Extruder gearing

[mopar]

Is there a reason why the Greg Wades extruder uses 9 & 47 tooth herringbone gears? Is this ratio the best or is it just what happened to be used? Thinking about replacing mine with a pair of GT2 pulleys, but those pitches aren't standard. I could make them myself out of aluminum if that gearing is the best, but if 10 & 50 would work that would make things easier.

Also plan to make my own hobbed bolt out of 8mm drill rod and use snap rings to keep it spaced between bearings. It will give me a better fit in the bearings as well as the pulleys.

Thanks.

[printbus]

There's nothing that magic about 9:47 that I am aware of. In parsing the source and comments in the various openSCAD predecessors for my refinement of Greg's Wades, it was evident that the provision for 9:47 gearing was fairly recent. Also, once you step away from Greg's Wades, there are other ratios that are used, down to the 1.75mm direct drive extruders that have the filament drive pulley right on the motor shaft.

[mopar]

That's what I was thinking printbus. I've looked at several different extruders and I saw a range of ratios including the direct drive with a dremel bit. Although I would think that one would be hard on stepper bearings with so much pressure being put against them. I like the Wades style extruder, just don't like the use of gears. Almost impossible to get zero backlash with printed gears. It's not like the teeth have a perfect profile and everything is perfectly concentric to the CL. Especially since we're using a bolt as an axle. Obviously there were reasons for doing this and it makes sense when you consider the tolerances these printers were designed for.

Being a machinist and having some printing hours under my belt with a good understanding of mechanics I'm looking to improve things personally where I can. I would love to see hundreds of people say that a particular type of extruder is best which would convince me to just buy a whole setup, but I haven't seen anything like that so I'll stick with improving my wades. Moving the extruder of my X axis to reduce the weight on the carriage would be great, but with the inherent problems that come with those type of extruders I don't see any benefits of the wades style.

Thanks.

[printbus]

That's a good point about the direct drive extruder putting a lot of stress on the stepper motor bearings. So much 3D printer hardware is based on an idea some guy had and prototyped in his garage or basement, not necessarily on good product design.

If you haven't seen it, e3d now offers a 1:3 geared extruder - Titan Extruder. That might be an option to look at. I wanted to give it a shot, but I don't think there's a reasonable way to retrofit it onto the aluminum strut carriage design that my MakerFarm i3v uses. I'm currently using the e3d hobbed bolt that is fabricated from 8mm stainless steel stock rather than a bolt. Since it is threaded on both ends, I can adjust the position of the notch to the extruder body without playing games with shims or washers like with the bolt type.

If you stick with Greg's Wades, I encourage you to take a look at the refined version I mention in my first post. A primary objective in my overhaul of the openSCAD designs was to provide a user with designs they can tweak rather than being stuck with someone else's finished result.

[Roxy]

Is there a reason why the Greg Wades extruder uses 9 & 47 tooth herringbone gears? Is this ratio the best or is it just what happened to be used? Thinking about replacing mine with a pair of GT2 pulleys, but those pitches aren't standard. I could make them myself out of aluminum if that gearing is the best, but if 10 & 50 would work that would make things easier.

The ratio can be anything that prints OK. I've been running a modified Wade's extruder for a couple of years. I wanted as low of gear ratio as possible. So I was scaling up the big gear and shrinking the little gear. It turns out, 9 teeth is pretty much at the lower end if you want the teeth to mesh nicely with the other gear. When you get below 9 teeth, the gear is getting small enough you start loosing a lot of strength too.

On the big gear... I actually moved the motor mount further away so I could scale up the big gear. I'm actually running a 9/76 gear ratio right now.

[AutoWiz]

I like the Wades style extruder, just don't like the use of gears. Almost impossible to get zero backlash with printed gears.

If the 2 gears were closer to each other in size than a little play between the 2 might be some small amount of filament movement lost. But just a little bit of freeplay in the 9:47 gear reduction is really not a noticeable amount. Don't take my word for it look at how many more steps now equals a mm in marlin. If the gears are set up tight aside from wearing if they are printed gears they can go into a bind and cause extrusion problems. make sure there is a tiny bit of freeplay at a bunch of different positions because the gears are 3d printed and are not perfect.