Chop Gun or Hand Lay

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

  1. mrbcurry1
    Joined: Nov 2012
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    mrbcurry1 Junior Member

    I build fiberglass racing bodys for go karts. I am just wondering if I switch using a chop gun system, does it hold up in same layer thickness?
     
  2. upchurchmr
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    upchurchmr Senior Member

    No, it is well known that when Corvettes made their bodies using a chopper gun the strength was very low and the weight was very high compared to a hand layed hull. They did chopper gun for the very low cost. Due to the fact the motors were large and they had no real competition they accepted the weight. Chopper gun fell apart in a crash in little bitty pieces.
     
  3. messabout
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    messabout Senior Member

    I affirm the information given by Upchurch. Chopper gun method is OK if cheap and dirty is what you need. Seems to me that weight would be an important factor on a racing Kart. If so, a skillful hand layup is the way to make both light and strong parts.
     
  4. mrbcurry1
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    mrbcurry1 Junior Member

    what I was thinking was to chop the in the important parts of the body where it takes hits layup.
     
  5. upchurchmr
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    upchurchmr Senior Member

    Heavy, weak.

    Those racers will not thank you.
     
  6. tunnels

    tunnels Previous Member

    Yes !!it can be exactly the same or even better because dosent have any joins or overlaps !!
    How do you think the csm matt is manufactured !!same glass, same method ,of chopping just its done evenly and to a specificweight per square meter!The choper moves at a constant speed along a rail and the motor maintains the same speed as well so depositing the same amount of glass onto the table .
    A chopper gun is no differant . constant speed and movement of the hand and constant speed of the choppe motor and you have csm matt ! same
    People are against chopper guns simply because they dont know how to use them properly . A gun laid panels are just as good as hand laid , same resin same glass but its the skill of the operater that is in question !! how good is he ??

    You need to have a set of accurate digital 0.00 scales and sit the glass roll in top set to zero and then very accurately measure the surface area you want to spray of its 2 x M2 x 450 grams = 900 grams so thats what you need to spray not over and not under . you have to visualize in your mind as the glass and resin is being sprayed to keep it 100% even and a constant thickness. . if you want to be more presice then you measure your resin the same way .
    i have taught many operators over the years and very few are any good . if you dont completely understand in your mind all thats going on all the time no amount of teaching and showing will ever sink in and you will have problems forever . its completely up to you .
    Gel coating is that same !!,its an art you either got it or you havent . :eek::confused:
     
    Last edited: Dec 10, 2012
  7. tunnels

    tunnels Previous Member

    What a load of rubbish !! there is nothing wrong with the chopper gun its the person holding the gun thats the problem not the gun . Have you ever used a chopper gun ?? i have spent most of my life and spent many many days spraying glass . what you have just written is typical of some one that dosent understand much about them . any machine is only as good as the person using it . i have lived and breathed chopperguns and i can listen 50 meters away and tell by the sound of the mpotor and the speed of the pump if the operater is using it properly . Doesnt mater what brand ,I was bought up with Venus and Glasscraft or poly craft but have used many others as well . even as a factory manager i spent one day every week spraying and using chopper guns . its a constant job maintaining and keeping them completely up to 100% working condition . :eek:
     
  8. tunnels

    tunnels Previous Member

    Chopper guns are only doing what the operater is telling it to do!!, dirty is all about settings and the way its used !!. once a dirty operator always a dirty operater .
    I could use a gun all day long and never get covered with crap, if you work clean then thats what the job will be clean and neat and tidy !!.and if you dont point the gun at the job then the glass goes where its pointed . Poor crafts men always blame there tool . :p
     
  9. tunnels

    tunnels Previous Member

    Of all the post here i very much doubt any one has ever used a chopper gun or maybe even seen one being used . it all here say ,and exadurated stories repeated and they grown each time they are told .
    The guy that taught me to spray watched for 2 minutes and walked away . when he came back after id finished he said i cant show you anything because you are a natural .
    Before that I had used a saturater gun for 6 months before i got handed a chopper gun .
    FOR me its so simple and easy to use !!,if you understand its workings and what does what and I know them inside and out,and back and front !!, i have written operator manuals and service manuals along with trouble shooting wall charts and serviced guns for long long time !!.
    99,9% of problems are operator problems !!
    Just like fibreglassing the same 90% is just caused by bad workmanship .

    One factory i went i was told the gun was always wet and used to much resin so i took the gun off the operater lowered the pump air presure and sprayed a patch !! the glass was so dry the guys couldnt roll it !! .
    The same operater used to have lots problems and was forever stopping in the middle of jobs but after watching him operate and use the gun for 5 minutes the problems were all set up to slow the jobs on purpose !!,so i advised the forman to fire him , when he went the problems went with him .
    How can a company employ a foreman that dosent fully understand the job hes employed to over see . Beats me !!:confused::(
     
  10. upchurchmr
    Joined: Feb 2011
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    upchurchmr Senior Member

    Tunnels. With all due respect, you are out of your freaking mind.

    This is the first lesson you will ever get in a composites class. No amount of talk will change that.

    Help the poor guy out and don't give him BS.

    CSM is worth just as much as chopper gun, very little. Can you build things with it? Yes. Not to the same strength and stiffness as cloth.

    Mrbcurry1,

    Don't listen to anyone. That includes me. do a test even if you have to pay someone to make a chopper gun panel for you. weigh it and then break it where you can tell what was the force when it broke.

    Best advice I can give you. Find out for yourself.

    Good luck

     
  11. tunnels

    tunnels Previous Member

    Ok one layer of 450 gram csm over the gelcoat and then a 600 gram double bias and finshed . its what i used for Midget car tails and its bends a mile before it breaks good for inpact and easy to repair is you have to !! you asked about chopperguns so i told you . :eek::confused::D:p
     
  12. mrbcurry1
    Joined: Nov 2012
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    mrbcurry1 Junior Member

    thanks everyone for the input, I mean I took some moulds to a buddy of mine that makes semi back fenders and we tried it out a few weeks back, we sprayed with a chopper. I have not had to time to test it yet but will soon. I have the system ordered, but I can always use it to build my moulds till I get the hang of it, see where I am at. I'll keep everyone updated see what happends.
     
  13. upchurchmr
    Joined: Feb 2011
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    upchurchmr Senior Member

    Mrbcurry1,

    Weigh them and measure the thickness before you start breaking.
    The goodness for racers is strength/ weight.

    Anything will work on a car if you don't care about weight.

    And if you don't it might work great for you.

    I knew some guys who did the same - semi fenders for a major company. They couldn't care less about the weight. An engineer friend worked on the cab. They did two as a test, one chopper, one hand layed. The chopper gun weighed 2X and was not as strong. Don't know what they ended up with, but the hand laid did not require a crane to put on the frame. Most of their decisions were just what was cheapest.
     
  14. tunnels

    tunnels Previous Member

    there you go again repeating other peoples stories that have been handed down and been added to as time goes by .
    choppered orhand laid if the same weights of materials are used (resin and glass) the chopper will win out because there are no joins or over laps , the resin is much better mixed and at a slightsly higher ratio so its stronger and its pluses all the way !! .
    Read a chopper gun is only as good as the person using it !! get the message???:confused:
    I held a operators certificate issued by DNV when i worked in Tahiti . All the work i have done for the past 10 years is all done to better than survey standard no mater what survey standard you choose !
     

  15. upchurchmr
    Joined: Feb 2011
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    upchurchmr Senior Member

    Tunnels,

    Engineering tests don't care what kind of a certificate you hold.
    I have no problem with your quality of workmanship - I'll accept you can make it perfect.

    Perfect chopper gun is still weak for a given weight.

    This is not second hand stories about the strength of chopped fiber.
    I tried to give examples of people who actually did other parts, just so you would talk about the real issue.
    If you don't want to understand I will leave you alone.

    READ THIS: no chopper gun can ever reach the same strength as a laminate (unless you deliberately make gross errors).
     
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