Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
Too dull to shave with?
I use disposable razors because they perform reasonably well, last a month or more each and are incredibly inexpensive.  I use nothing special double bladed ones because for no real reason I think they perform better than single blade models.  I bag of a dozen costs less than $10 and I’m good to go for a year or so.  When they get too dull to use they join billions of others to help fill our landfills with plastic crap that will survive there for the next 400 years or more.

I have probably about average beard consistency.  Not like a wire brush but not peach fuzz either.  If I don’t shave for a day it’s very visible and scratchy. 
Today one reached the point where I decided it needed replacing with a new one.  I think it has been in use for more than a month.  It was not horribly dull.  It did not grab, yank or tear hair out but required 3 or 4 passes over the same area to get the job done.  In a pinch it could probably have been used for another couple of weeks but I decided its useful life had passed.  Here is a picture of it.

I’ve often wondered as to the sharpness when I decide one has reached its demise.  I was guessing it would be 300 or so.  This time curiosity got the better of me and I decided to actually measure the sharpness.   I “disassembled” it and removed the two razor bands using a process that resulted in eliminating any possibility of reassembly.

The little strips of metal are incredibly wimpy, thin and flexible.  An impressive job of design and engineering to make a razor out of them that performs as well as they do.  To perform the measurement I gripped the metal strip with two needle-nosed pliers and grasped the razor band with the jaws maybe 3/16” apart from each other.  This stabilized the blade between the jaws of the pliers enough to perform the measurement. 
I took a total of 3 measurements, two on one blade and one on the other.  I was truly surprised by the results.  As I mentioned I was guessing to see something like 300, but instead the measured sharpness with the PT50-B was:
65, 75, 75
Those are impressive numbers, thanks for sharing. I’ll bet nobody could make those 1000 years ago.
The same curiosity bug bit us about 4 years ago. The blades removed from the disposable razor  we measured were in the 50's.
It seems like whiskers are so soft compared to disposable steel blades that there are hardly any steel atoms disturbed at all.

Also seems straight razor steel is just hard enough to maintain an edge through a shave, but also soft enough to re-align the edge on something slightly tougher than whiskers.
(11-24-2019, 01:39 PM)Mark Reich Wrote: It seems like whiskers are so soft compared to disposable steel blades that there are hardly any steel atoms disturbed at all.

Also seems straight razor steel is just hard enough to maintain an edge through a shave, but also soft enough to re-align the edge on something slightly tougher than whiskers.

That makes perfect sense to me.  I mean, rubbing stainless steel against skin and cutting whiskers does not seem like that demanding a chore.  That said, cheapo disposable razors do indeed get dull.  Looking at the images of the blade I declared as too dull to shave with there was obvious corrosion and crud on the edges.  I don’t know if the dullness was due to rolling, corrosion or crud buildup, but its useful life had passed.
While he did not say it, I happen to know that the numbers Mr. Mike posted, ~50, were measurements of new unused blades.  The thing that amazing me was that the blades that I declared too dull to shave with were still pretty sharp, 65, 75, 75, only 15 to 25 duller than new unused disposable blades. 
15 to 25 is a pretty narrow range of sharpness between usable and too dull to shave with.  Obviously one test is very shaky ground from which to form any assumptions, but in this case a 15 to 25 reduction of sharpness was the difference between a useful razor and additional plastic in the landfill. 

For you straight users, what is the sharpness when they are good shavers and need attention?  Do they compare to disposables?
I think the numbers alone probably don't tell the entire story. I have not done any measurements, but I have used a lot of double edged safety razor blades to shave with. I generally get about 7 shaves before I consider them to be too dull to be worth my time. This is a luxury decision of mine. The blades I use cost around $0.17 each, so it's pretty affordable. For $17 I get 100 blades and those last me well over a year. ...and the way I use the blades, I get really, really good shaves almost every time.

Back to the sharpness and blade feel. As I was evaluating DE blades, I tried probably 12 or 15 different brands and models. There are marked sharpness differences between some of them. A lot are pretty close. But the feel can be quite different between blades. The one I ended up choosing, I was slightly biased against: The Gillette Silver Blue. It turns out this blade has a coating on it that makes it feel more smooth than a regular stainless steel blade. I think it's platinum, but I can't be sure.

Also, I occasionally get a blade, straight out of the package, that gives me bad shaves. Not horrible, but definitely rougher and worse than normal. In most cases corking the blade (drawing the edge through cork a few times) fixes this. I think that sometimes their process at the factory is imperfect and they leave behind burr material on the edge.

I also think that edge denting might play a roll in blades seeming "worse", but I have zero evidence to back that up. It's just a theory.

You'll know it if you dent an edge Brian when using our instrument and I understand that your observation, with regard to denting. is likely not based on use of our instrument.   When using our instrument, the dented reading won't be 50 but 150 or 350 depending on the depth of dent. Having said that, we've never witnessed a dented edge when measuring DE razor blades and we've measured plenty of all ilk, brand and description. The almost exclusive instance of dented edges we are aware of come from some of those who sharpen straight edge razors but there has been the rare occurrence of a knife(s) exhibiting this problem as well . A foil edge might not sever test media without denting - a structurally sound and even sharper edge will always sever the test media without denting. Microtomes measuring in the 10 range are tested everyday without denting so it's all about proper edge formation.

We've tested plenty of surgical tools that dent as well but these were made of 301 or 304 stainless so were not hardenable. 

To me, a dented edge is like sending a warning flare up to the sharpener - If a hardened  steel edge dents while cutting a .009" polymer test media using only  50 grams of force (more or less) - it's time to review the grinding/deburring process being utilized.
I was not being verbose enough in my description.  What you've said makes sense.  Let me try to also make sense.  Smile

The postulate here is that DE razor blades get uncomfortable for the person shaving, yet their measured sharpness only decreases by a small number of points.  So what might account for that?  I theorize that the blade is staying measurably sharp, yet is developing a more rough finish on the edge.  It's sharpness is also decreasing, but not by that much.  If the finish gets rougher, then the shaver is probably going to feel it.

My description of "denting" was probably not descriptive enough.  What I mean is "roughening" of the edge finish due to impact with the stuff being cut:  hair, skin, etc.

My theory might be wildly incorrect.  As I said, I have no experimental evidence whatsoever.  Well, other than noticing that my DE blades get dull when I use them.  ...and that's not much of an observation.  Smile

Here's a good site with extensive razor blade sharpness testing. As usual, Feather blades are the sharpest:
Steve G,
Obsidan knocked edges are 1 molecyle thick - also for 1000 years ago.
The best quality steel cant come below 15 molekyles thicknes what I know...

When you se a grinding stone from the stone age (6000 years ago) they did not sharpen their tools with them, they make scarry sharp edges duller by grind the edge so that the edge is more durable so it hold to work with as long time as possible.

People understood things like this for 6000 years ago...

An edge shall only be as sharp it need to be for its purpouse. Not sharper then that.

Forum Jump:

Users browsing this thread: 1 Guest(s)