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Straightening a bent sawblade

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Cheshirechappie

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Some weeks ago, I invested a few pounds - less than a tenner including postage - in an Ebay panel saw (22", 10tpi) with the intention of turning it into a rip panel saw. It's been a bit of an on-and-off job, but it's done.

The saw as received was a bit of a mess - rather grotty handle, rust, blunt and with a toothline like waves on a pond. No problems here - new handle (beech, modelled on an old Drabble and Sanderson which is particularly comfortable and beautifully curvy, finished with three coats of Danish oil, left for a week to harden then burnished with a soft cloth - very nice to the touch), rust removed (turned out to be a Spear and Jackson Spearior 88 when the acid-etch emerged from the rust and muck, so a good piece of steel), toothline straightened by jointing, reshape, set and sharpen. Nothing particularly tricky, just takes a bit of time. However, the tricky bit was that the blade had a couple of kinks in it. How to get these out?

Well, of course, Google is your friend here. There isn't much on sawblade straightening, but what there is suggests three basic methods. The first is to identify where the kink is, place it over a bench edge, and work it out with finger pressure. That didn't work in this case - does work on some steels, 'cos I've done just that with a Roberts and Lee Dorchester 26" rip recently. The second method is to pour boiling water over the sawblade, and then bend out the kink - that, however, seems to be more applicable to gentle curves rather than kinks. The third method is to hammer out the kinks over an anvil.

Now, there is much mystery about the latter method - but it worked for me. For an anvil, I used a block of mild steel about 3" by 6", and about 2" thick, filed flat and clean on top, held in the metalworking vice (which I've mounted over the leg of the bench, so there's no 'bounce' when you hit things). The vice is not a big one, just a 4" Record 1-ton basic vice, but like I say, securely mounted. For hammers, I used two; both ball-pein, one 1lb, and one 2 1/2lb, both with the flat faces angle-ground to a slight curve, and polished with emery cloth to about 1000 grit.

The drill (apparently) is to locate the kinks. The recommended method is to hang the sawblade vertically, toothline towards you, good light source behind, and use two short straightedges (about 12" long), one each side to find any out-of-straightness. I didn't do this; I put the handleless blade on a piece of kitchen worksurface, and by gently poking with a finger, found where it didn't lay flat. Mark the kink with chalk. Now, transfer to the 'anvil', and with the small hammer, tap gently on the concave side, either side of the kink. Then turn over, and with the large hammer, knock the kink flat. This takes several goes to find the right weight of blow, and it's best to just give one or two blows, then check progress on the kitchen worktop. The light blows on the concave side stretch the metal, lengthening that side, the heavy blows distort the bend in a controlled fashion. Finally, bend the blade by hand into as much of a curve as you dare, both ways, to settle any remaining stresses.

Somewhat to my surprise, this worked.

That left me with a very slight hollow (about 1/32") along part of the blade, which I wasn't able to get rid of. It's not visible when you sight down the blade, but you can just detect it when you do the 'poke test' on the kitchen worktop. However - it turned out that that didn't matter.

Having got the blade as flat as I could, I put it in the sawvice, jointed the toothline straight. I did this without any jigs, just holding the mill-file by hand - conventional filing to get rid of the really high bits, then lay the handle-less file on top of the toothline, in line with it, and with moderate finger pressure, move it along several times until a 'shiner' appeared on all the old teeth. I used Bugbear's tip here of using a straight piece of thin timber as a straightedge to check progress - much lighter than a metal one. Then reshape (about 10 degrees of rake, again judged by eye), then set (minimally), then a final pass with the sawfile to sharpen.

Out of the sawvice, fit handle (salvaged the screws and medallion from the old handle), and gave it a test-drive.

Wow! Cut like a dream - tracked beautifully, left a superb finish. So the slight cockle left in the (admittedly fairly flexible) blade didn't seem to have any adverse effect on performance. I've tried it on 3/4" softwood, and a piece of 2 1/2" hardwood. Ate the lot, no problem - and no deviation from a straight cut.

Job done!

Was it worth it? As a learning exercise, definitely. As a way to get a tool to do a job, probably not - the total time involved was about 10 to 15 hours, and some semi-specialist kit had to be made. If the time were money, a £200 Lie-Nielsen would be more cost-effective. That said, using it brought a very special feeling of satisfaction. I suspect this is a tool I will always be rather fond of.

(Sorry chaps, no piccies - don't have a digital camera.)
 

jimi43

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Always a great feeling restoring something to use again...particularly that far gone!

I think for all our sanity you ought to get yourself a digital camera for your birthday....the words were drooling but pictures would have been wonderful..particularly of the handle!

Cheers

Jim
 

AndyT

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Quite so! Another really informative post, but pictures do help.
 

Cheshirechappie

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TobyC":urjyowzx said:
Is this where Google took you?http://www.wkfinetools.com/contrib/bSmalser/art/strSawBlade/strSawBlade1.asp

I would really like to see the handle you made, have you got a phone with a camera?

Toby
Toby, I'm sorry, but I don't have any device that takes digital pictures. Some years ago, I made a decision not to spend my hard-earned on things that would likely be supeceded in about a year or two; the camera/phone/computer/i-everything market still seems not to have settled down, so I probably won't bother for a year or two yet. (Computers are bad enough - this one is a mere three years old, and is creaking already.)

The link you highlighted is one of the most useful sources of help in a rather sparse field. There are about four other links with some information when you google 'straightening a saw blade', but not as good as that one, I think.

There are two old books by Robert Grimshaw, both with titles about three paragraphs long, but summarised as 'Saw Filing and Management of Saws' and 'Saws: The History, Development, Action, Classification of Saws of All Kinds' (also known as 'Grimshaw on Saws'). Both have some useful help on sawblade straightening, but no detailed treatise. (I looked these up on www.abebooks.co.uk expecting to find antiquarian copies at ludicrous prices. No - they are available as 'print on demand' copies - newly printed facsimile copies of an original volume, took about a week to arrive, cost just over £20 for both.) Can't really say I was overly impressed with either book - they are mainly about late 19th century power saws for lumber-milling, and their upkeep. Still, what's there is better than nothing, and is of some help.
 

AndyT

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The reason those books are available as print on demand is that they are out of copyright and have been digitised. They are both available as pdfs to read on your pc, phone, pad etc, print out yourself or pay someone else to print out. There was an excellent sticky of such stuff which seems to have disappeared at present, but meanwhile just use this link:

http://www.wkfinetools.com/mLibrary/mLibrary_index-1.asp
 

RogerP

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Cheshirechappie":wlh5mgrl said:
TobyC":wlh5mgrl said:
Is this where Google took you?http://www.wkfinetools.com/contrib/bSmalser/art/strSawBlade/strSawBlade1.asp
I would really like to see the handle you made, have you got a phone with a camera?
Toby
Toby, I'm sorry, but I don't have any device that takes digital pictures. Some years ago, I made a decision not to spend my hard-earned on things that would likely be supeceded in about a year or two; the camera/phone/computer/i-everything market still seems not to have settled down, so I probably won't bother for a year or two yet.
I'm afraid you will wait forever. The "the camera/phone/computer/i-everything market" is work in progress and always will be.
 

AndyT

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I respect CC's attitude - it's easy to throw hundreds of pounds away on electronic kit if you want to 'keep up'. But I just did a quick search on eBay looking for Digital cameras / compact / new / sorted by price. There are some under £20 including p&P and quite a wide choice under £30, any of which would be perfectly serviceable for taking medium sized snaps to upload to Photobucket and display on here. Cheap just because they are not the latest model.

And just to give you another friendly nudge, once you have one you will start to find all sorts of other uses where a film camera would make no sense. It can work as a sort of electronic note taker - how did this thing I am dismantling fit together? Which way is the footpath on the map on the information board back at the car park?
What does the bump on the back of my head look like? etc etc.
 

Cheshirechappie

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Getting back to the original subject - several of the references mention the use of a wooden block as the support for hammer-straightening saw blades, usually an end-grain block with a slight crown to it's working surface, rather than the metal 'anvil substitute' I used. Does anybody have any experience of trying such?
 

TobyC

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This is from Henry Disston and Sons, Inc., Lumberman Handbook, Published 1907. It doesn't say anything about a crown.



"Now comes the Blocking," which is an important operation and requires the highest order of skill. Each blocker is provided with an anvil and lignum vitae block on which he corrects any slight irregularities that may have been developed by the previous processes. The blades then undergo the "Polishing" process, then through the important operation of "Stiffening." As to this latter, the different processes and hammering under which the blades have passed, has altered the arrangement of the molecules in the metal and in order to restore the desired qualities and spring they are stiffened in a special bath, which was originated and is known only to Disston".


The boxy-looking iron anvils that I've seen that were made for saw blade smithing, were dead flat. Like this.







Toby
 

Cheshirechappie

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Now that's interesting, Toby. I had success in removing the gross kinks on my 'anvil', but not the slight dishing. Maybe different defects respond better to different support surfaces when dressing them out.

I'm fairly sure that in one of the googled links, Mark Harrell of Bad Axe Toolworks was removing a slight curve from a sawblade by hammering on a long-grain slab of hard maple. I might give that a try, if I can find a suitable slab of hard enough timber.
 

Cheshirechappie

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If you google 'Cabin Woodworks' and search for '$2 handsaw', there's a description with pictures. (Sorry I can't do the link - I used to be able to, but since I've had Interweb Exploder 9 foisted upon me by my lack-of-service provider, I can't find how to any more. Maybe I should try Firefox or something.)
 

TobyC

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Mark took my handsaw and bent it double in both directions to check the springiness of the metal. When the saw popped back in to shape it had passed the spring test. Then he sighted down the saw and pointed out the saw had a curve in it and would not cut straight with the curve. In addition the saw was very dull. Otherwise this was a perfectly good old saw that could be easily put back in great cutting order.

Mark straightened the saw by laying it on a flat maple board with the short or concave side of the saw facing up. You would not think of something as thin as a handsaw blade to have a short and long side but from a metallurgy standpoint the short side is what caused the saw to curve in one direction. He administered a series of small taps on the short side of the saw with an antique Disston hammer (I think Mark has a tool problem) that had been manufactured over a hundred years ago for the express purpose of straightening saw blades. After a few taps Mark would sight down the blade and then repeat the tapping until he was finally satisfied he had stretched the metal on the short side until it equaled the long side. These taps were light enough they didn’t leave a mark on the metal but heavy enough to change the composition of the metal…don’t try this at home.




Toby
 

Cheshirechappie

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Thanks Toby - that's the one. Thanks for the wkfinetools link to Mr Wilbur's book as well - I'll follow that one up.
 

TobyC

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Notice that it says "Mark straightened the saw by laying it on a flat maple board with the short or concave side of the saw facing up."

Toby
 

Cheshirechappie

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Yes - interesting - because 'Grimshaw on Saws' suggested a wooden block with a slight crown. I've also seen conflicting advice on metal anvils, too - some say flat, one said you want an oldish anvil with a few hollows and crowns on it.

For what it's worth, my 'anvil' is flat (though nowhere near the 200 - 250 lbs recommended by another source, more like about 5 lbs), and that worked OK at removing kinks, but not at flattening the slight hollow. That, of course, may be my inexperience rather that the equipment.

With all this slightly conflicting advice from different sources, I suppose the only thing to do is to suck it and see - try something, and see how well it works, or not. The problem is then trying to work out if failure is down to incorrect equipment or to inadequate technique.

Oh well, scope for experiments! I could end up with some very mangled saws at some point....

Erm - cough - would anybody like their sawblade straightening?...... No?...........Don't really blame you...
 
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