit on the extruder. I then, of course had to printer the main gear at 1.1. I am still having issues getting the captive nuts to fit in the slots. I've done all calibrations on the printer and circles are, well, circles and the 100mm x100mmx50mm test print is perfectly spot on ( http://www.thingiverse.com/thing:195604 ). I am printing in PLA 204 with the bed unheated.

STEP Calibration Piece (X, Y and Z axis)
by voltivo

Scaling is the wrong way to change the ID of the small gear.
If you're only changing it by 10%, then the easiest way to change the ID is a drill. (It's pretty common to have to drill out holes anyways.) If you really want to change the printed ID, open up the model in openscad, change the ID and export your own STL files.

If it were just the ID of the small gear I wouldn't have an issue. I'm also having issues with the slots for the captive nuts being far too small. I'll work on it...I really wanted to try this extruder....fantastic design.

Scaling still isn't the right solution.
It sounds like you have a problem with over-extruding, or possibly you just need a better slicer program.
It is normal for 3d prints to become slightly bigger/fatter than what the dimensions of the model, which is why you normally subtract 0.1 - 0.2 mm in all directions to make room for some swellling/warping/whatever. That extra space is already there in the model, so if it's not enough, you might have a problem with your printer or slicer.

I recommend trying a different slicer, and/or perhaps reduce the extrusion rate?

If you really want to change the size of the inner dimensions, doing it in openscad is the right way to do it.

PS: Trick for when the captive nuts don't fit: Use a soldering iron at low temperature and just push the nut in.

I took the captive nuts and put them to the grinder to resize them...I'll try the soldering iron technique as well. I've adjusted the extruder and it seems calibrated. I did another calibration tower, a cube, a spinner, and finally a nickel calibration. they are all spot on now. Seems I was close before but still a few tenths a millimeter off. I'm printing the remainder of the extruder now. Planning to build it this weekend.

So would that be 970 for 16th microstepping?

Yes, although, this time I used google to calculate the value, and I got 973.28 ( https://www.google.se/webhp?sourceid=chrome-instant&rlz=1CAZZAB_enUS635US639&ion=1&espv=2&ie=UTF-8#q=200+*+16+*+47+%2F+9.0+%2F+(sin(pi%2F10)+*+10+*+7%2F32+*+25.4) )

(1946 for 32 microsteppings.)
Not sure why I keep getting different values...

Could you explain a bit how you calculated your steps per mm?  I'm having trouble getting the same answers you did with that equation, and my stepper has different values.  Thanks!

Weird, now that I retry the calculation I get 1939 rather than 1946.

Either way, here is how I got that number:

47/9 = teeth on large gear / teeth on small gear
sin(pi/10)10  = circumference of a decagon of size 1 (the bit has 10 teeth)
25.4 = the diameter of the bit

Thanks a lot.  I'm having trouble getting the math to work out to what you suggest above though, maybe I'm missing something?

For 200 steps, 32 micro:

steps microsteps 47/9 = 200 32 5.222 = 33422.08
(sin(pi/10) 10 7/32 25.4) = 
10 .21875 25.4 = 0.3046539714

33422.08 / 0.3046539714 = 109705.0527403694

Quite a bit higher than 1939.  Thanks for your help, I've got mine printing but am having a lot of trouble getting the steps/mm dialed in.

If you're using a sin() that takes it's input in degrees rather than radians, then you need to use sin(180/10) instead.

is the Qty (1) 602 bearing supposed to be 608? I bought several of the 602's by mail and they are way too small.

 Oops, yes it's supposed to be a 608 bearing.
Sorry about that.

did you intend to say the assembly requires a qty (1) of the 608 bearing? i bought several 602 bearings in the mail, and they were way too small! The 608 is 8X22X7 which looks like it is about the right size.

The Dremel 115 High Speed Cutter is 5/16" and $5.95 on Amazon.

The 115 bit should also work with some minor modifications to the scad file. It may produce a smoother feed since it has more teeth. I went with the 196, which produces a stronger feeder since because of the smaller diameter. I haven't noticed anything uneven about the feed and I'm very happy with the extruder so far.

dremel bit 196 is $6.52 with prime shipping from Amazon.

Still a hobbed bolt is only $8 from Printrbot store.

dremel bits are throw away items. even dollar stores have sets for next to nothing... You can even choose your style..

This is a real DUH! Or is that DOEY?

GREAT! I spent too much time worrying over this item and here I've got twenty or more dremel bits around the house. This IS COOL!!! :-D

I love it! How can I get it to work with a bowden system?

I would like to see this work with a bowden system as well (Rostock). I don't like the setup I have with the Airtripper. Just needs different mounting and an adapter to hold the nut / tube.

Try the extruder-to-hotend part on this page : http://www.thingiverse.com/thing:26963http://www.thingiverse.com/thi... for 3mm filament extruder to bowden part.

Printrbot Bowden Cable mod
by sponnet

Which stepper are you using?

It is a nema 17 stepper. The actual model is no longer in production though.

Excellent. This is very similar to the stock feed drive gear in the Up! printer (but the Up! has a fixed-position roller bearing instead of a pivoting spring-pressure thing). The nicks in the filament do not adversely affect extrusion.

that is a brilliant idea... cheap bit and available practically everywhere.

actually, one thought occurs, put the 608 bearing back in and add a "chuck" (with some a bit of a lip) to the top of the large gear so when you push the large gear thru the 608, the 608 compresses the chuck and the lip sits on the "fillament" side of the chuck

Not sure why you would do this....

To re-use 608 bearings? (Probably not worth it unless you can replace both r2zz bearings with 608 bearings, and I don't think there is room for it next to the dremel head.)

To avoid flattening the dremel bit shaft? (I don't think the chunk would be strong enough for that.)

However, if you wanted to use a 608 bearing, a simple tube (8mm outside, 3mm inside, 6mm long) would probably work pretty well as an adapter.

I was thinking more strength than anything, as in it all rotates around the 1/8" shaft (i think thats right?) which i would have thought would be a little too flexible?

The shaft is fairly short, and made of hardened steel. I'm not worried about it bending or flexing. I think the main extruder block will crack long before the dremel bit gives out.

Wow, very interesting idea.

Can you post images of the filament after its been pulled through the extruder, to show the 'Bite marks'?

Awesome work!

Getting a good picture of the bit marks is not easy, but here is a picture at least.

Thanks for the pic!

Looking pretty awesome, will have to give this a go....

the marks to me look as if they would not

negatively impact the extrusion.

I am in the process of making a 'crap strap'

(scavenged parts etc)

and this will almost certainly be incorporated.

Seriously interesting development. These bits are most likely more consistent in both quality and diameter. If I ever get annoyed with my hobbed bolt this will be considered, thanx!

Would genius be to strong a word?

Running to lowes when it opens!!!!!!! need dremel bit!

I think genius should be spelt Genius!! ;)