Gantry sag as seen by a BLTouch

Topics around mechanical design, controller and electronics. Mods & hacks welcome.
zemlin
Posts: 527
Joined: Sat Oct 21, 2017 2:02 pm

Gantry sag as seen by a BLTouch

Postby zemlin » Sat May 23, 2020 2:24 pm

I recently swapped out the control board in my N2 for a Duet 2 Wifi. In the process I added a BLTouch probe to the print head.

One of the weaknesses of the Raise design is the 8mm rods supporting the print head. They deflect slightly with the weight of the head. This isn't usually a significant issue because prints that cover a larger area are normally printed with a larger nozzle/thicker layer.

I'm a mechanical engineer in the industrial machinery business and when I bought my N2 and N2+ I did not expect machine tool precision, so all in all I've been satisfied with these machines. Any machine of this size at this price point is going to have compromises in design. My machines have been very reliable and have printed a lot of parts with very few issues.

That said, with the BLTouch in place, it's pretty slick to be able to cover the bed with parts in a build and not worry about the first layer anymore.

Just as a curiosity, I put a 12x12 piece of 3/4" MIC6 aluminum on the bed. I set the corners as close to level as I could (my 4-point measurements are about 50mm in from each corner), and then ran a 15mm grid over the whole plate (except for the front 50mm where the probe can't reach). Assuming the MIC6 is quite flat, any deflection in the bed mesh is coming from the sag in the gantry. Here's what I got.

4 corners
N2 Bed Mesh 1.JPG


Full bed mesh
N2 Gantry Sag.JPG

Ressegger
Posts: 18
Joined: Sun Nov 17, 2019 12:28 am

Re: Gantry sag as seen by a BLTouch

Postby Ressegger » Tue Jun 02, 2020 11:55 pm

i there anything that you lost by going to the duest? im thinking about doing the same thing to my pro 2 plus

zemlin
Posts: 527
Joined: Sat Oct 21, 2017 2:02 pm

Re: Gantry sag as seen by a BLTouch

Postby zemlin » Wed Jun 03, 2020 2:53 am

Ressegger wrote:i there anything that you lost by going to the duest? im thinking about doing the same thing to my pro 2 plus

The touch screen. I tried to get it to boot up on Ubuntu so I could just run a web browser on it. I did get it to boot up from the SD card, but there were lots of issues that I'm not smart enough to solve - display brightness, contrast, rotation, drivers, etc.

I've been thinking about getting a 7" android tablet to fit in the box, but on my phone the web interface drops some of the buttons for the small screen size - things I wouldn't want to lose - I'm concerned the same would happen with a small, cheap tablet. For now my iPad lives by the printer.

Other than that, no. I've very happy with the change, and the Pressure Advance and Dynamic Acceleration features have me printing faster with better part quality. It's all so programmable, I find I keep adding macros and tweaking the setup with simple g-code commands. No need to compile a custom firmware.

A6y_N0rma1
Posts: 37
Joined: Thu Aug 03, 2017 5:25 pm

Re: Gantry sag as seen by a BLTouch

Postby A6y_N0rma1 » Fri Jul 03, 2020 8:16 pm

zemlin, how hard was it to swap out the boards? Just wondering if it's something I want to tackle or not.

zemlin
Posts: 527
Joined: Sat Oct 21, 2017 2:02 pm

Re: Gantry sag as seen by a BLTouch

Postby zemlin » Sat Jul 04, 2020 12:44 am

I spell out some of the process in a few posts here:
https://forum.raise3d.com/viewtopic.php ... 428#p54231
I have the advantage of having two printers, so while one was down for the upgrade I could make the parts I needed. It's far from a plug-and-play endeavor, but there weren't any major challenges. I'm no electrical wizard, but I'm comfortable with a soldering iron and heat-shrink. You'll want to have a good crimp tool as there are a lot of connectors to swap out. I did a lot more to my printer than just the board swap, but I had more time than usual as I did this during the covid shut down.

Feel free to fire back if you have any specific questions. Probably better to post in one of the other DUET-focussed threads, as other users might have advice to offer.


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