Gngnggng!!! Flattening the backs of plane irons is boring.

[woodbloke]

Derek- even with a wide polished bevel, the angle I make on the back is 0.73deg, this is using a rule which is .45mm thick and the edge is 35mm away from the rule. I'm with David on this one as I can't see that such a miniscule bevel makes any real and significant difference -Rob

 

[Derek Cohen (Perth Oz)]

Hi Rob

A very low angle for the micro back bevel actually produces a wider mbb.

My point is that the Ruler Trick is fine if you intend to do so each time. But, if like myself on most occasions, you hone freehand, then wish to renew the edge by stropping, etc, then it is difficult to do without some degree of dubbing the blade. For a couple of years I would use the RT religiously after each honing, and it worked very well because I only used a honing guide. I have no problem with its use in this contect. My understanding is that this is how David conceptualised its use. I no longer use it much since I can remove the wire edge by honing/stropping alone. And I prefer not to have a mbb since it is easier to "feel" for the very early signs of a wire edge if a mbb is not used.

Note - this is not about getting an edge sharp. This is about the ease of freehand honing. It is also not about the ease of honing the first time one creates an edge (since Rob Cosman demonstrated in one of his DVDs), but about the refreshing of this edge as one works.

Regards from Perth

Derek

 

[woodbloke]

Derek - penny's finally dropped ....no honing guide. Now I understand - Rob

 

[Pekka Huhta]

Just as a side note: I do the initial flattening of the chisel/iron backs with the side of a Tormek grindstone. I'll get the back flat on the 10-20 mm area I usually flatten in a few minutes and then it's just a matter of minutes to polish the back with "fine", "finer" and "ridiculously smooth" oilstones. It wasn't easy at first, but nowdays I get them very nice without any grind marks.

Flattening the back seems to be a cultural thing as well. Over here all the old woodworking books instruct that the back should be touched as little as possible to avoid wearing the thin cast steel on a laminated iron. It goes so far that when a very old relative looked at my tools he was astounded that although I have such a pile of tools, I have not learned myself to sharpen properly "without ruining the edges that way" - pointing at the flattened backs.

Looking at the chisels and plane irons I have got from eBay someone definitely has misunderstood "flattening the back".

Pekka

 

[woden]

I've been flattening the backs of some blades recently and it really is a chore. I've went for coarse sandpaper glued to a piece of plate glass to grind the steel. One of the things that annoys me is that if you decide that enough's enough for now and move on to polishing the blade up through the sandpaper grits you've then got to undo all that careful polishing if you go back to flattening it some more with coarse paper again. Not to mention that it seems like a waste of finer paper when you're only going to be undoing it all when you go back to flattening again.

Derek, are you still using the disc sander for doing the donkey work when flattening backs as you demonstrated over at the ubeaut forums? In the end I decided to go for an intermediate speed (1425 rpm) grinder for doing the bevels but would seriously consider getting a disc sander and dial magnet to do the backs.

 

[Derek Cohen (Perth Oz)]

Hi Woden

No, I prefer to use sandpaper over the disk sander for the backs of blades. It is just more reliable, that is, less error prone.

The key to using sandpaper is that you:

1. must use a long glass plate. Mine is 1 metre long. This reduces effort quite significantly.

2. Stay with a coarse grit (80 - 120) until the surface is flat. Do not get impatient and attempt to move on until this is so. This is the most important stage. Get this one right and all the rest combined take a fraction of the time to do as this one.

3. Do not skip grits as you remove scratches. Go 80-120-180-240-360-600-1200-rouge. Note that the back of the blade only needs to be flat (you can stop at 180-240 grit), not polished and it is just the 1" behind the bevel that goes up the grits.

Do it once and do it right. This method really takes little time.

Regards from Perth

Derek

 

[woden]

Thanks for getting back, Derek.

No, I prefer to use sandpaper over the disk sander for the backs of blades. It is just more reliable, that is, less error prone.

Awww, schucks. I was hoping you wouldn't say that as the disc sander seemed like a dream system in terms of ease of doing the job. Did you find out it was error prone the hard way, ie. a few blades got irretrievably gouged or something?

1. must use a long glass plate. Mine is 1 metre long. This reduces effort quite significantly.

Yeah, the piece of float glass I managed to get my hands on for nothing is 900mm long and 15mm thick so it does the job well. But when you say use a long plate are you saying that you need to run a strip of 80 grit (or whatever you're using for the initial flattening) all the way along it? If so, I take it you use 80 off a roll?

How long would you say is too long to flatten a blade this way? What I mean is after how much time rubbing on the 80 grit would call it quits if the blade still wasn't flat and opt for a micro bevel using the ruler trick?

Note that the back of the blade only needs to be flat (you can stop at 180-240 grit), not polished and it is just the 1" behind the bevel that goes up the grits.

But surely it involves little extra effort or sandpaper to polish the full 2/3 inches (obviously no further back than the slot) or so that you've been flattening on the 80 grit all the way up to a fine polish. It's just that I fear if I reduce the distance I'm polishing down to only 1" or so the blade is more likely to lift by accident and dub the edge. Maybe it works for others but that's just my own worry.

Finally, would you ever go below 80 grit to 60 or even 40 in an attempt to flatten a particularly stubborn surface?