Straightening saw blades

[Michael Ray Smith]

Despite my vow not to buy any old saws unless the blade was as straight as an arrow (a good arrow), I have a couple with relatively minor bends. I remember George Wilson saying that pouring boiling water over the blade, then working quickly before it cools, is a good way to straighten blades. Sounds reasonable but a bit messy and awkward. Any reason steam won't work? Seems like it would be a lot easier than lifting and pouring boiling water. The steel will probably get a few degrees hotter, but it can't get any hotter than 100 C.

[george wilson]

As long as you can get it hot enough in a wide enough area,I guess steam would be o.k.. Easier for me to make a quantity of hot water to douse a blade with than a big bunch of steam,though.

[Michael Ray Smith]

Thanks, George. I'll let you know how it works.

Mike

[george wilson]

Be on guard for rust caused by the steam. I think,after considering it,that steam might rust the blade faster than a sudden douse of hot water. Steam has air and free oxygen in it more than water does.

[Steve Bates]

Michael, your comment about steam not getting much hotter than 100C is wrong. Water boiling stays around 100C until it finishes changing from liquid to gas. Then the gas (steam) WILL get hotter as heat is applied.
Basic distilling principles is all. I don't want anyone getting a severe burn.

I've tried this but I don't have a proper anvil so I got hammer dents. No heat involved. http://www.ukworkshop.co.uk/forums/viewtopic.php?t=18501

My two pennies

[Michael Ray Smith]

Sorry, but I'm right about this one. If I hold a saw blade over a pot of boiling water, or in the plume of steam coming from a tea kettle, the steam coming out will be no hotter than 100 C because all the heat is applied to the bottom of the pot. I suppose if it was in a pot in which heat were being applied to the sides of the pot, so that the steam was superheated before it left, you'd be right, but that's not what I plan to do. Besides, once the steam hits the cool saw blade and water starts condensing, it will be not hotter than 100 C. There's a very easy way to tell whether steam is superheated -- if you can see it, it ain't. The visible part of steam is actually tiny drops of liquid water, and if there's liquid water at atmospheric pressure, it isn't hotter than 100C. You can't see superheated steam until it gets far enough away from its source to cool enough for some of it to condense.

However, steam even at 100 C can burn you much worse than water at 100 C because of the heat of vaporization. Basically, when water at 100 C hits your skin, it will immediately drop below 100C. When steam hits your skin, it stays at 100 C until it gives up the heat of vaporization (which accounts for much more heat then the drop of a few degrees in temperature as the water hits your skin).

Now if we were talking about steam generated in a boiler operating above atmospheric pressure, it would be a different kettle of well-cooked fish.

Not to worry. . .

Mike Smith, B.E Chemical Engineering, M.S. Chemical Engineering


Michael, your comment about steam not getting much hotter than 100C is wrong. Water boiling stays around 100C until it finishes changing from liquid to gas. Then the gas (steam) WILL get hotter as heat is applied.
Basic distilling principles is all. I don't want anyone getting a severe burn.

I've tried this but I don't have a proper anvil so I got hammer dents. No heat involved. http://www.ukworkshop.co.uk/forums/viewtopic.php?t=18501

My two pennies