Shattering a Car Window

[oli]

Hey Everyone,

 

For a project at uni I am simulating gun fire on a car door, the bullet holes are no problem but what I am struggling with is how to shatter the window safely.

 

My first idea was to use a tape a maroon to the bottom of the window and set that off, do you think the power produced would be enough to shatter glass?

 

Doe anyone have any other suggestions on how to make this is realistic as possible, I would usually go off and test with different items but due to the cost implications this impractical.

 

Thanks

 

Oli

[paulears]

spring loaded arm with solenoid release with a point tip - like the thing used in trains and buses to break the windows. It doesn't need to poke up much above the sill bottom, so when it breaks, you don't really see it.

[oli]

spring loaded arm with solenoid release with a point tip - like the thing used in trains and buses to break the windows. It doesn't need to poke up much above the sill bottom, so when it breaks, you don't really see it.

 

 

Thanks Paul, is this a make item or would I be able to buy one somewhere? If so what are they called?

[Russ83]

Try Emergency Glass Hammer. Homebase seem to do cheap ones, but anything with a metal point and a bit of weight behind it should do the trick.

[oli]

Thanks for that, do you not think the Maroon would give off enough power to shatter a window?

[AndyJones]

I think the maroon would have more than enough power. I further believe that if you were to simply tape a det to the inside of the window that would also have enough power to shatter the window. However, Pyro and glass do not mix, I would be worried about flying debris which could fly off towards the audience, or towards other cast members and injuring them.

 

Andy Jones

[dbuckley]

Well, in my youth I witnessed the aftermath of a banger being taped to a shop window, and although the window wasn't shattered, it most certainly was cracked. (the perpetrator of this act died tragically in his twenties of a heart attack)

 

Given that car windows are designed to shatter, I'd speculate that a small maroon gaffered to the corner would make the window dissapear.

 

Certainly medium maroons are capable of laying waste to 4x2 chunks of wood, having personal experience of that fact.

 

Having that personal experience, I can say that this is a dangerous thing to do, and isn't something I'd do on a stage with people on it, nor by an audience less than a long way away.

 

When I did it it was a re-enactment of the Battle of the Alamo, this being the trick to drop the fort's gates. It worked a treat, but there was nobody within dozens of meters. Had there been someone within say 5m, I'd pretty much guarantee that they would be dead or dying, due to the projectiles launched by the maroon, in my case, fast travelling wooden spears.

 

Maroons are designed to be fired in bomb tanks, and there are reasons for that.

 

On the other hand, a little metal spike that tw@ts the corner of the car glass will work, and be relatively safe, in that the glass will not fly a huge distance, and not at explosive powered speeds.

 

If I were doing the Alamo again, I'd use trick hinges, and just whip out the pins. Same effect, and so much safer...

[themadhippy]

a little metal spike that tw@ts the corner of the car glass will work

The automatic center punch,the tool of choice for vandals everywhere.

[oli]

Hey,

 

Thanks for those, I might see if I can get car window from a scrappy and have a go.

 

There wont be any audience or cast members as this is a Specialist Project that will be watched by my tutors (from a safe distance) and videoed for future reference. I also have to do all the appropriate H and S and risk assessments as part of my project.

 

Ideally I would like to have one bullet hole in the middle of the window with the class cracked around it, as this is a live project I think this will be really hard to get right!

 

Thanks for your help on this one and any more ideas would be greatly appreciated.

 

Oli

[scjb]

Really, you need a proper bullet hit, like a D80 from De La Mare Engineering. Unfortunately, you are going to struggle to find someone willing to supply you. You may find you have to go down the route of physical...

[Russ83]

If this was a ballistics exercise for the engineering department then I would expect the glass to be in an isolated empty room with sealed walls and floor so that the glass can be safely swept up. However as you are on a theatre course I'm assuming this is not the case.

 

Personally I would avoid putting pyrotechnics next to glass as my head starts to hurt just thinking about the risk assessment! You would have to have some means of containing the glass but you need to remember that whatever you do to contain the glass will also contain the explosion which under these circumstances could make things worse. Maroons....well that would be impressive but go back to thinking about an isolated room. Microdets or even igniters with laminated glass might be used on a film/TV set but it is not something I have enough practical experience of to comment on.

 

My safe thoughts would be to cutout the bullet hole in the glass and replace it with a small clear plastic disk, a couple of drops of water or 3-in-1 oil should help mask the cut lines but this is worth experimenting with using a normal piece of glass first to find the best combination. Laminate the outside of the glass (minus the hole) with sticky back plastic (the clear book covering type) then rig up a solenoid with a sharp metal tip or a sprung glass hammer in one corner inside the car. Hopefully this will be enough to shatter the glass but ensure it is held in place. Whether the small disk falls out or not does not matter as you will still get the illusion of the hole as it is see through. You can test the solenoid/hammer on normal glass first but you will still need a couple of proper windows to get it right. A visit to the local scrap yard would be in order.

 

Another option could be sugar glass but this will probably shatter and fly everywhere (and thats just unpacking it!) You could then use a BB or spud gun to shatter it during the scene assuming no-one is actually in the car but again you are getting into projectiles on stage and risk assessments.

 

If someone is inside the car and you have someone around who is good with metalwork and tools then you could try fixing a clear piece of plastic to the edge of the door frame on the inside and then have a pre-shattered window in the down position ready to be moved into place on the sound of the gunshot. You would need to rip out the normal winding mechanism and replace it with a basic pivot lever so the glass can appear in a split second. With appropriate sfx and lighting this could work and is by far the safest and is also very easy to rehearse and reset.

[Seano]

It doesn't need to poke up much above the sill bottom, so when it breaks, you don't really see it.

Maybe I'm missing something obvious here, but if the door is going to be modified anyway surely there's no reason not to attack the glass below the sill out of sight completely? Perhaps the outer skin of the door would also help to prevent bits of glass from being thrown out away from the car.

[p.k.roberts]

The more common technique if pyrotechnics are being used to break glass is to use a small pyro device to drive a captive punch/nail/pointy thing at the glass rather than have the pyro device in direct contact with the glass. This then works in the same way as the 'vandal friendly' automatic centre punch. A google for 'pyrotechnic glass breaker' will throw up some results.

[adam2]

Whatever route you choose, it would be well to carry out trials, this need not be expensive since the side windows often survive crashes that write off the car.

Windows are therefore very cheap from scrap firms.

[oli]

thanks for all the replies, have managed to get hold of a couple of windows from the local scrappy so will have a play in the next few days, I'm thinking of putting sticky back plastic on the outside edge of the window and using a microdet in the middle to try and achieve what I want whilst making the glass stay in position.

 

Will let you know the results!