Belt tensioners for RoMaxV2

[hubrigant]

Being frustrated with the "jam a screwdriver in and lift" method of tensioning the belts, I modded my RoMax to use these devices, modeled after some made for the v1 by gabrielk (http://forum.seemecnc.com/viewtopic.php?f=35&t=1169).

In mine, I took advantage of the v2's top plate, which eliminated the top axle from the original version. I also lucked out in that the friend whose shop I borrowed to make them had hexagonal aluminum bar stock in 3/8" diameter, which made drilling easier. Using such thick bar, though, meant that I couldn't use the stock axles, and the added width meant that I couldn't find long enough machine screws in the one hardware store I stopped at, so I made new axles out of 1/8" steel rod that I put threads on each end for #6x32tpi nylon lock nuts.

The other change that happened as a result of using the top plate as the support was that I drilled/tapped the bar stock to hold threaded rod that went up through the top plate and put the adjuster nuts up top. This makes them easily accessible for adjustment without having to remove anything.

[ZakRabbit]

Great idea and fantastic execution! Thank you for sharing with us.

[lumpy_potato]

How tight do you feel belts should be? Like get a finger under the belt and pull a bit, and its taut? or you can't really pull the belt at all?

[3D-Print]

Nice job! I like the set up.

[3D-Print]

How tight do you feel belts should be? Like get a finger under the belt and pull a bit, and its taut? or you can't really pull the belt at all?

I'm not sure there is a consensus of a measured target tension. There are ways to measure belt tension and it would be interesting to know an average tension that works for various printers/users within the forum.

[hubrigant]

I've tightened the belts twice now, once with the screwdriver lift method and once with the new tensioners. The first time, I lifted the screwdriver until it felt like there was some resistance on it. The result was the were stretched, but not particularly tight.

With these tensioners, there's almost no effort involved in turning the adjuster nuts, so I couldn't go by that. Instead, I kept plucking the belts like the string on a guitar as I adjusted. I adjusted one tower until it seemed right and then adjusted the others until they matched the pitch the first makes when plucked. It's pretty faint, but I could try using my guitar tuner to measure the resulting frequency if anyone thinks that'd be useful.

I haven't run a successful print yet with the new tension, although I don't think my current problems are tension-related. I re-zeroed Z height and calibrated the height at the base of each tower when I was done tensioning. I then tried printing the test cube, but it was getting late for me, so I cheated and tried having MatterControl print via USB rather than run out to my computer to get the SD card. Enough was different that MatterControl had the nozzle too high off the bed for any chance of adhesion, so I gave up for the night. I'll try and run the test cube that I'd been using tonight and share the results.

[3D-Print]

You will find a number of discussions regarding belt tension. Here is some FYI.

(http://forum.seemecnc.com/viewtopic.php ... 1169#p9487)

[3D-Print]

Here is a link to what I did for my belts. This has worked well and since I added these tension devices, I have had no trouble with the print head coliding with a print. Still doesnt address to accurately adjust the belt tension, regardless of the tension device any of us use.

(http://forum.seemecnc.com/viewtopic.php ... &start=106)

[hubrigant]

I just checked, and my belts are all tightened enough so that, when the carriages are at home position, plucking the belts cause them to resonate around 100hz. By ear, I was able to get the three "tuned" to +/- 5hz, so they're pretty close to the same amount of tension.

Still no clue if it's right, but at least if they're wrong, they're a) easy to adjust now, and b) all wrong together

[lumpy_potato]

Belt tension is kind of a weird thing. There's no real tool that people have easy access to in order to adjust them. You want the belt tight, but not too tight. The tighter it is, the more force the stepper motor has to apply in order to move it. You certainly don't want it tight enough that plucking it gives you a good note. A fairly reliable gauge is to touch your middle finger to the tip of your thumb and then press on the "meaty" bit of your hand below your thumb joint. You want your belts to have a similar feel to them when you press in the middle of the belt on the inside track with the carriage moved all the way to the top or the bottom.

g.

From http://forum.seemecnc.com/viewtopic.php?f=37&t=8855

So they should not be so tight where you can get them to get a good note, just taut enough where they have some resistance when pushed and maybe a bit more. This is probably the closest to an 'official' that we can get so hopefully it is of some use.