Jet work - taking a microscope to it

Discussion in 'Fettling Forum' started by presscall, Mar 9, 2020.

  1. presscall

    presscall United Kingdom SotM Winner SotY Winner Subscriber

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    I’d some work to do before eyeing up the results at 100X magnification.

    93E31290-5730-4C91-9BFE-CA94E397587D.jpeg


    THIS Russian stove, a ‘Prim Compact’ was the project.

    AF01F6E2-A72B-4FDA-8A73-959B2F791380.jpeg


    The standard jet fuelled over-rich. The unused spare was the same, so wear wasn’t the issue so much as the wrong specification by the manufacturer at a measured 0.34mm diameter orifice.

    Maximum output.

    C46CBFBC-25CC-4F16-BCAC-20C0ED474339.jpeg


    ... and lowest simmer.

    93BD91AB-7944-4C13-8F54-321A7944BD51.jpeg


    The solution was to install a short length of 25-gauge hypodermic needle in one of the jets in a technique I first featured in THIS post, effectively reducing the jet orifice to 0.23mm diameter.

    @Tony Press hit upon the capability of a hypodermic needle to ream out its own clearance hole in a jet, simply rotating it by hand while gently applying pressure.

    78B1E20A-AB65-404A-AA97-89CD4507E9B4.jpeg


    The tip does the job.

    F9EAC318-D00A-413B-9805-E807B187D3BA.jpeg


    Once the hole is reamed the end of the needle is ground square, any burrs around the cut edge removed by inserting a 0.23mm pricker wire a few times. It’s then pushed into the jet orifice a little way so that barely any projects inside the jet to avoid creating a projecting edge to snag the burner’s auto-pricker wire.

    I didn’t photograph this particular jet at this stage but on a lipstick burner repair this is how it looks after silbrazing ...

    8D6AFDFC-D910-4079-BA49-9F3335E5D63A.jpeg


    ... and when trimmed and cleaned up.

    95BBA3CC-E56E-4132-A1DE-E0499EFCCEEB.jpeg


    Final stage was to slim down the burner pricker to clear the new jet. Judicious use of a Dremel abrasive drum, rotation lengthwise along the needle towards the tip.

    16259E9B-438B-47C0-AA30-7EE30B64777E.jpeg


    Tried out with the jet installed.

    D6138739-342E-4B1C-B093-C36FFFB23578.jpeg


    The results examined through the microscope.

    The spare jet, left, and the re-worked one

    BC5C3AC5-CB6A-40F9-90D9-659871B3902E.jpeg


    The spare jet orifice and surround at 36X magnification ...

    C2F91918-41F6-4C54-AE9B-25AC1030066E.jpeg


    ... and at 102X magnification.

    A3B9B9C1-D7FB-4EC3-AF37-01B60FD1DF4F.jpeg


    The re-worked jet at 36X ...

    40A3887F-2EA2-4A88-9F04-46C9928B0019.jpeg


    ... and at 102X. Stainless steel hypo needle ‘liner’ can be seen.

    1E4A2F94-AB2E-493A-BB1D-1F9305DC9FA6.jpeg


    The fuelling of the stove is now what I was aiming for, at maximum output ...

    92EB693F-7A82-480C-8C7C-64832AFD54ED.jpeg


    ... at a medium setting

    4DEF3977-830F-4979-93AD-381166754EC8.jpeg


    ... and at a simmer.

    514720E8-6591-49F6-8F03-37A0DD5894F9.jpeg


    The stove still puts out ample heat and will be less wasteful of fuel.

    0429B1B1-2925-43C1-9CD5-530A1F73CC4A.jpeg


    John
     
  2. Afterburner

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    Microscope is very useful tool for looking/checking small work/items. :thumbup:

    Workshop microscopes with measurement capabilities are best options for work shop use. About a year ago I bough pallet full of junk from local school. There was a Mitutoyo workshop microscope under the other stuff: Sold: Mitutoyo Toolmakers Microscope 25x25mm I didn't complain too much. :lol:
     
  3. ally

    ally Subscriber

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    gobsmacked! very impressive

    :)
     
  4. presscall

    presscall United Kingdom SotM Winner SotY Winner Subscriber

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    Cheers Afterburner, Ali.
    @Afterburner Great find with the Mitutoyo! I’ll get by with my Busch Rathenow meanwhile ...
     
  5. hikerduane

    hikerduane Subscriber

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    Nice work. Wish I could view my peened lipsticks to see what is going on. 75% to 80% minimum flame direction is acceptable.
    Duane
     
  6. jrs08

    jrs08 Subscriber

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    As always, great tutorial on stove repair! This is probably a stupid question, but I'm curious as to how you were able to take such high quality images through a microscope? What equipment did you use?
     
  7. presscall

    presscall United Kingdom SotM Winner SotY Winner Subscriber

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    I-phone, lens hand-held over the microscope eyepiece where my eye would be. All credit to the phone’s electrickery to focus and get the exposure right.
     
  8. jrs08

    jrs08 Subscriber

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    Unbelievable, I would never have guessed an IPhone could gather enough light through a lens to take such images. It's truly an amazing age we live in!
     
  9. Afterburner

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    @presscall That Mitutoyo is handy size to use. Older one is heavy and takes more space: One solution for thread measurements

    @jrs08 For DSLRs there are special attachments that you can also use to take pictures through microscope. During film era they made them and you can fit them to digital camera also. I have these for Canon:
    [​IMG]
    [​IMG]
     
  10. Ed Winskill

    Ed Winskill United States Subscriber

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  11. CRAZY CRAB

    CRAZY CRAB United Kingdom Subscriber

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    to fix problem, just make jet hole smaller, a good fix and a good way of doing it
     
  12. Simes

    Simes Subscriber

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    John, what made you go straight for 0.23 rather than a 0.32?

    Only mentioning as 0.23 was occasionally used by some manufacturers for fuel saving. I appreciate this is a generalisation.

    I don't have the facility to check, but I have a feeling that a jet at 0.34 would be considered seriously over large. The percentage area increase for fuel flow I've not done the sums for.

    Given the general shortcomings elsewhere with the stove, it may be possible the jets weren't actually made to the intended 0.32.

    Apologies but couldn't trust I could remember to ask at Newark. :(
     
  13. IvanN

    IvanN United States Subscriber

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    You can’t deny those results! Thanks for the excellent (as always) pics. Great instructions
    Ivan
     
  14. dogface

    dogface United States Subscriber

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    As close to perfection as the hand of mortal man can achieve, or, you do fine work Presscall, impressive.
     
  15. flangset

    flangset Norway Subscriber

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    A genuine stove wizard! :clap:
     
  16. presscall

    presscall United Kingdom SotM Winner SotY Winner Subscriber

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    Thanks fellas!
    Your argument’s sound Simon and I’ve asked myself that since doing the job. Probably an over-reaction on my part!

    Mind you, it’s still no slouch when it comes to boiling performance.

    I’ll install a 24-gauge needle in the other jet just to see if that still gives the wrong mixture.
    Exactly, there were indeed a number of manufacturing shortfalls with the stove and 0.34mm was their orifice size - pricker wire a close fit in the jets, pricker measured with micrometer - which came as no surprise as another fault.

    I’ll work on the other (spare) jet and report back.
     
  17. presscall

    presscall United Kingdom SotM Winner SotY Winner Subscriber

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    @Simes
    Outcome.

    I took a photo this time of the jet just after installing the length of 24-gauge hypodermic needle and after I’d boiled it in water for a couple of minutes to dissolve the borax flux crust.

    A684F9D1-2EE9-4E02-B209-4CDE0E7CA432.jpeg


    Protruding needle cut off (diamond grit wheel in Dremel) and surface sanded on wet-or-dry cloth - jet rubbed on cloth held on flat surface.

    B18170F1-08EA-4634-A06D-E67477AF6D71.jpeg


    Through the microscope.

    0033157A-80B6-4DE0-BBF0-3A7A0E3BC824.jpeg


    Pit in surface of brass, top left. Barely visible to the naked eye.

    1461A514-BCCF-4339-AAE2-9769325BEF02.jpeg


    View of rear of jet ...

    21DB574A-E1AC-4B0A-89C7-A72B8EAE05D2.jpeg


    ... and at 36X magnification.

    26DBF19B-8050-4FCB-83C8-9AA001E408E8.jpeg


    In action on the stove, max, mid-output, low simmer.

    BF6F5144-FAD7-44FF-8069-2DC28ADC9F0A.jpeg

    EEB2884B-024B-4BE5-9B1A-6ED09D80B1A5.jpeg

    8390FFBE-2994-449C-9A3E-1254CB949323.jpeg


    Without testing boiling times it seems more powerful (as you’d expect) than with the 0.23mm jet, which isn’t so evident from the photos.

    The un-reworked jets must have been way oversized. The stove’s 0.34mm pricker must have been a looser fit than I judged it to be.

    John
     
  18. Simes

    Simes Subscriber

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    My take on that is you have far fewer outstanding jobs around the house than I have. :D

    A neat result that you can now swap to different jets knowing their relative performance.

    With the collapse in crude oil prices I'd not be worrying to much about using the 0.23 for quite a while. I'm going to be checking on heating oil prices for the next week or so.

    It was probably the prudent approach to go 0.23 initially as it may have proved difficult to reduce further if 0.32 hadn't been succesful.
     
  19. Marc

    Marc Subscriber

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    Beautiful work, John.

    The hypodermic needle should resist abrasion from the pricker much better than just a hole in the brass, too. These repairs will likely last quite a long time.
     
  20. presscall

    presscall United Kingdom SotM Winner SotY Winner Subscriber

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    Reward to myself for redecorating the hallway and kitchen!