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Thread: My Mercury Ratting Rig

  1. #46
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    Fine work indeed.
    THE BOINGER BASH AT QUIGLEY HOLLOW. MAKING GREAT MEMORIES SINCE 15th JUNE, 2013.
    NEXT EVENT :- May 4/5, 2024.........BOING!!

  2. #47
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    Quote Originally Posted by evert View Post
    Impressed by all the piston work you've been able to turn out the last weeks!
    I find that making Pistons is a bit of a challenge and also a time consuming pain in the neck.
    But, once I got into the mind set of making them it made sense to carry on and make all the ones I needed in one long lathe session.

    The Mercury piston came about by accident due to the firing cycle of my Original 35, the Mercury piston is being made to a 70mm stroke, but I've left the option to long stroke it to 80mm with this piston if needed --- I'd just have to machine 10mm off the back of the top hat.



    All the best Mick

  3. #48
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    And Relax

    Completed piston :-

    image.jpg



    That's 45grams less than a factory piston.



    And my welding :-

    image.jpg



    I may tidy this up at a later date as I couldn't be arsed to sharpen my lathe tools.




    Next up is a custom Spring guide from 316 stainless steel --- this will actually be a bit more involved than it sounds.
    On cocking, the back of the piston hits the threaded block on a Merc which acts as a stop, as my piston is shorter than standard then the base of the guide will have to extend into the cylinder to act as the piston stop.
    So besides having to drill for the latchrod I'll have three different ODs to machine to act as a both a guide and a piston stop.




    All the best Mick

  4. #49
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    Piston stop?

    I don't understand.

    I have in front of me a Mk4 piston and trigger block,the piston rod passes through the centre of the block and chamfer
    on the end sets the sear and it click into the bent. The piston skirt does not touch the trigger block (it has clearance)
    and I cannot see a reason for it to do so .

  5. #50
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    Quote Originally Posted by crowbar View Post
    I don't understand.

    I have in front of me a Mk4 piston and trigger block,the piston rod passes through the centre of the block and chamfer
    on the end sets the sear and it click into the bent. The piston skirt does not touch the trigger block (it has clearance)
    and I cannot see a reason for it to do so .

    Cheers for that --- you've made me take another look at it and you're right.

    The trigger on this gun is what you get on MK6 Airsporter and though the piston skirt comes very close to hitting the back block threads there is indeed a 5 thou" clearance between them.
    My initial assumption was that BSA had built this in as a safety device so that once the trigger was set you couldn't force the latch rod further into the back block as the piston tail acted as a positive stop.

    I've actually been comparing the various BSA trigger units I have wondering what to use on this gun. :-

    image.jpg



    image.jpg



    image.jpg



    At first I was going to use an Airsporter MK2 unit but it's a false two stage unit with very few benefits, so now I'm leaning towards using the MK6 Airsporter unit with the MK4 Airsporter over travel screw.



    All the best Mick

  6. #51
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    Lovely work and a mighty fine looking piston there, Mick.

    Come on, admit it. You love making these!
    THE BOINGER BASH AT QUIGLEY HOLLOW. MAKING GREAT MEMORIES SINCE 15th JUNE, 2013.
    NEXT EVENT :- May 4/5, 2024.........BOING!!

  7. #52
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    a very pretty piston. Now just machine that o-ring crap off the end and stick on a d28 seal and you'll be golden
    Always looking for any cheap, interesting, knackered "project" guns. Thanks, JB.

  8. #53
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    Quote Originally Posted by Shed tuner View Post
    a very pretty piston. Now just machine that o-ring crap off the end and stick on a d28 seal and you'll be golden
    If the latch rod had been longer so that I didn't have to weld the top hat in just where the seal arbor would have been I may have considered using one, Jon.

    More importantly though, a 28mm Diana seal is £12.50 and O rings cost me about 20 pence each.

    image.jpeg




    All the best Mick

  9. #54
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    Quote Originally Posted by T 20 View Post

    Next up is a custom Spring guide from 316 stainless steel --- this will actually be a bit more involved than it sounds.
    On cocking, the back of the piston hits the threaded block on a Merc which acts as a stop, as my piston is shorter than standard then the base of the guide will have to extend into the cylinder to act as the piston stop.
    So besides having to drill for the latchrod I'll have three different ODs to machine to act as a both a guide and a piston stop.
    By way of a little update, I've now decided to go with this plan for a few different reasons.

    A) --- I like the idea of not relying on the trigger Sears for a positive stop on the piston when cocking.

    B) --- The original setup had 116mm of spring room when cocked, with my new piston I have 138.5mm of Spring room and I only want 100mm with the spring I'm using. So making a Spring guide that extends into the cylinder and piston will soak up the Spring room.

    C) --- So far I've shaved 45grams of weight from the piston, the spring I'm using weighs 30 grams less than the factory BSA one and the BSA Spring guide weighs in at 44 grams, that means I'm removing 119 grams from the gun's all up weight.
    By making stainless steel Spring guide in four different diameters it works out that it'll weigh somewhere in the range of 145-150 grams.

    My idea here is that the gun will weigh about the same as standard ( well within 30 grams) but the moving components on firing will be lighter so lowering the recoil.

    Having rough cut the guide this morning It weighs in at 536 grams, so it looks like I'll be knee deep in swarf by the time I've finished machining.




    All the best Mick

  10. #55
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    I do find most guns shoot better with more spring room... I guess it reduces the differential between the cocked and uncocked loadings for a calmer acceleration.. pity you couldn't find a way to retain it without spacing it out... howsabout a sleave affixed to the end block, that abutts the piston skirt just after cocking ?
    Always looking for any cheap, interesting, knackered "project" guns. Thanks, JB.

  11. #56
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    Quote Originally Posted by Shed tuner View Post
    I do find most guns shoot better with more spring room... I guess it reduces the differential between the cocked and uncocked loadings for a calmer acceleration.. pity you couldn't find a way to retain it without spacing it out... howsabout a sleave affixed to the end block, that abutts the piston skirt just after cocking ?
    I could easily keep the spring room, Jon, but I just don't want it.

    The coilbound Spring height of the 28 coil HW95 Spring is 84mm, in my Original 35 I have the spring compressed to 100mm when cocked for 11.6ftlbs.
    As I'm attempting to run the same bore, stroke, Spring and piston weight in my Merc it makes sense to keep the same spring room by way of an experiment.
    Once I've finished machining the new Merc Spring guide I'll have 110mm of Spring room when cocked --- I've allowed 10mm for top hat and slip washers.
    If I don't have enough Spring room I can easily machine 10mm off the guide to get to 120mm of Spring room when cocked.

    I'll get a picture up when I've finished machining so you'll get a better idea of what I'm upto.




    All the best Mick

  12. #57
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    Quote Originally Posted by T 20 View Post
    I'll get a picture up when I've finished machining so you'll get a better idea of what I'm upto.
    Here you go, Jon. :-

    image.jpg

    image.jpg

    image.jpg


    The spring space inside the piston when cocked is now 110mm before slip washers.
    The latchrod can't be forced into the Sears too far now as the largest guide diameter acts as a stop.
    And the spring guide weighs in at 146grams which adds just 27grams to the overall weight of the gun.

    It'll be a laugh if this lot don't work.




    All the best Mick

  13. #58
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    ?

    I can see that the large dia flange willl give more rigidity but what does the bit that goes in the piston do,would a flat face
    from the large dia to the spring guide not work then you would have more room for spring tuning with doughty washers.

    I would machine a two piece spring guide with the large back block drilled and countered bored and a standard type spring guide that fits through the back.
    Last edited by crowbar; 14-06-2022 at 12:01 PM.

  14. #59
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    Quote Originally Posted by crowbar View Post
    I can see that the large dia flange willl give more rigidity but what does the bit that goes in the piston do,would a flat face
    from the large dia to the spring guide not work then you would have more room for spring tuning with doughty washers.

    I would machine a two piece spring guide with the large back block drilled and countered bored and a standard type spring guide that fits through the back.
    I'm working on the theory that 100mm of compressed spring room should put me in the right ballpark power wise, so the bit inside the piston is just to take up 10mm of the 120mm of spring room inside the piston and to add weight to the static part of the gun.
    Effectively this piece takes up the space of 5 Dowty washers (which I'm running low on), if I find that I need more Spring room I can simply machine that 10mm piece off.
    Another spring that I'll be trying out is a 25 coil HW99 Spring which will need even less Spring room than I have now --- basically I'm just leaving all my options open at present.



    All the best Mick

  15. #60
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    My Mercury Ratting Rig

    Quote Originally Posted by T 20 View Post
    If the latch rod had been longer so that I didn't have to weld the top hat in just where the seal arbor would have been I may have considered using one, Jon.

    More importantly though, a 28mm Diana seal is £12.50 and O rings cost me about 20 pence each.

    image.jpeg




    All the best Mick
    Lol love the cheeky frankie pic, good work on that piston . will be interesting to see how it shoots, think you made the right decision with the later trigger btw.

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