Many 3D printing forums and blogs lecture on the quintessential importance of a perfectly level print bed. Achieving this state of printing nirvana is however a tedious and difficult task. Checking the height of the bed at various points requires you to move the print head to that position and then carefully lower it until it is almost touching the bed. You can then note the position by sending an M114 command to the printer.
Deciding whether it is “almost touching” involves a bit of judgement and the print head only moves in 0.1mm steps anyway, so the measurement is never really that accurate. Also this method means that for every point you measure you have to raise the print head, move it to the right position, lower it a step at a time, get the position from the console, move print head up again, expire of boredom etc.
My dad observed this process during a visit and used his powers of old-school engineering to suggest using a dial gauge instead. With a dial gauge attached to the x-carriage you could whizz the print head around the bed and just read off the bed height at each position. He then managed to pick up a dial gauge with an accuracy of 0.01mm, now we’re talking! All that was needed was a way of mounting the dial gauge to the print head.
A quick look on thingiverse showed that many other people have had the same idea. However they were all either for different printers or different dial gauges, so we set out to make our own. My dad drew out a scale design (on paper, like with a pencil and everything), then I put it into OpenSCAD and we ran off a few prototypes. Originally the plan was to glue the holder to the x carriage on the Huxley and use a screw to secure the dial gauge, but once we had the first prototype we thought we could play around with making everything snap fit.
It seems to work very well. Based on the measurements I made just now one end of my bed is around 0.3mm lower than the other. I knew it was bad, but I didn’t realise it was that bad – I think I have got away with it so far because most of my prints have been quite small and positioned in the centre of the bed. Now that I have a way of measuring the bed position I am going to try adding some thumb screws to make adjusting the bed easier, then finally I may be able to attain the impossible dream of a level bed (I will also have to add new tape to my print bed, it has got quite torn up recently through over zealous hairspray use and semi-drunken part removals).
If you want to make your own the .stl and OpenSCAD can both be downloaded from thingiverse
Things that went wrong this time
It seemed like everything that could go wrong did go wrong while making this part
- First of all the belt slipped off the y cog during a print. It has clearly been slowly working its way further down the motor shaft for the last year and chose this moment to wreck the print
- Then the threaded rods that give movement on the z axis fell out of their flexible couplings (again during a print). There was much cursing
- The most terrifying failure came when I started up after replacing the z axis. I started to heat up the print head and the Wife pointed out that smoke was coming off the print head. I looked at the pronterface screen and saw that the printer thought the temperature of the head was -237 degrees C, so it was merrily pumping every amp it could into the superpowered heater cartridge that is installed in the printhead. I hastily shut down the printer but not before the leads for the cartridge started to char and the nozzle got clogged up with melted teflon. Clearly the thermistor contact had broken momentarily and the printer had interpreted open circuit as a very low temperature. I often leave the printer going overnight or when I am out of the house so this really scared me – if I hadn’t been there to switch it off it could have caused a fire. I had read that this issue existed in old versions of the firmware but never got round to checking whether my firmware had the problem or not. Public Service Announcement: upgrade your firmware to avoid burning down your house. Aside from saving lives and property it will also stop you from having to unblock your nozzle which is a pain even when using the fire method
- Then the x axis belt came out of the x carriage, making the x axis the 3rd axis to fail in 48 hours
- Then the other side of the belt came out of the x carriage, making me kick myself for not securing that one at the same time as the first one
- Then the first side of the belt came out again, leading me to reevaluate my method for holding and tightening the x belt
- …and then it worked