Blade Geometry Help Required

Hi I am a new convert to straight edge shaving and SRP forum and have spent many hours reading through various informative posts on the subject (Great Site BTW!!!)
As I have succesfully shaved a few times now with my (wife's grandfather's) restored ERN Crown & Sword, and a new Dovo Prima I am hooked!

So much so, that after looking around this site, esp. at some of the restores / custom jobs that I would like to have a go myself.
I am an Mechanical Engineer working in the Formula One industry so I know my way around metal working & metallurgy, I do however require a little info regarding blade edge geometry.

I am in the process of scheming up a custom design on CAD, and have a nearly finished design, but I have a few questions regarding the blade / cutting edge geometry.
Attached is a section of blade I have schemed up and wondered if I have my geometry correct for the grinding? (there is clearance between the stiffener and the line between spine & edge so it won't interfere with honing)


Attachment 96804
The 0.15mm edge I am leaving is so I can make sure the grinding opperations do not take off too much of the edge and I can hone that final bit producing a cutting angle of 13°

So main questions are:
1: Do you think the overall dimesions are acceptable?
2: Is a 13° cutting angle too shallow / too steep? (I am planning on using Stainless Steel 17-4PH)
3: Do I need to have a shallow hollow grind on the opposite side?

Many thanks in advance.

Hello, and welcome.
This is quite a broad subject you're asking about, but in a nutshell:

1) I see that you have basically 2 hollows. Keep in mind that after you're done grinding, you need heat treatment. At this point there is still some thickness needed near the edge to prevent warping. After heat treatment, you need to grind again to the final dimensions. Virtually all razors have 1 single hollow that runs right up to the edge. Id start with single hollows if I were you.

2) A 13 degree angle is possible, but I prefer a bit wider angle, 15 to 17 degrees. this is easier to hone, and a bit stronger.

3) If you leave the other side flat, you're going for a japanese style asymmertical grind. Do a search for kamisori and you will find many pics of what that means. Now, the back side should always have a slight hollow, because otherwise it will be a disaster to hone it properly. Razors are hone by laying them flat on the hone, and if the back side is truly flat, it becomes a nightmare to remove any amount of metal.

I don't know the steel you are working with. Keep in mind that you should be able to achieve a rockwell C hardness of 58 to 62. Not less, and definitely not more if you want to be able to hone it. I'm sure I haven't covered all of your questions so feel free to ask away. It is always nice to see people starting to make their own razors.

I would shoot for a 16 degrees total at the edge. Yes both sides need to be hollow. Once both of these criteria are met you can scale the blade to whatever width you want any where from .625 to 1 are within the norm.

Charlie

Edit: Bruno, types faster than me

Many thanks for your comments!

I was indeed going for a Kamisori influence, and thought I would only hone on the one side, hence the striaght back, but may revise that.
Thanks for the advice on angle I will increase the angle accordingly.
My initial plan is to go with a 6/8" blade x 50mm (sorry I'm in UK so SI are my units of choice, apart from blade width of course).

Still a little unsure on what is best Stainless to use as I am going to try something a little different.
I work in F1, so love all things modern, but I also love the traditional side of the SE razor, however I do not have access to a forge, but I do have access to a great workshop.

Therefore I was looking at blending the traditional design style with modern manufacturing, and so I was looking at machining the blank to the desired shape, part grinding, final heat treat, then final edge prep.

I am initially thinking of trying some 17-4PH, which comes in a ready heat treated state, base hardness is ~40Rc it is very strong & tough (we use it for studs all over the car, it has a yield stress >1.1GPa, and I could possibly get the edge shot peened to work harden a little more, but looks like I may have difficulty getting an edge hardness of >58Rc?)

From what I have gathered, edge hardness is very important, but so is toughness, and yield strength so that the edge is not easily worn.
In my experience there are not too many stainless steels with a Rc>45, yet most of the stainless we use is some of the strongest steels around, and most are 38-45Rc, but with yield strengths in excess of 1.2GPa. Do you think this would be acceptable?

If not do you have any suggestions of which Stainless steels could be used, and what heat treatments would need to be applied applied?
(I have also since looked at the Forge section and gathered a lot of info from there, and am continuing to read on.)

Many thanks again, I'm learning so much as I go along!!!

I've tried making kamisori grind razors - 4 so far, 2 turned out usable, but still not "professional" looking. I ground the back side with an 8 inch wheel - 10 or 12 would probably be better. You could try a carbon steel for your first attempts - O1 or 1095 would be good choices. Good luck, and keep us informed about your results. What F1 team do you work for?

AEB-L. ATS34, cmp154 (basically the same as ats34) are all stainless steels that would work. I would use the RC hardness that Bruno recommended. Razors are not really that tough but need to be hard and abrasion resistant.

Charlie

Hint:

Get a traditional Kamisori, Measure, Look, Feel, Shave, ask yourself over and over Why ???

Understand that Kamisori are a different style of razor they are shaved differently and honed differently, I would suggest you learn why that is before making one..

On the other hand you can just jump right into the deep end :)

Well, if you are interested in a couple of prototypes first, then buy some O1 or 1095 or 1084. It is easily available in the UK, and heat treating is easy.
That would get you some experience with machining. 40 HRc is plain unusable for making a razor so don't go there.
The benefit of O1 is that you can do the heat treatment yourself so you have the chance to try your prototypes without incurring the additional costs of shipping + paying for the treatment.

If you want stainless, then ATS34 is a common choice. If you're in the uk it should also be relatively easy to buy niolox in Germany.
Shipping is not expensive, and it is a knife quality stainless. Heat treating recipes depend on the specific type of razor. The people that can sell you a specific type of stainless can also tell you how it should be heat treated.

For tool steels, you can do this yourself with an improvised forge, a magnet and a bucket of oil or water. HTing stainless is more complicated and requires modern equipment.

Cheers for the advice,

I see this as an opportunity to get a decent stainless SE, as my other half will not entertain me buying a another razor after shelling out for a new dovo and having the old one restored (both normal steel).

So if I can get a homer sorted through work at nominal cost of a couple of beers, then happy days!!!
I will see if I can source the stainless you suggest, failing that I will try O1 or 1095 series.

Oh I currently work for Force India.

I will post a CAD representation tomorrow of what I have in mind to see what you think.

Thanks.

Don't forget Bohler. They supply some great steals. In stainless you can use N690 which is heat treatable up to 62Hrc (I'm currently using this steel for straights that I'm also making), or for something more 'high-tech' you could use something like M390 (powder metallurgy) which would work for a razor but it's tough stuff, and you'd have to have access to professional HT facilities to properly follow the HT spec sheet.

Otherwise for high carbon steel you could use K460 which is the same as O1, and as mentioned you can't go wrong with that...

Bohlersteels UK - Tool Steel

Hope that helps.
Cheers,
- Mike

- keen to see what you produce. Machining a razor sounds great, if I had the kit that's what I would do :)

Again many thanks for all your support and advice, it is most apreciated!

Although this site needs to stop giving me ideas, I love all your custom blade designs, and as a result I've just bought a Gold Dollar to make my mistakes on (£2.50 delivered :dropjaw:), & 2x sheffield steel blades to reclaim / modernise <£30 all in and I have a few ideas for mixing the latter with a bit of carbon fibre.

Anyway, I love the look, and tradition that surrounds the Kamisori, and would love to try one first, but my wife would use the Kamisori in un-mentionable ways if I went out and spent the best part of £200 to try it, she better not read this as the new blades could end up the same!

This way I get to have a go at making something very traditional looking, but in a modern way, designed & made by me, will hopefully shave well and will be something I can pass on to my newborn son when he gets older. If it turns out pants, then I havn't lost a great deal of cash, and will still look good in my new collection.

As for the steel, after looking around O1 steel might be the better choice for the first batch (I plan on making 5 in the first match), from what I can see, I can harden and temper it relativley easily at home? (Bohler could be a good source, thanks for the heads up)

Will update in the morning with model and some of my ideas.

cheers.

Dave

Ok as promised here are some images of what I'm proposing:

Thinking on this overnight, I will go for O1 tool steel, as it will be much easier as my first attempt. If it works then I will progress onto more exotic stainless steels, at a later date

first off here is the 'blank' which I will heat treat. (what are your suggestions for edge thickness for this stage?)
I have made sure I will end up with a 17° cutting edge, and the COG of the blade is bang on dead centre, so it should have a nice ballanced feel.

Attachment 96848

and below are some configurations I'm considering:

This one will be polished all over with a 'parachute cord' handle / tang wrap:
Attachment 96849

This one will have a polished blade, satin finished elsewhere, with a carbon wrap applied to the tang, and carbon inlay details in the spine.
Attachment 96850

And finally, this one will be as above, but with viton O rings applied to recesses in tang, and the FWD hole details left open.
Attachment 96851

All comments good and bad are much appreciated.

Regards

Dave

Your designs share a common flaw.
The part of the spine that touches the stone when honing HAS to be free from the rest of the construction.
With this I mean that if you lay the blade on the stone, only the spine should touch, regardless of the exact position of the razor. The tang should never touch the stone.

If you don't design your razor like that, the following will happen:
1) you start honing and remove metal, both from the spine and the edge
2) you will never position the razor exactly the same during your honing strokes.
3) the part of the spine that is not always on the stone will wear down slower than the rest
4) if that part of the spine is then positioned on the stone instead of off it, the spine and edge contact with the stone will be wonky.
5) the blade will wobble during honing, the bevel of the edge will get a slightly different (variable) angle and the razor will never get sharp.

This will make a major difference during honing and maintenance.

Common ways to solve this are to make the spin just a fraction thicker than the tang, or creating a fuller between the tang and the spine. Or something else. You want the spine to be free on the stone (within reason of course) without being hampered by the rest of the blade.
Thickness pre-HT should be 1 to 2 mm.

To clarify my suggestion of a fuller as a possible solution, look at this:
Attachment 96852

This was one of my first prototypes, and it had a problem around the shoulder.
So I used my dremel to grind 2 fullers that separated the spine from the tang.
That way, the spine and the edge can lay on the stone, and if the spine wears down over time, the fuller between the tang and the spine insures that the spine will wear down evenly, thus allowing the edge to always have the same contact with the stone.

The wear is of course very little over time, but with razor edges we're talking about micrometers, and if there is a wobble in the spine, there will be wobbling around the edge. Since the wear is so small, another obvious solution would be to have the spine a hair thicker than the tang at the junction between spine and tang.

Thanks for the advice Bruno, I see what you are saying.

I have left clearance to the tang, so when honing there is plenty of clearance between the full edge and the corresponding spine contact so the tang should not interfere.

I'm not sure if this OK then, as from what I can see, the clearances are not too disimilar, to the clerances between the edge and shoulder on a traditional straight?

If you look closely at a traditional straight (without hone wear) you'll notice that the spine is a hair thicker than the tang.
If the spine and edge are on the hone, you can slide the tang over the stone and it won't make contact.

On razors with bulky shoulders that cannot slide over the stone, the tang usually tapers from the spine in a way that the first bit of the spine near the shoulders doesn't touch the stone.
And on smiling razors the geometry is a bit different of course, but the same principles still apply -> even with small differences in individual honing strokes and wear over time, the part that touches the stone should always be the same.

Cheers Bruno, again advice is taken on board.

Billet of 6x20mm O1 tool steel has been ordered, just need to finish up the blank design so I can get it to the machine shop. (£9.60 for a 500mm length)

I have made a few mods based on the recmendations, and here is the lastest incarnation.
Attachment 96945 Attachment 96946


As suggested I will leave a 1.5mm thick edge on the blank before heat treatment and I will apply a Ø5" shallow grind to the back face, and will ensure I get a cutting angle of ~17°.
I don't want to ruin the overall look I was going for with the tang, nor increase the amount of machining required (less likely to get the homer made!) so I have taken the front face grind all the way out and also added some fullers. Is this more like what is required? or do I need to re-think the whole tang?

Many thanks.

Dave

Hey Dave,
That will work just fine. After you make the fullers, you have 2 ridges between the blade and the tang, according to those pics.
If you file them down just a hair so that they can freely slide over the honing surface without touching it, you will have a very good clearance between the spine and the tang, and you should be able to maintain the razor without any issues.

Btw, since the back of the blade is on the hone as well, you need those fullers on that side as well. You pic doesn't show if they are there or not, so I thought I'd mention it explicitly.

:tu:

Be sure to post pictures of your progress.

Once again cheers Bruno,

Yeah those fullers are indeed on the reverse side as it does the job on that side as you described & helps the aesthetics considerably.
Really excited about this little project now, just need to get the blanks cut so I can get the heat treatment sorted, then I can play around with the design.

You will enjoy shaving with your "own" blade. Gives a sense of accomplishment that relatively few ever know. Glad you chose a well known, quality steel for your first razor, the 17-4 would have been a major disappointment. It was never intended to hold an edge. I would recommend making at least one traditional ground blade out of the bunch. You wont need to change the overall design. Unsolicited advice, sorry.

There is some info on the kamisori geometry on the forum. I am going to study it well when I do a kamisori grind. I am thinking that centuries of experience beat my own enthusiasm. I made my first razor out of an old file and it is a real ugly piece but when sharp it shaves pretty well. It is near to a kamisori, it shaves a little different than the western grind. My goal was to do a test blade to see if I could even grind a razor.

Take your time and have fun.
Jeff

Did I mention that blade was (is) a real hack job. Don't be afraid to make mistakes. I now make my razors at the speed of inspiration.

Jeff

Almost forgot, I left my blades around .030 to .040 inch ( .76 to 1.0 mm) thick at the edge and had zero warping.

Cheers for the info & encouragement.

Well bit of mixed fortunes at the moment, I have 2 lengths of steel on my desk, ready & waiting, CAD drawings complete, but the guy who was going to do the machining is flat out with updates for the next major car upgrade, so looks like he will only be able to machine 1, maybe 2 blanks and it wont be for a while. (but hey ho, patience is a virtue)

Apart from that I have sorted out the final geometry, so that I will only need to grind the back face on a 6" wheel and this will then give me the clearance as suggested and will leave me with a final 17-18° honed edge.

I have also sorted out the heat treatment which I should be able to do at home. I can source some tempil sticks (Temperature indicators) which should enable me to use a propane torch to heat up to 800°C accurately, and then I can temper the blade in the kitchen oven (when the wife is out of course ;) )

Will be intersting to see how it all turns out, at the very least I will end up a nice looking blade that will just go on show, but in an ideal world it will look good and shave like a spanking new Dovo, only time will tell.

I kno this is an older thread, but just wondering if there were any updates? Also, I doubt you will be able to HT the O1 in open air with a propane torch, or even MAPP gas for that matter. optimal heat treat of O1 requires a soak time of 15-20 minutes at temperature, it will give an ok hardness with just a couple of minutes at temp and quenched in Canola oil, but I suggest you look up coffee can forge and two brick forge for simple inexpensive forge design which will help you get the most out of your propane torch. Have the oven pre heated to your tempering temperature (400-450*F) and immediately after quench and cooled down to 300*F or so go striaght into temper. 2 cycles of 2 hours each.

I am currently making my own kamisori from 1084 and just about done sanding before HT. Also, sounds like you are relying heavily on modern machinery, you know these things were around long before CAD and CNC... :D. Grab a file and hacksaw, some elbow grease and a six pack of your favorite brew, then have at it! Nothing wrong with a machined razor, but there sure is somethin special about a truely hand-made piece.

BTW, I learned a lot of valuable info from this thread!


-Xander

Quote:

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Originally Posted by fast14riot

I kno this is an older thread, but just wondering if there were any updates? Also, I doubt you will be able to HT the O1 in open air with a propane torch, or even MAPP gas for that matter. optimal heat treat of O1 requires a soak time of 15-20 minutes at temperature

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+1 My first time with 01 I failed with a torch. One of our generous razor makers offered the advice that 1095 was better for torch ht, or as I now call it "hillbilly heat treating" lol