PT50- Slight Mods

[grepper]

Mr. Mark graciously and most grandmotherly explained, "I was teasing, of course, Mr. Grepper."

Thanks for that Mr. Mark.  Whew!  I was emotionally crushed and left but to cower in the corner in search of a rock under which I could crawl and hide from life.
 
TMF – Test Media Fixture
 
I seriously doubt that the mod I did changes the readings.  The length of the threaded media is for all intents and purposes the same, it does not change the tension compared to the un-modified version at all, and test media does not stretch.  Even if it did, I would think that the very short difference in length between the mod/un-mod versions would be of little or no consequence.   I noticed no difference before/after I did it.  That said, like I mentioned, I have not done razor blade testing to verify and I see no real reason to do so.  But, I may get around to it eventually just for grins.
 
I get the idea that the BESS certification process is a grueling process and not for the faint of heart.  But, that’s what it takes to have a reliable, predictable standard.  A good thing.
 
Because the media so effortlessly slips under the screw, it’s way easier to hold just the end of the media whilst pulling it under the screw, rather than having to wrap it around a finger.  My average length of media per test is 1.75”.  It’s a way faster, smoother and easier operation.  "I really like it", fearlessly exclaimed grepper.
 
I would not want to grind the mortise off because it positions the media and holds in place.  I don’t see how it impedes the process at all.  But maybe you are on to something.  Could you please explain you thinking and more about how you might implement that?  (I like mods).
 
I put a LOT of thought into that mod and considered many different options.  One of which was just to get rid of the flat side on the fixture.   Just not having that side flat raises the screw and makes it easier to get the media under the screw.
 
Other than using a lathe to make the little knob, I did the drilling on a mill and grinding/polishing on the Kally.
 
Mr. Bud is correct.  The PT50A is 1 gram resolution, faster processor, more rugged and can measure up to 3,000 grams (the B is 2,000g).
 
BTW, I like your cork idea.  I've thought about widening the slot a couple of times, but I think your idea makes for even a smoother operation.  It would be one thing if the fulcrum was fixed to the platform so as to ensure perfect centering of the blade over the slot in the TMF, but since the fulcrum is stuck with a magnet and easily moved anyway I think your idea works very well indeed.  Even if the cork eventually chips away, so what?  Super easy to replace.

[Mark Reich]

It sounded like you needed a grandmotherly pat on the head, Mr. Grepper.    

My Test Media Fixture (Thank You, Gentlemen) was different  than yours, Mr. Grepper. The anchor side was not flat like ours are now. Mine had another mortise down the flat side, which inset the path for the media, and the anchor screw, into the body of the TMF another .050" or so. The only recourse was backing the screw out an extra couple turns every time, which is why I ground that mortise off, and now my flat side looks like yours. 

I definitely like your design, Mr. Grepper. They have knurled brass thumb nuts at the hardware store, which I would spend an hour making a copy of, if I had a lathe... Having the anchor screw/stud/nut  at a 45° angle on the upper corner sure seems optimal to me.

The only other thing I still wonder about is the propensity for the media to be affected from being in direct contact with the locking screw. I bet no one would pull the media around the other side of the screw and expect it to stay tensioned, right? It seems like the same thing to me. 

To my chagrin, I've found media tension makes a big difference. Since I couldn't get all my thumbs to fit around the media and the anchor screw of the TMF, I was using a hemostat to hold the media. It was so easy to pull the media taught, I was artificially lowering my scores. 

I'm not sure if the media auto-tensions when tightening the anchor screw, but a little washer between the screw and the media makes sense to me, so I'm going to try it in hope my standard deviation bottoms out.  

You're right, cork is easy and free, and it's like laying a fine edge on a silk pillow, no matter where you place the blade. It's much easier than having to line up the fulcrum and TMF. 

I can understand the sanctity of standardization, but I also understand how critical it is to be able to test efficiently. If testing isn't quick and easy, guys are less apt to do it to the best of their ability IMHO.

[grepper]

"The only other thing I still wonder about is the propensity for the media to be affected from being in direct contact with the locking screw."

I've puzzled over that too, but at least from what I can tell it does not.  I just very gently pull the media under the screw head and tighten it.  I've never noticed it get over tensioned at all.  I suspect that due to the smoothness of the surface of the media that it has little proclivity to be grabbed by the bottom of the screw head.  Or, maybe the side against the fixture grabs enough to cancel out the influence of the screw head.  However, I don't think a washer could hurt in the slightest, and may even preclude the possibility of additional tensioning due to tightening the screw. 

I've spoken with Mr. EOU about how tension influences the readings and was informed that unless it is excessive tension should have little effect.  That said, optimal tension is 100g.

"I bet no one would pull the media around the other side of the screw and expect it to stay tensioned, right? It seems like the same thing to me."

Well, start watching this @ 3:30:

https://www.youtube.com/watch?v=zUasWd9mUUQ 

"Since I couldn't get all my thumbs to fit around the media and the anchor screw of the TMF, I was using a hemostat to hold the media."  

!  Wow! That sounds like a pain the the butt.  

The 45° angle of screw works great!  Super easy to grab onto and just as easy to slip the media under after only unscrewing the screw by 1/4 of a turn or so.  I can literally do it in a second or two.  It's super fast.  You could probably do it with only stumps for hands.  With the screw at the angle, you can see how the media does not have to be pressed against the fixture at all to get it under the screw.  Just pull the end of the media down at an angle away from the fixture and tighten the screw.  Like I said, I suspect my cat could do it and he has paws for hands.

If you want to do it, look carefully at the pics I posted.  The screw must be just to the side of the top mortise, and the head of the screw must be wide enough to go over corner the mortise.  I flattened the edge just a bit so the media presses against a flat surface rather than a sharp corner.

Just make sure the fixture is very securely positioned in a vice to drill the 45° hole for the stud.

If you use a screw rather than a stud with a threaded head as I did, when the screw is tightened the media is grabbed by the threads of the screw and sucked into the hole.  This causes problems.  If you go the screw route, bore a slightly larger hole at the top of the hole for the screw.  If you check out your current fixture you will see that oversized bore at the top of the hole for the screw.  If you use a stud with a nut rather than a screw that step is not necessary.

While this simple mod worked extremely well for me, I'm not recommending anyone do it without carefully reading and understanding the possible contraindications mentioned previously in this thread.

[EOU]

Nice piece Grepper! Of course we learned of Grepper's modification some time ago. We also wondered how his modification might affect the accuracy of the measurement. We duplicated his modification to a close degree here and tested. We also sharpened and deburred knife edges in precisely the same way as Grepper did and then we compared readings (our unmodified fixture versus his modified). We concluded that, if there is a difference, it is insignificant to the point that it can't be measured. 

At EOU we don't split hairs. BESSU does and that is a good thing.  EOU's purposes and BESSU's differ in this way. BESSU's only mission is preservation of the standard. The standard is what allows KG in Australia to accurately and meaningfully communicate his research results to us in USA and for EOU to compare sharpening results with Grepper in Michigan while using the same measuring stick. EOU has an additional goal though and that is to help sharpeners improve their sharpening capabilities. In order to accomplish this goal sharpeners only need know if a given sharpening procedure made the number go up or down. In the instrumentation world this is referred to as absolute versus relative measurement. Both means are used and both have their place. Accurate communication is important but so is improvement. That's why we don't quibble with customers over 7 or 8 pts. of absolute inaccuracy as long as the error is of a predictable and consistent nature.  BESSU does quibble with 7 or 8 points of absolute error. In the end, it makes for a solid partnership.

Within the next year, we will design a new test fixture that addresses the "ease of use" issues that Rick Kr, Grepper and others have identified. We will submit that fixture to BESSU for testing and hope that we catch them on a good day. Obviously, we didn't with test clips which still remain unapproved.

Thanks to everyone who have taken the time to experiment with improvements of all sort. It is much appreciated and very helpful.

[eddosedge]

It sounded like you needed a grandmotherly pat on the head, Mr. Grepper.    

My Test Media Fixture (Thank You, Gentlemen) was different  than yours, Mr. Grepper. The anchor side was not flat like ours are now. Mine had another mortise down the flat side, which inset the path for the media, and the anchor screw, into the body of the TMF another .050" or so. The only recourse was backing the screw out an extra couple turns every time, which is why I ground that mortise off, and now my flat side looks like yours. 

I definitely like your design, Mr. Grepper. They have knurled brass thumb nuts at the hardware store, which I would spend an hour making a copy of, if I had a lathe... Having the anchor screw/stud/nut  at a 45° angle on the upper corner sure seems optimal to me.

The only other thing I still wonder about is the propensity for the media to be affected from being in direct contact with the locking screw. I bet no one would pull the media around the other side of the screw and expect it to stay tensioned, right? It seems like the same thing to me. 

To my chagrin, I've found media tension makes a big difference. Since I couldn't get all my thumbs to fit around the media and the anchor screw of the TMF, I was using a hemostat to hold the media. It was so easy to pull the media taught, I was artificially lowering my scores. 

I'm not sure if the media auto-tensions when tightening the anchor screw, but a little washer between the screw and the media makes sense to me, so I'm going to try it in hope my standard deviation bottoms out.  

You're right, cork is easy and free, and it's like laying a fine edge on a silk pillow, no matter where you place the blade. It's much easier than having to line up the fulcrum and TMF. 

I can understand the sanctity of standardization, but I also understand how critical it is to be able to test efficiently. If testing isn't quick and easy, guys are less apt to do it to the best of their ability IMHO.

Mark,

I'm replying to your last sentence.  When I decided to sharpen at a gun show earlier this year, I decided to go with the test clips because they are quick and easy.  I'm glad I did.  As everyone is meandering around your table you have about 5 seconds to get their interest.  ME:You need your knife sharpened?  THEM:Nah, it's already sharp.  ME:I have a sharpness tester, I'll test it for free.

About 80% of my business at the show was due to the BESS tester.  Once I tested one knife, others noticed and then I tested theirs.  The test clip made all the difference as there was almost no wait time between tests.  Of the 30-40 knives I tested, I cannot remember one score less than 300.  A few were in the high 300s and most came in between 400-600. My "sell" was that I would get the edge below 200.

If I had a TMF with Grepper's mod, I would have saved more than $20.00 as I went through more than 100 clips.  I would be interested in one if they ever came available.

Ed K.

[grepper]

I guess the clips are pretty popular. Just keep in mind that unless you wiggle the little posts that hold the media back/forth a few times to lessen the tension, the clips will produce a 20% lower reading than the BESSU certified TMF.

The mod is pretty easy to do. There are a few things you must get right for it to work well, but that does not make it more difficult, you just must understand what/why and do it more or less accurately. It's pretty well described / shown above. If you decide to make one and have questions I'll be happy to assist if I can.

[EOU]

We're still listening in Ed...and talking. You may see our version of the Grepper ATF much sooner than we indicated in our previous post. That's assuming that we don't run into any barriers with BESSU. Happy to hear that you enjoyed success with your PT50 at the show.

[grepper]

Mr. EOU.  "I'm confused", puzzled grepper.  When we first started talking you called it TMF, now ATF.  

So, how to proceed... TMF or ATF?  (Aluminum Test Fixture?)

[Mark Reich]

Thanks a bunch for all the input, Gentlemen. I'm a lot better informed.

[grepper]

Alcohol, Tobacco &  Firearms.