1) Purchase, Print and Prepare the Parts.
You will need to obtain a compression spring that is 6mm or less in diameter, 39mm long, .5mm section, and 20 turns. The diameter can be slightly less, and the length, section and number of turns can vary slightly. I found the spring I used in this model in one of many boxes of springs I've acquired over the years, a "Maxcraft 7707 200-Pc/ Spring Assortment" box. This assortment is available on line and in hardware / box stores.
I have attached a PDF file containing the list of printed parts which includes the part names, part counts, print settings and colors I used. The pumpkin halves are a mere .8mm thick and, as noted, I used PVA for support material since on the Ultimaker 3, PVA support provides very smooth 100% interface support for the interior of the pumpkin. However, other support material should work.
This model uses M6 by1 threaded assembly and may require a M6 by 1 tap and/or die to clean the threaded components.
Prior to assembly, test fit and trim, file, sand, etc. all parts as necessary for smooth movement of moving surfaces, and tight fit for non moving surfaces. Depending on the colors you chose and your printer settings, more or less trimming, filing and/or sanding may be required. Carefully file all edges that contacted the build plate to make absolutely sure that all build plate "ooze" is removed and that all edges are smooth. I used small jewelers files and plenty of patience to perform this step.
2) Assemble the Scissor Jack.
Start by attaching one "Arm Double Thread.stl" to one "Arm Single Thread.stl" using one "Bolt Shoulder 6 by 1mm.stl" as shown using a 3.5mm hex wrench or pliers. Do not over tighten as the arms must rotate freely. Repeat this process with the remaining two arm assemblies.
Attach two of the arm assemblies together using two "Bolt Shoulder 6 by 1mm.stl" as shown. Attach the final arm assembly to this assembly again using two "Bolt Shoulder 6 by 1mm.stl" as shown. The entire assembly should now easily expand and contract by pulling apart or pushing together the arms at either end of the assembly.
Loosely attach "Pumpkin Top.stl" to the end of the scissor assembly using one "Bolt 6 by1mm.stl" as shown.
Loosely attach "Pumpkin Bottom.stl" to the end of the scissor assembly using the remaining "Bold 6 by 1mm.stl" as shown.
Attach "Scissor Mount Hole.stl" onto the opposite end of the assembly using one "Bolt Shoulder 6 by 1mm.stl" as shown.
Attach "Scissor Mount Threaded.stl" onto the same end as "Scissor Mount Hole.stl" using the remaining "Bolt Shoulder 6 by 1mm.stl" as shown.
To align the pumpkin halves, slide "Scissor Mount Threaded.stl" over "Scissor Mount Hole.stl" as shown, then gently compress the scissor mounts together until the scissor jack is fully extended. With the scissor jack at full extension, align the pumpkin halves and fully tighten the bolts attaching the pumpkin halves to the scissor jack.
With the pumpkin halves aligned, pull the two scissor mounts apart, install the spring, then slide the two scissor mounts back together. Slowly compress and release the scissor mounts and test that the completed assembly extends and retracts fully.
3) Final Assembly.
Position the scissor assembly into "Case Bottom.stl" as shown, then thread one "Button.stl" into "Scissor Mount Hole.stl", and the remaining "Button.stl" into "Scissor Mount Threaded.stl" as shown.
Snap "Case Top.stl" onto "Case Bottom.stl" as shown.
Press "Stem.stl" into "Pumpkin Top.stl" as shown.
That's how I made Scissor Jack O'lantern.
Hope you enjoy it!