How flat does the glass need to be for scary sharp?

[matt_southward]

Hello all, this is my first post - so be gentle

I have lurked on here for a few weeks and have been really impressed by the content and advice, and general banter. Having recently started a re-skilling of my oldish bones (I'm 42) into furniture making I've found the info on here invaluable already - so thanks for that.

Anyway, introductions aside - onto my questions: I received the scary sharp 'starter pack' from Workshop Heaven today (yes I know Matthew posts regularly here) and got out my Veritas straight edge to confirm the flatness of the float glass only to find that it's not flat. As far as I can see it 'crowns' in the middle and my best guess is that it's out on each corner by (in the order of) 0.25 to 0.75mm. How significant a deviation is this in terms of it's use? Should I get an exchange? I picked up a piece of granite tile for a fiver from Topps tiles and that's flatter! I'm completely new to scary sharpening (but it does look good), up to now I've messed about with waterstones - with mixed success.

Thanks, Matt

 

[Phil Pascoe]

Test your straight edge against another one - float glass doesn't deviate that much.

 

[matt_southward]

Thanks for the reply. This is a brand new Veritas steel 24" straight edge - it's been out of the packet for 2 days - do you really think it would be out by that much?

 

[Mike.S]

Suggest you hold your glass against a pane of float glass e.g. in a window. If its flat then it should almost stick to it with suction but any crowning or twist should reveal itself. If faulty then I'm sure Workshop Heaven will be happy to replace it.

 

[Jacob]

Hello all, this is my first post - so be gentle

I have lurked on here for a few weeks and have been really impressed by the content and advice, and general banter. Having recently started a re-skilling of my oldish bones (I'm 42) into furniture making I've found the info on here invaluable already - so thanks for that.

Anyway, introductions aside - onto my questions: I received the scary sharp 'starter pack' from Workshop Heaven today (yes I know Matthew posts regularly here) and got out my Veritas straight edge to confirm the flatness of the float glass only to find that it's not flat. As far as I can see it 'crowns' in the middle and my best guess is that it's out on each corner by (in the order of) 0.25 to 0.75mm. How significant a deviation is this in terms of it's use? Should I get an exchange? I picked up a piece of granite tile for a fiver from Topps tiles and that's flatter! I'm completely new to scary sharpening (but it does look good), up to now I've messed about with waterstones - with mixed success.

Thanks, Matt

You have to bear in mind that scary sharp (and other modern methods) can be a bit ritualistic and obsessive about details. In reality your un-flat piece of glass won't make the slightest difference to your sharpening, but if your tile is flatter why not use it. Anything flattish will do, a piece of mdf frinstance.
Similarly with your straight edge - the closer you look the more inaccuracies you will find. Simpler to make your own from wood; as accurate as you can is accurate enough, but don't look to closely! And it's an exercise in making things straight, independently of bought gadgets and devices.

 

[Cottonwood]

If you want FLAT then I sudgest you get a cast iron AAA grade reference plate off ebay. Otherwise dont worry about it, use the topp tiles. FLAT is like the scarlet pimpernel, elusive, the more you try to find it the further away it gets. :shock: £64.50 for a piece of non FLAT glass and a few sheets of sandpaper..... =D> Well, anything with 3M wrote on it will cost an arm and a leg. Actually I'd be inclined to send the whole kit back, stick with the topp tile and emory paper off ebay, to see if you like that method. That has worked for lots of folk before the £££'s industry took over.....The thing I have found with sharpening is dont worry about it, its not a quasi religious, esoteric existential excercise (homer)

 

[Dangermouse]

I use a piece of polished granite offcut from my local stone mason. Got it for a fiver and then use ordinary wet and dry paper down to 2000 grit, everything I sharpen on that cuts like a laser beam though butter.

 

[Random Orbital Bob]

or.....just get a Tormek

 

[Bigus]

If you want FLAT then I sudgest you get a cast iron AAA grade reference plate off ebay. Otherwise dont worry about it, use the topp tiles. FLAT is like the scarlet pimpernel, elusive, the more you try to find it the further away it gets. :shock: £64.50 for a piece of non FLAT glass and a few sheets of sandpaper..... =D> Well, anything with 3M wrote on it will cost an arm and a leg. Actually I'd be inclined to send the whole kit back, stick with the topp tile and emory paper off ebay, to see if you like that method. That has worked for lots of folk before the £££'s industry took over.....The thing I have found with sharpening is dont worry about it, its not a quasi religious, esoteric existential excercise (homer)

I just went to my local glass works and asked them for a very flat 18x16" piece of glass and they cut me some 6.4mm laminated for just under a tenner which is spot on flatness wise.

My scary system is based on this chaps:

http://www.wwgoa.com/no-tech-sharpening-system/

I already had a honing guide from an oilstone kit I bought for a few quid off eBay, some sheet rubber to stop it sliding around and got some 3M PSA / honing fluid from Workshop Heaven.

Got to assemble it yet but if it works well then I might try to find a cheaper sandpaper than the 3M stuff.

Bigus

 

[bugbear]

Hello all, this is my first post - so be gentle

I have lurked on here for a few weeks and have been really impressed by the content and advice, and general banter. Having recently started a re-skilling of my oldish bones (I'm 42) into furniture making I've found the info on here invaluable already - so thanks for that.

Anyway, introductions aside - onto my questions: I received the scary sharp 'starter pack' from Workshop Heaven today (yes I know Matthew posts regularly here) and got out my Veritas straight edge to confirm the flatness of the float glass only to find that it's not flat. As far as I can see it 'crowns' in the middle and my best guess is that it's out on each corner by (in the order of) 0.25 to 0.75mm. How significant a deviation is this in terms of it's use? Should I get an exchange? I picked up a piece of granite tile for a fiver from Topps tiles and that's flatter! I'm completely new to scary sharpening (but it does look good), up to now I've messed about with waterstones - with mixed success.

Thanks, Matt

You have to bear in mind that scary sharp (and other modern methods) can be a bit ritualistic and obsessive about details. In reality your un-flat piece of glass won't make the slightest difference to your sharpening, but if your tile is flatter why not use it. Anything flattish will do, a piece of mdf frinstance.
Similarly with your straight edge - the closer you look the more inaccuracies you will find. Simpler to make your own from wood; as accurate as you can is accurate enough, but don't look to closely! And it's an exercise in making things straight, independently of bought gadgets and devices.

He''s paid for straight - why should he accept anything other?

BugBear

 

[Jacob]

Hello all, this is my first post - so be gentle

I have lurked on here for a few weeks and have been really impressed by the content and advice, and general banter. Having recently started a re-skilling of my oldish bones (I'm 42) into furniture making I've found the info on here invaluable already - so thanks for that.

Anyway, introductions aside - onto my questions: I received the scary sharp 'starter pack' from Workshop Heaven today (yes I know Matthew posts regularly here) and got out my Veritas straight edge to confirm the flatness of the float glass only to find that it's not flat. As far as I can see it 'crowns' in the middle and my best guess is that it's out on each corner by (in the order of) 0.25 to 0.75mm. How significant a deviation is this in terms of it's use? Should I get an exchange? I picked up a piece of granite tile for a fiver from Topps tiles and that's flatter! I'm completely new to scary sharpening (but it does look good), up to now I've messed about with waterstones - with mixed success.

Thanks, Matt

You have to bear in mind that scary sharp (and other modern methods) can be a bit ritualistic and obsessive about details. In reality your un-flat piece of glass won't make the slightest difference to your sharpening, but if your tile is flatter why not use it. Anything flattish will do, a piece of mdf frinstance.
Similarly with your straight edge - the closer you look the more inaccuracies you will find. Simpler to make your own from wood; as accurate as you can is accurate enough, but don't look to closely! And it's an exercise in making things straight, independently of bought gadgets and devices.

He''s paid for straight - why should he accept anything other?

BugBear

Certainly, send it back. All the kit in fact. And the straightedge. Non of them are needed.

PS Matthew's site says scary sharp is "affordable" which implies cheap.
This is misleading - the system is probably the most expensive of all. Look at the price of honing fluids - more expensive than very good malt whisky!
If you want to spend, spend, why not use whisky as honing fluid? Bells will do, and save you money. 10 YR old Laphroaig is cheaper than Honerite Gold.

 

[woodbrains]

Hello,

Why were you not having satisfactory results from the waterstones?

I agree that scary sharp will be more expensive in time, I think even Workshop heaven mention this at some point. The idea is, though that you can get an ultimate edge quickly and for only a little money initially. Your glass should be flatter than it is, though. The only advantage that I can see with scary sharp is you can always rely on a flat surface as there is no wear involved to the glass, granite, mdf whatever. If it is not flat in the beginning though, all bets are off.

Mike.

 

[Jason]

Unlike water stones and oil stones you can't flatten glass. So you need it flat from day one.

 

[J_SAMa]

0.75mm sounds like a lot. Veritas straight edges should be quite straight as they have good quality control. I'd suggest you find a piece of flatter glass, almost any float glass will work (the one you got is probably a 1 in 100 exception), including mirrors and windows.

That said I'd suggest you move on to sharpening on stones followed by leather sooner or later. Keep using 3M sandpaper and you'll have spent too much money before you realize it. I'd say 2 diamond stones+thin leather with a bar of honing compound. They'll last at least 10 or 15 years
If you don't want to spend that much on diamond stones then go for a Japanese waterstones. A 240/1000 combination stone will cost you half the price a diamond stone does. Problems are you'll have to some something to flatten them (or just buy two separate stones and flatten them with each other) and that they don't last as long.
Sam

 

[matt_southward]

Thanks for all the replies, and different points of view.

I had almost decided to keep the glass as the underside was a bit flatter, but then that meant that it rocked about a bit on the bench :shock: so I will be sending it back after all.

I certainly don't see scary sharp as cheap! The reason I went with it for the moment is partly that I couldn't afford the initial outlay for some diamond stones (which I'd have preferred), and partly circumstantial in that I wanted something fairly quick to set up for the various things I've got to sharpen. I had a bit of trouble with my combination waterstone because of it's softness - I was sharpening whittling knives on it and kept catching the edges, and so it was getting a bit beat up and uneven. Plus I can only just fit my plane irons on it. As I'm using a honing guide at the moment so that I can get some consistent results for the time being - there's not a lot of room on the stone AND I keep having to true it. Also my 'workshop' is actually a spare bedroom so sloshing water about is also a bit of an issue. So scary sharp was really just an interim way of getting my tools ready for work whilst I'm learning all of this. When I can afford it I intend to get some decent quality, decent sized diamond stones, for plane irons, chisels and knives and any 3M paper I have left will be handy for odd shaped sharpening needs.

I wasn't really obsessing over flatness, I was just a bit surprised that the glass was out by so much after all I've read about the flatness of float glass (after a closer look I'd say it's about 0.3-0.5mm out in each corner, though I can't find my feeler gauges to check).

Anyway, it's all part of the learning curve I guess - thanks again for all the input.

 

[Wiley Horne]

Hello all,

Just one small point. Float glass. Float glass is not a specialty glass. All window glass is float glass. That's how they make it. English man named Pilkington invented the process back in the 1950's. Everywhere you look, you see float glass. If you google 'float glass', you find info like this:

http://www.glassforeurope.com/en/indust ... rocess.php

If you go to your local glass shop and get an off cut out of their shorts pile, it'll be float glass. Now there's tempered and untempered--if you can find salvaged glass shelves from a refrigerator, they're tempered. But it's all float.

Wiley

 

[nanscombe]

How about using something like the glass out of a photo frame or would that be too fragile?

 

[woodbrains]

Hello,

But in theory, the molten tin the glass is floated on should be pretty flat due to gravity, so float glass is generally reliably flat enough for what we need. Tempered glas however, has been heated again and cooled rapidly, which makes it less flat. I think laminated glass is probably best, in fact and a bit safer than float if you drop it with wet hands.

Mike.

 

[Cottonwood]

Hello,

But in theory, the molten tin the glass is floated on should be pretty flat due to gravity, so float glass is generally reliably flat enough for what we need. Tempered glas however, has been heated again and cooled rapidly, which makes it less flat. I think laminated glass is probably best, in fact and a bit safer than float if you drop it with wet hands.

Mike.

I've said it before and will say it again, tempered (toughened) glass is never flat because of the way it gets processed in the kilns and cooled afterwards. If you were to put your vertitas edge accross it, you would sometimes almost fit a matchstick in the hollows.
If your getting a laminated float piece, better check what they laminated it in, how FLATT was the press and how even was the pressure to squeeze the 2 panes together to get an even film and elinimate air bubbles. We used a clear UV curing gel adehsive to join glass to glass. Obviously for upvc window applications mega flatness isnt critical, but if you want sharpening FLAT it might be a no no....

 

[matthewwh]

Hi Matt,

I would run some simple tests before you send anything anywhere.

The Veritas aluminium straightedges are only made to a tolerance of 3 thou, if my memory serves correctly. This is quite broad, you couldn't use it to check the flatness of a plane sole for example. Your glass should be substantially more accurate than the straightedge, and neither should be out by as much as 0.75mm so it becomes a question of what is being checked against what?

A third flat thing is needed - your kitchen worktop is probably flat to better than 0.75mm so it will at least be able to point you in the right direction. If you lay the glass and the straight edge on the countertop and apply pressure at one end you should be able to use a feeler gauge (the corner of a piece of paper would do) at the opposite end to establish which of the two items has a big gap under it.

The point of using plain float glass is that it is very, very, flat, at 10mm thick it is also very stiff. Toughened or laminated glass goes through further heat treatment which removes the natural accuracy of plain float glass.