What size are the STL and RGH Desiccant Cartridge Threads

Discussion in 'General' started by Joseph Zeglinski, Jul 18, 2017.

  1. Joseph Zeglinski

    Joseph Zeglinski Standard User

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    Hi,

    Can someone - at DL Tech Support - tell me what the "thread pitch and diameter" is for the two STL & RGH camera cartridges. I would like to find an appropriately sized (nylon) screw to act as a temporary "dummy plug" for the exposed CCD chambers, during the 4+ hours the desiccant cartridges are being recharged - as an alternative to just using tape.

    I checked - the SBIG CAD Drawing doesn't specify the thread spec for either cartridge. From my measurements, it seems to be about a ( 1/4" x 24 NF THD ), but that seems unlikely since nearest standard screw size diameters are either 3/16" or 5/16".

    Thanks,
    Joe
     
  2. Doug

    Doug Staff Member

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    Thread specs for the STL desiccant plug are .250 -28 UNF-2A

    Looks like the specs for the RGH are the same.
     
    Last edited: Jul 18, 2017
  3. Joseph Zeglinski

    Joseph Zeglinski Standard User

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    --- Thanks Doug,
    That was a quick reply. Glad you corrected my original thinking based on using a thread gauge on those tiny and cramped threads on the cartridges I have in the oven.

    **********
    BTW:
    Has anyone thought of making a small cylindrical "induction coil oven" with just large enough diameter for a couple (or so) cartridges?
    Seems like a tremendous waste of energy to fire up the kitchen oven for 4 hours just for this job - not to mention the possibility of any evaporated grease that might still be there in that atmosphere, which might get into the desiccant sieve and coat it - making it less effective, or even impervious to absorbing CCD moisture.

    I would AMOST be enticed into using the microwave oven - but don't relish the indoor "fireworks" display. Besides the manufacturers warn that drying desiccant sieve in a microwave, as I once asked, would fracture the crystals into a finer powder - (possibly dusting the CCD sensor chamber).

    Perhaps something like an old style (scrapped) automotive ignition coil might work. There may be enough tunnel space in the center, to drop in a couple of cartridges, and possibly the induced current into the cartridge aluminum wall would heat the desiccant sufficiently, with lots less power - assuming the cartridge case seam won't de-solder.

    As an astro-bonus - it does run on telescope standard 12 VDC, so in a pinch, could be used at a favourite dark site, if someone's desiccant wasn't quite dry enough that day.

    Just a thought.

    Joe Z.
     
  4. Doug

    Doug Staff Member

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    Don't use a microwave. The entire exterior of the desiccant plug is metal - including the business end - so microwaves won't even penetrate it. At best you'll get a light show; at worst you'll blow the magnetron. And the desiccant plug will remain nice and wet.

    You do want to have reasonable temperature regulation. It needs to be hot enough to recharge the desiccant - the type we use holds onto the water very strongly. But if it's too hot you might damage the housing. (It's not soldered - we use high temperature resistant epoxy.)

    Considering how often the plug needs to be recharged I don't think making a special gadget would be a net savings of resources. I'm not sure how much power a full-sized oven needs just to maintain its temperature, but I'd be surprised if recharging a plug cost $1 in electricity.

    FWIW we use a toaster oven (calibrated for temperature with a thermocouple).
     
  5. Joseph Zeglinski

    Joseph Zeglinski Standard User

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    Great idea, George,

    I like your way of doing this - the standard kitchen oven also heats up the house, which is bad in summer, adding to air conditioning load.

    Your "Toaster Oven" would be perfect. Can even operate it outdoors, after the hot dogs are done.

    Joe
     
  6. Colin Haig

    Colin Haig Staff Member

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    Just remember dessicant first, hot dogs as the reward. Helps deal with the grease ;-)
     

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