Microscope Pole

Overview

Materials

Microscopes

Here we will consider USB microscopes due to availability and cost. Bear in mind you will require two, but if one can be slightly better than the other then they can be swapped depending on the task at hand. It is possible to position the μRepRap under a bench microscope of the type used for electronic and crafting workstations, but the discussion of those optics is beyond the scope of this document.

Resolution Not Magnification

A variety of cylindrical format USB microscopes are available. Nearly all will claim some power of magnification along the lines of "500x" and this is completely meaningless. The important "magnification" factor is the number of pixels in the image sensor. 5 Megapixels should be considered the minimum, 8 MP is obviously better. A true "4K" resolution microscope is ample, though do make sure this is the actual size of the image sensor, not a software-interpolated value from a smaller image sensor.

Frame Rate

The number of frames per second is also important. Trying to precisely operate very small things with a shaky hand is made much more difficult if it is being done though a time-lagged video stream. Ideally a device with USB 3.0 data transfer speeds or better is required. Be aware that although a microscope may be capable of 10MP resolution, it may not be able to run at the full frame rate at that resolution. There is often a trade-off, and optimum image size vs. frame rate may have to be experimented with.

Mechanics

The microscope has to fit in the μRepRap such that it does not collide with the moving parts. This limits the maximum diameter to 40mm, ideally 35mm or less. The focusing mechanism needs to be responsive, with very little slack movement in the focus wheel. The lenses should be of good quality, though this is admittedly hard to determine from manufacturer's documentation.

Focusing can be done by moving the objective lens, which improves the magnification when the microscope is positioned close to the object. However some microscopes have a fixed focus and the "focus" wheel moves the entire camera mechanism back and forth inside the microscope housing.

Most microscopes come with some form of built-in illumination. This should be variable in brightness rather than on/off. A transparent cone is often fitted to the end of the microscope to allow the user to place the microscope on an object without cutting off the light. Ideally this should be removable so that the microscope can be positioned close to the μRepRap's moving mechanism without colliding with it.

The Pole

The pole is a 16mm diameter cylinder approximately 200mm long. Some microscopes come with a 16mm pole. In this example a length of extruded aluminium tubing was used, but even a length of dowel would suffice. If otherwise unobtainable, one could be 3D printed with the layer lines running along the length of the pole for strength.

3D Printed Parts

Hardware

• 8 of M3 x 25mm screws
• 16 of M3 nuts
• 8 of M3 flat washers
• Thread locking adhesive (optional)

Tools

• Small flat bladed screwdriver
• Screwdriver to suit M3 screws
• Nut Tool for inserting nuts
• Rag in case of adhesive overflow

Assembly

Eight thumbscrews need to be assembled. These will be used to fasten clamps to the pole and microscopes, and to lock the joints of the arms. If motion is particularly rough additional washers may be placed between moving surfaces, however some friction is desirable to prevent unwanted movement.

Clearing built-in support from a printed thumbwheel

With a small screwdriver blade, prise out the support material in each thumbwheel's screw hole.

Pressing M3 nut into a thumbwheel

Press an M3 nut into the hexagonal cavity on the other face of each thumbwheel. If it's a bit stiff, place it nut down on the bench and press on the top to send the nut flush.

Fixing the screw to the thumbwheel

Insert an M3 x 25mm screw into each thumbwheel via the screw head hole. To ensure the screw stays locked in, it is advisable to use a little thread locking adhesive. If using it, screw in the screw until 10mm or so is exposed, then place a small quantity of adhesive approximately 4mm up the screw's shaft. The intention is to have this enter the nut when the screw is fully tightened.

Tightening the thumbwheel's screw

Enthusiastically tighten the screw with the appropriate screwdriver - the thumbwheel may be used as a form of spanner. It should not break when you firmly tighten the screw. Consider this a challenge.

Inserting captive nuts to clamps, arms, and swivels

Insert six M3 nuts, one into each of the hexagonal cavities in the sides of the clamp jaws, and one into each of the nut slots at the base of each microscope clamp arm.

Fitting thumbscrew to a clamp with a washer

Take four thumbscrews and thread an M3 washer onto each. Screw thumbscrews into the sides of each of the four clamp jaws.

Fitting a Clamp Hinge to a Microscope Clamp

Take two thumbscrews and two more M3 washers. Again, thread a washer onto each thumbscrew. Use these thumbscrews to connect a Clamp Hinge to each of the two Microscope Clamps.

Fitting the hinged Microscope Clamp to the Pole Clamp

Take two thumbscrews and two more M3 washers. Again, thread a washer onto each thumbscrew. Run each thumbscrew through the longitudinal slot in a Pole Clamp, and screw it into the captive nut in the flat end of the Clamp Hinge - the ones you just fitted to the Microscope Clamps.

An assembled Clamp Arm

You can now fasten the Pole Clamps onto the pole, and fit the microscopes.

This completes the assembly of the Microscope Pole.

When the PIKA XY Table is complete, put the Microscope Pole in its 16mm diameter socket and adjust the microscopes so that one looks down on the centre of the Stage, and the other looks across the stage in the general direction of the Z Probe Assembly.