• On the Cutting Edge

    seminolemuscle02/12/2018 at 21:21 0 comments

    Engineering is all about problem solving; not just creating solutions, but achieving them with very strict constraints in mind. The more restrictions you add, the more intricate and clever the solutions become. In the realm of the lean hardware startup, there are restrictions aplenty: cost, time, personnel, available tools, complexity — and the list goes on.

    In this post, I’ll be stepping through the development of something seemingly simple that we would be flat-out screwed without: a chamfer tool.

    The Problem:

    I was working on a project that required sourcing a single plastic injection molded part that was to be delivered to our local assembly operation. Our problem presented itself when our first batch of injection-molded housings arrived from our mold-house in Shanghai:

    See any issues? Neither did I. It wasn’t until a colleague picked one up to create a full assembly that we discovered the terrible truth: “this bottom edge is waytoo sharp — we can’t sell this.”

    He was right. The edge was sharper than vermont cheddar — enough to potentially cut someone and needed to be dulled. I immediately checked the files I sent to the molder — our current model has a chamfer where it should; maybe the error was on their end and they’ll fix it for free?! Sadly, it was not. As it turns out, the culprit was a day’s lapse in version control and since the issue is a corner, the steel has already been drilled out of the mold and can’t be repaired. This problem is real and needs to be dealt with ASAP.


    The options are few, really:

    1. Buy a free-hand chamfer tool
    2. Buy a pipe-chamfer tool
    3. Design and build a tool

    Urgency determined that time took priority over cost, so we chose to try all three.

    We quickly ordered a well-reviewed hand-tool with express shipping. We knew the chamfer would be a bit inconsistent, but replacement blades are cheap and a little practice from a skilled hand might produce acceptable results. Our tool came in and we gave it our best shot:

    Yikes. Well, at least we know that’s off the table. It was a Hail Mary; we had much more confidence in Option B. Being that the diameter of our bottom edge is almost exactly 3 in, we figured that a pipe chamfer tool with variable standard diameters would do us justice.

    I popped on our housing and it sat pretty nicely on the inside edge. Not ideal, but it should suffice:

    Nope, not quite. It makes sense that we need constant force against this blade or it’s going to skip. Also, the 15 degree chamfer is less than ideal; lengths where the chamfer is consistent are still pretty sharp and the metal lip of the tool leaves an undesirable line on the softer plastic. At this point we’ve exhausted the quick fixes within our budget. Time to do some engineering.

    The Inspiration:

    The pipe cutting tool has the right idea:

    • A lip on both sides at the exact diameter of the housing will keep cuts smooth and consistent
    • A flexible mending plate that attaches the blade portion to the backing will allow the housing a bit...
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