Wednesday, January 21, 2015

MendelMax3 - Z Stepper Mount Flex - Part 2

After discovering the flex in my Z axis, I decided to see whether the flex was present just by moving the X-axis. I wrote the following snippet of gcode:
G28 X0
G1 X250 F3600
G1 X10  F3600
...repeat the above 2 lines 10 more times...
and this is what I saw (with the original MTW mounts):

I decided to design a brace, which looks like this:

It's designed to fit under the existing mounting plate:

And installs like this:

Now I get virtually no deflection:

About a day after I designed this, the MTW folks came up with a much simpler, easier/faster to print version:

These perform almost as good as mine, but are easier to install. Here's a video showing the deflection while moving the X gantry back and forth (sorry - it's slightly blurry):

I decided to use the MTW version due to end switch interference with my mount.

To summarize:
  • 0.1mm deflection using the MTW mount that came with the printer.
  • 0.03mm deflection  using the modified OpenBuild mount.
  • 0.01mm deflection using the MTW mount with the printed MTW braces.
  • 0.005mm deflection using the MTW mount with my heavy duty brace.
The MTW braces are available here.

My heavy duty brace is available here. I don't recommend using this because it has some fit problems (it interferes with the Z end stop).

Monday, January 19, 2015

MendelMax3 - Z Stepper Mount Flex

I suspected that there might be some flex in the Z stepper mount on my MendelMax 3 given that it's a fairly thin piece of metal (0.050" or 1.3mm powdercoated stainless steel):

The first step was to see just how much deflection that existed. So I set up a dial test indicator on the outside of the stepper mount, moved the gantry down a bunch of steps, zeroed out the dial indicator and then started to move up in increments of 0.1mm. I had a big ole chunk of steel that I rested on back portion of the MM3, and used that to hold the magnetic base that held the indicator:

Wow 0.09mm of deflection, mostly in the first 3-4 layers.

My gantry is setup with 2 direct drive extruders, which means that there is a fair amount of weight being moved up and down on the Z axis.

From what I had heard, the MM2 used thicker aluminium parts. I also discovered that OpenBuildsPartStore sold a NEMA 17 stepper mount that could be adapted to work. It appears to be 0.125" (3.16mm) aluminum:

I used an X-acto knife to score a line 20mm from the edge, cut along the line using a hacksaw (ok - not really - I used my metal bandsaw, but this could easily be cut with a hacksaw) and cleaned up the cut edge with a file. For mounting, I lined up one edge with the 2040 vertical extrusion, and squared with the frame:

I then repeated the same test using the OpenBuild stepper mount:

Much better, only 0.03mm deflection. I think that having some type of braced mount, using a printed part (either by itself or as a reinforcement to one of metal mounts), would yield even less deflection. I'll be following up with another bog post in the future once I get a chance to try that out.

Make sure you read Part 2 where MTW addressed the problem with some braces.

Saturday, January 10, 2015

MendelMax3 - GLCD Case

One of the options I purchased with my MendelMax 3 was the GLCD. However, it doesn't come with a case, and the cases designs from MTW are all for the MM2.

OhmEye (one of the MM3 beta testers) put together a really nice one. However, the GLCD panel I got didn't quite fit my board. My panel was 0.5mm wider and the whole thing is a bit thicker.

So I redesigned the top piece and since I was doing something from scratch, I decided to hide the black bezel around the LCD. In my case I printed the case in black, but if you used a different color then you my not want to see the black bezel.

I also created a spacer to go between the white and green PCBs:

The left side has a low spot to allow clearance for some of the compontents on the board:

OhmEye's STL parts include a spacer:

Which goes on the back of the board like so:

I also modified the back mounting piece by adding some reinforcements and mirroring the whole thing since I wanted to mount it on the right side of my printer:

I found that the easiest way to put everything together is to assemble it all on the back and have the screws just coming through the circuit board, and then put the top on.

I made a few tweaks to the model (increased the width of the slot around the emergency stop button, and added a bevel), which aren't included in the photo.
The parts pictured here were printed on my Bukito, and due to the size they tend to pull the blue tape up a bit. So there is a tiny bit of warping. I plan on reprinting all of these parts in PET+ when I get that working on my MM3.

Here it is mounted on my MM3:

I'd like it to be higher up (more above the front), so I'll redo the base, but I really like the way it mounts.

To summarize the pieces:
I used the base and spacer from OhmEye's STL files.
I used the knob from the MTW GLCD mount files.
The front and PCB spacer can be found on thingiverse and github.

Tuesday, January 6, 2015

MendelMax3 - Toolless Z adjustment

On my MendelMax 3, the Z endstop has a really short printed piece and a really long bolt.

The bolt has a phillips head, while all of the rest of the harware on the MendelMax 3 is hex.

After making numerous adjustments (in retrospect, this turns out to be due to my Z axis dropping, but that's another blog post), I wound up stripping the threads in the printed piece.

Rather than just print up another one of the included printed piece, I decided to print a larger piece which would incorporate a metal nut, be closer to the endstop switch, and also allow for toolless adjustment.

I lined up the adjustment screw with the button on the microswitch, which allows the lever to be removed. You can remove the lever by squeezing the end together:

Here are the parts (after printing, I lengthened the main piece by an additional 5mm):

The knob is a press fit ont the end of the bolt. I used a hexagon rather than a circle because the hexagon is more dimensionally accurate (See this article for a detailed discussion). I cheated and just use a six-sided piece, since the inner hexagon is what actually turns the bolt.

Bolt pressed into the knob: 

Here's the nut pressed into the bottom. I also filed the rim off the bolt so that the bottom of the bolt is relatively flat.

Here's everything assembled together. You could also use a locking lever from my Toolless Levelling post, instead of a spring.

Here it is installed (this is the tweaked version which is 5mm lower than the ones pictured above):

You can find my FreeCAD and STL files here.

Monday, January 5, 2015

MendelMax3 - Toolless levelling

My new MendelMax 3 uses a 3 point levelling system. There is a fixed screw at the back, and two adjustable screws at the front.

Once you get the levelling screw adjusted correctly, you tighten the lock nut to keep the adjustable screw in place.

With the full covers on, I find it practically impossible to get my fat fingers to hold an allen wrench to adjust the screw and also hold an 8mm wrench to tweak the locking nut.

Here's a photo of the adjustment screw (the screw on the left holds the bracket in place, and the screw on the right is the adjustment screw):

I decided to print up a knob which I could put on the end of the M5 bolt to allow rotating the nut by hand, and I made a locking lever which allows the nut to be controlled.
The black piece on the left is the locking lever, and the piece on the right goes onto the end of the bolt:

Here they are installed onto the nut and bolt. I find that channel lock pliers make installing press fit parts a bit easier.

The M5 bolt has a "cup" or rim around the edge, so I normally file that off and make the end of the bolt flat or slightly rounded. Doing this will also help to prevent the rim from scraping through the kapton on the heater. Screw the bolt into the locking lever until it just starts to come through:

Now thread the bolt into the bed. Once you've engaged the threads try moving the locking lever counter-clockwise. If it doesn't snug up, then you'll need to mark the nut, remove it, and rotate it to a new position and try again. In my case I tried several other positions and wound up back where I started, but from removing and reinserting the nut, it seated itself a bit better. The locking lever is shown in the unlocked position below.

 Here we see the lever in the locked position, and in my case the bolt head just clears the mounted plate. Looking at this photo again, I think I can make the adjustment head larger in diameter (hmm. maybe not - at least not without support. I may try a hex head bolt instead, instead of the SHCS)

You can find my FreeCAD and STL files here.