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Thread: Brass Back Slitting
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16th February 2019, 10:12 PM #16Member
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Thank-you for bringing this to my attention Ian. I have to admit, I haven't put too much thought into the 'hang angle' yet. I will continue to research in order to find out what will work best for me. I now know that as well as hang angle of the handle, I will also need to consider the height of the work piece and the rake angle of the teeth for each saw.
This sounds very encouraging. Like you say - other than the pure enjoyment of making the saws. It should be a great learning experience and one that will help with understanding the intricacies of a well made saw.
Thanks ,
Cameron
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16th February 2019 10:12 PM # ADSGoogle Adsense Advertisement
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16th February 2019, 10:28 PM #17
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17th February 2019, 12:08 PM #18
Dale
That is a very handsome bit of gear and a smart restoration. I want one!
Regards
PaulBushmiller;
"Power tends to corrupt. Absolute power corrupts, absolutely!"
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17th February 2019, 12:36 PM #19
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17th February 2019, 01:14 PM #20
Since I got mine I think two more have been acquired over on the metalwork forum one was complete with original base & motor and extra arbours. So they are around if you really want one Paul & Matt.
…..Live a Quiet Life & Work with your Hands
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17th February 2019, 07:04 PM #21
'Tis indeed a lovely old thing, but I won't lust after one. There was a time when I was seriously considering a (vertical) mill, but decided I had enough on my hands with sawdust-making machines. Besides, there's barely enough room to maneuver in the shed as it is...
Cheers,IW
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6th April 2019, 07:32 PM #22Member
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How deep do people tend to cut the slot into the brass back?
Cheers
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7th April 2019, 06:58 PM #23
Usually, I cut about 13-14mm deep on a 3/4 x 1/4" spine. That leaves about 6x 6mm block along the top. On final assembly I squeeze the bottom of the spine in the vise (gently!) to close the slot a bit, enough so it needs to be tapped onto the saw plate. I tap the spine down until it's a few mm shy of bottoming out, so it can be adjusted up or down to straighten the plate (if necessary) and bed it nicely in the receiving slot in the handle....
Cheers,IW
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10th April 2019, 08:13 AM #24Member
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oh rightio. This is about what I thought would be an appropriate depth. I have noticed some saws with only a 6-8mm depth slit but perhaps those saws are glued into the spine also?
Cheers,
Cameron
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10th April 2019, 10:45 AM #25
Dunno, Cameron, they may be. When I first started slitting backs, I was a bit tentative and probably only went about 8 or 9mm deep. That was partly because I had trouble keeping the slits dead straight, they tended to curve slightly as I went along - not at all desirable! After a bit, I theorised that with my dry-cutting setup, the blade was heating & distorting a bit, and the deeper the cut, the more it heated, leading to the aforesaid curve. So ever since I've been very careful to advance the saw not much more than a mm each time. Whether or not my diagnosis was correct, I've had straight slots ever since, thankfully.
I'm not in favour of glueing spines on. If you use a sensible grade of something like Loctite, you can get it apart without too much trouble, but there is always a chance you will need to pull it apart at some point, & I'd rather it was just a simple mater of tapping off a nice firm mechanical fit. But the main reason I think you should aim for a nice mechanical fit is because you can use the spine to tension & straighten the blade. I got this idea from someone else, originally, & it seems to make sense (& work). On final assembly of the saw, I crimp the spine in my (aluminium jawed) vise until it is a nice, firm fit over the blade, polish it up & tap it on the blade with about 10-15mm protruding at the front (if you happen to over-crimp it a smear of paste wax along the blade helps to ease the spine on). When the spine is sitting down straight & as far as I want it to go, I tap it back til it's snug at the handle end. This creates a bit of tension along the top of the blade & tends to straighten out any slight curve in the blade. Don't overdo the tightness, just enough that it will move under gentle tapping.
I'm certainly not keen on the idea of rivetting the spine to the blade a la Rob Cosman, it's not necessary & may be counter-productive in some cases, at least. Oth, a few breeds of saws were made with one of the handle bolts passing through the spine, so there are no unbreakable rules - just do what seems logical to you, I reckon.
One other thing: It's difficult to get the handle slot absolutely perfect, and any slight imperfection caused by switching the direction of cut or slight curve in the slot will transmit to the blade when you tighten the saw bolts. This is a problem common to all backsaws; I've seeen lots of Disstons & other reputable brands with that slight curve at the heel of the blade. It's nice to not have it at all, but if it does happen, it seems to have no effect whatever on the saw's function, it's only on the part of the blade that almost never sees any work, after all....
Cheers,IW
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10th April 2019, 11:10 AM #26
Cameron
To some extent the kerf is limited by the cutting depth of the slitting saw. They are often small diameter blades mounted on an arbour up to 1" or 25mm. This provides the limiting factor.
Traditional folded backs were of course full depth less the thickness of the material, but a task I have failed miserably at. I think Rob Streeper is the only person on this forum who has been successful with folded backs. (If anybody else has had success please chime in here). I recently made up some saws with deep backs (to replicate the saws I was copying), which IanW kindly slotted for me. Two of the backs were an inch deep and the slitting saw would not reach:
massive brass back.JPG
There was still more than enough metal to grip the saw plate. In fact Ian warned me about closing up the kerf too much and, despite that warning, on one of the four saws, the largest ( ) I closed it too much and caused myself a good deal of grief. I later increased the kerf just at the toe of the saw for "effect" with a Dremel type tool and a thin fibre disc. It probably does not extend down the back more than 10mm.
P1040883 (Medium).JPG
There is a little more information here (see post #2 and much more in #46):
A Crazy Saw Service
Literary alert! If you decide to read more of that thread you need to be a drinker so you can sit back and enjoy in a euphoric daze.
Regards
PaulBushmiller;
"Power tends to corrupt. Absolute power corrupts, absolutely!"
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14th April 2019, 07:08 PM #27Member
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Thanks for this Ian, makes sense. When I start slitting the back for my saw (In a few months time) I will employ this method - and keep my fingers crossed.
I also don't like the idea of gluing the spine on. My original plan for attaching the brass back to the saw plate was to use a fiction fit as you explained - crimping the spine to provide a small enough kerf and hence friction.
But I also like the idea of the fit being slightly more permanent. I know that Skelton saws use a friction fit on their saw backs but on some of their models they also use a pin through the back and the plate. Now I think the reason they use this is to create extra tension in the saw plate. As I understand, they have a pin through the brass back on the toe of the saw and then some sort of tensioning system used with the saw bolts at the back. I have no hope of making a system like this. But it did get me thinking perhaps I could pin the toe and then slightly off set a pin at the handle end in an attempt create some tension in the saw plate. And finally if I am really lucky, I will pull of a bit of hammer tensioning along the tooth-line to get the ultimate well tensioned saw plate. Anyway to start, I plan to attempt the friction fit technique is you have explained.
The other possibility I have considered and wonder if anyone else has tried is crimping the brass back whilst the saw plate is in place? Would this provide enough pressure and friction?
I did notice that some of the arbours have a 1 inch diameter but I didn't think this would cause me any problems. Thanks for bringing this to my attention Bushmiller.
I have ruled out attempting the traditional folded back for now. I can see myself failing miserably If I attempted it first up.
Wow that turned out well! I might actually use this method to get the folded back look also.
I have read through most of this thread (if not all) and really enjoyed it! I will go back and have a look at these posts though. Thanks for the tip.
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14th April 2019, 09:07 PM #28
Y'know CB, I've often contemplated the necessity/desirability of tensioning backsaw blades. I've never read anything that suggested backsaw blades were tensioned the way hand saw blades were, but that doesn't mean they didn't get some sort of hammer treatment. None of the saws I've made has a tensioned blade (other than the small effect of the spine as described above), and I don't notice any difference between one of my saws & say a Disston from the 1920s or 30s. By my reasonong, a tensioned blade wouldn't do any harm, but any advantage it may convey maybe just isn't worth the extra fuss. Is anyone able to shed light on this??
Cheers,IW
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14th April 2019, 10:59 PM #29
The other possibility I have considered and wonder if anyone else has tried is crimping the brass back whilst the saw plate is in place? Would this provide enough pressure and friction?
Hi CB.
I’ve been following along on this an Ian and Paul write so much more elegantly than me, and both have a ton more experience than me on making saws.
But I sound say to get a saw back to pinch the plate.
You would be better having the back pinched a smidgen smaller than the plate,than inserting the saw plate.
In effect forcing the back to open ever so slightly and in effect gripping the plate.
Having the plate in the back then trying to tighten the back up I would say would be difficult.
Just my two cents worth.
One last comment be very careful if this is your first tool making adventure it won’t be your last [emoji849].
Cheers Matt,
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15th April 2019, 05:01 AM #30Member
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I haven't read anything either that says historically back saws were tensioned in any other way than with the brass back. I have heard of some modern saw makers talk about getting tension along the toothline and I thought that hammering may have been a way to get this tension. I thought it could be worth trying this method and then comparing the results. I suspect you may be correct in regards to effort vs reward.
I did find this post on the forum: Saw blade tensioning for panel and hand saws post #6.
Thanks for this Matt. I have enjoyed reading many of your comments in other threads on the forum whilst I have been scrolling through the archive.
That is kind of what I was thinking re: crimp the brass back slightly smaller than the plate for a friction fit.
I have restored many old tools now but this is only the second tool I will be attempting to make. You are correct, it that certainly feels addictive. I have already planned to make more than one saw...
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