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Thread: Mirror Polishing Compression Tubes - The Evidence

  1. #1
    Hsing-ee's Avatar
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    Mirror Polishing Compression Tubes - The Evidence

    In the first frenzy of springer airgun tuning the sage advice was to mirror-polish the walls of the compression tube with a mild abrasive like Solvol Autosol. I've done this to a large number of springers, and it is a boring process both doing it and cleaning up the resulting mess.

    I think I might even have kept in in my old 'advice thread' 'Tuning the Older Springer'.

    This technique was advised in the days when most piston washers were made of leather; a few like the BSA and the Sussex Armoury, used 'O' rings while Feinwerkbau was well ahead with a nylon head (Sport) and steel piston rings (150/300 series). Maybe leather needs mirror-finish more than nylon or other plastics, I don't know. There are some who say you need some cross-hatched roughness on the compression cylinder wall to hold lubricant, but it must be pretty poor lubricant that can't do the job with mirror finish, it should work as roughness will still be there at the microscopic level even if it looks perfect and shiny.

    My question is; given the strength of the spring and the fit of the washer, does a mirror-finish make ANY difference in real terms to the efficiency of the power stroke? I have a feeling that it makes no difference whatsoever and that we have been wasting our time for years. There is also the possibility that after the polishing it is uneven, which if it DOES have an effect, won't help with consistency.

    Has anyone done a before and after friction experiment? I know that this might be different from when the spring is pushing the piston and there's a massive head of high pressure air in front of it pressing the washer against the walls, but I bet a simple test with weights and a timer would show the difference between mirror and factory finish is 3/16ths of sweet FA.

    Your thoughts please genklemens?
    Last edited by Hsing-ee; 27-05-2018 at 10:46 AM.

  2. #2
    harvey_s's Avatar
    harvey_s is offline Lost love child of David Niven and Victoria Beckham
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    Conventional wisdom from i.c. engine technology tells us that polished or glazed bores allows bore lubrication to bypass the sealing rings.
    Honed bores allow more complete bedding in and a retention of the lubricant where it belongs.
    I would suggest that where there is metal to metal contact - a honed bore and some vestigial lubrication would be the way to go....but for cylinders with pistons running synthetic bearings - polished would be better.

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    I don't bother anymore, you wouldn't tell the difference IMO. More importantly is to polish the cocking slot as these have proper rough edges in most cases.
    Plinkerer and Tinkerer

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    Quote Originally Posted by Hsing-ee View Post
    In the first frenzy of springer airgun tuning the sage advice was to mirror-polish the walls of the compression tube with a mild abrasive like Solvol Autosol. I've done this to a large number of springers, and it is a boring process both doing it and cleaning up the resulting mess.

    I think I might even have kept in in my old 'advice thread' 'Tuning the Older Springer'.

    This technique was advised in the days when most piston washers were made of leather; a few like the BSA and the Sussex Armoury, used 'O' rings while Feinwerkbau was well ahead with a nylon head (Sport) and steel piston rings (150/300 series). Maybe leather needs mirror-finish more than nylon or other plastics, I don't know. There are some who say you need some cross-hatched roughness on the compression cylinder wall to hold lubricant, but it must be pretty poor lubricant that can't do the job with mirror finish, it should work as roughness will still be there at the microscopic level even if it looks perfect and shiny.

    My question is; given the strength of the spring and the fit of the washer, does a mirror-finish make ANY difference in real terms to the efficiency of the power stroke? I have a feeling that it makes no difference whatsoever and that we have been wasting our time for years. There is also the possibility that after the polishing it is uneven, which if it DOES have an effect, won't help with consistency.

    Has anyone done a before and after friction experiment? I know that this might be different from when the spring is pushing the piston and there's a massive head of high pressure air in front of it pressing the washer against the walls, but I bet a simple test with weights and a timer would show the difference between mirror and factory finish is 3/16ths of sweet FA.

    Your thoughts please genklemens?
    The only part of a spring powered airgun internals that benefits from mirror polishing is the ends of the spring. The rest are just indulgance. Mirror polished surfaces are devoid pf microgrooves that hold the lubricant necessary to reduce the friction between metal to metal contacts.

    A.G

  5. #5
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    Hsing-ee,

    These days, I tend to finish compression tubes/cylinders with green ScotchBrite pad 'flaps' held in a slot cut in a dowel, and rotated in an electric hand drill.

    Have fun

    Best regards

    Russ

  6. #6
    look no hands's Avatar
    look no hands is offline Even better looking than a HW35
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    The only mirror polishing I do is the end of the springs as already mentioned and I polish the piston and rod (if it has one) and any area where a smooth polished finish my reduce drag (like the area on a Airsporter trigger block where the underlever pins through) I've also polished a fixed metal spring guide before to help the spring slide a bit better, the only time I've done any sort of polishing of a cylinder was when one of my Mercs had a stuck piston head and it had marked the inside of the cylinder when removed, I used a brake cylinder honing tool (the three legged jobby with the flat honing stones on them), which didn't actually leave it mirror finished but got rid of the marks, I did read once that two mirror finished surfaces when lubricated don't actually slide that well and actually sort of stick together (don't ask me if this is true or not).

    Pete
    Far too many rifles to list now, all mainly British but the odd pesky foreigner has snuck in

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    Quote Originally Posted by lensman57 View Post
    The only part of a spring powered airgun internals that benefits from mirror polishing is the ends of the spring. The rest are just indulgance. Mirror polished surfaces are devoid pf microgrooves that hold the lubricant necessary to reduce the friction between metal to metal contacts.

    A.G
    I don't go in for the whole mirror polishing thing either. However, once magnified, even polished surfaces will have the troughs and plateaus required for lubricant retention.
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  8. #8
    harvey_s's Avatar
    harvey_s is offline Lost love child of David Niven and Victoria Beckham
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    Quote Originally Posted by look no hands View Post
    ...I did read once that two mirror finished surfaces when lubricated don't actually slide that well and actually sort of stick together (don't ask me if this is true or not).

    Pete
    Yep, it's true - if you know anyone with a set of slip gauges - ask them to show you

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    Quote Originally Posted by harvey_s View Post
    Yep, it's true - if you know anyone with a set of slip gauges - ask them to show you
    You can do it with 2 panes of glass and the slightest smear of lubricant. They DON’T slide.

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