Top Hat Material?

Discussion in 'Piston & Spring' started by NeilM, Sep 9, 2019.

  1. NeilM

    NeilM Well-Known Member

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    No not the steamed felt type you sillies, the plastic thing that sits inside the piston and on the end of the spring.

    I need to knock up a top hat for a TX200 I am putting together, I have some nylon rod and also some Delrin rod. I am pretty sure either would do the job fine but does the collective know which one is preferred / will not break?
     
  2. RobF

    RobF Administrator Staff Member

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    I'm using steel for both. Just taken mine apart after a couple of years, just as good as new.
     
  3. NeilM

    NeilM Well-Known Member

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    Steel... OK.

    The one on the spring I have, which is too short and the one in the 97 are both made of a slightly soft plastic and I know at least one 'tuner' who makes guides, preload washers and top hats out of Delrin.

    Getting this TX on the road has been two steps forward one step back all the way, why I thought it would be any different once I had a few different springs I don't know... possibly just my natural optimism..... bah, humbug!
     
  4. Cooper_dan

    Cooper_dan Well-Known Member

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    I was in a pinch a while ago and 3d printed a top hat from pet-g (same stuff as plastic drink bottles). With a metal washer on either side.
    I intended it to be a 1 week tide over, but actually is done quite a lot more and several thousand shots with no apparent damage. I'm using a soft spring with quite a bit of preload, so I don't think the top hat is ever separating itself from the inside of the piston. And the metal washers prevent any rubbing damage.

    I think plastic can work OK
     
  5. NeilM

    NeilM Well-Known Member

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    Thanks for that.

    I am keen to get this TX up and running just to see if I like it, so I think I will have a quick sesh on the lathe this afternoon and see what I can come up with.
     
  6. Nick G

    Nick G Active Member

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    Depends if you want to add some weight or not , steel or delrin , I have had some nylon bar stored in my garage for some time and it has bent , I think I read somewhere that it takes in moisture .
     
  7. Cooper_dan

    Cooper_dan Well-Known Member

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    What bore/stroke/spring spec is it? TX's don't need much doing to make really nice shooting rifles
     
  8. NeilM

    NeilM Well-Known Member

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    Piston is a standard MK2 / 3, stroke is a few mm longer than a Mk1 using a latch rod Phil just spun up for me, seal is a blue one from 'Stralia and the piston bearings are standard AA. I have a couple of springs handed to me at a shoot yesterday the fav looking one is Mk1 spec, 14.5mm ID, 21.5 (ish) mm OD, 217mm long with three compressed coils at one end. I'll get it in and see what the velocity is like and what it settles to. I have a couple of longer, possibly softer springs 14mm ID, 21mm OD, 235mm long with no compressed coils, so we may end up with one of them, it is one big experiment / lash together at present to see if I prefer the Tx over my 97.

    Nick, thinking about it, Nylon doesn't like heat much, so I think I'll start with Delrin as that will be quick and easy to do and maybe try steel once I know what the 7.9grn vs 8.44grn pellet velocities look like.
     
  9. Cooper_dan

    Cooper_dan Well-Known Member

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    I've swapped from mk1/2 to a longer softer spring on my 85mm stroke (with a latch rod).
    Definitely preferring long and soft. Efficiency is higher, shot cycle more of a dull thud than anything else I've tried. Muzzle energy is higher with 7.9's than 8.4's which i cant be bothered fixing.
    Mine is about 38% efficient. Could probably push it closer to 40% if transfer port was messed with to suit 8.4's. Not bad for a 177 with essentially standard internals.
    With the mk2 spring it was more like 36%. So not too much in it i suppose.
     
  10. NeilM

    NeilM Well-Known Member

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    Top hat made, in and testing underway.

    7.9's running at around 805 fps, so 11.4 ft lb and 8.4's at 760 ish, so around 11.00 ft lbs... that's after the first 30 shots, so a lot of settling down to go yet, but encouraging.
     
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  11. Cooper_dan

    Cooper_dan Well-Known Member

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    This thread reminded me to take the 'temporary' top hat out again now I've found a steel one. Added 17g to the piston but still shoots very very well.
    TX200 is a lovely base to start from. Hope you enjoy yours as much as I do mine
     
  12. hmangphilly

    hmangphilly Can't Re Member

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    I'd leave that and shoot it for a bit Neil

    how's it feel ?
     
  13. NeilM

    NeilM Well-Known Member

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    Ahhhh Maestro, welcome, welcome.

    It feels pretty good.

    Less / softer recoil than the HW97 and it is a lighter setup as the action is in a GinB stock and currently has a Leupold EFR scope up top.

    I did some 30 yard accuracy testing earlier... well you have to do something while shooting it all in, and with some early H&N Sniper Mediums it is producing consistent and promising groups.

    I will take it to Mendip on Wednesday and plonk around the HFT course with it, once I have put a few hundred shots through it I will run it over the chrono again, give the barrel another clean and try it with some 'good' AA and JSB 8.44's.
     
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  14. Nomads HFT

    Nomads HFT Well-Known Member

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    Muzzle energy should be higher with the 7.9s, Dan - it doesn't need fixing.

    You could increase energy efficiency to 40+% with a sized closed face seal (HW etc.), but you'd risk seeing POI shifts with extreme temperature changes.

    The 2% energy efficiency you're getting with the softer spring is manifest as reduced surge displacement, albeit at the cost of a slightly higher piston final landing velocity (which you won't feel, and has no effect on accuracy).
     
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  15. Cooper_dan

    Cooper_dan Well-Known Member

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    With the steel top hat back in, measured efficiency is up to 39%. I'll be leaving it like this for a long time now. It feels the best it ever has, and should be super reliable. I should have taken your spring advice a long time ago!
     

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