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HW80 piston banding

Discussion in 'Anything Airgun Related' started by Jackroadkill, Apr 28, 2014.

  1. Jackroadkill

    Jackroadkill Donator

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    I'm thinking of banding my HW80, and I'm pretty sure that I have heard somewhere that the delrin bands from a TX200 will fit. Does anyone know if this is the case? Looking at pictures of the TX200 piston it looks as if the front and rear are different sizes, and if this is true, which one would fit the HW80 cylinder's ID? I have a lathe so am not bothered about having to machine the piston to accept the banding.

    If I'm wrong and the above isn't true, I'll try buttoning instead!

    Thanks,

    JR
     
    Last edited: Apr 28, 2014
  2. cloverleaf

    cloverleaf Super Moderator Staff Member Mod/Admin

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    The front of the TX piston runs in a 25mm bore while the rear runs in a 30mm bore. The HW80 has a 30mm piston bore, so you want the rear one ;)

    I know the '80 pistons have a fair bit of meat on them, however I'd advise you check the depth of the TX rings as they're fairly deep so you might not have enough wall thickness on the piston skirt to accommodate one. I've just checked a model I have of a TX piston and the OD of the bearing groove is 26mm; so you'd want a piston skirt ID of 24.5mm max IMO to keep a decent wall thickness.

    Surprisingly standardised split bearings of this type seem very difficult to track down - I'd have thought someone would offer a range of off-the-shelf sizes for general engineering applications..
     
  3. Jackroadkill

    Jackroadkill Donator

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    Thanks fella, that's much appreciated. So I'd need to make the grooves deep enough, which would be 2.75mm, assuming my tired brain has followed you!
     
    Last edited: Apr 29, 2014
  4. wonky donky

    wonky donky Donator

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    Make your own bearings from delrin. I've made a complete new piston which is much lighter than the standard item & is able to rotate like the TX piston. I have short stroked the rifle to 68mm as well. Images Here The rifle barrel is only at 90 degrees fully cocked, non of this free drop prior to engaging spring tension you can sometimes see on a short stroked rifle.

    The 80's firing cycle is terrible in standard form at sub 12fpe. mines an absolute joy to use now!
     
  5. cloverleaf

    cloverleaf Super Moderator Staff Member Mod/Admin

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    No problem :)

    The OD of the piston will be around 29.7mm ish at a guess; you want to make the groove 26mm in diameter; so you're effectively removing (29.7-26)/2=1.85mm depth of material. In practice you'll want to measure the OD of the piston and probably want to turn the groove a bit oversize (maybe 0.1 or 0.2mm on the diameter), fit the bearing and check for fit in the rifle's cylinder.


    Top work senior Donkey :D

    It's still 50g heavier than a TX piston though, but certainly not bad going considering how lardy the larger '80 item is to start with :up:
     
  6. wonky donky

    wonky donky Donator

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    Yes it certainly is heavier than a standard TX piston, however this is the prototype in the images.......the final version will be lighter, maybe? it all depends if I can be bothered to be honest......It's not difficult to do......My TX is running a 75mm stroke with a 190 gram piston in .177, that shoots nice as well, gets rid of all hold sensitivity.

    Modified the TX breech as well by making new compression cylinder nuts, TX images here, scales say 200 grams all up but it's 190gms now. ;)

    I'm a firm believer in re engineering most rifle for sub 12fpe as very few were designed to run down at this power. Makes a world of difference.
     
    Last edited: Apr 29, 2014
  7. JD

    JD Donator

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    What about just making the groove shallow and sizing the delrin band instead ?
     
  8. Jackroadkill

    Jackroadkill Donator

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    Well I've got a new piston arriving in the next few days so we'll see how it goes. Am already thinking about buttoning instead, though.
     

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