Monday, September 10, 2018

Passing the Ketchup

As in passing on some details so you can "ketchup" on some things I've been working on. 

First off, rev. 1 of the chair repair failed.  As commenter Raven suggested, the epoxy didn't bond well to the plastic.  I mentioned possibly making a small steel or aluminum plate in the original description, so I went with that approach and it's in now place.  I'm working from this chair.

The glue broke pretty much as soon as I applied any pressure to the arm, so this got put into place yesterday.  In addition to the metal plate, I put some superglue (cyanoacrylate) gel into the crack.  That didn't seem to bond well, either.  This fix probably isn't the best way to do it.  There probably should be two holes on each side of the crack, which would make the metal a bit longer. 

The other thing I've been working on has been my engine.  It still just won't turn over and keep running on its own.  One of the suggestions last week was to get a higher purity alcohol fuel, with people recommending as close to pure ethanol as I can get without buying 200 proof vodka.  In the US, this is called denatured alcohol, while in much of the English speaking world, it's referred to as methylated spirits

I was using a brand from the local Home Despot that was branded as "Denatured alcohol", which comes from adding methyl alchohol to the ethyl alcohol to poison it (or "make it undrinkable")   Research showed what I was using to be about a 50/50 mix of ethanol and methanol.  We have four major hardware store chains in town: Home Depot, Lowe's, Ace and True Value; none of them showed they carried anything with higher percentage ethanol.  Although guitar polishing frequently uses lacquer, neither of my usual sources had anything specified.  A bottle from Amazon arrived yesterday. 

The bottom line is that the engine tries to turn over but doesn't.  I've put together several troubleshooting videos (such as) in attempt to get comments from other engine modelers, and no one has pointed out anything obviously wrong.  Yet.  Something is causing just enough extra drag to keep this from running.   Flame eaters are kind of notoriously fickle to get run running.   This is the website of a rather "famous modeler" in the Netherlands, who says (autotranslated),
It is my experience that one needs just as much time for well adjusting all the parameters than to build the motor itself. There are several critical parameters that must be adjusted one by one and at the same time to their optimum. The problem is that this adjustments can only be done successfully if the engine motor already tends to go running properly and that is only the case if all these parameters are reasonably close to their optimum; so a somewhat "chicken and egg" story. It may happen that you are changing something, while another parameter is not properly adjusted or created. Then you hit sometimes further afield and that makes you desperate sometimes. But it is also my experience that in situations like this persistence always wins, so one should not be discouraged by all this. With enough patience and systematical approach adjusting the engine is very well possible. Once all parameters are set to their optimum they run merrily and fairly reliable and will amaze especially modellers of steam engines that usually build more "manlike" models like steam engines.


  1. A lot of the Engineered Plastics used today don't bond for beans with most commonly available adhesives.

    I probably would have used three screws on each side in a triangular pattern, but then I over-design stuff all_the_time.

    My neighbor was quite askance when I described the new mount for the vertical. He freaked out over me using 4" or 5" well casing pipe for the support!

  2. It's solid plastic, right? You have two choices, essentially. A sandwich side to side, or top/bottom. Plates on the sides should be easier, as they can be cut to match the contour. Top/bottom should be more than flat plate. That really should be square tubing bent to match the shape.

    Side plates should be cut to be near full height of the plastic, and with multiple screws running through both plates. Flathead for the inside for clearance, and acorns for the outside, or flathead on the outside for looks, and regular nuts on the inside if they fit and don't hit you.

    I suspect that the stress you put on the chair during use is asymmetrical. How you get in and out, perhaps.

    I would suggest at least 1/8 or 3/16 aluminum, but still would want 1/8 if steel. You should put screws at least every 1/2 to 3/4 inch apart. #8 or #10. You need a bunch of small ones, not a few big ones.

  3. Have you checked for any binding during the engine's rotating cycle?

    What did you end up doing about the spring? I'm wondering if some sort of hairspring could be used in place of the coil spring.

    1. That's what I've been doing for the last day or so. There was a little catch as the piston went past about 1/4 of the way in or out of the cylinder. It appears that's coming from the push rod on the valve - the rod that spring is on.

      As for the spring, I wound a couple with the size music wire that Duclos recommends and the number of turns he suggests, but when they uncoiled from the mandrel, they ended up too long. I have enough spring wire to make many more, but I'm not sure I need to.

  4. Here's a wild idea, is the plastic ABS?

    If so maybe you could just fuse it back together with some acetone or ABS pipe glue.

  5. Or if it's HDPE maybe try heat welding it with a heat gun and some scrap HDPE like water bottles.

  6. If you drill enough holes in it, you won't have to worry about the crack...

  7. Enough of the namby pamby!
    yank that plastic POS off, make a sand mold from it, and melt down some old mag wheels and cast a new arm out of aluminum.
    or, find the wealthiest neighborhood around and check the thrift stores for a new chair...
    Or, call Tasha's African herbal doc, his Anaconda oil ointment cures broken chairs also. (excuse the continental snake drift)

    1. I should probably comment to Will's comment, but there doesn't seem to be enough room on the inside of the arm for anything. It's either take this advice (I can pull the rims off my car!) or go over to wood like Aesop or Zendo Deb suggested on the other post. I probably have enough Baltic birch plywood to do one arm, but I'd have to do both. Seems like a bigger project than making a bigger plate for the one side.

    2. SI,
      Can't be melting down your OWN rims! Gotta find some just layin' around!
      Plan C- pull the arm, clean it up for the plug, and make a mold quick and dirty, maybe out of plaster. Wax it up and make a nice fiberglass or carbon fiber/epoxy arm. Should not take more than a week....
      Arm chairs are a PIA anyway, no way to sit in them and play guitar cause the arm gets in the way.