Establishing a steeper primary bevel

[Jonathan Elliott]

Hi, I have a couple of newbie questions as I get started with this sharpening system.  This is my first experience with sharpening blades and I have found Brent's website to be of utmost interest and am excited to get sharpening.  I bought a set of 5 Robert Sorby Excelsior chisels.  They said they come from the factory with a primary bevel of 20 degrees and a honed bevel of 25 degrees.  I bought a Silicon Carbide stone and made a stone vise to do the grinding but I'm wondering how I can avoid grinding the edge while establishing a new 25 degree primary bevel?  Brent always emphasizes grinding just up to the edge but never to grind the edge, is this possible when establishing a steeper primary bevel or do you have to grind through the old edge just the first time?  

Also, for some reason I can't wrap my head around the included angle on the slant jigs. which angle is this referring to exactly?  I made my jigs on the table saw and set the blade tilt to 40 degrees.  I had to run the jigs upside down (the side facing up during sharpening ran against the table saw top) so I'm wondering if that gave me a 50 degree included angle or a 40 degree one?  Hope that makes sense, thanks for the help!!

Jonathan

[Brent Beach]

Hi Jonathan

First, the 25 degree primary applies to plane irons! Chisels can have
much lower primary angles. I have many older English paring chisels that
have much lower primary angles.

So, don't change the primary angle unless the chisels are failing with
the existing angles.

Tell me more about these chisels! Are they coated? TIN? Are they turning
tools? Turning tools have different constraints from ordinary chisels.
Do you have a link to a page that describes your chisels?

The crucial detail about coated tools is that the coating must reach the
cutting edge. Or at least as close as the wear occurs. The basic premise
is that the coating reduces wear. If you home microbevels with these
tools you remove the TIN and defeat the goal.

Now, if you get wear bevels that wear through the TIN then the
underlying premise is false so you can work with these as if there was
no coating. I have not worked with coated tools, so don't know if wear
removes the coating. If it does, the whole deal is snake oil. If not,
the tools should last much longer.

So, short answer - don't change the primary unless the tool fails.

Second, try leaving the coated surfaces unhoned until you know whether
or not you are getting a wear bevel.

Included angle - If the saw is at 40 degrees from the table top, and the
blat of the jig is on the table top, then the included angle is 40
degrees. If you measure the blade angle from the vertical but the flat
of the jig is on the table when cutting, then the included angle is
90-40 or 50 degrees.

Brent

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Brent Beach
Victoria, BC, Canada

[Jonathan Elliott]

Brent, 

Thanks for the reply!  The chisels are bevel edged firming chisels.  I don't think they are coated at all, here is a link to them, they are the 2nd set down on the page:

https://www.thebestthings.com/newtools/sorby_bench.htm

I am using them as an all-around bench chisel, i.e. cleaning out dovetails, squaring up the corners of mortises etc.  I wasn't sure if the 20 degree primary was too fragile for anything more than light paring as I've heard 25 and 30 can hold up much better but I will stick with the 20 for now and see how they perform.  

Would you still suggest a 4-5 degree first micro bevel or steeper?  I want to use a very small back bevel on the chisels as well and the problem I'm running into is making a slant jig with dimensions that will allow me to use my full stone (8 inches) to grind the chisels (3.5 inch blade length) but not leave too large of a back bevel.  How big is too big for the back bevel and is one enough or 2 and 3 better like the front?  Thanks again for your help and for all the information you provide and research you have done, it is truly phenomenal!!

Jonathan 

[Brent Beach]

Hi Jonathan

On 2014-03-30 17:28, Jonathan Elliott wrote:
> Brent,
>
> Thanks for the reply! The chisels are bevel edged firming chisels. I
> don't think they are coated at all, here is a link to them, they are the
> 2nd set down on the page:
>
> https://www.thebestthings.com/newtools/sorby_bench.htm
>
> I am using them as an all-around bench chisel, i.e. cleaning out
> dovetails, squaring up the corners of mortises etc. I wasn't sure if
> the 20 degree primary was too fragile for anything more than light
> paring as I've heard 25 and 30 can hold up much better but I will stick
> with the 20 for now and see how they perform.

These are paring chisels - with those handles you won't be doing much
pounding with a mallet.

I would give them a try at 20 degree primary.

You can do the first honed bevel at 24 degrees and continue with the
usual slips.

If you have some trouble with edge failure you can still leave the
primary at 20 degrees for now but just do the first honed bevel at 29
degrees. In fact, you can work up from 24 until you find an angle at
which the edge is just fine.

I see that these chisels are harder than normal. That may mean more
likely to chip, but only time will tell.

The problems will arise when you hit small knots or when you try to
lever in very hard or very abrasive woods. If you are mostly using clear
wood and it is not one of the abrasive tropicals you should be ok at
these lower angles.

You might also find that with the very small chisels, 1/4 and 3/8, you
can easily exert enough torque on the edge that it is more prone to
chipping. Increase the honing angle there. Even there you won't need a
larger primary until you have used up enough of the chisel that you need
to regrind the primary.

> Would you still suggest a 4-5 degree first micro bevel or steeper? I
> want to use a very small back bevel on the chisels as well and the
> problem I'm running into is making a slant jig with dimensions that will
> allow me to use my full stone (8 inches) to grind the chisels (3.5 inch
> blade length) but not leave too large of a back bevel. How big is too
> big for the back bevel and is one enough or 2 and 3 better like the
> front? Thanks again for your help and for all the information you
> provide and research you have done, it is truly phenomenal!!

You only grind on the stone and never use the stone for back bevels. You
don't need more than 3 or 4 inch range of motion for honing and it is
only when honing that you need a back bevel.

If you are mainly using these for paring dovetails, keep the back bevel
as small as possible - thin jaw as thin as possible and no slips for the
back bevel. In general use, larger back bevels work fine.

Good luck,

Brent

[Jonathan Elliott]

Brent,

Thanks again for the recommendations.  I used the chisels quite a bit today the way they came from the factory (20 degree primary with 25 degree honed edge).  They seemed to work fine, I haven't gotten around to making the sharpening jig yet but have all the sandpapers adhered to glass and ready to go so I'm excited to get sharpening and have a real edge to work with!!

Jonathan