Actuator Assembly Redesign (v5.15 5.16)

This page is a bit of a working document, tracking the thinking on the actuator column assembly. The actuator column is pretty much unchanged from v5.13 to v5.15, with a screw coming down from the top and a nut held captive inside the column. The nut is at the top of the column, and the column is hinged at the bottom to the actuator lever. This is so that the nut doesn't get tilted as the microscope moves (versions without the pivot tended to jam after a degree or so of movement).

The elastic bands are used to pull down on the nut, so that the whole assembly is always in tension. This means that, when the actuator dips below the bottom of the microscope body, the elastic band is providing force to overcome the springiness of the plastic. If the elastic band is insufficiently strong, the microscope won't move all the way to the bottom of its travel.

The actuator column has two open sections, one either side of the casing at the top. These are used to pull an elastic band up through the narrow gaps at the side and hook it over the inner actuator column. This step is fiddly and annoying, and I really wanted to make it easier.

The foot also relied on two push-fit lugs to hold it in place - if the printer wasn't perfectly calibrated, these would snap off which, while it wasn't a big issue, was annoying.

In v5.16, this assembly is redesigned, using the improved actuator developed for the block stage. There are a few main changes:

• The nut is inserted from the side, not the bottom. This is much easier, and makes the actuator column smaller.
• There is more space either side of the actuator column.
• There are smaller hooks to hold the elastic band, enabling the use of a tool to push them in from below.
• The casing no longer has large holes at the top, as they're not needed.

The improved side-entry nut slot should be easier to use. The nut needs to be pushed in with one of its corners towards the back. As this is a little tricky to do by hand (they have a tendency to spin), there's a tool to do it (nut_and_band_tool.stl). There's no instructions yet, but the basic idea is to push the nut in with the tool, then screw in from the top as usual.

The feet work much as before - with a couple of important differences. The foot now has an opening all the way to the bottom, which means feet can be removed without removing the elastic band - great if you've messed up assembly. It also prints with a solid perimeter to improve bed adhesion - to get the band out and wrap it round the outside (as per the v5.15 instructions), you'll need to snap the thin layer with either a large screwdriver or (more neatly) the nut insertion tool.

The elastic band should be inserted from the bottom, after the screw has been screwed into the nut. This is important - otherwise the elastic band can snap the actuator! Hook the band over the two prongs of the insertion tool (the same one used above, but the other end). Then, insert it through the bottom of the foot and up the side of the actuator column. The slightly narrower side should be towards the outside of the actuator (i.e. the wider bit is towards the centre). Push the tool all the way in, and the elastic band should click into place. You might need to push down on the screw to stop the actuator rising up here - I might include a tool to hold it in place.

There are two thin bits of plastic connecting the actuator column to its casing - these need to be removed, though they should snap off when the band is inserted anyway.

Viton Bands

I've now got hold of some Viton O-rings that have several advantages - they should last much longer (won't perish with UV or moisture exposure) and they are exactly the right size, so don't need to be wrapped around the foot (much neater). The only disadvantage is that they are not quite as stretchy, so it's important to get the tension equal on either side of the foot. We now have a new elastic band insertion tool with two ends - this makes it quicker and easier to put the band in without snapping it, as it make sure both sides are stretched equally. It also gives a bigger flat surface to push on, so it should be comfier for your thumb as well!