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The Clothespin Trigger A ridiculously exhaustive essay on common problems

#1 User is offline   Carbon 

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Posted 24 September 2010 - 07:29 PM

I’ve talked to a lot of people, and seen a lot of SNAPs at wars and in pictures…and I know that getting the clothespin trigger (hereafter referred to as CPT) to work correctly is something that can take a bit of doing. From what I’ve seen, though, most problems with a clothespin trigger can be tracked down to one spot: the hole in the plunger tube.

For the lazy, here’s a TL:DR. If you’re having problems with a clothespin trigger, the hole in the plunger tube is probably too big.

For the reasons why, read on.

First, some explanations about how it works, and what the parts do, starting with that most visible part.

First things first: the clothespin does absolutely no work in resisting the force of the plunger spring. I’ve heard some comments from people about how their clothespin is “too wimpy” and how it can’t stand up to the force of the spring, or seen SNAPs with rubber bands around the clothespin to keep it shut. Both are symptoms of the same problem….and the only reason to put a rubber band on a CPT is if you like a stiffer trigger pull.

The clothespin serves as a lever with a return spring to lift the nail, and then put it back in place: that’s all. The work of resisting the plunger spring is done by the nail and the hole.

(A note about the hole in the clothespin: that actually needs to be a fair bit larger than the nail. We want the nail to slide straight up and down in the hole, but the clothespin moves on a pivot. Since its motion is circular, the hole needs to be bigger to allow for a bit of wiggle. After all, the clothespin is just lifting the nail. The spring is putting the nail back into place. All that can be done by the nail head, and doesn't need any contact on the shaft of the nail...so make the hole in the clothespin loose.)

For all practical purposes, a plunger spring cannot shear through metal. That’s why most any nail works in a SNAP trigger. The most important part is that the nail is only able to move straight up and down, and not tilt. This is why a snug hole is so important: the thickness of the PVC is what keeps the nail straight against the force of the spring (and is also why thinwall PVC doesn't work well with CPTs). The catchface ramp will also work most efficiently if the nail is straight up and down, with no tilt. If the nail is able to wiggle at all, then the clothespin has to start fighting against the strength of the plunger spring, and the motion of the plunger….and this is where diagrams come in handy.

Posted Image
Standard CPT: the plunger moves back, causing the ramp on the rear of the plunger head to push the nail straight down.

But what if the hole is too big? (Only a slight exaggeration of scale here, I've seen some SNAPs with nail holes this big...)
Posted Image
If the nail rocks back at all, then the direction it has to move becomes down and slightly forward...which means the nail is starting to fight against the plunger motion/direction. This also causes the nail to bind up in the hole.

If you manage to cock it, there are problems in the other direction:

Posted Image
The plunger is being held in place by an angled surface, rather than a straight up-and-down pin, so there's reduced surface area actually holding the plunger back. The nail itself is acting like a ramp, and helping the plunger head slide past it. This is why additional rubber bands are often needed to keep the clothespin shut: it's not that the clothespin spring is too weak, it's that the hole is too big.

So how snug should the hole be? he nail should be able to slide up and down without too much force, but not easily drop all the way in. After all, the clothespin is there to push the nail back in, so it doesn't matter if it sticks a little bit.
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#2 User is offline   TantumBull 

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Posted 24 September 2010 - 07:48 PM

Excellent explanation. This would have helped me a shit load before I was completely familiar with SNAP's; I'm sure that this will help many SNAP newbies.

#3 User is offline   Aquinas 

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Posted 24 September 2010 - 08:11 PM

This is so timely (I was just reading the SNAP threads extensively in preparation to make my own SNAP)... the trigger and the catch is always some of the most tricky parts to fabricate on a springer, and this really cements my knowledge and understanding of how the CPT works. Thank you.
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#4 User is offline   GoldHawk 

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Posted 25 September 2010 - 12:57 PM

View PostCarbon, on Sep 24 2010, 11:29 PM, said:

….and the only reason to put a rubber band on a CPT is if you like a stiffer trigger pull.

I'm going to have to disagree on this point, sometimes if the nail is just a tiny bit too short or if the head of the nail was rounded off too much and as a result won't catch properly, a rubber band works wonders.
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#5 User is offline   Carbon 

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Posted 25 September 2010 - 01:14 PM

View PostGoldHawk, on Sep 25 2010, 03:57 PM, said:

View PostCarbon, on Sep 24 2010, 11:29 PM, said:

….and the only reason to put a rubber band on a CPT is if you like a stiffer trigger pull.

I'm going to have to disagree on this point, sometimes if the nail is just a tiny bit too short or if the head of the nail was rounded off too much and as a result won't catch properly, a rubber band works wonders.

My meaning is that a rubber band is not needed for a CPT to work properly. In my example, as in yours, a rubber band is a band-aid for a CPT that wasn't made correctly (hole too big, nail too short). I'd always choose to drill a new hole or cut a new nail, rather than deal with a rubber band.
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#6 User is offline   Fome 

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Posted 25 September 2010 - 07:30 PM

View PostGoldHawk, on Sep 25 2010, 01:57 PM, said:

View PostCarbon, on Sep 24 2010, 11:29 PM, said:

….and the only reason to put a rubber band on a CPT is if you like a stiffer trigger pull.

I'm going to have to disagree on this point, sometimes if the nail is just a tiny bit too short or if the head of the nail was rounded off too much and as a result won't catch properly, a rubber band works wonders.


If your nail is too short then you will have issues with your catch releasing unintentionally from either bumping the plunger handle or vibrations when you're running. You can't "fix" a nail that is too short unless you reduce the amount of plastic that the clothespin rests on.

View PostCarbon, on Sep 25 2010, 02:14 PM, said:


I'd always choose to drill a new hole or cut a new nail, rather than deal with a rubber band.



I definitely agree. "Fixing" a trigger that isn't constructed properly is an absolute nightmare, not to mention a waste of time. Clothespins and nails are mega cheap, it's worth making several crappy triggers to make one ideal one instead of spending hours forging a crappy trigger into a barely functional one which will just give you durability and reliability issues later. SNAP triggers should be smooth and easy to pull, they should catch nicely even when you pull the plunger back slowly, and they should stay primed even when you drop the gun.

I like to actually adhere my clothespin to the PVC with a small dab of hot glue before I even drill the hole, then I clamp the clothespin horizontally so it can't shift while drilling. This ensures a nice straight hole through all 3 layers, I can then re-adhere the clothespin with a different adhesive or just pile on more hot glue.

Also, sometimes your trigger will be difficult to pull not because it's constructed wrong, but because the hole is actually too tight. If the wood or plastic is compressing around the metal (especially prevalent in nails that aren't completely smooth), then the trigger will have a very hard pull. This can be remedied simply by pulling the trigger several times to wear down the surrounding walls. If you have just constructed a trigger and you're unsure why it's a bitch to actually use, then keep pulling that trigger to see if the problem lessens.

#7 User is offline   Daniel Beaver 

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Posted 25 September 2010 - 09:04 PM

It is worth getting your first SNAP trigger right. After that, you can use it as a guide in order to make every subsequent trigger have the proper length on the nail.

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