Hardening mower blades

My father has recently made up a press to press out mower blades. I
was just wanting to know if you had any on how we would
go about hardening them Any that you could send would be
most helpful. Darren McGinty

Darren: Not too many lawn mower blade technicians on this list. If
you have a large enough torch and a big enough bucket, I suppose it
would be possible to temper the blade but if you don’t do it just
right I would be affraid that the blade might become too hard and
thus brittle. Hit a rock or a root and snap, the blade goes flying.

Tempering is done by heating the metal object to a bright orange
color and then quenching it rapidly. Then the item must be sanded
down to bare metal (so as to see the color change), reheated slowly
and softly to soften the metal. Tools are usually heated to a straw
yellow at their bussiness end. I have no idea what color you would
look for on a mower blade.

PS. Sorry i forgot one more important thing. When the metal turns
straw yellow it must be quenched quickly.

Hope this helps
Michael R. Mathews Sr.


How you harden and then temper the blades depends on the type of
steel you are using. Typically when making tools you first heat the
steel to the "critical temperature"which, if I recall is the point
that a magnet will no longer “stick” to t he steel. Be very careful
to heat evenly and to not overheat. If it looks like a sparkler,
you’ve heated it too much and it is better to start with a new piece
of steel.

If I remember correctly, with the 1095 steel I used to make some
wood carving tools I did the following:

I heated the steel to “critical temperature” and then let it cool
slowly to anneal it. If a file “bites” it is properly annealed.

I then ground and sharpened it to a "pre-honed"stage. Be careful to
not overheat it during this process. A good rule of thumb is to keep
it in the quenching water as much time as it is on the grinding

When it is shaped and sharpened to a “pre-honed” stage (ready to put
a final sharpening on it. If too fine an edge ) , it should be
hardened. Again, bring the steel evenly to the “critical temp”. (be
careful not to burn the thinned, sharpened edge) Immediately plunge
the steel in oil. I used mineral oil. Make sure to completely
submerge the steel and swirl it around so it cools evenly. If the
oil ignites, put a lid over the bucket to extinquish it.

Test the hardening. A file should not “bite” into it now. If it
does, repeat.

If fully hardened, it should now be tempered. (draw some of the
hardness out) It should be tempered according to its use. Some tools
can be much harder than others. I would think for a mower blade, it
should be on the softer side. Maybe, about what an axe would be. It
takes a lot of abuse and you don’t want the edge to crack. You should
be able to find a tool making text that will give you the specs for
the type of steel and tool. With the 1095, I put it in the oven and
brought it up to about 450degrees. This drew out about t he right
amount of hardness so I could easily sharpen the knives on a stone
but they would hold their edge.

I hope this helps. I found a couple good books with color charts
and temps for various types of steel and tools.

Don’t pretend to be an expert but this worked for me. Good Luck, Chris
in Rainy Ketchikan, AK

    My father has recently made up a press to press out mower
blades. I was just wanting to know if you had any on
how we would go about hardening them Any that you could
send would be most helpful. Darren McGinty 

Darren, this is a tricky thing to do correctly. First, let’s
clarify (a word I use too much). You will HARDEN then TEMPER the
blades. Hardening is just that, and tempering is a removal of
enough hardness to reduce brittleness and improve toughness. Also,
although critical temperature can be approximately guaged from the
loss of magnetism at heat, this is not an accurate judge of the
transition that steel undergoes when it reaches the right
temperature to be hardened. Also, the liquid used to quench the
steel (cool it quickly form red hot to black) must be appropriate
for the type of steel being used. Oil is right for some, water for
others, and still others must be left to cool in air in order to
harden properly. Tempering must be done to the right degree for the
tool, as already stated in another post, and the time and
temperature of tempering should be carefully considered. The best
thing to do, in my opinion, is to find out what kind of steel you
are using for the blades, and follow the maufacturer’s heat
treatment instructions, or search the web based on the type of
steel, ie: O-1, 1095, ATS-3400. Having said all of this, you can,
and many others have, acheive acceptable results just "eyeballing"
all of these factors…but with something as potentially dangerous
as a shattered mower blade to look forward to, why not do a little
home-work? You might find steel metallurgy as fun and fascinating
as I do… Good luck. Danny Rondeau

            My father has recently made up a press to press out
mower blades. I was just wanting to know if you had any information
on how we would go about hardening them Any that you
could send would be most helpful. Darren McGinty 

Darren, first, what your asking about is more in the realm of
industrial fabrication and manufacturing. I would suggest that you go
to the library and ask at the reference desk about a set of 20 or so
books called the Th omas register. If you can think of something,
this book will have a listing of companies that make or sell it,
even jewelry. You will find companies that specialize in hardening
and tempering so tha t the blades that your dad makes will be
uniformly hardened. Have you thoug ht about what will happen if an
improperly tempered blade hits a rock at hig h speed? In this day
and age of lawsuits you will want very good liability insurance.
there will also be listings of companies that sell this type of
coverage. I use this register sometimes when I am brainstorming
about a project. I hope I gave you some good advice and directions
to go. good luck!

Honorably, Gerald A. Livings

Hi Darren, My wife mentioned this topic and I am writing you under
her email address. My email is Montana@nucleus.com .

The way I would proceed with this project is to fabricate a method
of producing the blades out of a grade of steel that is hard enough
to hold an edge for several months, but soft enough to facilitate
ease of working. This would not be even close to brittle.

Should I still want to pursue a longer lasting edge, I would ‘also’
offer a premier grade of lawnmower blade which is a standard blade
with hard surfacing steel melted on to the cutting surface either by
a torch or a plasma spray. This is how some gears are constructed.
That way the surface offers years of wear without the gear having a
brittle characteristic.

Regards, Dan Bahr Technical Support Inc. Power, Control, &
Mechanical Solutions Karen Bahr “the Rocklady”
(@Rocklady) K.I.S. Creations
May your gems always sparkle.