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#9769 - 08/12/06 03:18 PM PIT Pan Tension Systems - Principles and Observations
Hal Offline

Registered: 07/17/00
Posts: 10172
Loc: Blue Creek, Ohio, USA
PIT Pan Tension Systems - Principles and Observations

I first saw the PIT (Paws-I-Trip) Pan system at an NTA Convention in the early 1990's. I really like this system for big traps and big animals. The PIT system creates pan tension simply by leverage. It does not require friction, or the tightening of a nut and bolt, to create pan tension.

But it still remains a mystery to most folks as to how it works. I?ve tried to explain it a hundred times. But now I'm am going to take opportunity of this media to try to explain this with the use of some visual aids.

Illustration 1

On a normal trap, the notch or release point of the pan/dog is directly above the hinge point (blue dotted line). Here a minimum of pressure on the pan is required to move the pan downward and release the dog. In order for us to get some "tension" on that pan, we have to install a nut and bolt at the pivot point and tighten it.

Illustration 2

In order to understand the PIT leverage system, it may be helpful to look at something entirely opposite. Look at the illustration above. If you had a pan system that had an engagement point behind the pivot point (closer to the jaw) -- that trap wouldn't even stay set. Look how the dog would just "upend" the pan, and fire the trap of its on accord. (I once bought some traps like this! )

Illustration 3

Now look what happens if you move the pan/dog engagement point on the other side of the pivot. While before the dog was trying to "up end" the pan, now it is trying to "pick up" the back of the pan. It is actually pulling the pan up in the air. This "pulling up" leverage is what gives you the frictionless pan tension.

Illustration 4

In order to hold the pan in place, and keep it from riding back up on the dog, a PIT dog has a bump on the end which serves as a mechanical stop. However, the bump on the dog is not the defining feature of the PIT system. If there is no mechanical advantage, there is no PIT system.

The advantage in the PIT system is that it doesn't require friction, making it very consistent from one time to the next. There is nothing to go out of adjustment. The disadvantage in the PIT system is -- there's nothing to adjust. What you see is what you get. This is why I find PIT systems more adaptable to large animals. The heavy pan tension needed for large animals is hard to maintain with a nut and bolt.

There are a number of things that will influence the resulting PIT pan tension. Spring strength is one. Stronger springs mean more tension. Four-coiled PIT traps will have a higher pan tension than 2 coiled.

Illustration 5

Another major influence is where, between the eye of the dog and the engagement point, the jaw actually lies. Given a dog of equal length, the further the jaw is from the eye of the dog, the more force it will exert on the pan. This can be a consideration especially with inside laminated or wide faced jaws.

Illustrations 6

There is one other way to change the pan tension. If you can move the engagement point back a little closer to the pivot, the pan tension will decrease. Again the problem is that these systems are not adjustable.

I could be mistaken here (but I don't think so). I think that all the PIT pans are spun off one die. This is the one that establishes the "kicked back" legs which moves the engagement point forward, thus making the pan tension. And that is designed to produce about three or four pounds of pan tension given "average" circumstances. This is the pan you'll see on a #5 or a CDR. From this point forward, the remaining pans are made simply by cutting down the target area of the #5 pan.

These pans all have different target areas, but note that the legs are all the same.

I do realize the economy of this enterprise. Dies ain't cheap. But if there were a second pan, with less angled legs, as in the middle on Illustration 6, it would be more suitable to lighter pan tensions. Say the two pound range.

Of course if you move the engagement point all the way back to the pivot point, like at the bottom of the illustration, you no longer have any leverage advantage at all.

Illustration 7

Another way to increase or decrease PIT tension is ostensibly by bending up or down on the end of the dog. But this has its limitations.

(continued next post)
Endeavor to persevere.

#9770 - 08/12/06 03:31 PM Re: PIT Pan Tension Systems - Principles and Observations
Hal Offline

Registered: 07/17/00
Posts: 10172
Loc: Blue Creek, Ohio, USA
At The Bench

Just to satisfy my own curiosity, I took some brand new traps out of inventory, and outfitted them with PIT systems. I'm really only looking at smaller traps here so I got a Bridger (BD) 1.65 and an Oneida Victor (OV) 1.75 to play with. Here is a note on this. These two traps require a different kit. The dog on the BD kit is 1/16 inch shorter than the OV kit.

The kits for these traps are the ones in which the pan clamps over the spring pin. The other kind of kit comes with a bracket that replaces the pan post. On this second style kit, a bolt holds the pan in place and this could be tightened to increase pan tension, but rarely would you want to increase pan tension on a PIT system.

Set up with a straight dog the BD set off at 2.5 lbs. (Average of 6 tries.) That wouldn't be too bad for a combination fox coyote trap. I wanted to try to get it down to 2 pounds, so I bent the dog. Fist thing I found was when I bent the dog, it was now too short, and the pan stuck up too high. I had to swap out and get one of the longer dogs like I was using on the OV.

These are the three dogs.

I tried two different bends. One in the middle of the dog, and one near the tip. The "middle" bend was about 15° the "end" bend was about 20°. However, these bends made little perceptible difference in how the trap fired. There may have been the slightest decrease, but still the trap fired so close to 2.5 lbs that I'd be lyin' to tell you otherwise. So I took the end-bent dog, and bent in some more, down to about 35° off horizontal. That did give me 2 lbs of pan tension, but I would not want to bend the dog much more than that.

This is how much I bent the dog to get 2 lbs of tension.

The OV 1.75 trap, with a straight dog, measured 4 lbs every time I set it. I wondered just how much of this was spring difference so I took the springs off the OV and put them on the BD. The result was an increase on the BD from 2.5 to 3 lbs. I wish I could have done the reverse but the BD has Gibbs type springs and they would not fit on the OV. So I did the next best thing.

Remember I said these two traps have a different kit. I got one of the shorter dogs from the BD and put on the OV. Then I had to bend the end of the frame inward to get the pan level. Of course bending the end of the frame inward meant the eye of the dog was getting closer to the powered jaw. (see Illustration 5) Sure enough, when I got the pan leveled the trap showed 3 lbs of tension, the same as when I had installed these OV springs on the BD trap.

I put a shorter dog on the OV trap and bent the frame in, giving it the same dimension as the BD. Using the same springs, the traps gave identical readings, 3.0 lbs.

Then I had to go back and rethink what I did in installing longer dogs on the BD trap, when I had to start bending them. I think putting on the longer dog, negated anything I had done in bending that dog. Obviously bending the dog shortens it and I'll bet you more is accomplished when you have to bend the trap frame inward than there is in putting any certain angle on that dog. In lieu of actually owning a shorter dog, I?m guessing you could ?over roll? the eye of the dog to shorten the tang, then bend the trap frame in to accommodate it, and level the pan. Of course you are limited to how much you can bend the frame in.

There was one other test in regards to spring strength I could make quickly. It's easy to 4-coil the Bridger?s so I slipped a set of the booster springs on. The pan tension that was 2.5 lbs went up to 3.5 pounds with the booster springs. When I 4-coiled the bent dog (2.0 lb) trap, it went to 3.3. I was a little surprised that there would be this much increase.

4-coiling this trap, it went from 2.5 lbs tension to 3.6 lbs tension.

Here's is the bottom line on these PIT systems. As it stands now, the current PIT systems are designed to give 3 to 4 lbs of ambient pan tension. If you bend the dog, you might get this down to 2 pounds. But on many traps with strong springs you will not be able to get the tension this low no matter what you do. If you have a trap on which you want 2 pounds or less of pan tension do not use the current PIT systems.

You can get yourself in trouble with these things. Mind you I have a whole box full of pans, dogs and bases and I can make just about any combination I want. I put some "based pans" on some old Herters #4 for beaver. I didn't have any dogs long enough so I had to make my own. (I welded a short PIT dog on top of, and beyond the existing Herters dog.) They felt kind of heavy but what the heck a beaver is a big animal right?

I put them in service. Tracks on the bank showed that beaver were visiting my castor mounds, but there sat my traps, unfired. Finally I pulled them up and took them back to the bench. I had between 8 and 10 lbs of pan tension on every one of those traps. In order to make these traps set at 4 pounds, I had to add an extension to the back of the pan that moved the engagement point closer to the pivot. Then I had to cut off the dogs I had so laboriously made, and replace them with another, shorter, PIT dog. (It was this little incident that taught me it is better to really "measure" pan tension, rather than go by "feel".)

This is one of the Herters traps with a modified PIT pan.

This PIT system is not magic, it's mechanics. Right now it is "adapted" to traps with a jaw spread ranging from 7.5 to 5 inches through a series of progressively smaller pans and dogs. But in each case, large trap or small trap, the pan tension measured in the middle of the pan is going to be three to four pounds. That's the mechanics. You can vary this slightly by bending the dog. But don?t count on changing it drastically with this method.

Frankly, I believe there is a market for a PIT system that would yield two pounds of ambient tension. This would be a very good fox/coyote setting. But the mechanics would have to be changed to accomplish this. I asked Mr. Medvetz about this a while back, and he didn?t think these would sell well enough to recoup the cost of the dies for cutting a two-pound pan. (Mind you this entails the angle of the legs and not just the ?size? of the target area.) I should think dogs would not be a problem because a two-pound pan would require a shorter (and not a longer) dog.

Right now, the only way you are going to get two pounds of pan tension on these kits is to shorten the dog, by bending them if you wish, and bend end the cross frame inward if you can. And depending on the trap, you may never get it down that low. So, if you do want anything less than two pounds do not install PIT kits on your traps.

smile -- Hal
Endeavor to persevere.

#9771 - 08/12/06 05:59 PM Re: PIT Pan Tension Systems - Principles and Observations
Jonathan64 Offline

Registered: 11/29/05
Posts: 31
Loc: Northwestern New York
Thank you for taking the time, energy and interest in preparing that incredible lesson plan in trap physics to share with this part of the world!!!! A remarkable piece of work from a top rate teacher.

Thanks again.



#9772 - 08/12/06 06:36 PM Re: PIT Pan Tension Systems - Principles and Observations
Mac Offline

Registered: 05/24/04
Posts: 71
Loc: Maine
Excellent post filled with great info.

#9773 - 08/13/06 02:04 AM Re: PIT Pan Tension Systems - Principles and Observations
animalpest Offline

Registered: 08/18/05
Posts: 197
Loc: Western Australia
Good explanation of why I dont both with PIT's Hal.

Now if I could just get my foxes to grow a bit heavier ....

#9774 - 08/15/06 01:42 PM Re: PIT Pan Tension Systems - Principles and Observations
wmthrower Offline

Registered: 08/26/03
Posts: 143
Loc: Mexico, NY
Great explanation Hal!! I was unfamiliar with the PIT system but now I feel educated to the finer points of the system and how it works.

Thanks for the photos and illustrations.

#25456 - 10/25/17 01:33 PM Re: PIT Pan Tension Systems - Principles and Observations [Re: Hal]
Archive Offline

Registered: 03/12/03
Posts: 1486
Dated for search.


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