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Pistol Grip Wrench

Geoff

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Description

After watching the YouTube video Pistol Grip Wrench [Remake] by Hand Tool Rescue (one of my favourite channels,) I was inspired to create a version of my own - partly to work on my CAD skills, and also because its ridiculousness amused me so much.

Modelling was done directly from the original patent illustration from https://patents.google.com/patent/US1733288A, with some changes made to suit FDM printing and my choice of hardware, as well as a few personal touches.

Full tool length is 22 cm, which I estimated broadly to be a fair size (too large for younger hands.) Jaw capacity is 32 mm.

Please read the full description before going ahead!

Possible future improvements

Options for printing jaw parts in a different orientation
Fully-printed gear and shaft sets including a trapezoidal lead screw
Click-together construction to eliminate all fasteners
Option for thicker grip scales
Fully scalable design

Hardware required

Normal Part	Optional Equivalent(s)
M5 x 60 screw, fully threaded. Any head up to about 9mm wide, but not countersunk.	M5 x 65 threaded rod, M5 hex nut glued on one end.
M5 square nut - approx 8 x 8 x 4 mm type.	M5 full hex nut. Less than 4mm thick may cause a little jaw wobble.
M4 x 40 screw (most types of head should work)	Any 4mm rod, glued to gear(s.)
M3 x 10 screws (x5). Button, cheese or low head socket cap.	M3 x 12 countersunk - ideally shorten to 11mm. M3 x 10 socket cap (stands proud of surface.)
M5 x 12 countersunk screw
M3 x 25 button head screw or similar small / flat cap.	M3 x 10 socket cap - OK but sticks out more. Any 3 mm rod, glued in place.

Print Settings

Print either all at once or in different colours, whatever takes your fancy.

The gears and jaw parts are designed with quite close tolerances for minimal play. If part dimensions print a little off spec, then a little post-processing might have to be done. If in doubt, run a flow calibration test.

The parts are modelled with 0.4mm nozzle and 0.2mm layers in mind. The orientation in all the STL models is as intended for printing. No supports are needed.

I don't think the material used matters all that much, but an important consideration is shank stiffness for the Main_Body part - I went with PLA for that this time because of that. ABS is a good choice for any parts too - tough, but also easy to trim and file smooth if fit adjustments are needed.

3 perimeters and around 30% infill are good, but I recommend reinforcing the shank of the Main_Body part with more infill to increase strength. The included .3MF file has this modifier applied.

100% infill on the pin is also a good idea.

Assembly Notes

Benefits from some explanation! :)

Gear 3 Grind opposing flats on the edge of the M4 x 40 screw head, checking it is a snug fit into the gear pocket, then seat in fully. If gluing, make sure the shaft is as true as possible and the gear isn't wobbling.
Gear 2 / Gear 4 Place screw and gear into its slot and allow for a tiny bit of play. Make a mark on the body next to a hole on the gear edge. Remove gear, place screw back into slot and make a similar mark on the shaft, aligned with the previous mark.
Gear 2 / Gear 4 Start to file or grind down a round groove at the marked point. Check progress occasionally under bright light. With screw located in the gear, look through the side hole and turn the shaft until you see light to check progress. Keep grinding the groove until you can insert a piece of 1.75mm filament over the screw groove (The gear filament holes may need enlarging carefully with a small drill bit if they are too tight for the filament to enter at all.) Place the assembly back into the body slot and check that the fit isn't to tight or loose. If so, try widening the groove a little.
Gear 2 / Gear 4 With pliers, push the filament through the hole firmly - it may take some force. If the filament is loose then glue it in place. Trim the filament on each end, neat and flush with the profile. The gears should not move on the shafts at all.
Place all gears on the body - before closing the body plate, the gear set should look like this: --> Hold the body plate in place and test the gear action, checking for binding. Any blobs or top surface unevenness on the gears needs clean-up so they run smoothly enough. The raised U-shape grooves on the body plate might need some smoothing down with a small round file, if they are causing a little friction on the screw shafts. When it all works nicely, screw the plate on from the front. It helps to hold it tight together while doing this, because as the M3 screws start to seat themselves in the printed threads, a tiny shred of plastic can be pushed up and the casing may not close really neatly.
The jaw slide and/or shank may need a little filing or scraping to move smoothly together. Make sure to check the action along the entire shank before pinning the fixed jaw in place. Drop the M5 nut into the jaw slide and roll it back some of the way on the screw. Fit the fixed jaw onto the top of the shank and push the octagonal pin firmly all the way in. It should be a very tight fit. The pin faces may need a little sanding down if they are too tight to even start in the hole.