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Good way to sharpen a bench shear


#1

I am wondering if there is a good way to sharpen a bench shear. I am
helping set up a ‘beginner’ metals lab at Miami University in Oxford,
Ohio, where I teach in their Craftsummer program each summer. A shear
available to us has been well used, perhaps abused, and is sorely in
need of blade sharpening. This facility is aside from the undergrad
and graduate student metals lab, and with budget constraints we are
not able to purchase everything new. Thanks for any help anyone can
give…

Thanks,
Ginger Seiple


#2

Hi Ginger,

I can’t remember who’s teaching at Miami in the main program, but my
memory is that there is still a real program. You might ask
whoever’s there where they get their blades sharpened.

First and best option is simply to pull both blades out of the
frame, and take them to a tool & cutter grinder. They’re a company
that resharpens industrial tools. There’s got to be one down in
Dayton, and I know there were several in Columbus when I lived
there. That’s what they do for a living, and they’ve got the gear to
do it right. Probably about $50 or so. (Look for industrial drill
bit and end mill resharpening services. )

You might also call local printing companies, and ask them who
resharpens the blades for their paper cutters. Same guys, same gear.
They probably won’t know it’s the same sort of deal, but if you
show them the blades, they’ll figure it out. (Industrial paper
cutters go through a couple of blade sets a year, while metal shears
go years between regrinds, if they ever get reground at all, so
they’re not as familiar with them.)

The guy in the next industrial bay over from Knew Concepts is a
cutter guy, and he does outstanding work, if you feel any real
urge to ship your blades to California. (Seems silly to ship them
all that way, but if you want to, contact me directly.)

Getting the blades back in and shimmed correctly will be fun, but it
shouldn’t be too hard.

Next option would be to pull the blades, and very carefully touch
them up on a belt sander. Make sure you copy the angle of the
short side (edge) of the blade, and only grind the edge of the
blade, not the faces. The edge is the thin side that forms the
thickness of the blade. It’ll be tilted down at an angle. (Probably
somewhere around 5 degrees.) That angle’s important, so make sure
you set the belt sander’s table to match it. Do NOT try to
hand-hold this. Set the table, and use it as a guide to make sure
the angle stays even. Take a grinding pass, then dunk the blade in
water. Rinse, repeat. The goal is to never let the blade get hotter
than what’s comfortable in your bare hands. If it gets overheated,
it’s ruined. (overheated too hot to hold, or if you see any hint of
rainbow colors.) (It’ll be way too hot to hold before the rainbow
colors show up, but if they do, you’re cooked.)

If it’s a guillotine shear, it’s important that you take one smooth,
continuous pass across the blade, so that the top stays straight,
with no nicks or dents. If it’s a plate shear that has curved
blades, just remember to echo the curve that’s already there, and
don’t leave nicks. For something like this, I’d probably use a 120
grit belt. A worn 120 if there’s not much to come off. Make sure
it’s grinding well before you risk your blades on it. Practice on
scrap first.

If you’ve done it (or seen it done) once or twice, it’s not hard,
but that first time can be a real ‘learning experience’ if you’re
winging it.

For whatever that was worth,
Regards,
Brian


#3

OK, you are looking for a “grinding” shop. You can ask at any local
machine shop for These are specialized shops that grind
flat surface. Sharpening is there game. You will have to take the
blades off. That said, shear blades are usually reversible. The side
against the table and upper mount may be brand new and never used.
Removing the blades and either sharpening or reversing will require
figuring out how to set up and adjust the clearance. One unadjusted
whack can ruin the blades!

You can also check with local sheet metal shops. The guys that make
duct work for heating and cooling. Ask about traveling services that
come to those shops and sharpen and adjust on site.

Good luck, Bill
Bill, Deborah, Michele & Sharon
Reactive Metals Studio, Inc


#4

Hi Brian,

Thanks so much for the you provided Re: sharpening a
bench shear. I knew it had to be grinded with precision to be done
correctly and you have given me what is necessary to do the job. I
clearly understood your directions and appreciate you taking the
time to be so thorough. You, like Ganoksin, are a good deed doer!

And yes there is still a real program at Miami, with the amazing and
talented Susan Ewing still chairing the dept. Geoff Riggle runs the
undergrad and grad labs, where I teach my classes. The studio we are
equipping is for the new Art Center that is part of the Craftsummer
Program, which now needs to be self-supporting. This studio will
allow members of the art center a place to learn and practice their
metal art all year long. Thanks again.

Sincere regards,
Ginger


#5

Hi Ginger,

Thanks for the vote of confidence. One note though: I was assuming
you probably had a bench shear, rather than a big floor shear. The
floor shears have very long blades, and those really are best done by
pros.

I got talking to another orchidian about shears privately, and I’ll
append my comments about putting the blades back on to this, they may
be of some use to you.

Regards,
Brian


#6

Hi gang,

For reasons best known to Hanuman, my comments about how to
re-attach the blades got chopped off of my last reply, so here they
are again.

Getting the blades back on is fiddly, but it’s not rocket science.
The big thing to do is to make sure you don’t try to stomp the
blades until you’re sure that they won’t crunch into each other.
It’s better to start out with too much of a gap between them, and
work your way in until they’re tight enough, in a couple of passes
if necessary. The gap between the blades is the critical bit. If you
don’t have a feeler gage, they don’t cost much. It would probably be
a good idea to use a feeler to figure out what the current gap
between the blades is before you dismount them. Then adjust them
back to whatever gap that is as a starting place when you put them
back.

Depending on the gage of metal you’re trying to cut, the gap gets
smaller and smaller, until it’s eventually down to almost nothing.
Almost nothing being on the order of 0.001". The smaller the gap,
the better it handles thin metal. Thin metal bending over and
jamming in the shear may not be a function of the blades being dull,
it may just be a function of the gap between the blades being too
large. The problem is that if the blades actually ram into each
other, they trash themselves instantly. So close is good, but too
close is a disaster. For thicker metal (>14ga, the blade gap needs
to go up, so if the shear was set up for thicker steel to begin
with, the blade gap may be set too wide for thin silver.) The other
problem is the quality of the shear. The old DiAcros are built like
tanks, so when they take a bite, the upper blade stays perfectly
aligned. Some of the cheaper knockoffs we’ve been seeing lately are
lightly built enough that the upper blade flexes out of alignment,
which causes it to hit the lower blade. What it really causes is the
blade gap to be set wider so that the upper blade doesn’t hit the
lower one as it flexes. Which means that the shear can’t handle thin
metal very well. If it’s a newer, less robust shear, pay attention
to the current setting of the blade, and work your way in tighter
only as you test it to make sure the upper blade won’t flex into the
lower one while cutting the thickest stock you plan to use.

Does that make any sense?

PS–> Remember: longer blades are actually large pieces of
spaghetti. All of those set-screws that attach them to the frame are
important. It’s very easy for the blades to go back on warped.
Which means that the blade gap may be just fine on the ends, but
totally out of whack in several spots along the middle of the blade.
The thinner blades on the newer (cheaper) shears make this
especially likely. Remember to check the whole length of the blade,
and to adjust all the screws individually if they need it.

Regards,
Brian