Scalefour Forum

Winander wrote:...One thing I did have a problem with was distinguishing different 'sizes' of blade. I bought a packet of various sizes but they all look the same to me. Is it just the teeth per inch that differs? I was expecting some blades to be bigger.

Yes it is basically the teeth per inch than counts, though as the teeth get less frequent, the blades do get (just) visibly thicker. It is difficult to tell similar grades apart. I find I can get a reasonable comparison between two blades by running my finger nail down the teeth, but I do wonder if jewellers have a better method which doesn't involve a magnifier and counting teeth.

If your careful and the blade is nice and taught they shouldn't break all that often. I can get quite a bit done with a single blade over several sessions and it will only break when it starts to wear out. But then one night, when I'm being particularly careless or cack handed I can get through several very quickly. That is either a sign that I'm using too course a blade (not enough teeth) or that I really should go and do something else.

Will L wrote:Yes it is basically the teeth per inch than counts

The basic rule when sawing, regardless of the type of saw or the material is to have at least three teeth in contact with the thickness of the material being cut. The web site for Eileen's Emporium lists piercing saw blades with 32, 44, 52, 60 and 80 teeth per inch.(TPI) If my sums are correct a 60 TPI blade will have about 2.4 teeth per mm and an 80 TPI blade 3.2 teeth per mm. 1 mm is 0.039 inches and 0.5mm is 0.019 inches so that should give a guide as to how many TPI you need for a given thickness of material. The basic saw tooth profile has a vertical front face which is the edge that does the cutting and a sloping back face. (Someone who knows how to put a drawing on here can do that ) The vertical face should be towards the handle.

Having the blade the correct way round will held with the cutting and reduce breakages but identifying the correct way will probably need a magnifier although the expert can tell by running their finger tip lightly along the teeth. Buying a pack of assorted blades may seem a good idea but you would then have to tell them apart. Probably better to buy separate packs and keep them separately.

Terry Bendall

The blades vary in thickness. The ones I have go from 0.3 mm for 1/0 down to 0.18 mm for 6/0

Two links that may be useful - how to use a piercing saw and dimensions of blades.
http://www.guildofjewellerydesigners.co.uk/articles2/jewellery-making-techniques/462-the-piercing-saw
http://www.vallorbe.com/Download.php?f=documents/Scies_montures_gb_e.pdf

Thanks for the interesting links Andrew.

From the first:

Piercing saws are designed to be used vertically. If you try to cut with the blade held in a horizontal position all you will achieve is lots of broken blades.

Entirely logical if you think about it; the blades are fragile and horizontal cutting increases the risk of the blade carrying the weight of the saw in addition to all the other stresses upon it. My interpretation of the remainder of the advice is that the cut stroke is downward, which is contrary to normal sawing, and why Terry says the vertical front face of the blade (that cuts) should be facing the handle - something that raised my eyebrow.

Thanks also to Will, Bill and Terry for the other advice.

regards

Packs of multiples of many sizes are available cheaply: e.g. http://www.ebay.co.uk/itm/Jewellers-Saw-Blades-Pack-144-Various-Piercing-Blades-/300384437593?hash=item45f04ec559:m:mJiPm-dJVhZWQ6dPqxPHLXg. 4/0 is fairly fine and 6/0 is very fine. I'm not sure how those grades translate to teeth per inch. I bought a pack from this vendor a while back and they seem fine.

Winander wrote:the advice is that the cut stroke is downward, which is contrary to normal sawing,

Yes it is but fret saws, coping saws and bow saws, all used for cutting curves in timber also work in this way. For all other types of saw the blade cuts on the forward stroke. The reason of course is that they are all fairly thin blades that need to be kept in tension when cutting.

Terry Bendall

Terry Bendall wrote:... fret saws, coping saws and bow saws... all fairly thin blades that need to be kept in tension when cutting.

... so the blade is tensioned by the pull stroke, whereas a push stroke would de-tension the blade. You're never too old to learn, I've just checked my coping saw and the blade is the wrong way round, as every blade ever fitted in it

Thanks Terry

regards