Gas station without pumps

2017 November 8

Bathroom timer knob

Filed under: Uncategorized — gasstationwithoutpumps @ 10:26
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On Saturday, as a break from the mechatronics midterm, I rode my bike over to Gary’s Plastics (105 Bronson, opposite the Pacific Edge climbing gym) to get some acrylic sheet for cutting out electrode holders for my applied electronics course.  It took me a while to find the place, because 105 Bronson is mainly a metal-working place.  Gary’s Plastics has only a tiny sign on the side of the building, and they are at the back of a junk-strewn parking lot.

I bought the 1/4″ acrylic sheet I needed at a much lower price than San Lorenzo Lumber, which had only 1/10″ sheet, but it was clear that they did not stock a lot of stuff—if you want something specific, you probably have to order it in advance or go over the hill to TAP plastics.

While I was there, I picked up a scrap of white HDPE for another project—fixing the knob on the timer for the fan in my bathroom.  The knob for the timer broke about a year ago, and my first thought would be that it would be a trivial fix, as I had several knobs available that I had bought for various projects.  Unfortunately, none of them fit!  The standard knobs are all for 6mm shafts, and the timer had a 4.77mm shaft.

The bare shaft, which is too skinny for standard knobs, which expect a 6mm shaft.

For a while we used pliers to turn the timer on, but this was inconvenient and ugly, so I kept looking for a different solution. After a while, I found a part that was designed for a 5mm shaft, though it wasn’t intended as a knob—it is an aluminum coupler base for the Eggbot.

The aluminum coupler base from the Eggbot—looks ok but rather hard to turn with wet hands.

We used the Eggbot coupler for quite a while, but we all got irritated by the difficulty in turning it. Eventually, my son noticed that the set screw for the coupler was a standard 10-32 screw thread, and we stuck in the only 10-32 screw I happened to have on hand (I have a lot of 10-24 screws, but those have too coarse a thread).

The result worked well and has a certain “there-I-fixed-it” charm, but did not really appeal to my wife or me.

I took the scrap of HDPE, cut off a chunk with my new bandsaw, drilled a hole through it with my drill press, put it on my wood lathe (a tool that has sat idle in my garage for at least 20 years), and turned a decorative cover for the screw. HDPE is much easier to turn than wood is—there’s no grain to tear out!

I didn’t quite get the dimensions I wanted—the screw head is wider than the handle rather than matching, but the result is much better that the bare screw.

I still have enough of the scrap to make a couple more attempts, and one of these days I’ll redo the handle to be wider with a flat-head screw countersunk in, rather than a pan head sitting on top.

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