Illustration of Safety Razor Parameters (Blade Exposure, Guard Span, Blade Gap, Etc.)

Discussion in 'General Shaving Discussion' started by ShavingByTheNumbers, Oct 17, 2017.

    While some safety razor parameters have been generally illustrated before, here at B&B and elsewhere, a more comprehensive picture has now been created.


    The general illustration above shows the blade and shave planes and the parameters that follow around the blade cutting edge for a blade loaded in a safety razor: blade angle, handle angle, blade exposure, guard span, cap span, blade gap, free-end distance, clamp distance. Free-end and clamp distances were measured for the first time with my photo analysis of the Edwin Jagger (EJ) DE89 head (B&B URL). Important details that could not be simply illustrated are included at the bottom of the picture. For example, I rigorously define blade gap based on personal experience in measuring the quantity with my accurate set of micrometer-measured feeler gauge blade combinations (B&B URL).

    Blade gap is commonly associated with razor aggressiveness, but, at best, blade gap only loosely relates to razor performance. Blade exposure, guard span, and blade angle, on the other hand, are very important performance parameters with respect to aggressiveness and efficiency. Unfortunately, these three parameters are not easily measured. Photo analysis is the primary method for measuring the illustrated parameters, but physical measurements, such as for blade gap, should be used when appropriate to complement or supersede digital measurements. The illustrated parameters around the cutting edge apply both to double-edge (DE) and single-edge (SE) safety razors. The first note in the picture about using a blade with a nominal width for analytical purposes therefore applies similarly for DE and SE razor blades.

    The illustration included here might be updated in the future, and if that happens, I will update this thread accordingly. Regardless, it is hoped that this picture or an updated version will become the premiere reference illustration for safety razor parameters around the blade cutting edge.
  1. Very useful illustration! Thank you very much! :thumbsup:
  2. Should be stickied in above group
  3. I'd suggest adding that pic to the wiki entry here: Blade Angle
  4. Terrific illustration! Thanks.
  5. You're welcome. Thanks.

    I'm honored. Thanks.

    That's a good idea. Thanks.

    You're welcome. Thanks.
  6. Yep, should be stickied.

    Sent from my iPhone using Tapatalk
  7. Thanks. As expected, I'm already aware of things that need improving with the picture---thanks, @Cal---so if you or anyone else have recommendations, please let me know. If a sticky were applied, I'd rather have the updated picture at the top, but the only way that I know how to do that is to start a new thread. I don't see a way to edit the image and replace it with another. That would be nice to do.
  8. I love the work you've done on this!

    I'd love to measure each detail and mock them up in a CAD program, but I don't think I have time for that. I have calipers/mic/feeler gauges; but is macro photography the best way to gather info?

    I have a lens tube for my DSLR, but as you've discovered the setup is a huge pain and ensuring you've got a consistent perspective is going to be essential to getting consistent/reliable measurements with a camera. I have a flatbed scanner, and I think that might be more reliable... but I'll do some testing.
    Last edited by a moderator: Nov 10, 2017
  9. Ad Astra

    Ad Astra Ambassador

    Absolutely awesome data, and a labor of love in the service of the shaving public.

    Kudos and BZ!

  10. The stewards can sticky posts. But they try to keep stickies to a minimum. Stuff that we want to preserve is better left to the wiki.
  11. Thanks, AA. :001_smile
  12. I get that. The blade angle page (link), as recommended above by @TheVez2, looks like the best place, but I couldn't figure out how to get there in the ShaveWiki or from the main safety razor page (link).
  13. Great picture, thanks! One parameter I'd be interested in might be called the "contact angle range": For a razor with positive blade exposure placed on a flat hard surface, the range of angles for which the cutting edge makes contact with the surface. A function of blade exposure, blade angle, blade gap and guard span. I suppose. The reference surface could be slightly concave to allow results for razors with negative blade exposure.
  14. I'm already working on an update that includes steep- and shallow-angle shaving, if I can include it. As far as how angles and spans change with that, which depends on the specific razor, I showed that with my recent analysis of the EJ DE89 head (link). A curved reference surface is something that I've thought about before, but I can't justify using that different reference surface for the analysis.
  15. Yes, you're way ahead of me. Somehow I'm not surprised. ;) One reason I'm interested in this parameter is that I'm now routinely using a razor that has much larger positive blade exposure, but also much larger cap span, smaller blade gap and (I assume) smaller blade angle than the DE89 or the similar Merkur 34C. The result is, you can shave with a slightly more shallow angle than you can with the DE89 style, but also with a much steeper angle (and cut your face to ribbons in the process if you're not careful). That greater "contact angle range" is what I think of as more aggressive.
  16. From the main page, under intro, click on Interactive guide to DE Shaving : Interactive Guide to DE Razor Shaving

    Then under DE Shave, click on The importance of blade angle: Blade Angle
  17. Blade angle range from steep- to shallow-angle shaving does relate to aggressiveness variation, but scaling down the razor profile size makes smaller spans and exposure while maintaining the same angles, so the "contact angle range" would stay the same, but razor aggressiveness would go down. I get what you're saying, though. The larger the spans and exposure, the more variation you get with performance between steep- and shallow-angle shaving. It is very important.
  18. That's hard to find. Earlier, I was at the Interactive Guide page, but I didn't see the "importance of blade angle" link. Also, blade angle is important, but one could argue that blade exposure and guard span are just as important, even more so under normal circumstances since they vary a lot more than blade angle. The blade angle page focuses on changing the blade angle through handle angle changes with a given razor and blade, which is great and important information. I don't want to mess with that. I wouldn't mind my illustration being there in the least, but my illustration belongs more with a general page about razor geometry and performance, which may or may not exist.
  19. August West

    August West Moderator Emeritus

    Remember that the angle of approach on re-entry must be precise or the capsule will ricochet back out in space.

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