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artisteric

CGF, Certified Grumble Framer
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Michigan
I've spent the last 30 minutes mulling over previous posts on the best sharpening methods.

Most of you swear by hollow ground sharpening, and some of you swear by flat ground sharpening.

So what's the verdict? What does Morso say about how to sharpen their blades? I know Tech Mark automatically does hollow without giving an option. Is it a conspiracy? Do they want your blades to dull faster for more business?
 
I'm sure someone will tell me I'm wrong but isn't a hollow ground a sharper edge and a flat a more durrable edge? So it's just up to you as to what you want?
 
Sharper??? You should be able to shave with both, if the sharpening houses are any good.

Some houses are "we do it all".... run. and take your blades with you.

A "Bed" grinder slowly makes passes back and forth and the bed is dead flat. The angle for our blades is 30 degrees... which is the most optimum for strength, and a shear-slicing cut. Any thing less, creates a thinner blade and a sharper angle.

The sharper/thinner blade angle is great for a razor blade, but for mashing your way hundreds of times through lumber, and paint, and compo[stone] it takes strength and durability.

What happenes on a hollow ground is the leading edge heats and anneals [which is a softening of the micro edge] and the micro leading edge mashes down.

On a flat ground, the "body" which is thicker right behind that micro edge doing the actual cutting, acts as a heat sink and vibration sponge... leaving the micro edge to remain cooler and stronger...[read in here: sharper] and thus productive longer.

A small bed grinder costs about $20,000 and a wheel grinder and traveling jig... about $500...

Heat.. is the other concern here... a wheel grinder, unless it is a water wheel, will over time anneal the entire blade due to heat build up in the grinding.

ALL bed grinders are slow and water cooled to wash the slurry off the grinding surface.

It's your money.
 
Right what he said.

My guy does both but suggested flat for durability. He is about 100 and he and his dad work 6 days a week in the same shop his dad started in his 20's. When you ask, "Can you sharpen ________?" His responce is always the same. "Was it sharp when you bought it? Then I can resharpen it."

Why should I fear this guy Baer?

I have no complaints with him plus he does it same day and charges $5 a set.
 
Jay, Be afraid, be VERY afraid.... this guy will suck out all the stupid in your brain and insidiously instill intelligent honest education.

....and you will never be the same again.

You are so lucky to know this guy.

I had his estranged uncle back when I first started really finding out about glass and mirrors....

This guys grandfather had started Crown City Glass in Pasadena, CA. Charlie had learned at his Grandfathers knee because his father was to busy working.... and when I came along his son and grandson were running the place so Charlie could grind a 3" bevel on a 1/2" thick glass then mirror the back....ANY kind of mirror.

I once took him an old 1850s Chippendale frame... he looked at it, and asked, "is this still hanging in the front hall of the O'Conners place?" yup.

"OK, then I'll have to age the mirror, Daddy replaced that back in the early '20s... it had a 3" bevel with crystal notching on the crest."

[turned out he was close friends with Joe O'Conner and had always admired his Grandfathers work] I picked up the new mirror the following day.... he had worked most of the night.
 
Greetings:

Here is some info about sharpening chopper blades:

http://www.tech-mark.com/sharpen.htm

http://www.tech-mark.com/morsochopperinfo.htm

So these folks advocate hollow ground blade sharpening. They say it is what is recommended by the manufacturer.

I tend to believe that a hollow ground blade is sharper. Sharpness is due to the thinness of the edge. A flat ground blade at 30% vs. a hollow ground blade at 30% can not physically be thinner and therefore not as sharp. However, does it really make a difference? I don't know. Maybe flat ground is sharp enough.

Durability? I would tend to agree that flat honed blades should stay relatively sharper longer since the edge is thicker. I am not sure why the manufacturers recommend hollow grinding.

Okay. Heat? Annealing the blades through use? Baer. You must be one hellofa chopper **** if you can heat your blades up to the point of rendering the metal!

Annealing is used to cause the metal to be less brittle and more workable so it can be more easily shaped while cold. It is a heat treatment process whereby the metal is heated to extremely high temperatures and then slowly cooled in a controlled manner in order to cause the atoms to settle into certain patterns and structures. This creates a soft structure and large grains with poor toughness.

Once a metal is worked or machined, it is then normalized. Here the metal is heated and then allowed to cool relatively quickly in air creating fine grains with uniform structure.

The metal is then tempered. Carbon is released from the nucleated areas, allwoing the sturcture to deform and relieve some of the internal stresses. This somewhat reduces hardness, yet increases toughness.

So... I really don't believe that the metal, even the micro fine edge of the blade will acutally become softer with use of the chopper. Yes, it could and does become dull, but this is not really due to extreme heat and annealing, rather simply reshaping of the micro edge through blunt trauma. Minute particles of the sharp edge are deformed and reshaped each time the blades strike the moulding.

So is the jury out? Do we really want our chopper blades to be flat or do should we be having them hollow ground?

I like your Mirror story!

Warmest aloha,

Bill
 
Here is a really simple diagram showing the difference, as I understand it.

hollowground.jpg


In flat ground, the blade is sharpened on a flat surface. You can see that the bevel has no arc to it.

In hollow ground, the blade is sharpened on a round surface. So you see the exaggerated arc.

The edge is most certainly sharper on hollow ground. It also cannot last as long. I'm guessing that the morso people aren't as concerned with how often you have to sharpen your blade as they are wanting you to have sharp blades. Like Baer pointed out, we do chop all kinds of materials.

If I were paying shipping+$30 a pop to have my blades sharpened, I certainly would opt for longevity over sharpness that can't be that drastic in the first place.
 
The first time I sent my blades into Tech Mark, they hollow ground sharpened them from a previous flat ground sharpening without asking me first. Cost me an extra $30

Is this all they do??

I think I understand now, the cut with a HG blade is sharper but the edge wont last as long as an FG blade.

My blades are on their way to Tech Mark right now, should I call them and ask them to FG sharpen my blades? I really don't mind pressing harder on my chopper pedal to get a cut, I just wanna save money! don't we all?
 
The joys of being the boss. Wouldn't it be nice if there was a book called "The Correct Answer to Every Question You Will Ever Ask as a Frameshop Owner."

If I were in your shoes, I'd leave the order as is. I don't think there is a huge difference either way.

Carry On.
 
artisteric,

Just by asking that question, I think you know the answer.. You now know how long the sharp lasts on a hollow ground... so try the flat and find out which seems to work for you.

Personally, if I sent my FGs to a company that didn't FG but went a head and HGed them, then charged me an extra $30 surcharge.... I'd never be sending them another piece of metal.

But I'm just picky that way.

I have a Tormek grinder and I grind my own planer and jointer blades. The Morso will fit in my jig just fine..
but we still send those knives to the knife grinder because all they do is Flat. They also will also make blades.. think about the tool steel morso, the next step would be Carbide... but too brittle... so the next hard and tuff is A-11... and they say it will retain the edge 3x longer... then there is the all time great A-4 but the sharpening is 3x but if you only have to sharpen them once or twice a year...: :D
help.gif
 
FG vs HG is tough to compare, because they are two different processes, and the comparison is often one process by one vendor with the other by a different vendor. However in my experience, having our blades FG by three or four vendors over the years and then switching to TechMark's HG, we have found (by keeping close track of chops/sharpening) that the HG not only does a better job, but they last more than twice as long. Again, that is TM's HG cuts better and lasts more than twice as long as X,Y,Z & Z2's FG.

As for TM HGing FG knives, AFAIK they only HG and it's their (written?) policy to charge extra the first time if you send them FG knives.
 
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