Alternate belt tensioning method (Page 1 of 3)

Great idea. Can you post the stls?

I measured the distance between the front bearing and the back rod centerlines, and they're identical on both sides (302 mm).

The frames themselves are stamped from sheet metal and machine folded, so they're pretty consistent in terms of dimensionality.  Additionally, if any frame twisting occurs, you just end up with a parallelogram, but the length of the sides won't change.

I printed all the parts, but have yet to install these blocks on my printer, but I'll probably be doing it in the next few weeks.  As for the "enclosed" bearings, I already use a similar design on my printhead carriage, and it's never been a problem.

As for the STL's, there are 4 models:  The clamp, 4 required (2 per end block), the right side block, and the left side block. 

For the left block motor mount, I also printed an additional bottom ring.  It's printed flat, so it has much better sheer strength to resist the pull of the head carriage belt on the motor.  So once you print the block and the motor ring, just line it up, and glue it at the bottom.

EDIT:  NOTES:
The clamps are held in place with 3mm socket head screws no longer than 8mm.  The holes in the block are undersized (2.5mm), so the screws will simply thread in, no nuts needed.

At the bottom of the each block, there are 2, 2.5mm holes.  They are there for optional grub screws. 

The holes for the rods are 8mm, so they should be a tight fit for the smooth rods, however I like to drill out the hole slightly to so the rods can be removed easy, and I use grub screws to keep them in place.  Your choice.

The right side carriage also has the mount point on the side for the end stop.

Last but not least... 

HAPPY NEW YEAR !!

BTW any thoughts to increasing the thickness of the mounting section for the x motor?  Someone on here a few months back posted a modified lawsy carriage but thickened the bottom mounting area to reduce warping caused by the hot motor (though having a fan should theoretically help.)  Thanks!

EDIT:  Found what I was talking about: http://www.soliforum.com/topic/5118/sol … gs/page/3/

Are you going to use LM8UU bearings?The ones that I have measure 15mm OD If try to force then in the carriage starts to crack.

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I did use LM8UU.  After I printed the parts, I used a little round file to remove some of the burring inside, and to enlarge the hole a bit.  It's supposed to be a tight fit, but not enough to crack the part.

I my particular case, I didn't need to remove much material, but if your extrusion is a bit heavy, you might have to remove a bit more.

The holes are currently 15.1mm diameter, and the bearings are 15.0mm.  I can enlarge the holes a bit if you need, but I need to know how much. 

NOTE:  You can wrap some sandpaper around a AA battery, and use it to sand the inside.  The battery diameter is 14mm, so with the sandpaper, it should be just about 15mm.

BTW, for the left carriage block, make sure you mount the motor first, before inserting the linear bearings, or you won't have access to the 2 inset screws.

I'm expecting some flanged bearings next week for my back "Y" Rod, so I'll take that opportunity to also change the carriages and the print head.  Meanwhile here are my prints of the complete "X" carriage.

Very nice work, but do you anticipate any durability issues with this?  It seems the whole carriage will be shot as soon as you either overtighten a bolt or assemble it more than a couple times, which could easily happen if it takes a few tried to get the tension right?  I have had issues with stripping screw holes into ABS before, so I am skeptical that this would work long term.  Would it be practical to somehow mod it to have a nut trap?

Nice!  I want your cad skills.  Just curious- what program do you use and do you do this professionally or is it just a hobby for you?

Anyway, my solidoodle has been working great with the Lawsy carriages and I didn't think I would find anything that would motivate me to take it apart unless something breaks but I think this will be it.

Would you recommend printing this in ABS or nylon?

Just letting everyone know: newer batches of Solidoodle 4 (and maybe Workbench series will too) have a slightly modified X carriage design which uses a 3d printed clamping piece to attach the belts to the carriage. Unlike this mod though it's for closed loop belts and isn't made up of two pieces like pirvan's design to allow to tension both belts equally by seeing how many teeth  are out, instead it uses two screws on the front brackets to tighten the belt by moving the front pulleys front or back instead, which I think is a terrible way of belt tensioning because you not only have hard time making both belts same tension but also have hard time making the pulley perfectly parallel too because you move it front or back with two screws on each side, not one.

But I will say that from few months using this carriage, I haven't had any problem with the belt teeth wearing off or not staying in place. 3d printed clamps work just fine.

@pirvan: would you consider to post or maybe allow me if you don't have the time to repost your mods on Thingiverse?

Fair enough.
I just thought since most of the mods like the original printable carriage this mod is based off of, printable extruder, and direct drive mount and many other solidoodle mods are there it would make sense to have this there as well so people could find it easier. Don't think an internet forum (that requires registration for downloading, is not as well organized) is a very good place for this.
But I get your point.

Sure, I'll take some photos soon.

I measured my spare belt which is a GT2, but I also checked the MXL belt and other than the profile of the teeth (trapezoid vs. involute), the 2 belts are nearly identical (tooth spacing, width of tooth and thickness of belt cord. 

Since the clamp engagement is for locking down the belt, not motion smoothness, or backlash minimalization, these clams should work on either belt type.

Here you go.