This article originally appeared in the April, 2015 edition of Keynotes.
Introduction
This article can be digested in 3 ways: a DIY method to change the function of the 700 Series ET trim used on a Sargent 8800 rim exit device, an example of the thought process associated with thinking “outside of the box” and using it in the field effectively, or a combination of the two. It is intended primarily for institutional locksmiths because it requires benchmark testing in the field and I cannot imagine that is cost efficient for a locksmith company under most circumstances (unless you have a spare door and hardware at your shop). Not to mention, a locksmith company is more inclined to provide a solution with a warranty; that is a selling point after all. Can all locksmiths take away something from this? Absolutely, but for the most part an institutional locksmith is going to benefit a lot more from this article.
The Situation
We have 3 residential halls on campus that use Sargent’s 8800 rim exit device with the 700 Series ET trim (Figure 1) on all mechanical, electrical, and transformer rooms; 10 doors in all. The problem is that when these buildings were renovated the contractors chose to use Sargent’s 13 (ANSI 08) function: key outside unlocks/locks trim. Essentially, it’s a classroom function trim. We all know the potential problem with classroom function locks: employees forgetting to lock up. This creates potential safety and liability situations, especially considering the contents of these rooms, which we should always do our best to avoid.
Figure 1
The solution is simple, right? Use storeroom function trim. Sargent sells a kit just for this called the
607-2 Locking Slide Replacement Kit. A 607-2 slide kit costs me $64.11 and is retrofit-able. 10 doors, that’s a total of $641.10. You may be thinking, “$64.11? I get it for far less than that!” I’m an institutional locksmith at a small college. I’m not a large volume costumer; I don’t get the
good pricing (not that I would expect or demand it – I understand why things are the way they are). That’s a good bit of my monthly budget, however.
What if I could modify the existing 700 Series ET trimtrim to accomplish the same goal of converting it to storeroom function but at a substantially cheaper price? It’d have to be reliable, cost efficient, and easily crafted in order to be worth the effort.
Warranties, Underwriter Laboratories Listed Hardware, and Other Considerations
Before we touch on any field modifications, let’s discuss potential implications and liabilities. First, the trim and slide kit carry 5 year warranties. Altering either voids the warranty. My trim was out of warranty already. What did I have to lose? Ruining one slide and buying the kit? It was worth the tradeoff.
And without turning this into a primer on the difference between Underwriter Laboratories (UL) Marks, I’m only going to hit on a few points with regards to them (UL Listed, UL Certified, etc.). The absence of a UL Mark, usually a sticker, does not mean that the hardware has not been evaluated and met UL requirements and you have free range to make any field modifications.
Fortunately, UL has an online database that will allow you to determine if the hardware has met their requirements. There are a number of fields in the search area of the website that can help you find the product in question very efficiently. Of course, so will product literature from a manufacturer. I have found in my own experience, however, that it’s much easier to go straight to the source (UL) to avoid scouring a manufacturer’s website for that information. That’s just my preference though.
If, for whatever reason, you determine that a modification is necessary to a UL Listed product you can request a Field Evaluation from UL. In fact, if you’ve ever see a “Field Evaluated Product” badge, that was a result of this program. More information can be found at http://www.ul.com/field.
And hopefully you’re all well versed in field modification requirements of the publications adopted by your state, NFPA 80 for example. If not, please do your homework. It’s only a matter of time before you encounter a job that requires a code adherent field repair or modification.
For the record, the Sargent 8800 rim exit device on this door is UL Listed but the 700 Series ET trim is not.
Thinking Outside of the Box
It was time to find out if a field modification was plausible. The 700 Series ET trim with Sargent’s 13 function operates like a safe combination lock in some respects. The handle has a notch in it just like a gate in a combination’s wheel. The cylinder’s cam interfaces with the stainless steel locking slide (according to a Sargent exit device tech) that has a protrusion, much like a fence, at the bottom. When this protrusion enters the notch, the handle is locked in place. Figure 2 shows the 700 Series ET trim unlocked and figure 3 shows it locked.
Simple enough, right? Therefore, it would stand to reason that if I could force the slide into the notch consistently until retracted manually by the cam then I would have my storeroom function. A compression spring could accomplish that job but what kind of compression spring did I need?
The Physics
Thinking outside of the box is one thing but having it work with physics is an entirely different thing. I could have found a spring, altered to make it work, and hoped for the best. But, I’m a calculative person and I would hope any outside the box thinker is as well.
All springs eventually fail but their fatigue, or failure, limit’s likelihood can be reliably calculated; almost predicted. This is accomplished by a mathematical equation known as the Soderberg Criterion. It calculates a spring’s failure limit using known attributes such as minimum and maximum forces applied, wire diameter, the outer diameter of the spring, spring free length, etc. It even goes so far as to consider the material’s yield stress, which can be found for any and every metal and it’s alloys you’re likely to find at the local home center or online. Suffice to say, it is a comprehensive equation.
I purchased a spring I believed would work, cut it to a length I had determined would fit inside the trim, and ran it through the equation. Did it pass Soderberg’s muster? Yes, with room to spare. If you’re not good with math don’t worry, there are online calculators just for the Soderberg Criterion. I used one and if you find the need to test the failure limit of a compression spring in the future a simple Google search will produce the online calculator.
This is an example of using math, physics, engineering, etc. to help figure out if a field modification is going to work reliably long term. Graphs, equations, tests, etc. all exist that can assist with field modification assessments. In this case, my only concern was the spring’s failure limit. I would recommend that any locksmith replacing a compression spring in the field that did not come from the manufacturer use the Soderberg Criterion equation to determine if the replacement will work. If you only take one thing from this article, let it be that.
The Engineering
If facing the 700 Series ET trim from the inside, or the side containing the internal parts, there is a perfect spot between the trim body and the right side of the locking slide (Figure 4). I decided that would be the best place for the compression spring.
Figure 4
Before I started drilling and making alterations, I needed to do a bit of measuring and math. As seen in Figure 5, the mortise cylinder’s collar determines the distance between the cam and the part of slide it interacts with. Likewise, it controls the distance between the cam and the portion of the trim body I wanted to install my spring. As it was currently installed, I couldn’t fit my spring in the area I determined would be best. I simply changed out the collars and I had my needed space.
Figure 5
Now, how to anchor the spring so that it stays in place and works as it should with the slide? I was limited at the top by the mortise cylinder’s nut. I figured that would be the top point of the spring so I drilled and put a spring, or roll or tension, pin there. Next, I “Dremeled” a notch into the locking slide to accept the compression spring (Figure 6).
Figure 6
I didn’t get careless; I needed a snug fit that could hold an ample portion of the spring. Also, remember it’s a stainless steel part. I don’t have to really worry about sacrificing the strength of the slide by removing the portion of material I did. I also knew the compression spring didn’t have the force to shear the spring pin. With all that done, I now had a place to put my spring and have it hold reliably (Figure 7). (Note the file marks on the cam; that was done to clean up burrs created due to incorrect cylinder spacing via the collars).
Figure 7
Bench and Field Testing
With the modification installed I, like any manufacturer, performed benchmark tests in shop prior to field deployment. 500 in all. Did my fix hold? Yes. Was that the end of my testing? No. In hand or in vise is one thing, on door in conjunction with device is another. That got another 4000 cycles before I determined the fix a success. 4000 key turns via Best’s ED211 Mortise Cylinder Wrench (Figure 8). This was a very tedious and mundane process but it was worth it. I pulled the 700 Series ET trim off of the door and brought it back to the shop to evaluate its performance.
Figure 8
Each door gets between 1 and 2 uses per day. Let’s assume 2 a day, 365 days a year for 5 years (my anticipated usage vs. Sargent’s warranty period). By testing the fix 4500 times, I’ve essentially benchmarked just over 7 years of use and it still works. I’m confident with that; that exceeds what Sargent would have warrantied by at least 2 years. Now it was time to take it off the door and see what, if anything, occurred and if anything needed to be altered.
The Results
Figure 9 shows the benchmarked compression next to a brand new, unaltered spring of the same make. You can see that the spring used in the benchmark tests is slightly more compressed but that’s to be expected after 4500 cycles.
Figure 9
Figure 10 shows the inside of the ET trim. There are two very faint wear marks. The mark indicated by the pointer is from the spring and the mark to the right of that is from the portion of the spring mounted to the slide.
Figure 10
Figure 11 shows the slide. The only wear marks I see are where the cam interfaces with the slide but that is what one would expect.
Figure 11
Figure 12 shows the spring pin. Enough wear to remove the coating but not much beyond that.
Figure 12
Figure 13 shows the spring with the side that interfaces with the slide. Again, very little wear. If this is what I can expect after 4500 cycles, then I consider this field modification a success.
Figure 13
The Math
One spring and one spring pin cost me $0.95 and $0.12 each, respectively.
Remember, we have 10 of these devices on campus. That brings my total, parts only, to $641.10 for the 607-2 kits and $10.70 total for the springs and spring pins. The difference is $630.40.
Now, I did have labor involved. In all, I spent nearly 4 hours creating and testing the modification over the course of a month. For argument’s sake, the average locksmith in America makes $19.15 an hour according to the U.S. Bureau of Labor Statistics. That’s $76.60 additional labor just to create and test this field modification.
It takes me 30 minutes to perform my modification per ET trim (that’s taking it off the door and reinstalling included). I’d guess I could replace the 607-2 kit in half the time, or 15 minutes. So, labor wise, that’s 5 hours for the field modification; 2.5 hours for the 607-2 kit. Using the same average wage, that’s $95.75 vs. $47.88, respectively.
In sum, the 607-2 slide kit costs me $688.98 (parts and labor) and my modification cost me $183.05. Do you see why it’s worth at least considering altering a non-UL listed, non-fire rated piece of hardware to change its function, repair instead of replace it, etc.?
Furthermore, let’s assume the spring from a 607-2 slide kit and my spring breaks at the exact same time, outside of the warranty period. These are the only two I can imagine breaking; the rest of the slide assembly is darn near bullet proof. Of the two, which is more costly to fix? Which is easier to fix or which can be fixed faster (I don’t have to remove any parts to replace my spring – the 607-2 kit has installation instructions for a reason)? Which spring is more readily available? I may be partial but I’m going to go with my field modification on all questions (apologies if you have the 607-2 slide kit or their unique flat spring en masse on hand). Regardless, these are questions you should also consider when considering a field modification to a product.
So what’s the point of all this?
Well, it saved me over $500 but I hope it got your brain juices flowing. When a fix or hardware change is necessary don’t assume the right answer is to go straight to the manufacturer or distributor’s catalog. We’ve illustrated that with a bit of outside the box thinking, math/physics/engineering, and testing we can create our own solutions. My fix was not an isolated case; this sort of stuff happens on a daily basis to all of us. Do you think I toss defective Sargent 8200 series and Best 40H mortise locks or harvest them for their working parts? Are you guilty of the same? We’re hoping to fix a lock problem without buying a direct replacement or use the good parts elsewhere, which is the basis of most field modifications.
Our trade was started by individuals who hand crafted locks. Don’t be afraid to modify hardware so long as it doesn’t sacrifice its life safety and security qualities. Warranty voiding is at you and your customer’s discretion. Math, physics, engineering, etc. are rarely a gamble. With the right knowledge and tools, outside the box solutions will rarely be a gamble either.
