Simple Machining Process Repairs Broken Control Knob

[Francisco] is helping his mother with a repair to the headlight knob on her Ford Ranger. Above you can see the broken knob on the left, and what it is supposed to look like on the right (taken from [Francisco’s] own vehicle for reference). We’ve encountered split shafts on plastic knobs before and decided it was not something that could be fixed. But he didn’t give up so easily. He mentions that you can purchase a replacement for a few bucks, but he has the means to repair the knob by machining a metal bushing.

The idea is that you mill a metal ring whose inner diameter matches what the outer diameter of the plastic shaft should be. By inserting the broken knob in the ring, the plastic is held tightly together as if it had never broken. In the video after the break [Francisco] uses a metal pencil body from his junk box and a mini-lathe to cut the bushing to length, and mill the inner diameter to his specifications.

He talks about the difficulty of getting replacement parts in Chile, where he lives. But we think this kind of thrift is a great example for all hackers. If you’ve got the tools why not use them? And if you don’t have them, here’s a great excuse to procure them!

49 thoughts on “Simple Machining Process Repairs Broken Control Knob

  1. “And if you don’t have them, here’s a great excuse to procure them!”
    I can see that one going over well with the significant other.. “Honest, it is better to spend several hundred dollars to repair this $4 part than it is to replace the $4 part….

    1. With respect to Francisco, we don’t know enough about him to use this repair, to justify tool purchases. His shop may be how he makes his living. Even in the USA you need a pretty good income to have a home shop like this, even at that even they accumulate it over the years. Also this fix could have been made by using hand tools. Yes it would had taken longer. Home shops generally are a leisure time activity, so time saved isn’t really that critical. I’m on of of those never been married sorts, hell I have a difficult time to justifying spend money to myself. Perhaps that’s why I never married :) but I have never been a skinflint, and have own nice things. Fransisco talks safety, but doesn’t protect his eyes when he actually starts the machining.

  2. I fixed a similar knob on a ’99 Honda Odyssey, except instead of a round shaft with a D hole in the middle it had one flat tab and a C shaped tab next to it, hard to explain without pictures…… but perfect for jamming in the clip off a bic pen’s cap….. that repair has lasted for years.

  3. @hawkeyeaz1, the mistake is in telling the SO it’s a $4 part! :)

    Besides, when the unobtanium framitz on your ’59 Wartburg goes south at 8:45pm on a saturday night, you have no choice but to make the part so you can have it on the road to go to Sunday dinner at Mom’s house, right? ;)

    1. Funny. In the event asked me to bring them the T- handle reamer out of the toolbox, I wouldn’t know what I was looking for. Now i they asked for the tapered reamer, that I would find, if it was there. Anyway a good set of hands tools can get you put of a bind most the time. Less expensive, and will complement power tools when you can afford to procure those.

  4. My local kiwanis club has a second-hand shop kinda like a giant salvation army, and they have an excellent electronics section. Behind the counter they have huge bins full of knobs they pull off electronics that are beyond repair. I just got to pick through them to get knobs for a synthesizer project I’m working on.

    There’s something magically joyful about knobs.

  5. I had an AC knob break like that on an old Pontiac. I fixed it by dabbing a little super glue along the crack and then wrapping the outside of the post with a thin gauge metal wire. I twisted the ends of the wire together with needle-nosed pliers which squeezed the crack closed. That held for at least 4 years (when I traded the car off).

  6. I used to do this all the time on older stereos, etc. Except instead of fabricating something as crazy/extravagant as a metal ring, Just wrap a small cable tie (zip tie) or two around it, and affix with some CA (super) glue..

  7. This gets into one of my pet peeves about low quality knobs. My current car, the radio knobs broke within the first year. It probably would have been covered by the warranty but they would have just broken again. I was able to secure the shaft hole and fill the knob with high strength epoxy. The car is 8 years old and my repaired knobs are holding up great. Kind of weighty now but good.
    I suspect his repaired knob would outlast any replacement part he could get from Ford.

  8. There are companies which have made these replacement sleeves for fifteen years or better. But machining seems a bit much. There are many different commonly available pipe types, all with different materials and diameters.

  9. not sure if it’s been mentioned, but you could just go to an auto parts store and buy a spring-clamp set that’s used to seal small hoses on your car. epoxy them in place and put the knob back on the equipment. no lathe needed. costs about 10c or less…

  10. Polymorph, for heaven’s sake.

    First joint the split part with superglue. Then melt some polymorph, which behaves and looks like white nylon except it melts in boiling water. Pack the cavity in the knob with a dab of polymorph and fit it onto the shaft. Job done – But reversible, unlike with epoxy.

    1. meh… electrical tape. i wish that stuff were banned from existence. it doesn’t adhere all that well and it leaves a sticky goo all over everything. when I need electrical tape, i use a stretchy rubber tape that bonds to itself, but not the wires.

    1. That’s exactly what I was thinking. I have a cracked pair of safety glasses hanging above my lathe as an example of what happens when you use a parting tool on aluminum and feed it a bit too fast at the end of the cut.

  11. What I’ve done before in other applications, and could be done here (if there’s enough room behind the knob), is put a small automotive hose clamp around the shaft. That always worked for me.

  12. My mom had a knob on her washing machine break. A replacement knob was $80 bucks (insert an insane number of exclamation points). I found out her stove used the same diameter, so we would shuffle the knob between the stove and the washer. The washer now had a note saying “broil=delicate, bake=color safe, preheat=pre-wash”.

  13. I love how he starts the video by removing the lathe chuck wrench key from the chuck, and then telling us how bad that is.

    His next project should be adding a spring to the key so it can’t be left inserted.

  14. Lots of good suggestions here.

    The adjuster on an automotive hose clamp might not clear the dash hole in many cases.

    Brass is tubing is good, and available in a many sizes. But it is expensive these days, and you’d need a cutter. A good hardware store would probably let you borrow a tubing cutter.

    Epoxy’s toxicity should not be ignored, even if it doesn’t smell bad.

    My personal favorite method for this repair is stainless steel safety wire, as used in aircraft. A one pound roll will set you back $8, but it lasts many years and it lets you do serious Stuff that nothing else will. I like the thicker stuff.

    1. the clamps they use for fuel lines and such don’t have an adjuster at all. you just use a pair of pliers to open them up wide enough to slip them into place. they’re commonly available and usually come in an assortment of sizes on the help! displays at the auto store.

  15. JB Weld to the rescue. If you use JB or some quick dry epoxy and put some wax or mold release agent on the metal shaft you can put the knob on it after filling the inside of it with JB weld and it will take a nice mold of the shaft. Just pull the knob off before it hardens all the way Then after it dries it will be just like new and still removable. Molding is king with old car parts

  16. Assuming the shaft hasn’t shed any parts, a far simpler fix is to smear a blob of epoxy on to the part, then wrap in cotton.

    When it hardens, you’ve got a super strong fix.

  17. I just used supe glue, held ittogether for a few seconds longer than a minute. seems to be working.

    2001 GMC yukon denali with Bose. why is every single knob on this head unit split down one side? the buttons never get touched because there is controls for it on my steering wheel.

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