Some observations and a question or two

[rsser]

The generous posts of forum members in this sub-forum and in Handtools and machinery have been terrific aids in my coming to terms with chisels, plane blades and soles and the like. Thanks all.

One thing that's emerged is that between a good diamond stone and two lengths of float glass the lapping results can vary ... a puzzle cos they're all supposed to be flat.

Mostly now for flatening and lapping I use a bit of 10mm thick float glass and stuck-on fabric backed paper sitting on 19mm thick MDF. I've learned that unless the paper is absolutely flat you do of course take more off the corners which defeats the whole point (except perhaps for a jack plane iron). Apart from that I wonder whether such paper has some give and that might cause the same problem as well. Any comments on this?

Just recently I added some 3M micro-abrasive sheets to the kit: 15, 5, and 0.5 micron. The glazier reckoned 6mm float glass on a flat surface should do. I pulled out a couple of lengths of 19mm MDF that had done light service as shelves, checked them with a straight edge and they're not flat. Makes me wonder now whether or not all MDF out of Bunnies is flat too. Reason I checked was I recalled Derek posting that he mounted his glass on three layers of MDF. (... but laminating might or might not cancel out bows in the MDF).

So now of course the question is how flat is flat? (btw, I keep all this away from machined cast iron surfaces since I don't want water or grit around them, and unless destressed before machining they're not going to be flat either :C ).

With spray-on adhesive I've found that if you're heavy handed on glass to take fine papers you get build-up and that doesn't help either :no:

To end, the 3M micro-abrasives 'feel' different from everything else. Sorry to be so vague. Why do folk speak so well of them? Why can't we buy the stuff here in Oz? They've done a fine job of producing a mirror like polish but are they all that much better than going down to 2500 grit W&D?

It's all a bit obsessive when a plane iron edge might only last 10 minutes but there is a certain amusement to be had trying to count your nose hairs in the reflection of a lapped cutting tool (copyright ScarySharp).

Appreciate hearing about your experience.
.

[joe greiner]

Hi, Ern.

I can't claim to have much finesse with sharpening, and never tried to count my nose hairs. I generally omit the adhesive to avoid possible uneven-ness, and lay the paper directly on the glass. The paper tends to curl, but time to replace by then anyway. I don't go that fine, either, so maybe not as scary sharp as it could be.

Joe

[mic-d]

Perhaps you should try paper-backed wet and dry and break the back of it before sticking it down with water only. As I understand it, the fabric backed stuff is spongy enough to roll up slightly in front of the edge .

Cheers
Michael

[rsser]

Thanks guys ... food for thought.

[BAZMick]

G'day Ern!

I work a bit with MDF and find on hot or dry days the upper face will start to curl up, no matter what the size or thickness.:~ No way of getting it back successfully either, we have tried turning the panel over as soon as we see it. Best way we found was to seal both sides with a spray on lacquer or paint (mineral based of course!!):doh:

Like Joe Greiner, and you know as well that I'm no expert. I have been told that float glass is by far the most reliably flattest surface you can get aside from a machined surface, but that would be prohibitively expensive exercise. Just don't stand your glass upright, as over time it will get thicker at the bottom than the top because it's still technically a liquid; that I have actually seen for myself pulling out some 100 year old windows on a renovation once, the panes were a full 2-3mm thicker at the bottom:o . Belive it or not!!:U

As to sticking down the W&D as flat as possible I couldn't comment other than maybe to suggest to use a light machine oil like air tool oil as it won't evaporate like water and maybe won't curl the ends up when the water drys out of the paper.:whatonearth:

Cheers to all and Ern, I love that waterstone.

Bazzy

[hansp77]

if you are dealing with any of the spray adhesives I have used (for screenprinting- not scary sharp), then just give the glass a wipe over with a turps soaked rag.
It should melt the adhesive residue off in a flash.

[rsser]

Thanks Bazzy ... glad to hear the stone's found a good home ;-}

Good point about MDF ... the new strip had in fact been sealed on one side but not the other. Might well account for the bow.

And glass a liquid eh? So if I don't get the port down fast enough it'll end in my lap ;-}

Thanks Hans .. a good tip to recover from overspray.

[BAZMick]

Ern if you've got port that old I'll be on the next flight down and knockin on your door offering some of my N'Qld Silky Oak.:tongueroll: I'm a young man and will find some more good timber, but port like that doesn't grow on trees!!:U

Bazzy

[Cliff Rogers]

Ern if you've got port that old I'll be on the next flight down and knockin on your door ......
Study this picture. :2tsup: http://www.woodworkforums.com/attachment.php?attachmentid=50866&d=1184589083

[Cliff Rogers]

Did you see it? :?






















He has plactic cups just in case glasses leak. :D

[BAZMick]

Cliff, my hat is off and I'll be scrapin' the boots on the mat so man the peephole, but just gotta stop by a mates place in Cape Tribulation after and borrow his chainsaw.

http://www.leuracellars.com.au/list.asp?id=27&start=50

Got the cups!

[Cliff Rogers]

Ern is a fine host & easily plied with timber. :2tsup:

[Chris Parks]

To raise this thread from the dead. Someone mentioned machined surfaces being flat, I have some very thick marble slab and use it, the point being it is surface ground. You should be able to get some at the stone masons who do headstones etc, just look for the nearest cemetary.

[kman-oz]

A note on warping MDF also; I've experienced the warping router table top problem and it also seems to be a result of not sealing both sides. Over winter it expanded on the underside, but in the recent warmer weather it's straightened out again. I only sealed the bottom last week when I was satisfied it was flat again.

You may also note that most production router table tops made from chipboard/MDF are laminated on both sides, presumably for this very reason.

I'm still yet to decide how to keep my new glass/MDF lapping plate flat.... any suggestions?

[rsser]

LOL, buy your gravestone early, and lay the MDF/float glass flat on it. From time to time ponder the inscription you might want on the headstone ... eg. 'Now at last he got it really flat' :C :U

[derekcohen]

I really do not believe that "warping" MDF is an issue. If it is hot enough to warp MDF, or you leave your lapping board in the sun, or generally fail to be sensible with your tools and jigs, then nothing will be expected to work anyway.

There is probably more variation in the sandpaper than the surface of the MDF.

There is probably more variation in the glue under the sandpaper than of the MDF.

I believe that using water tension to hold sandpaper on glass is short sighted for lapping as it curls as it dries and this dubs edges. Glue it flat and unmoving on glass. Get the substrate to the glass as flat as possible as glass bends. That is why I use 3 layers of 3/4" MDF, and then it goes on top of a flat bench.... just trying to minimise the chances of an unflat surface, but not getting too paranoid about it.

Diamond plates will differ from one another in terms of scratches since the diamonds stuck to the surface are not even in height when the plates are new. In fact, it is rare to get any lapping/honing surface to be the exactly the same as another because of so many extraneous variables. Don't sweat it.

This is not NASA - this is woodworking!

Regards from Perth

Derek

[rsser]

Tested against a Veritas straight edge, my bit of 3/4" MDF was certainly not flat over a metre's length. It had never been in the sun; as noted, it was sealed only on one side and had had light use as a shelf.

Happy to post a pic and the figures.

[kman-oz]

I really do not believe that "warping" MDF is an issue. If it is hot enough to warp MDF, or you leave your lapping board in the sun, or generally fail to be sensible with your tools and jigs, then nothing will be expected to work anyway.

I have to dissagree with you here Derek. I've aquired some 8mm glass at 1100mmx270mm which I intend to use as a lapping plate, after glueing it to two peices of 19mm MDF laminated together. At time of purchase and laminating (cold and damp, the workshop isn't temperiture controlled) the MDF was as close to perfect as I could expect, but priorities changed and it was layed down on a shelf for about a month before the glass was glued on.

Last week, during the warmer weather I picked it up again with the intention of glueing the glass onto it and noticed that the top surface was now quite obviously concave. This time I stored it standing on it's side in the hope that what ever moisture - or lack thereof - had effected one surface might equalise. When I looked again yesterday evening it was very close to completely flat again.

Still, my confidence in MDF is shaken. I have observed that MDF recently seems to have less glue in it, perhaps a cost cutting measure, could be effecting its ability to retain/repell moisture?

For the record, none of my tools or materials see either rain or shine :)

[chrisp]

Just don't stand your glass upright, as over time it will get thicker at the bottom than the top because it's still technically a liquid; that I have actually seen for myself pulling out some 100 year old windows on a renovation once, the panes were a full 2-3mm thicker at the bottom:o . Belive it or not!!:U

I understand that one's a myth. The float glass process (Pilkington) wasn't invented until the 1950's and glass before that wasn't always flat. Some of the very old glass was made by a spinning process and the glass panes were cut for a disk of glass - it was thicker at one end than the other. The convention was to install it with the thick end down.

[rsser]

If memory serves Derek, you have 3 sheets of MDF under your glass.

Why is that?

[derekcohen]

Tested against a Veritas straight edge, my bit of 3/4" MDF was certainly not flat over a metre's length. It had never been in the sun; as noted, it was sealed only on one side and had had light use as a shelf.


I've aquired some 8mm glass at 1100mmx270mm which I intend to use as a lapping plate, after glueing it to two peices of 19mm MDF laminated together. At time of purchase and laminating (cold and damp, the workshop isn't temperiture controlled) the MDF was as close to perfect as I could expect, but priorities changed and it was layed down on a shelf for about a month before the glass was glued on.



If memory serves Derek, you have 3 sheets of MDF under your glass.

Why is that?

Em, I did answer this earlier ...

"Get the substrate to the glass as flat as possible as glass bends. That is why I use 3 layers of 3/4" MDF, and then it goes on top of a flat bench.... just trying to minimise the chances of an unflat surface, but not getting too paranoid about it."

It seems to me to be a sensible precaution if you live in a humid or wet environment, that is, if you think that the MDF will absorb moisture ... seal it all around. All I can say is that I have not experienced any of these problems (but I seem to be in a dry, low humidity workshop where I rarely have rust even on tools that lie around for weeks).

Regards from Perth

Derek

[John Saxton]

Some years back I bit the bullet and acquired thru my local glass bloke a section of 19mm glass ...heavy as ...and flat as mounted with ply backing no flex and with a frame with a handle ...need an extra serve of breakfast to lift it onto the bench but does the job magnificently.

All up cost about $45 bucks for getting it flat and right ...never regretted spending the ,money since.:2tsup:

Cheers:)

[Toolin Around]

Em, I did answer this earlier ...

"Get the substrate to the glass as flat as possible as glass bends. That is why I use 3 layers of 3/4" MDF, and then it goes on top of a flat bench.... just trying to minimise the chances of an unflat surface, but not getting too paranoid about it."

It seems to me to be a sensible precaution if you live in a humid or wet environment, that is, if you think that the MDF will absorb moisture ... seal it all around. All I can say is that I have not experienced any of these problems (but I seem to be in a dry, low humidity workshop where I rarely have rust even on tools that lie around for weeks).

Regards from Perth

Derek


Good point brought up by Derek that applies in most areas of woodwork especially when if involves movement. You want to make sure that you have an odd number of layers. For some reason an odd number of layers tend to be more stable than an even number of layers. This becomes very evident when doing bent laminations. 2 layers or 4 tend to move and warp out of shape over time more than 3 or 5. Don't ask me why but over the years I've been caught by this a few times.

[fletty]

Hi Ern,
I also use 3M lapping film and get it in Oz from Shelleys Lapidary Supplies www.shell-lap.com.au (http://www.shell-lap.com.au)
The first time I ordered it I accidently bought the film without self adhesive and now that's all I use. The backing nomex is so smooth that water is all that is required to hold even a half sheet to to the glass. There is a micro photograph in Leonard Lee's book on sharpening that shows that the nomex is smooth even when viewed at a squillion times enlargement.
I have been meaning to go to the glass place and get 2 pieces of 10mm float glass but, in the spirit of procrastination, I am still using a piece of 4mm window glass!
Fletty

[JDarvall]

I think most errors come from the user anyway......I mean.....not applying even pressure..etc........I'd put more concern there than getting the surface perfectly flat.... I'd just use glass and be happy to assume its flat enough.

also with sandpaper, you'll notice that as the centre of the sheet tends to wear faster than near the edges,,,,,,,to me that means as you lap away the edges of your blade will see more fresh grit than near the centre....just have to drift it off that worn patch on occation and touch the fresh stuff.......which to me is a possible source of rounding blades as well........happened to me a couple of times.

I'd just get a piece of glass and do your best, and not spend forever thinking about it.... ultimately your really only concerned with the characteristics of the very edge. Its angle....polished both sides....If its a chisel or BU blade for a plane you want the back flat......if its Bevel down doesn't really matter that much. IMO.

[rsser]

Thanks guys for the tips and advice.

I confess to getting a bit obsessive about flattening - given all the work involved IMO you might as well get the gear in the best shape so you get the best result.

And the things is, when you've started flattening a chisel or plane iron back, it sticks out like dog's b*lls if you haven't succeeded :doh:

Fletty, thanks for that source of the micro-abrasives. The stuff sure does a wicked job.