Thread: rasp teeth pictures

David

Thank you for those macro pix. I will have to work out how I can do some of that photography. I'm not sure if it is me or the camera that struggles with the technology.

Regards
Paul

Paul, I use one of the grungiest old little hand scopes from an era of "wow, you can do that at home?" ghee whiz stuff where every new little device seemed like an i can't believe it moment.

it takes only low resolution photos, and I've attempted twice to replace it with newer hand held scopes, but they have way too much digital noise in their pictures for some reason.

Of course, I have a true metallurgical top lit microscope, but it needs a flat surface and the depth of teeth are way beyond what it can do.

I haven't had as much luck with quick pictures using camera setups, though a top camera in a dissection scope always seems like an attractive idea. Once you get into real cameras that fit in eye pieces, they are priced like digital cameras were in 2001, though. no idea why.

A saw handle rasp in process. In theory, this will be heated later and bent in a wood form when it's orange hot.

There is one thing that's not trivial, and that's shaping a piece of bar stock (or forging) and getting the hardness back to slow process annealed.

I made a blank before this one out of W2 steel, which is very low hardenability. It's still (by itself) in vermiculite, cooling too fast and though it's easy to put a few teeth in it, the abuse forces me to go back and sharpen and fix the tip on the graver every couple of rows.

I also have starrett O1 on hand, which is coarse spheroidized, or somewhere at least softer than fine spheroid. But you have to be careful - if you heat it to hammer it, the amount that O1 will air harden ends the game. If you shape it, you have to be careful to not heat it too much while grinding. I ground and filed this blank from a paring chisel blank (but turned backwards to avoid the end that I'd hammered a taper into) after giving up on the W2 blank.

And started to add teeth, but it's still a bit hard.

https://i.imgur.com/6h2RsBH.jpg

the holder for it is just a piece of wood with screws and 45 degree bevels on the side. Once you've gotten as much done as you can do on the flat, you just tip it 45 degrees and then the edges are presented upright.

I thought I had a smart idea by going top down because initially, you can set the tip of the graver between the row of teeth above it - as the graver goes in, it moves an ideal amount to make a next row. The fact that I probably heated this blank a little while grinding it is unhelpful, so I've sort of lost my way on neatness due to frequent trips to the belt grinder with a squirt bottle and fine belt to re-establish the tip of the tool.

My idea isn't that smart, though - here's why - I learned why the stitchers work bottom up - if the teeth are ahead of the graver and the graver slips a little, your fingertips just go into the rasp teeth above them, and they don't cut deep, but since you're grasping the graver, you get blood all over the teeth in small amounts.

This isn't that big of a deal - figure like tiny abrasions on your fingers - but it's a big deal in the sense that blood makes for a lot of rust.

The point of this test rasp is to make something like the gramercy saw rasp but with a slightly tubbier end profile and then much bigger teeth. If it's no good, I'll just throw it away.

It'd have been much smarter to use flat stock and make a flat first rasp - the initial mill softness wouldn't be threatened and one of the things that knocks the tooth off of the graver is not nailing the angle holding the graver to the blank.

the softeness is so critical, though - of the blank being stitched. You could do a whole rasp with a soft blank, but if it's even just a little hardened (we're talking about going from something like 5 hardness to 15), every little issue adds to the graver tip taking abuse and it eventually comes off. It takes only about 45 seconds to reshape it, but it's annoying. as it's coming off, you can feel it. If the tip is perfect, it literally will stick in the blank just placing it on the blank and it's far easier to get the strike.

There's an element like chiseling here, too - when you pinch the tip of a chisel and let it flop around, it's stressful on the edge. When you do it with a graver in steel and the graver slips or flops, it's *really* hard on the tip.

In my test pieces with flat stock, I've gotten to the point that I can just "tap tap tap tap tap" and everything is pretty consistent. With the half round, it'd take a week of tapping to get decent alignment and keep rhythm.

Nobody asked this question, but the answer to how you cool even a water hardening steel slow enough to get really low hardness is to heat it and other stock all at the same time and put all of it as a pile in vermiculite. Vermiculite is almost magical, but when something thin and light like a rasp blank is placed in it alone, the cooling is still too fast and you can feel that the tip is harder than the rest of the blank. I guess I'll need to find some buddy steel for the W2 to see if I can get it to get as soft as the delivered O1 bar stock from Starrett.

I also noticed a person bias while toothing this thing. for some reason, in my mind, it seems reasonable that the teeth at the tip of the rasp should be smaller and I started to pummel in bigger teeth working toward the tang.

i didn't think about doing this and do it, I just did it and realized later what I was doing. the tooth height isn't much higher, and it's progressive - the teeth are fatter and wider.

Now that I sit back and think about that, it doesn't really make any sense.

Originally Posted by D.W.

I also noticed a person bias while toothing this thing. for some reason, in my mind, it seems reasonable that the teeth at the tip of the rasp should be smaller and I started to pummel in bigger teeth working toward the tang.

i didn't think about doing this and do it, I just did it and realized later what I was doing. the tooth height isn't much higher, and it's progressive - the teeth are fatter and wider.

Now that I sit back and think about that, it doesn't really make any sense.

David

Isn't that like the progressive tooth rip saws, which were done that way to make starting the cut easier. I would have thought that would apply to your rasp in the same way. The grain of the rasp should be regarded as that of the teeth at the tang. While it might in fact be a distinct advantage with coarse rasps, it would not be needed on fine teeth. However, if it was there, I doubt it would be an issue.

Regards
Paul

Originally Posted by Bushmiller

David

Isn't that like the progressive tooth rip saws, which were done that way to make starting the cut easier. I would have thought that would apply to your rasp in the same way. The grain of the rasp should be regarded as that of the teeth at the tang. While it might in fact be a distinct advantage with coarse rasps, it would not be needed on fine teeth. However, if it was there, I doubt it would be an issue.

Regards
Paul

I think I was just thinking that finer teeth in the short narrow bend made sense (they're not hugely fine, though). I have no idea if it's a detriment, but of it was useful, it would appear historically.

But yes, same idea as a rip saw. Back half of the cut mire aggressive when needed.

I think files did the work of the fine rasp in the old days, though. I'd have to look at the seaton book, but i recall a coarse rasp or two and then wood files instead of very fine rasps.