Sketches for the UBH (Utility Blade Holder) project. The UBH was designed to be a thinner, lighter replacement for my folding pocket knife. Holders for disposable Stanley utility blades are a popular choice for this type of application and many designers have created their own versions. To serve as an effective replacement, the tool needed to be deployable/retractable with one hand and, at minimum, needed a pocket clip and a locking mechanism to keep the blade in position when cutting under pressure.
The first functional iteration of the UBH, the UBH-MK1. Creating detents for open and closed resting positions that a normal person could operate proved to be quite a challenge. Finding the right tolerances to allow the blade to move freely back and forth also proved to be an issue.
This iteration had two significant drawbacks: the useable cutting edge was very limited and there was no hard lock that kept the blade deployed when cutting under pressure. I had experimented with a frame lock-type feature, but it was too difficult to unlock with one hand and often failed under high cutting pressure.
The UBH-MK2 solved the two major drawbacks of the previous design with a longer cutting edge and a switch-type hard lock.
By leaving part of the body cover open, I was able to maximize the usable cutting edge. The solution to the hard lock ended up being quite simple, though I had to create an additional part to solve the problem. A sliding switch in the blade carriage allows the user to deploy and lock the blade in the cutting position with one hand.
From the outset, I knew creating a pocket clip was going to be an issue. I didn’t have access to sheet metal equipment, so making a clip out of metal would be difficult. You can purchase off-the-shelf pocket clips, but many of them were the wrong size, the wrong color, already had branding on them, or were very expensive. I thought about cannibalizing a cheap pocket knife for the clip, but this seemed like a rather wasteful strategy. The solution ended up being a 3D printed pocket clip with a rather unique geometry to accommodate the shape of the UBH’s body. The clip is printed from the same nylon-carbon fiber composite as the blade carriage and cover. It works great and the tension can easily be adjusted in CAD.
To maintain a narrower profile, the UBH’s body had to be machined from aluminum. There’s no reason this part can’t be 3D printed as well, but the presence of captive nuts would require a larger body. All the CAM work was completed using Fusion 360 and the body was machined in two operations.
The UBH body starts with a 1.5” x 3.7” piece of 6061-T6 aluminum that is cut and machined to size from bar stock. The stock gets mounted in a pair of soft jaws and positioned against a vice stop.
The first operation decks the backside of the body, completes the profile, drills and taps the holes for the pocket clip, and breaks any sharp edges.
For the second operation, the part gets flipped over and remounted against the stop. The dial indicator shown here is used for measuring part deflection upwards as a result of clamping pressure; this allows successive parts to be mounted with a consistent force.
In this operation, the body gets machined to its final thickness, the pocket is created, the holes for the cover are drilled and tapped, and any remaining sharp edges are broken.
Machining complete for the UBH body.
Like the GHK project, my intention was to create a prototype with a more finished appearance. In order to get paint to adhere better, the UBH bodies are media blasted and washed to remove any machining imperfections, contamination from the machining process, and to increase the surface roughness. Machine screws are inserted into the body to protect the threads from both abrasives and paint.
Media blasted, washed, and ready for paint.
Similar to the GHK project, the UBH bodies are painted and laser engraved to achieve the final look. Again, powder coating would have given a more durable finish, but it requires specialized equipment and a dedicated oven for curing. A very small number of UBH-MK2 bodies were machined, so hard anodizing these parts would have been prohibitively expensive (cost per part). I took some lessons from the GHK project and tried to keep the paint thickness even across the UBH’s body, which is easier said than done. Small variations in paint thickness can lead to dramatic differences in the appearance of the laser markings.
I printed a fair number of prototypes for this project, mostly due to issues with fit and the inherent difficulty associated with printing nylon and nylon-based filaments. An important lesson learned here was to keep CAD geometry material-specific. Greater clearances in the CAD model can unlock more material options, but usually results in poor fit in one or more areas of the assembly. The best option was to adjust the model for a specific material, slicer, printer, and extrusion multiplier. Change any one of those things and the model needs to be modified accordingly.
An assembled UBH-MK2 prototype. There are still a number of improvements that can be made including a more durable paint finish on the body, a switch printed in a more visible color, and more aggressive jimping on the sides of the body for improved grip.
Blade deployed and locked.
Rear shot of the finished UBH-MK2 prototype.