Protocols for SCAG Setup

How to prepare the McGrath Lab Surface Contact Angle Goniometer (SCAG) from a disassembled form. I will create detailed posts on potential uses in the future.


  • Based on the McGrath Lab SCAG as it was on May 16th, 2013
  • Instrument layout:


  • All bolts and set screws are 1/4-20’s. The angle screws are 10-32’s.
  • Loosely = only moves with hand-force, Tightly = unable to move with hand-force.
  • Proper right-angle alignment is critical to the setup. It is useful to have a leveling tool with right angle edges to do this (I used the one in the McGrath Lab, pictured below). The recommended method of determining a right angle between components is to loosely secure the bolts/screws that restrict the movement of the position being adjusted, press adjacent sides of the right-angle tool into one parallel surface and one to-be perpendicular surface of the first component w/respect to the position being adjusted (the side of the track and the underlying surface are useful for this), and then aligning an edge of the component with a third side of the right-angle tool.
  • Leveler


Setting Up the Stage (crescent wrench, 1/8″ allen wrench, phillips-head screw driver):

  1. Attach the Base to a car on the track using a 1/4″-20 screw to loosely secure the leftmost hole on the base to one of the rightmost holes on the car. Use the square corners of the leveling tool to set a right angle between the base and the track, and then tighten the Base screws. It should look like so:BASE
  2. If the Stage is not already assembled and attached to the Main Support Pole (MSP), place the pin in the mid-length hole on the MSP, and then enclose the pin with the bottom-side groove on the stage and the brackets and secure the two sides tightly — the MSP belongs in the stage’s slot with the short end coming out the top. Finally, tightly attach the angle plate to the bracket that surrounds the MSP with the long 1/4-20 screws. This is what the bottom of the stage should look like after all this is done correctly:StageFull
  3. Use the leveler to make the long side of the stage run  perpendicular to the track, and then tighten the MSP set screws at the Base.
  4. Insert the longer end of the MSP into the Base so that the Stage sits at a height that will work with the range of heights the Camera and Light Source structures are capable of.
  5. Insert the 0° angle screw in the top hole of the angle plate or whichever angle screw you desire in the second hole, and secure it with moderate tightness. The SCAG should now look like this:StageBuilt

Setting Up the Camera (1/4″ Allen Wrench):

  1. Place a Specimen Disk marked with perpendicular diameter lines in the disk holder of the Stage and orient the lines to be perpendicular to the Stage sides (there are marks about the holder’s circumference to match the lines with).
  2. Attach the Telecentric Lens to the PGR Chameleon USB Camera (the threads should be covered by screw-on caps when not engaged).
  3. Attach a short pole to the C-mount of the camera and attach a disk stand to the pole. Tightly secure the disk stand to the Translation Stage (TS), making sure that the pole is perpendicular to the TS and that the Telecentric Lens is parallel with the long edge of the TS (use the leveling tool).
  4. Attach another short pole the middle bottom-side hole of the TS and insert it into a short pole holder that is attached to a disk stand.
  5. Use the leveling tool to position the structure on a car so that the Telecentric-Lens/TS  are axially colinear with the longitudinal line of the marked disk and the front edge of the Telecentric Lens is ~65mm from the eventual centers of the wells on the specimen disks. You may need to match edges rather than sides with the leveling tool sides, putting the leveling tool’s axis at an angle with the vertical.
  6. Secure the car and the structure’s disk stand tightly. The result should look like this:CameraFull

Setting Up the HI-LED Collimated Light Source (1/4″ allen wrench, strong fastening material):

  1. Insert the HI-LED into the back of the Collimating Lens and secure with the tiny set screw located towards the back of the Collimating Lens, illustrated here:
  2. If they are not on the Base Plate already, secure two small bolts with matching cylindrical heads through the front ends of each of two adjacent slots. Be sure that same-side bolts have the same head dimensions.
  3. Strongly secure the unflared portion of the Collimating Lens’s body to the bolts on the Base Plate using the metal bracket as shown below.
  4. Attach a short pole to the bottom-side middle hole of the Base Plate. Insert the pole into a pole holder attached to a disk stand.
  5. Position the structure on a car so that the Collimating Lens is axially colinear with the longitudinal lines of the marked disk and the edge of the Collimating Lens is nearly touching the Stage.
  6. Secure the car and the structure tightly.
  7. Adjust the height of the structure (or adjust the rest of the SCAG) so that the top of the stage meets the mark on the rim of the Collimating Lens, maintaining the aforementioned colinearity. The result should look like this:CollLight_Setup2

Assembling the Syringe Holder (Teflon tape, pliers may be useful):

  1. Once you have determined the approximate length you need the telescoping arm of the Holder to be — the needle must pass vertically through the hole on the Aligner — place a generous amount of Teflon tape on the engaged threading to create a stable articulation. Use pliers to help screw if you have added a little too much tape.
  2. Screw the wing nut up against the base of the Holder.
  3. Loosely attach the Holder to the top of the Needle Control Pole (NCP) — the “top” is the non-reduced end.
  4. Loosely attach the Lever ~2.5″ from the top of the NCP. The result should look like this:HolderFull

Assembling the Micro-Syringe Pipette:

  1. Gently slide the glass vessel onto the projection. Do not apply any force to the dial.
  2. Very Gently slide syringe needle onto the glass vessel. Do not apply any force to the dial. The result should look like this:SYRINGEFull

Setting Up The Needle and Aligner (1/8″ Allen Wrench, phillips-head screwdriver):

  1. If the Aligner is not assembled, attach the parts  as pictured:AlignerFull2
  2. Place the large (.50″) hole of the Aligner about the MSP such that its body hangs over the stage and then loosely tighten the corresponding set screw.
  3. Attach the Post Translator by threading its screw through the 1/4″-20 hole on the Aligner until it passes the surface by a few millimeters. Place the Translator’s threaded hole on the screw such that the knobs face the back edge of the Aligner and then finish threading the screw. Tighten the connection by threading the Aligner about the bolt — the knobs should now be approximately facing the near long edge.
  4. Place the Micro-Syringe Pipette (μL liquid dispensing device) in the Syringe Holder and tighten the hold. Adjust the length of the telescoping arm to allow the needle to pass through the Aligner. Place the telescoping arm on the NCP and, if  you can do it safely, pass the needle vertically through the smallest hole on the Aligner by making the Holder lie flush against the translator. Finally, tighten the wing-nut against the end attached to the NCP. The result should look like this:NeedleAligner2

Fabricating Angle Screws (10-32 screw cutter, 10-32 thread clearer, surface-angle measurement tool [.01° tolerance preferred, .1° allowable], wheel or belt grinder, right-angle tool, caliper):

  1. Establish a right angle between the Stage and the MSP and calibrate the surface-angle measurement tool (SAMT) on the current surface of the Stage. Make sure that you remove the SAMT when the stage is not supported by a screw or hand — they’re expensive!
  2. Starting with ~1″ 10-32 Phillips-head screws, place a screw you wish to modify in the second hole of the angle plate so that the screw end is touching the MSP
  3. Place the calibrated SAMT on the stage surface and adjust the angle screw until the stage is at the desired angle. Measure the length of the unengaged threading between the screw head and the angle plate.
  4. Cut-off a section of the screw equal to 2-3mm less than the measured length.
  5. Round the end of the screw with the grinder and clear the threads.
  6. Reinsert the screw into the second hole of the angle plate and measure the resulting angle. If incorrect (it will likely take a few attempts) grind away a small amount more or restart with a new screw.

**The only absolutely essential Angle Screw is the 0 screw. If a range of unspecified angles is appropriate, you may simply adjust the inserted length of a single screw — be sure to lock the position with a hex nut against the angle plate for repeated imaging!

Posted in Instrumentation, Protocols (Public)
2 comments on “Protocols for SCAG Setup
  1. Tejas Khire says:

    Great job Yaron!! Just a small concern: every time I plug in/out the usb to the camera, I am afraid that the process might just shake or misalign the camera. If you can get hold of a 2-way USB extension cord, we can keep it connected to the camera and plug in/out of the computer. That way camera will remain untouched. Again, an excellent job!

  2. Jim says:

    Very well done. And thanks for the detailed post.

    Yeah after seeing the duct tape, it should go. Even a belt would look more professional, but a clamping piece made of plastic should be simple to make compared to some of the machining we’ve already put into this thing.

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