Chop Gun or Hand Lay

Discussion in 'Fiberglass and Composite Boat Building' started by mrbcurry1, Dec 3, 2012.

  1. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Tunnels, you're correct in that a chopper gun application, is only as good as the gun holder, but it's physical properties, even with the best application, are well established, though considerably less stiff and strong for the same weight and thickness, as in a hand layup. Arguing anything to the contrary is, well frankly foolish, considering how commonly understood and available this information is.

    Simply put and assuming a level playing field of two technicians: one working the gun, the other doing a hand layup - the net result will be the copper gun laminate is heavier, not as stiff, nor as strong as the same thickness hand layup. A good chopper applicator can get close to a bad hand layup, but this isn't a fair comparison, no more then comparing a bad chopper laminate to an expert hand layup. Hand layup isn't the bee's knees either, which is why bagging and infusion are also employed, but there's absolutely no debate about where chopper gun laminates, even with folks as skilled as you doing it, live on the list of layup options and the resin/fiber ratio tells all. Arguing otherwise, just proves, well . . .
     
  2. tunnels

    tunnels Previous Member

    Sorry i am a non believer !!

    Sorry you can quote what ever you want i know that choppered lay up can be and is better over a big area .If exactly the same weight of glass and resin are used !!
    First off the chopper has no overlaps and second theres no joins and as long as the same amount of resin is used the glass to resin ratio can be exactly the same so how can you say its differant ??
    please explain in detail, i really would like to know !! :confused:
     
  3. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    It's silly to discuss any technical issues with you Tunnels, as you're arguments can't be supported with facts, let alone a practical understanding of the engineering, process or physical attributes of the subjects you seem to take a stand on.

    If what you say is true, why has every major manufacture abandoned chopper gun layups, in favor of a more costly, in both labor and materials method? Silly business owners I guess, of course assuming you're correct. Hell, they don't want to make a higher profit margin, preferring to adopt more costly materials and methods instead. There quite frankly isn't a single laminate engineer that could possible agree with your assessment of chopper laminates being as stiff, strong and light as any of the other techniques employed. This isn't opinion, but simply engineering 101 and frankly easy enough to look up, maybe you should try it some time.

    Chopper gun laminates are the weakest, because of resin/fiber ratios and the fiber orientation in the laminate. Cloth is next up on the list, because fiber orientation (often continuous) can be arranged along load paths, but hey, you'd have to have a clue about this sort of thing, which you clearly don't. Directional fabrics are next up on the list, guess why - fiber orientation again, which can be more closely tuned with load paths.

    Just because you don't understand something, doesn't mean it's incorrect - it just means you don't have a clue.
     
  4. FMS
    Joined: Jul 2011
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    Location: united states

    FMS Senior Member

    There must be more to this than meets the eye. I know I read an older thread in which Tunnels argued against the use of fabric where half the fibers were oriented 90 degrees to the load on a stringer repair. He argued for more efficient orientation where all fibers carried load. Therefore he is thinking about the importance of fiber orientation on weight for a given required strength.

    There is no control of fiber orientation when spraying with a chopper gun, isn't that correct?

    I wonder if there are parts where random orientation is close to ideal, where there is no more stress in any one direction than any other?
     
  5. tunnels

    tunnels Previous Member

    Manufactures including the one where i am now i have advised them to take the choppers off there guns and just used them as saturater gun . trying to find and teach some one to be 100% consistant every hour of every day is almost impossible ,but hand laid glass and a saturator units is cool . at least you know the resin catalyst ratio is consistant from one end to the other .
    I have spent hours watching rolls of glass being made , including Chopped strand matt in all its differant weights , plain woven roving and rove matt with csm on one side , unimatt also with csm on one side again in differant weights then double bias also in differant weights . ,
    One guy i worked with his brother owned a glass materials manufacturing company , he was a glass weaver and made all his own equipment to manufacture the glass cloths etc . Plus he would make cloth specially to what we wanted . for differant boats we were making .
    I am not into engineering and studying papers and pouring over pointless rows of figures . unless i actually see how the tests have been conducted i take very little notice of information on paper but i do take notice of what i see with my own eyes and hold in my hands !!.
    Now think about the side of a hull !! you hand lay it , it has overlaps and joins . like i said the same glass weight of glass done with a chopper can be the same thickness all over ,not just here and there with overlaps and joins .the only way a hand laid can compair is if you butt the csm so there no overlaps , but thats not practical is it !! strand length i have used a 3 blade chopper and removed one blade so you have a mix of long and short strands That was interesting
    Personally i like the 4 blade spindle and just use 2 blades its easy to spray its easy to roll and wets well is a little prickly when its finished as the long strands dont lay to good round corners and over edges . sorry i am not convinced that hand laid glass is better than a chopper gun job . Its 100% the operater thats responsable !! Have you ever measured parts of rolls of csm . you'd be amazed at the variations of weights and thickness with in just one roll !!
    Sorry i been doing this job for to long !! :confused:
     
  6. JTF
    Joined: Nov 2012
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    Location: Bayswater

    JTF Junior Member

    I agree 100% with tunnels. I to have spent many years on a chopper gun. When I sprayed we peeled the floor once a week witch is good as I had minimum wastage. I go on holiday for 2 weeks and my laminators would be pulling there hair out. They where all covered in glass and had the peel the floor every morning. Dirty operator dirty job. Clean operator everyone is happy. It all comes down to gun and pump maitenece and using the right settings. I will be in the market for a new gun next year I like glascraft Indy.
     
  7. tunnels

    tunnels Previous Member

    You are a little confused and talking about two completely differant things :?:

    A chopper gun sprays catalysed resin and chopped strandof glass all at the same time there is no oriantaion of any of the glass strands they are 100% random !! :eek:

    Now talking about possibly woven roving and where only 50 % of the strand were actually holding the stringer BUT if you used double bias 45/45 *then 100% of the strands of the glass were working at holding the stringer !!.
    Best to know and understand what the materials all are so you dont get confused !! :confused:
     
  8. powerabout
    Joined: Nov 2007
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    Location: Melbourne/Singapore/Italy

    powerabout Senior Member

    chopperguns are good for things like reliant robins but you wouldnt want it used in a McClaren would you
     
  9. tunnels

    tunnels Previous Member


    YEAH I HAVE A FRIEND !!
    another trick is to hold the gun quite close to the surface and spray about 30mm back from the edge of what ever you are spraying and use a roller and drag the wet glass to the edge thats even cleaner !!! also standing and blowing the glass onto the mould instead of away and over the edge .
    Because i was the only gun operater on one factory i used to continuously work between two moulds all the time so the gun went continuously for hours on end ,without looking at scales i can spray 450 grams almost perfectly and consistantly all the time . when i was making small catamarans i only looked at the scales at the begining and could gun the hulls and decks to within .2 of a kilo of each other . if you do the same job often enough you have the instinct to know if its light of heavy .
    Something lots of operaters miss is the glass stands drop off over the side of the resin spray , specially when they dont use the cover over the chopper and rollers !!

    My first job when i got here to china was to strip, clean and recondition 5 venus chopper guns and 2 venus gelcoat guns and get them completely operational again . then to discover no one in the company knew how to use any of them . So then had to spend a few weeks teaching one person to use and how to use and what weights if glass had to be sprayed etc etc . so on the 28 mtr boat we just finished i removed the chopper and used the guns as saturator units only !! that was a blessing and the guys went through the the layers of glass very quickly . During the early stages before the mulds were completed i found here 2.0 metre wide rolls of glass with a 275 gram Csm on one side so spec-ed that and it saved lots and lots of time and fewer joins across the hull so had a smoother surface to work over all the time . its never a chore if you think smarter before the job starts and make life easyer for everyone .Thats what the name of the game is all about!! :p:D
     
  10. powerabout
    Joined: Nov 2007
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    Location: Melbourne/Singapore/Italy

    powerabout Senior Member

    arent chopper guns illegal now due to the atmospheric release of the styrene which slowly makes you ga ga...without knowing it??
     
  11. tunnels

    tunnels Previous Member

    I dont think so . sex and booze is the same it should be illegal its all most young guys think and talk about ! :mad::confused::eek::D:p
     
  12. powerabout
    Joined: Nov 2007
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    Location: Melbourne/Singapore/Italy

    powerabout Senior Member

    which part
    guns are illegal - I guessed that
    styrene makes fries your for brain - thats fact
     
  13. tunnels

    tunnels Previous Member

    You know when you have to much styrene in your system when you have a hot shower and you can smell it coming out of you skin !!!!:eek:
     
  14. tunnels

    tunnels Previous Member

    Chopper gun laminates are the weakest, because of resin/fiber ratios and the fiber orientation in the laminate.
    fibre oriantation of chopped strand matt ??? you must be kidding !!. Its random and always has been for ever !! Chopped strand matt in the roll form is that same thing for heavens sake !! and as for the resin to glass ratios again its up to the operater and has nothing to do with the gun !!.
    If he just sprays up a patch of glass and walks away and hangs up the gun without rolling his own spraying how the hell will he ever learn whats good and whats not good !! .
    Im sorry you can chase me for as long as you like i will not give up on this !! and as for chopper laminates being the weakest !! Rubbish !!!!!:eek:

    Ok if i make two test panels each one one mtr sqr and i lay 2 x 450 grams of csm glass cut from a roll and
    the second panel i gun .900 grams of glass showing the 0.900 on my 0.000 digital scales !!
    plus i know that the resin is from the same drum as the hand laid glass and both catalysed at 1.5% and they both go off in the same time as each other then how can there be any differance between the two panels ??
    And each panels weighs the same when they have gone hard and been trimmed !!. If i handed them both to you how can you tell which panel is which ??? how could you define a differance ???
     

  15. Herman
    Joined: Oct 2004
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    Location: The Netherlands

    Herman Senior Member

    Please guys. Lets HELP this poor guy with his Go-Karts, instead of fighting over a chopper system.

    I have a question for the Go-Kart guy:

    There is Go-Karts and Go-Karts. What is the purpose of your Go-Karts? Are these rental/fun arcade type, or are these high-speed (semi-)professional drivers, or anything in between?

    My father used to make Go-Karts for rental, and my duty was to test them out. Boy, I demolished a lot. But with some small mods we arrived at a reasonable quick but virtually indestructible rental kart (suitable for indoor). The fairings were roto-moulded in PE, and lasted quite long.

    For the professional series you quickly arrive at carbon, for its stiffness and weight, and add some aramide to contain the wreckage after a mishap.

    Somewhere in between can be glass fabric, which can be quite lightweight as well (do not forget the aramide)

    CSM/Spray-up can be for the low-low end. I doubt there is a weight advantage over carefully rotomoulded PE versions.

    On CSM vs sprayup I can comment that although it is possible to achieve the same results, in 99% of the time it does not work that well due to uncontrolability of the spray gun (balancing the amount of fiber with the amount of resin). There is nothing but the air pressure locking the spray speed with the pump speed. Get it wrong, and there goes your Vf. Choppers always tend to sway around a bit, and I guess that is why I never saw both a scale for resin weight and fiber weight, preferably even combining the 2 for a Vf ratio.
    The other factor is that you do need good bubble busters. And as these people are the ones that are the lowest on the "pecking order" you can guess where I am heading to. If you pay peanuts, you get monkeys....

    Sometimes my eyes water when I see a crew working with a chopper. Resin a bit on the fast side, 2 guys rolling their asses off, hardly making it to bubble bust everything, and with dubious quality. After a certain time one of the rovings gets pulled out (there is usually 2 strand of roving being used in the chopper). Takes a while before the guy notices. (and during that time he is spraying only half the glass).
    Same can be done for a "bedding layer" for foam. A wet layer, mde by pulling one string out of the chopper. Some scrim cloth foam is squashed in (quickly, remember the fast curing time...) Fill the kerfs? Why? Spray over it again, and there is your high quality cored boat.
     
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