Y-axis Gear Drive

switching to spectra fishing line helps a lot but not for the Y-motor drive belt.  I would guess that if you have that kind of backlash you haven't put the pillow block bearings on that rear Y-drive rod.
http://www.soliforum.com/topic/4824/how … -for-ever/

I have yet to see a gear set that doesn't have some play in it.  I think your (grob) on the right track with the direct drive.  I also think a good spider coupler will solve most of your issues.  I just wish you would hurry up and perfect it so I can upgrade mine

You're right about the tension - if it's too much the bushings will bind up. Replacing the bushings with bearings goes a long way to helping with that (see this thread here), which then means you can tighten the belts a bit more.

With the x motor, where exactly is the wobble?

So is the backlash caused by the Y-belts on the side?  Spectra line will help in that case as you can tighten it up to the point of breaking things.  Same for the X-belt.  It takes a few runs to get the line tight but once that's done you really don't have to mess with it again.  It's a very cheap upgrade and if you don't like it just switch back to belts.

The other day I tried posting on this thread, but ended up posting my idea on the wrong thread.  So here it goes.

I've been toying around with ideas of driving the "Y" drive shaft using gears set at right angles to each other.

Originally I was thinking about using a worm gear to drive the "Y" rod.  The idea was to install a slip on worm on the rod, then drive it with a gear at a right angle with the motor installed on the back of the printer from the outside.

Never the less, I got an earful from some of the readers about how slow this would be. 

It's true that worm gears are usually used in gear reduction setups, but in this case it would have been the opposite.  In a standard setup, the worm provides the rotational input, and the main gear is the output.  Depending on the number of teeth on the gear, and the number of threads on the worm (4 in this case), the gear reduction can be as low as 5:1. 

So my idea was that if we shift the input to the gear instead of the worm, then the worm (in our case the "Y" drive shaft) would rotate 5 times faster than the input, but it could be slowed down as needed.  The one thing I didn't take in consideration was that the torque required to drive this setup would be more than the standard motor is capable of.

So it's not very practical to use a worm gear.  However, that brings us to helical gears.

Helical gears can engage at right angles as well, and 2 identical gears would provide a 1:1 gear ratio.  The additional advantage of the helical gears is that the have a lot of surface engaged in the mesh, which tends to reduce backlash dramatically.  The disadvantage is the additional friction speeds up wear and tear on the gears.  This can be compensated for (to an extent) with good lubrication.

So what about something like this?  Let the pundits rip me to shreds...

Nah,  I might consider something like this for when I'll be building my next printer from scratch.  But for now my printer is already pretty decked out and changing the configuration yet again is not going to get me any closer to the "perfect print".  It's just one of those ideas I tossed out there that might work for someone that's still into modding their printer. 

This would actually work pretty good, if you could find just the right gears. I looked around and I did find a few small (12mm OD) helical gears with 5mm bore.  One fits the motor shaft directly, the other would have to be drilled out to 6mm for the "Y" drive shaft, then cross drilled and tapped to install a set screw.

The problem is that to make this work, the threads must be at a 45° angle, and most of the small gears I'm finding are somewhere around 30°.  I found lots of large (25mm+ OD) with 45° threads but they're simply too big.

Anyway, just thinking out loud.

I had never heard of the Greg's Wade  direct gear setup, so I had to look it up.  Most of these setups are in reference to the original RepRap Wade extruder, to which Greg made different modifications for either gear reduction or direct drive setups.

Most of these drive setups were designed to provide more torque to the extruder by using some sort of gear reduction, and almost all of them rely on printed gears.  Those are fine for extruders where backlash is not that important, but they wouldn't do very well as power transmission for the motion control because of their general sloppiness.

Anyway, there were 2 reasons for my suggestion:

1.  The OP was looking for alternatives because he's trying to reduce the amount of backlash that exists between the motor and the drive shaft. 

Replacing the belt with a direct drive setup (motor coupled to the shaft directly with an inline coupler), would eliminate that backlash altogether, but then the motor would have to be installed on the outside.  This setup does have a couple of drawbacks:  Torsional and axial deflection which would be minimal but present non the less considering the small diameter of the drive shaft

2.  90° drive.  While most people would probably balk at adding a motor to the sides of the frame, they would probably be more inclined to do so at the back, since the back of the printer already has a bunch of stuff on it.

A helical gear setup lets you drive the shaft at right angles.  Additionally, helical gears have a few added advantages over spur type gears.  Fast, very quiet, capable of supporting higher loads due to the larger tooth surface engagement.  On helical gears, teeth mesh gradually, and at any given time 3 or more teeth are engaged.  This also translates into much tighter gear mesh with less backlash.

Then there's the location of the gear drive, which would be nearly centered.  If you put pillow blocks on each side  of the bearing (or build a gear box for it), you minimize any of the axial or torsional effects I mentioned before.

The only thing you have to account for is the lateral thrust helical gears produce (they will try to push the shaft left or right depending on the direction of rotation).  End caps and/or thrust bearings would take care of that.

So we took care of most of the slop induced by motor connection to the the "Y" drive shaft.  But that still doesn't take care of any of the problems that the end carriage belts have.  You still need to adjust the belts just right, makes sure the 2 sides are aligned, etc.  Maybe some kind of single belt/pulley setup ???