bevel angle measured - with and without tape

[cityjim]

Just curious as to the added angle one would get with electrical tape . I read here a couple times that one layer adds like "maybe 0.1 degree or so" . I used 3M Super 33 black electrical tape . It states 0.007" for thickness on the item description .

I measured the bevel angle on four of my straights . They are in 4/8 , 5/8 , 6/8 and 8/8 heights . And I know which ones fade away from being sharp first . Turns out they are the shallow angle bevels . Anyway here goes .

Now one would think a tape at 0.007" thick wouldn't alter the angle much . And was I surprised . One layer of electrical tape adds 2 and sometimes 3 full degrees . Depending on if the angle is almost to the next number or not . Safe to say one layer of tape adds an easy 2 degrees to the bevel . My angle finder has an accuracy of +/- 1 degree . That explains the 2-3 degrees per layer findings .

My 8/8 Henckle Friodur was 15 degrees with no tape . My little 4/8 scrapper was at 12.5 degrees to nearly 13* . You have to pay attention when shaving with this little guy . It will kiss (cut) you in a hurry . The 5/8" blade was at 20 degrees with no tape . That was a surprise . As this edge is super sharp and lasts a long time . This is one of my favorite shavers . The 6/8 was at 15 degrees .

Had to tape up several razors to bring them up to around 17-18 degrees . Resetting the bevels on all my razors now . So far one razor is much much improved in sharpness and edge holding (4/8" scrapper) . The others I bet will be also on my next shaves .

I used an Empire Magnetic Angle Locator . Similar to the one in the picture . Placed it ahead of the pivot pin on the blade . Gently held the blade with my four fingertips flat on my Spyderco UF hone . Made sure the hone was level of course first .

Lastly I measured the 5/8" razor on both sides . One side was 20* with no tape . Other side was 21* and no tape . Little bit sloppy there but what can you complain about for a $25.00 antique store find ?? lol


cityjim

 

[highball]

very interesting stuff..i read on a different site that A piece of 0.006" electric tape is worth 0.92 degrees on a 6/8 razor

 

[cityjim]

Guess it all depends on the razor in question . How thick the spine is and so forth .

I wasn't expecting to see much of any change with one layer of tape . But plain as day I was getting basically a full 2 or more degrees of an increase in angle . Things that make you go hmmmm .


cityjim

 

[mparker762]

If I don't stretch the tape then it will add roughly one degree to a 6/8 razor. And if you do the math assuming 0.007" thick then that's pretty close to what pops out of the equation:

honing angle = 2 * arcsin(spine thickness * 0.5 / blade width along the side)

If I do stretch the tape then it's only about a half a degree - I always stretch because it improves the feel of the razor on the hone. Which is why I claimed that for the Hart a layer of tape would probably add less than half a degree, since it's somewhat bigger than a 6/8.

Also, keep in mind that the tape will wear, so the actual addition to the honing angle will be less than what we're measuring when it's fresh. It's not unusual for the tape to come off the spine worn halfway through where it was touching the hone.

 

[English]

And as the tape wares, the bevel on the edge will be curving ever so slightly.

 

[Seraphim]

How did you make sure that the angle measurementy tool was matching up with the actual cutting edge?

When I calculate tape differences I use a CAD program, measure the spine thickness, the distance fron the cutting edge to the honing bevel on the spine and set up a scale drawing that clearly shows the angle. And what happens when I add a thickness of tape to the spine.

It is remarkable what a difference a single layer can make.

 

[cityjim]

How did you make sure that the angle measurementy tool was matching up with the actual cutting edge?

When I calculate tape differences I use a CAD program, measure the spine thickness, the distance fron the cutting edge to the honing bevel on the spine and set up a scale drawing that clearly shows the angle. And what happens when I add a thickness of tape to the spine.

It is remarkable what a difference a single layer can make.

I took the rather crude approach . I used an angle finder people use making roll cages and such . Placed the razor on the hone and measured across the shank . I measured just as you would hone the edge . Wanted to recreate the angles in a real world situation (honing) .

First picture is the angle finder placed on top of my Spyderco UF hone . Notice the dial indicates 0 degrees .


Second picture is me gently , using my four fingertips holding the edge flat on the hone . Being careful not to distort the blade by presing too hard on it . Then measuring across the shank of the blade . In this picture you can clearly see 7.5 degrees . And when you combine 7.5 and 7.5 degrees you get a combined bevel angle of 15 degrees .

And to see what you get with one layer of tape just add one . I already checked this one with one layer . It increases to 17 degrees . Comes out to a full 2 degrees with 1 layer of 0.007" tape .


Forgot to add , this angle finder has a large magnet on the bottom . It sticks nicely to the shank due to the shank being steel . This helps keep itself flat on the shank .


cityjim

 

[Seraphim]

I took the rather crude approach . I used an angle finder people use making roll cages and such . Placed the razor on the hone and measured across the shank . I measured just as you would hone the edge . Wanted to recreate the angles in a real world situation (honing) .

First picture is the angle finder placed on top of my Spyderco UF hone . Notice the dial indicates 0 degrees .


Second picture is me gently , using my four fingertips holding the edge flat on the hone . Being careful not to distort the blade by presing too hard on it . Then measuring across the shank of the blade . In this picture you can clearly see 7.5 degrees . And when you combine 7.5 and 7.5 degrees you get a combined bevel angle of 15 degrees .

And to see what you get with one layer of tape just add one . I already checked this one with one layer . It increases to 17 degrees . Comes out to a full 2 degrees with 1 layer of 0.007" tape .


Forgot to add , this angle finder has a large magnet on the bottom . It sticks nicely to the shank due to the shank being steel . This helps keep itself flat on the shank .


cityjim

Aha!

OK, now I see the razor is hanging off the hone, and so you get a clear shot at edge and spine. Nice. Thanks.

 

[cityjim]

Aha!

OK, now I see the razor is hanging off the hone, and so you get a clear shot at edge and spine. Nice. Thanks.

Exactly . I placed the edge only on the hone as you spotted .


cityjim

 

[gugi]

calipers is cheaper, far easier, and you get at least an order of magnitude better precision.

with your method you have to ensure three separate planes from completely different objects meet at a line simultaneously - you have systematic errors on the order of few degrees.

 

[cityjim]

Gugi ,

please demonstrate your method for us . Please include pictures of your step by step procedure .

Where are my errors at Gugi ?

The only error I see is the one that is stated on the angle finder box . This being the error of the angle finder itself of +/- 1 degree . But I could be wrong . Wouldn't be the first time lol .



cityjim

 

[GsSixgun]

Gugi ,
The only error I see is the one that is stated on the angle finder box . This being the error of the angle finder itself of +/- 1 degree . The pictures don't lie .
cityjim

Which means in all actuality your statement of 2-3 degrees is outside the error factor of the device... Nothing wrong with yer experiment but the +/- 1 degree on the device is to much of an error factor to begin with

This experiment has been done numerous times with way more exacting measurements and I have found even in my own experiments that it bears out the old findings of between 1/2 and 3/4 of a degree on most razors...with 70 micron tape...

 

[mparker762]

Gugi ,

please demonstrate your method for us . Please include pictures of your step by step procedure .

Where are my errors at Gugi ?

The only error I see is the one that is stated on the angle finder box . This being the error of the angle finder itself of +/- 1 degree . But I could be wrong . Wouldn't be the first time lol .

The angles on both sides of the blade are unlikely to be the same.

The shank is unlikely to be parallel to either the blade or the theoretically perfect blade.

The two sides of the shank are unlikely to be perfectly parallel to each other.

The shank is very narrow, much narrower than the blade itself, and unlikely to be perfectly flat.


All these sources of uncertainty add up. You're much better off measuring the width of the honing flats on the spine at their widest point in a couple of places along the blade, then measuring the distance from the edge to the back of the honing flat on the spine in a couple of places and on both sides of the blade (*not* the distance from the edge to the back of the spine). Average the spine thicknesses and blade widths, and use this to calculate the honing angle.

But for simply calculating the contribution of the tape, a simple back-of-the-envelope calculation with reasonable-but-made-up numbers tells you the absolute maximum that the tape can increase the honing angle for a 6/8 razor is a tad over 1 degree.

 

[cityjim]

Thanks guys for posting on this . I agree with all of the issues that were brought up . About the angles not the same on both sides and so on . I already saw that when I measured the opposite side on one razor . Good stuff .


I can bet NASA would laugh at my setup . But I do get repeatable measurements everytime off this again admittedly crude setup . I remove the razor , reinstall on the hone and the bevel angle is the same .

One thing I did was to turn the angle finder around . To see if the shank was not flat . I got the same measurements of course . Because the shank didn't move duh .


There are many chassis and fabrication shops that use the same tool I use . If it works on a chassis it should be more than fine for a simple razor . If the chassis is not straight then the vehicle dog tracks down the road or becomes unstable .

Since I applied tape to nearly all my razors , the edges have been really sharp and seem to last a lot longer . The ones in the 15 to 13 degree range would get 1-2 shaves then turn into soap scrapers . Now at 17-18 degrees they are still going strong .

Under my microscope I can see the new angle from the added tape . Clearly not the same angle . It's more than obvious to the eye .

Bottom line this seems to work for me . Not much else to comment on .

 

[mparker762]

Razors with very shallow honing angles definitely don't seem to hold an edge as well. The "normal" honing angle for straight razors is generally considered to be 17 degrees, and I've also noticed that shallower angle edges don't last very long, hence my concern about my Hart, though hopefully they've got the right steel and the right heat treating regimen to hold an edge even at that shallow of an angle.

 

[cityjim]

Razors with very shallow honing angles definitely don't seem to hold an edge as well. The "normal" honing angle for straight razors is generally considered to be 17 degrees, and I've also noticed that shallower angle edges don't last very long, hence my concern about my Hart, though hopefully they've got the right steel and the right heat treating regimen to hold an edge even at that shallow of an angle.

+1

What was your Hart at like 13 degrees ? Man that is shallow for sure .

I found another razor at 20 degrees . This sucker shaves and shaves all day long . It is really boooring in a good way because I don't have to do anything to it . Like a quick touch up on the Spyderco UF is not needed . Just strop it a few licks and it's ready . I think the one thing that keeps it going is the razor is borderline heavy . The weight seems to help plow through the whiskers easier .

I agree with you . I find very nice results with the 17 and 18 degree angles . Anything lower , for my beard anyway , just doesn't last . You can see it when you rinse the blade . Nothing comes out but lather .

cityjim

 

[cityjim]

Which means in all actuality your statement of 2-3 degrees is outside the error factor of the device... Nothing wrong with yer experiment but the +/- 1 degree on the device is to much of an error factor to begin with

This experiment has been done numerous times with way more exacting measurements and I have found even in my own experiments that it bears out the old findings of between 1/2 and 3/4 of a degree on most razors...with 70 micron tape...

GsSixgun ,

70 micron tape is the same as 0.0027559055118 inches . Or just say two thousandths thick .

My tape says 0.007" or seven thousandths of an inch thick . So my tape is 3.5 times thicker than yours .

So 3.5 * .5 or .75 (your figures) is 1.75 or 2.625 degrees respectively of an increase . Which is what I was originally stating at 2 to 3 degrees max . The 3 degrees probably has a slight fudge factor in there . But that is what I was reading on my short 4/8 razor . Again an average of 2'ish degrees increase in bevel angle per layer of 0.007" tape .


http://www.onlineconversion.com/length_all.htm


Looks like we found the same thing .

cityjim

 

[mparker762]

GsSixgun ,

70 micron tape is the same as 0.0027559055118 inches . Or just say two thousandths thick .

My tape says 0.007" or seven thousandths of an inch thick . So my tape is 3.5 times thicker than yours .

So 3.5 * .5 or .75 (your figures) is 1.75 or 2.625 degrees respectively of an increase . Which is what I was originally stating at 2 to 3 degrees max . The 3 degrees probably has a slight fudge factor in there . But that is what I was reading on my short 4/8 razor . Again an average of 2'ish degrees increase in bevel angle per layer of 0.007" tape .


http://www.onlineconversion.com/length_all.htm


Looks like we found the same thing .

cityjim

Your measurements are off, no matter how you try to rationalize them. But for the brand of electrical tape you are using - the 0.007" thick tape - the results your machine is returning are physically impossible, or you aren't measuring what you think you are measuring. Or something. Because tape with that thickness will not produce that amount of increase in the honing angle.


I'll do the math for my Hart razor:


Hart with no tape:

S (spine thickness) = 0.185, W (blade width) = 0.81
A = 2 asin (S/2w) = 2 x asin(0.185/(2 x 0.81)) = 2 x asin (0.185/1.62) = 2 x asin (0.01141975...) = 2 x 6.55... = 13.12 degrees.



Hart with 0.007" tape:

S (spine thickness) = 0.185+2x0.007 = 0.199, W (blade width) = 0.81
A= 2 x asin(0.199/1.62) = 2 x asin(0.1228395...) = 2 x 8.056... = 14.11 degrees.



So the amount of angle added by the single layer of tape is 14.11 degrees - 13.12 degrees = 0.99 degrees, which is considerably smaller than the 2-3 degrees of difference your machine is claiming. QED.


If your machine is measuring 2-3 degrees then your machine is wrong, or you are using it wrong, or there are some other sources of error in whatever it is you are doing. Because your machine is telling you that 2+1 = 4.

That number I just calculated is a *maximum* by the way - if the tape is stretched at all when it is applied, or wears at all during use, then the actual difference in honing angle will be less. I have done this sort of measurement on razors that I was actually honing, and found that in practice the difference is more like 0.5 degree for a 6/8 razor.

Edit: And if that tape was on there the entire time from 1k or 2k on up to the 30k hone, then the difference is much less - only a few tenths of a degree - because of accumulated tape wear, which may be the basis for the 0.1 degree number you mentioned having heard in your original post.

 

[r0ckrat]

Additional question only somewhat related... In the image below, the device is measuring both bevel angles together at once, isn't it? The combined angle of the "V" edge on the razor? Not 1/2, or the angle of a single bevel?

 

[cityjim]

Additional question only somewhat related... In the image below, the device is measuring both bevel angles together at once, isn't it? The combined angle of the "V" edge on the razor? Not 1/2, or the angle of a single bevel?

rOckrat ,

One side of the blade only . Just the way the picture indicates .

The combined bevel angle is the sum of both sides of the razors bevel angles .

Some Japanese razors have a single bevel . But those are pretty rare these days . Here is a link to a killer straight .

http://www.japanwoodworker.com/prod...LUI7XY0WT4WQ&pf_id=05%2E001&dept_id=22924


cityjim