Steel flatness and bevels

[Don Hanson III]

I received some 1084 and some 1095 from Aldo a month or so ago. Both have a very good surface. I still don't have a real grinder yet besides the 1 x 30 and the house needs a new roof, etc., so I was really pleased with the surface cause I'll be doing a lot of hand work. The 1 1/4" bars seem to have been cut on a band saw. The only rolled edges I've seen are on the ends of the bars. The 15" wide plate of 1095 is the same as the bars of 1084 with rolled edges only on the ends of the plate.

Cool. Strips saw cut from sheet are goin to be pretty flat. All the 1084 I have from Aldo is hot rolled bar stock, was from his first 3 batches several years ago.

 

[P.Brewster]

Also the 0.001" is kind of a mythical number, some of the best surface plates you can get are only guaranteed to 0.003

No, nothing mythical about 0.001", and no, most granite surface plates are far more accurate than 0.003".

"The flatness tolerances for three standard grades are defined in the federal specification as determined by the following formula:
Laboratory Grade AA = (40 + diagonal squared/25) x .000001" (unilateral)
Inspection Grade A = Laboratory Grade AA x 2
Tool Room Grade B = Laboratory Grade AA x 4."
(http://www.tru-stone.com/pages/faq.asp#question4)

If we look at Starrett's spec sheet here http://www.starrett.com/docs/data-sheets/tru-stone---bulletin-807.pdf?Status=Master, we see a AA-grade 30" diagonal plate is flat to 35 micro-inches or 0.000035".

 

[newdebate]

That looks like it was slit to width. Could have been cut off a surplus coil of lawn mower blade stock.

Wow, a lot of varying opinions. At this point I have no idea what the suppliers tolerances are but I will be checking this before ever buying another piece of steel...

Here's an example of what the majority of the steel looks like. I ran this one on few passes across the platen to help show the high/low spots...

The cup is plainly visible without a straight edge while looking down the length of the bar--I'll try to get a decent picture of it this evening. I did manage to grind this piece down flat and took off roughly .010 until the cup was gone. I know my grind technique is far from perfect but I'm assuming cupped steel like this will cause evenness problems while grinding the bevels (unless I grind it flat, of course...) ?

 

[John Katt]

No, nothing mythical about 0.001", and no, most granite surface plates are far more accurate than 0.003".

"The flatness tolerances for three standard grades are defined in the federal specification as determined by the following formula:
Laboratory Grade AA = (40 + diagonal squared/25) x .000001" (unilateral)
Inspection Grade A = Laboratory Grade AA x 2
Tool Room Grade B = Laboratory Grade AA x 4."
(http://www.tru-stone.com/pages/faq.asp#question4)

If we look at Starrett's spec sheet here http://www.starrett.com/docs/data-sheets/tru-stone---bulletin-807.pdf?Status=Master, we see a AA-grade 30" diagonal plate is flat to 35 micro-inches or 0.000035".

Do you know anyone who builds knives to those specifications ;0)

also I apoligize, I seem to have forgoten a zero when I made my statment about .001 it should have been .0001

 

[Don Hanson III]

That looks like it was slit to width. Could have been cut off a surplus coil of lawn mower blade stock.

Sheared from plate. But have seem a little cup in HR bar stock.

I think Aldo is coming out with a line of 1084 lawn mower blades.

 

[John Katt]

I think Aldo is coming out with a line of 1084 lawn mower blades.

Exelent that will go nicely with the Hayabusa engine upgrade I just put in my John deer ;0)

 

[Nathan the Machinist]

Sheared from plate. But have seem a little cup in HR bar stock.

I think Aldo is coming out with a line of 1084 lawn mower blades.

...that's really not a bad idea...

 

[newdebate]

A shear produces alternating burr-up and burr-down edges. Steel slit through an arbor of ring knives has the same direction burr on both edges, as in the photo.