Hi, I am considering to buy a sharpness testing scale, I found and it seems that it is recommended, the PTA50: now there are at least 3 versions, the PTA50A;PTA50B and the PTA50C, Any recommendation which it is the best to buy and why
in your opinion it is so, please?
Thank you.
Alf.
Alf,
the PT50A is sure the best of the three you named. They differ mainly in the processor speed of the scale and its resolution.
PTA 50 can handle 25 measurements per seconds with a resolution of 1 Gram, while, afaik, PT50C does 5 measurements/sec with 25 grams resolution. The B-model is somewhere inbetween.
So if you're determined to buy one, go for the PT50A. It's not a must-have, but sure helps with developing your sharpening methods.
You find a quite concise comparison here: https://www.edgeonup.com/PT50-Series.html
Mike
Alf,
I have an older version of the B. Same accuracy, one more button to push. I suspect the B is the practical choice for most of us. That said, I don't think the A model was available when I bought mine. Liking overkill, I would probably have chosen it.
Check out bessex.com. It's the forum for BESS and Edge on Up. I've been a member since it began. They are a good, helpful bunch.
Ken
Thank you Mike and Ken, much appreciate your feedback. One more question, can you test the sharpness of a Wood Chisel with one of these ?
Another question What is the meaning "25 measurements per seconds with a resolution of 1 Gram"
I tried to look it up, but without success.
Thanks.
Alf
Hello,
why do you need to measure BESS value? I'd rather invest in a good microscope - you'll see what's going on on the whole edge, not at single/few points...
jvh
Jvh, but will by looking only, one can check the sharpness?
Alf
Quote from: dusmif on May 28, 2021, 10:24:17 PM
Jvh, but will by looking only, one can check the sharpness?
Alf
Alf,
it depends. Sharpness for what? For the lowest BESS or for real use?
Sharpness is only one part of the problem. You have to consider also the real use, edge toughness, edge retention, corrosion resistance. You have to remove burr completely.
BESS shows you the sharpness in one point of the edge at a given time. When you repeat the measurement the next day you will get a value ca +20 g higher due to the oxidation of the edge. The BESS value will increase significantly after a few cuts etc.
With a good microscope... what do you think, is it sharp? (And you can still use cigarette paper, hair etc.)
https://youtu.be/QG_z9ynBht8?t=122
https://youtu.be/NXz7WB_qhqk?t=92
https://youtu.be/8LS17P0k4hw
jvh
That is very interesting,You got a point. Thank you for sharing.
Alf.
Quote from: dusmif on May 28, 2021, 09:24:42 PM
One more question, can you test the sharpness of a Wood Chisel with one of these ?
Another question What is the meaning "25 measurements per seconds with a resolution of 1 Gram"
Thanks.
Alf
Alf,
these "25 measurements" can be a bit misleading. It just means the measured value (finally on the scale's display) is updated 25 times per second. It is an advantage if that happens as often as possible, as the measured force is gradually increased when you move down the blade. (Imagine, if a scale would just do one measurement per second, you could have cut the thread before the scale even noticed). So a higher rate adds to accuracy.
jvh,
I agree with you that the BESS Tester is just one means of evaluating sharpness, among many others.
Real use, edge retention etc. play an important role, of course. Also oxidation and a the loss of sharpness after a few cuts occur, but are not related to a certain test method.
I can just speak for myself, but the bess tester and a good microscope (thanks for mentioning) have helped me a lot in developing my sharpening and deburring skills.
Mike
EDIT: Yes, you can measure chisels, too, at least wider ones. But for chisels I think testing them in a "real life" environment is more useful than just getting a BESS value. :)
Thank You Mike, that was very helpful.
Alf.
Mike Brubacher, the inventor, recommends the PT50B for most users.
Thank You All for your help and advice, I appreciate it very much.
Alf
I have the PT50A. With a do-over I would probably get the PT50-B. I find I don't put much emphasis on the 1g resolution (for example is 80BESS really better than 84). Also so many variables with BESS testing (thread tension etc).
After a sharpening session I'd definitely want to know if I was more at 125 or 85, but not so much whether I'm 90 or 92 BESS...
Re the BESS tester - which I purchased because I'm not a reasonable person, and also because it intrigues me - there is one thing I can't seem to wrap my head around :
Thread tension obviously plays a key role in the result, as the tighter the thread, the earlier it will break.
I've seen attempts at standardizing thread tension by hanging 100g weights and such, which is fine.
But unless I don't use it properly, it seems to me that the tightness of the screw plays a key role in thread tension. So much so that it seems one can break the thread just by tightening the screw. So you'd obviously get much better BESS values with a thread that's on the verge of snapping.
Did I miss something ?
Cheers,
Nick.
Nick,
you're right, that's sure something to be considered.
It's one of the reasons why comparability of results from different person's testing might be somehow limited.
However, in a reasonable range the effects are probably not that serious. If you use the PT50 to compare your own results you will probably have a somewhat consistent technique of tensioning and tightening. The manual advises to not overtension. Light pressure for the screws is also explicitly mentioned.
But I think one could deliberately affect results by extreme overtensioning the line or overtightening the screws.
I think we're reasonable enough not to do so (despite of not being reasonable enough to avoid buying a BESS tester :) )
Mike
Micha,
Thanks for your insight. I agree with all your points, it just seems to me that for something that is supposed to "certify" sharpness, being dependent on the user notion of "tight, but not too tight" is some kind of a loophole.
I'll try to experiment a bit to see how the bess value varies for a single knife with different - yet still complying with the "not overtight" requirement - settings, and let you know. Maybe it's negligible.
Quote from: tgbto on June 10, 2021, 08:48:46 AM
Re the BESS tester...
...
Did I miss something ?
Cheers,
Nick.
That... they have their own forum (http://www.bessex.com/forum/)? ;)
Quote from: cbwx34 on June 10, 2021, 02:04:30 PM
Quote from: tgbto on June 10, 2021, 08:48:46 AM
Re the BESS tester...
...
Did I miss something ?
Cheers,
Nick.
That... they have their own forum (http://www.bessex.com/forum/)? ;)
The BESS exchange is bessex.com. For more in depth BESS discussions, it is an ideal reference.
Ken
I made a video a few months ago showing the effects of thread tension on BESS score... And also how BESS scores can be artificially lowered by chopping down on the thread, rather than gradual progression of pressure. On the latter point I managed to get a Mora basic down to 16 BESS
https://youtu.be/dG2rQ6CjTyc
Quote from: Ken S on June 10, 2021, 02:37:03 PM
Quote from: cbwx34 on June 10, 2021, 02:04:30 PM
Quote from: tgbto on June 10, 2021, 08:48:46 AM
Re the BESS tester...
...
Did I miss something ?
Cheers,
Nick.
That... they have their own forum (http://www.bessex.com/forum/)? ;)
The BESS exchange is bessex.com. For more in depth BESS discussions, it is an ideal reference.
Ken
I definitely missed that. Thanks !
Quote from: BradGE on June 10, 2021, 09:52:46 PM
I made a video a few months ago showing the effects of thread tension on BESS score... And also how BESS scores can be artificially lowered by chopping down on the thread, rather than gradual progression of pressure. On the latter point I managed to get a Mora basic down to 16 BESS
https://youtu.be/dG2rQ6CjTyc
Brad, this is a brilliant video that hadn't shown up in my results yet. Many thanks!
Quote from: BradGE on June 10, 2021, 09:52:46 PM
I made a video a few months ago showing the effects of thread tension on BESS score... And also how BESS scores can be artificially lowered by chopping down on the thread, rather than gradual progression of pressure. On the latter point I managed to get a Mora basic down to 16 BESS
https://youtu.be/dG2rQ6CjTyc
After having seen the film, I wonder what the value of a BESS measurement means. Even the 'prestressed' measuring bridges do not give any unambiguous measurement.
In my opinion, the tolerance is near ± 30, but at least ± 10.
Quote from: Dutchman on June 11, 2021, 10:26:04 AM
Quote from: BradGE on June 10, 2021, 09:52:46 PM
I made a video a few months ago showing the effects of thread tension on BESS score... And also how BESS scores can be artificially lowered by chopping down on the thread, rather than gradual progression of pressure. On the latter point I managed to get a Mora basic down to 16 BESS
https://youtu.be/dG2rQ6CjTyc
After having seen the film, I wonder what the value of a BESS measurement means. Even the 'prestressed' measuring bridges do not give any unambiguous measurement.
In my opinion, the tolerance is near ± 30, but at least ± 10.
In my experience +/- 10 is probably fair - I doubt it's as much as 30. So difficult to know though, because are you measuring, exactly the same part of the edge, and/or did the first test impact the quality of the edge for the second test? Certainly the operator has to carry the responsibility of working carefully to get good, useable results. But as others have said, for comparing one's own results I'm confident that my BESS 80 is sharper than my BESS 100... But how my 80 compares to someone else's 80... no way to know. Only by using standard weights (100g etc) or the pre-tensioned clips can we narrow that gap a bit, but regardless we have to count on each other to not 'chop' during the measurement.
Hi Brad,
I agree, except for the pretensioned clips.
I wonder whether testing with a bit of slack in the line would lead to more commensurable results by eliminating the pretension factor completely.
But that's just a hypothesis for now. But I can't see any disadvantage in not having tension.
Maybe I'm missing something?
Mike
Hi Micha,
I'll play with that idea of slack and report back. I think there might be an issue that if the edge doesn't land exactly in the centre of the test line then as you press down the apex will slice the media slightly laterally as it makes its way to the lowest point of the 'V' that will be created in the line... But I'll try it.
Regarding the pre-tensioned clips, you're not the first person that doesn't like them, but my experiences have only been positive so far...
Brad,
I'm looking forward to hearing about your observations.
I just did some 50 tests without any measurable tension and found the results quite reproducible in a narrow range of +- 10 grams.
When tensioning the test line (arbitrarily, without using a weight) just with my fingers, the results tended to be lower, up to +40 grams .
Pretension up to 100 grams didn't have so much influence.
As it's way more comfortable to fix the line without notable tension, I think I'll keep to that.
I'd be interested in Mike Brubacher's thoughts, too, guess I'll drop him a line.
Mike