Thread: Couple more back saws

Originally Posted by derekcohen

......
I turn my back for a day or two (no internet) and you go and build a couple more master pieces!

Ahr, yer just slowing down, Derek, admit it....

Originally Posted by derekcohen

......How much set are you putting on the saws? I removed all the set from my LN dovetail saw some months ago and have been using it sans-set since. In Jarrah it will bind a little, but a touch of wax fixes that. It certainly cuts cleanly, and of course it is easier to place on the line and saw a kerf where you want it to be.

Funny you should ask. For years I have just set saws by the highly scientific method of "that looks & feels about right". Then I got the new 'blue' Somax, & in the box was an insert written by someone at LV, which suggested the 'average' amount of set should amount to 50% of the saw plate thickness(i.e. 25% each side). At last, a truly objective method, says I. So I tried measuring set with calipers on the saw, but got frustratingly un-repeatable results. Then a small light came on, so I hauled out the feeler gauges & measured the kerf. Success - or at least highly consistent results. Interestingly, I discovered that except for the first saw I tried, the amount of set I favour leaves a kerf quite bit less than 150% of the plate thickness - mostly 125% max., and yes, I tend to put less set on a rip. My new 'favourite' DT made from 0.45mm plate leaves a kerf somewhat less than 0.53mm wide. I suppose if you regularly cut high moisture content & soft, fibrous woods like pine, you would want more set, but I cut mostly 'crisp' woods, fortunately.

Can't say I find it EASIER to saw to a line without set - I would have said quite the opposite, in my case. While you can certainly get away with no set for shallow rip cuts, you have to be deadly accurate with your starts if you are trying to split a line - it is very difficult (& messy) to adjust the cut once started, without a little free space in the kerf. When you are used to a particular saw, you can usually start it on the correct line & angle from 'muscle memory', of course, but there are times when it doesn't happen, & it always seems to be on the most critical cut, for me!

So to maintain a little 'steerage', & to keep the saw more versatile & able to cut straight to its full depth when necessary in a variety of woods, I prefer to have some set. I can understand why some prefer not to set - it's extra bother, and it does take a fair bit of practice to do it consistently. You would think a saw set would give you consistency without even thinking about it, but it doesn't - you have to school yourself to make every squeeze exactly the same pressure. It's only now that I've been setting scores of saws that I can get a saw to track true straight off the file without any 'adjustment'. (But if I haven't sharpened a saw for a while, I seem to lose the touch again! )

As for a taper-ground DT - after you, 'ol buddy! I have discussed this with RayG, & we both agreed, after each of us had tried to sand off a few thou of sawplate manually, that the end didn't justify the means. I'm sure you could do it by fitting a drum sander with a slightly angled base & appropriate paper, however, I really don't think it's the best way to go.

The thin-plate dovetailers ARE the answer, I reckon. It took me a couple of goes to work out the optimum size & depth of blade, which (in my hands) seems to be no more than 230mm long, and a maximum of 50mm of blade exposed, otherwise, the spine can't stiffen the business edge enough. However, that's a perfect size for me, for routine cabinetry d-ts. My last couple of 0.45mm plate saws are the best I've done yet, and I reckon that's the answer. Of course, like my passion for 'hybrid' filing, I may change my mind in due course, after further mucking about......

See ya - the sun's out today in Brissy, so looks like it's back to yard work & less shed time, again.

Hi Ian,

I really have to start checking here more often, yet another couple of beautiful saws

I think I have a working method for taper grinding saw blades.. I now have the surface grinder up and running

There's a relevant thread on the Metalwork forum, and a video of some early tests is here https://www.woodworkforums.com/f65/ne...ml#post1320564

The saw plate would be held on the mag chuck and shimmed by the amount of taper.

How much taper do you think would be a good starting point? I'm thinking 2-3 thou on a 20 thou plate.

Regards
Ray

Hi Ray

I am considering modifying an old saw plate I have - from a 18 ppi Crown gent saw - and taper grinding it. Now the thing is that I do not have machinery. It would have to be done by hand. But does this also mean 'by eye'?

I had been thinking of just using the round end of a stationery belt sander to sand away metal up to about 1/4" from the teeth. Just a few strokes either side of the plate. This should remove about .01" (=.02 for both sides together) which, considering that set is about .03", should be enough to prevent the blade (sans set) binding in the kerf - which is what taper grinding is all about.

What do you think?
Is there a way of controlling the amount of metal removed this way? Or even just determining how much is removed?
Is there another/better way to do this by hand?

Regards from Perth

Derek

Hi Derek,

A belt sander does work, Lui's handsaw ( see thread here Making a new rip saw. - Saw Discussion Forums ) was tapered using a belt sander, the trick is to avoid any heat build up which will warp the plate. Then re-polishing can be a time consuming process.

I think you are out by a decimal point in the taper required. 0.003" would be better

I once tried using a flap disk in an angle grinder, but it's almost impossible to avoid hot spots and warpage. I'm hoping the surface grinder with it's flood cooling will do the trick.

There are some really nice belts available that might be good for taper grinding, I'm thinking the 3M trizact belts would be worth investigating. Also you can get scotchbrite belts that might be good for polishing.

Definately worth a try.

Regards
Ray

Hi Ray

Yep, .003" and not .03"!!

The problem is how to keep this even and constant ... although my head said that it does not matter that much. All we need to do is relieve the plate a touch so that it does not bind in the kerf. Affter all I have a LN sans set that saws well up to about 3/8", and after than benefits from wax (and then is fine).

I have 3M trizact belts from 600 to 1500 or 2000 (can't recall which) ... from the time I used the belt sander as a sharpener. Keeping the heat down should not be too hard as long as one uses a light touch and cool the steel with a wet cloth before it gets more than a little warm.

Thanks for the link. I'm off to check it out.

Regards from Perth

Derek

Originally Posted by RayG

Hi Ian,

I really have to start checking here more often, yet another couple of beautiful saws

They only happen when you're not looking, Ray...

While I wasn't looking, you & Derek have have had a complete conversation!

Originally Posted by RayG

.........How much taper do you think would be a good starting point? I'm thinking 2-3 thou on a 20 thou plate.

I guess I would approach it like this. I've been measuring the kerfs of various saws. Averaging it out over a number of saws that were good to excellent, it seems like a kerf that is in the vicinity of 20% wider than the saw plate gives the right fit in a variety of soft to medium-hard woods. For very shallow cuts, this could be at least halved, (or maybe done away with altogether - see Derek's earlier post). I have a feeling that tapering will need even less clearance, because not having to set the teeth means they are going to be more even (but I may be wrong). Your suggestion of 2-3 thou means a taper of 10 to 15%, so should be in the ball-park, I reckon.

I'm having trouble imagining how you could shim the plate without a tapered shim. It's going to have to be pretty well supported, to prevent flexing under the grinder. I guess you will show me in due course...

My approach would be more low-tech, like Derek's. I reckon if you made a wooden platform & planed a slight side-to side taper, then buried some rare-earth magnets in the surface, you could send your saw plate through a drum sander a few times - light quick passes should avoid heating past any critical temperatures. You only need to work on one side, so only one side to repolish. My problem is, I don't have a drum sander, and I don't know who has one that would let me chew up a few fine belts.

Hmmm, the germ of an idea just started working somewhere in the deep recesses - I'm thinking of a low-tech drum sander that could cope with coolant (H20). I knew I bought that mini-lathe for a reason.

It may be some time before I show a tapered back saw, however.......

Cheers,

Originally Posted by Richie Rich

Thanks heaps for the info Ian, have had a quick look at the site and will have a few hours of reading to do. Do you use the router bit that leif describes for your handles ? Could you anneal hard brass with an oxy plant to reduce its hardness a bit like annealing aluminium sheet!, just a thought.Anyways thanks again, cheers for now Richie.

Sorry Richie, I missed your post in the page-flip.

I don't use anything but hand tools for shaping. The shapes I like are not really attainable with rotary cutters, so it's the knife, chisels, rasps files & cloth-backed paper route. Not conducive to production in commercial quantities, I'm afraid - even after a lot of practice, it takes me about 1/2 day to make a handle.

You certainly can anneal brass, and that would be how you would do a bent spine. I think the Norse bloke said he had to anneal a couple of times to get a 180 degree bend without cracking on some of the bits he used. I considered bending way back, but as I could not get soft brass, decided it was too much bother. And without a panbrake, getting a perfectly straight spine is going to take some effort.

If you have a drill press, and are prepared to spend about $30 at McJing's for an arbor & a slitting saw blade, it takes about an hour to make a jig. By cutting the slot in several shallow passes, you can get a nice, straight slot that fits the plate exactly. A tiny squeeze in the vise, and you have a perfect fit.

Cheers,

Originally Posted by IanW

I'm having trouble imagining how you could shim the plate without a tapered shim. It's going to have to be pretty well supported, to prevent flexing under the grinder. I guess you will show me in due course...

Hi Ian,
I'm still thinking about how to do that, the magnetic chuck will pull down pretty hard and bend the saw plate, which then springs back after it's released. I think a thick (maybe 1/2") laminated plate, made from alternating layers of brass and steel to conduct the flux through to the work, could be shimmed to the desired taper without distortion and would support the saw plate evenly and keep it flat.

Still pondering, .... Derek simpler approach will probably mean he'll have his tapered backsaw finished later tonight..

Regards
Ray

Hi Ian, Thanks for the information, I will definitely look into the arbor and slitting saw. Do the slitting saws come in a range of thickness's for the different saw plate thickness's ? I was rummaging around in goggly and found some half hard brass ( sounds like someone in cold weather), do you think that this would be worthwhile to try or a waste of time. For the blade tapering, could you use an old flat oil stone and do it by hand?, no heat to worry about but would be messy I guess and probably hard work. Just an idea, cheers for now Richie.
ps had a look at Ray G's website, simply brilliant.

Ray

Not as elegant as pure taper, but if you ground the first side to within, say, 1/4" of the toothed edge, couldn't you simply place the ground section on the chuck, overhanging the unground part, and again grind to within 1/4"? This effectively gives constant relief rather than taper, but to my thinking achieves equivalent result. Maybe also works for belt sanders?

Cheers

Si

Hi SiJ,

Never thought of tapering an existing saw, I was thinking of new saw plate.. but your idea is correct, the taper doesn't need to be linear, so long as the tooth line is a few thou thicker. After all that's what you do by setting the teeth. Swaging the teeth is another alternative to settting, but it's not practical for smaller teeth.

Hi Ritchie, Slitting saws do come in a variety of thicknesses ( and qualities) for light intermittent usage, I think the quality of the cheaper ones is fine.. slitting saw | eBay

A good source of brass, in all different sizes and alloys is George White George White | Australia's leading stockist & distributor of non-ferrous metals - Product Details

And, thanks for the comments on the web site, much appreciated.

Regards
Ray

Hi SiJ,

Never thought of tapering an existing saw, I was thinking of new saw plate.. .

Hi Ray

That's exactly what I suggested earlier.

...the taper doesn't need to be linear, so long as the tooth line is a few thou thicker.

That's good lateral thinking. However there is a reason for tapering the steel and not just reducing the thickness evenly (if I have understood you correctly). Tapering makes it possible to resharpen the teeth even though the plate becomes progressively thinner.

Our points are the same nevertheless: all we need do is reduce the thickness of the steel behind the teeth a few thou. That would be the equivalent to keeping the plate the same and extending the tooth line a few thou with set.

The question is "how much should we leave for the toothline of a dovetail saw"? I suggested 1/4" before. Is this sufficient?

Regards from Perth

Derek

Originally Posted by derekcohen

<snip>
The question is "how much should we leave for the toothline of a dovetail saw"? I suggested 1/4" before. Is this sufficient?
<snip>

Hi Derek,

I don't really know. But trying to think it through...

If we can saw up to 3/8" on a saw with no set and without binding , then it would seem to make sense that if the taper starts somewhere less than 3/8" from the tooth line it shouldn't bind. So that would start to set an upper bound to the distance of the taper from the tooth line. The lower bound would depend on whether you want the saw plate thickness to decrease too much on subsequent resharpenings. If the taper is only a couple of thou over the width of the plate then it probably doesn't matter if the thickness decreases from 20 thou to 19 thou after 1/3 of the plate has been sharpened away.

So the answer is, yes, I think 1/4 probably sufficient. I'm still uncertain about how much taper is required however.

I think Ian's reasoning of 10-15% seems about right.

Time for some experimentation.

Regards
Ray

Originally Posted by Richie Rich

I was rummaging around in goggly and found some half hard brass ( sounds like someone in cold weather), do you think that this would be worthwhile to try or a waste of time.

Yairs, after last week, it's not only the steel bridges missing some nuts round here....

Getting serious: if you're going to bend it, I would imagine starting with softer material would be a good move, but it would probably still require annealing to get a full bend. If anyone here decides to go down that path, I will watch with great interest, as it always seemed like too much trouble to me, but it may be easier than I expect.

The only brass I can get from a local brass supplier is 380 alloy, which has high machinability, but is too brittle to bend much. However it is stiff & does a good job as saw backs. Brass prices have shot up phenomenally in the last year or so, but a piece suitable for a saw back should cost less than $15, depending on size......

Originally Posted by Richie Rich

......For the blade tapering, could you use an old flat oil stone and do it by hand?, no heat to worry about but would be messy I guess and probably hard work. Just an idea......

Richie, my lad, you are young & energetic, so you may have the stamina, but if you have ever had to take a couple of thou off a chisel back, for e.g. you will know how long it takes to rub away a ridiculously small amount of hard steel! I've tried taking very shallow rust etches out of saws with various types of sanding papers, and have usually failed to make much impression. So any saw tapering that I get involved with is going to involve some electron-burning - sorry, planet.

Cheers,