Thread: Plate glass for lapping planes and stones??

".... minimum charge of £17 but I got it down to £15."

Woden, pardon me if I am telling you something you already know.... but most junk (secondhand) yards here have a few piles of glass stacked around and you can get a decent sized sheet (well, 18" - 2' x 12" etc) thickish... for a few bucks. If it is broken, just be careful till you get it home and trim it up. I have a #5 that needs a bit of lapping and this will be my preliminary skirmish at the process.

Hi Woden

Make sure the glass is on a flat surface - it bends! I have mine stick to three layers of MDF.

The longer the better - mine is 1 meter long - but this also emphasizes the importance of a flat, stable substratum.

The longer the lapping surface the more one does in a single stroke (this statement ignores the difficulties and dangers in the lapping process, per se).

Use Zirconion Oxide (blue) belt sander belts (80 and 120 grit) glued to the glass as your first "stage". These last longer than anything else on the market and are cheaper and less frustrating in the medium term.

Regards from Perth

Derek

Originally Posted by derekcohen

Make sure the glass is on a flat surface - it bends! I have mine stick to three layers of MDF.

The bendiness (or ease of bending or elastic modulus) of glass is about the same as for Aluminium. So imagine the amount of force you need to bend a piece of Al which is the same length and thickness and you would be pretty close.

Using wood as a support: Depending upon whether you apply forces across or along the grain, wood is between twice as easy and the same bendiness as glass/Al. so as Derek says - you'd need lots of wood to get decent support.

Steel is about 3 times LESS bendy than Al/Glass but getting a really flat bit could be difficult. Tungsten is about 5 time less bendy but . . . .

BTW: Bendiness is unrelated to the amount of bend you can put into something before it breaks.

[WARNING] pedantic spelling discussion ahead!
Derek; It's the second time I have seen your "Zirconion oxide" spelling. I believe this should be "Zirconium oxide" which is the same as "zirconia". I understand the blue belts are a "zirconia alumina abrasive". Good belts BTW. [/WARNING]

Clear as mud?
Cheers

Originally Posted by woden

The 40 grade I've been using just doesn't seem to be suitable for blades/chisels at least.

Would 150 grade paper be a better starting point for blades with maybe a decrease to 100 for plane soles?

woden

I start at 180 grit wet and dry for my chisel and plane backs - works OK for me. I guess if you had a really rusty older blade you would need to bring in the big guns, though.

jas

Originally Posted by woden

Is flattening more crucial for chisel and blade backs than for plane soles as the burr can't be chased properly when sharpening if the back's bellied?

Again, this is just another opinion. Seem to be a few floating about. And hate to step on anyones toes......so please put IMO in front of everything I say

For chisels, generally its more crucial.....if its back is curved thats how it'll cut.....and you don't want that eh , you want your mortises or whatever to cut straight.....but having said that, I've heard from some who actually like the back of their chisel a little bowed.....

To keep it flat, try and lower the back of the blade handle end first onto the grit then lever the edge down, before you stroke the grit....and the opposite before lifting the blade off...Cause if you make a stroke with the handle raised even a little, it could spell much effort to remove. ie. its not flat any more. And theirs a little angle you've but right on the edge.

If your not into a backbeveling method, then try and flattern your plane blades backs flat as well to keep the angles under control( I should have said that eariler I guess) ...same method as with that chisel (last paragraph).......but because a plane cuts differently to a chisel, where the blade is not guiding itself, its not important with plane blades to keep it perfectly flat. Thats why backbevelings the bees knees, because it takes little effort to put a little shine on the back as compared to the entire surface area of a flat blade (sense I'm confusing you....I'm trying) ...and in doing so you will probably help the cut on #### timber.

Your not trying to raise a burr with that plane.....your just flatterning the bastard...... ...its not a blade, you don't want it to be sharp.

Originally Posted by woden

Oh, the float glass will only come in 10mm thick pieces I've been told. Will this still be thick enough not to flex?

yep....she'll be right mate.....if you can't see or sense the glass flexing as you lap, don't worry about it. Really.

Buy some of that glass, lock it onto some thing flat somehow (glue ?..whatever)....spray adhere on sandpaper (blue or Zirconium stuff if you wanna be flash) ...and lap away in one direction, stopping on occation to eyeball the sole.....as soon as you get those high spots, stop ! and move on to the next thing.

Is flattening more crucial for chisel and blade backs than for plane soles as the burr can't be chased properly when sharpening if the back's bellied?

Woden

Flattening the back of a blade is crucial for BOTH plane and chisel blades. Note that I did not say "smooth", I said "flat". Both use the back of the blade to register, the plane against the bed and the chisel against the work.

The difference is that you can use a backbevel on the plane blade when honing, but NEVER on a chisel blade. The plane blade needs to register but the blade edge does not. The chisel blade edge obtains its accuracy from the registration process, so it must line up with the back. One can accept (often desire) a chisel back that is dished like a Japanese chisel blades' back, but NEVER the other way, that is, where a back is bellied.

Jas

You can sand with 150/180 if you wish, but I would not - it will take forever and cost a fortune uin sandpaper. A little 80 will take it down, then 120 will remove the scratches, then 240 ... (I tend to double the grits as I progress from about 110/120 upward). I would not dream of using 40/60 grit - this will leave very deep scratches, too deep to remove easily.

Regards from Perth

Derek (... Derek, say after me .. Zirconiun ....Zirconiun)

What I have found is that water will hold your sandpaper on a sheet of glass which is OK for a bit of roughing before you put it on your waterstones.

I like to use a benchgrinder to do my preliminary sharpening. Then 600 grit waterstone and work my way through to 8000 grit waterstone.

Using a beltsander is pretty neat but I've found the belt takes more from the sides than the middle of the blade. I use a grinder because i have learned how. I have no trouble keeping it straight and square, as cricketers say soft hands.

If you want something flat the Japanese make steel pieces of flat that they use to flatten the backs of their plane blades and their chisels too using abrasive paste. Have a look on Japantool and you can get one for about $30

Studley