Making sharpening stones

[sdjp]

Anyone every tried, or got any insight into, making a (synthetic, obviously) stone?

I've a couple of plans ahead that involve making some tools with odd shaped cutting edges. There's lots of ways to approach that; by far the best is to mill the shape, then harden (And, if needed, stick a grinding point in the mill for a precision finish). Lacking a mill, I'm looking around for other options. I can get pretty close by various options (file + harden + grind, depending), but the final shaping seems to me to be best done with a shaped stone.

I can, of course, buy a stone and then shape that; I've got the diamond tooling for that, but grinding is never fun at the best of times, and grinding something friable is almost certainly going to be significantly less fun that that.

Hence the idea of seeing if I can form a stone roughly into the right shape; let it cure, and then minimal grinding to produce the desired surface.

For a proper polishing, I'm thinking MDF + various compounds or diamond paste; but I don't think that it would work well as a substrate for the coarser grits (say, 220); although if anyone's tried that, I'd be interested.

(There's also a degree of wanting to be able to make _everything_ needed to make something - although that's always a dangerous impulse to indulge; he says, whilst indulging same… :? )

 

[Inspector]

Nope but I watched my father take a stone from the driveway and flatten and shape it on the cement sidewalk beside the house.

I would make the shapes wanted and wrap sandpaper around it.

The only other option that comes to mind it to find a Potter and use different clays for a range of abrasive qualities, or mix abrasives that can take the heat of firing into the clay.

Pete

 

[Dave D]

How about 3M sharpening paper from Workshop Heaven stuck to a wooden former, starting with 100 microns which I believe translates to around 150 grit.

 

[Cheshirechappie]

You don't say what the tools with odd-shaped cutting edges are intended for, but if they're to cut wood, it might be worth a trick some moulding plane makers used. They tempered the irons to a spring temper, so that whilst not as hard as most woodworking edge tools, they would do a fair bit of cutting before needing resharpening. Some brace augers and, of course, saws used about the same temper. The advantage was that they could be reshaped with files, and only the final edge dressed with slipstones (or fine abrasive paper on a suitably-shaped stick).

Course, if the tools are for cutting metal, you're back to a lower temper and grinding of some sort!

 

[jimmy_s]

I would think you would need to use a phenolic resin (novalac type) and a crosslinker such as hexamine to form the substrate along with some reinforcement.

Please see attached link on Phenolic Resins and applications

https://www.plenco.com/phenolic-novolac ... resins.htm

 

[nanscombe]

I wonder if you could form something from wheel cement and grit on a former of some kind?

The Polishing shop

 

[sdjp]

Thanks guys, lots of good thoughts there.

How about 3M sharpening paper from Workshop Heaven stuck to a wooden former, starting with 100 microns which I believe translates to around 150 grit.

Always possible, but there's a minimum and maximum radius of curvature to which you can bend paper. In particular, one of the plans has a pretty sharp 60 degree corner, and that sort of bend never comes out right with sand paper, and is worse at the coarser grits. (The 3M might be better for that? I've mostly used local store wet'n'dry papers)

You don't say what the tools with odd-shaped cutting edges are intended for, but if they're to cut wood, it might be worth … temper[ing] the irons to a spring temper

They are for wood, think 'gouge of unusual cross section' - although the plan is to make a fairly standard circular gouge first, for experience, before getting exotic. Spring temper is an option - but a little beyond my current heat treatment equipment at present (short of waving a torch around, which does lack a little in precision…) I'm also not sure that it would stand up to use with a mallet - spring tempered tools aren't usually used like that, so I don't know if that would be too much.

I would think you would need to use a phenolic resin

For a powerd grinder, probably. The big advantage of phenolics is they work up to high temperature. For hand grinding through, it would be a little overkill. It's not clear that something a bit more conventional (like an epoxy) would be inferior, once the heat production problem is removed.

Also, phenols and formaldehyde are both on the Poisons list; and appropriately too! Anything that has an LD50 specified for _skin contact_ is not something to be taken lightly! I've handled worse, back in my lab days, but still something I'd want to be sure I needed to deal with before going down that road.

I wonder if you could form something from wheel cement and grit on a former of some kind?

And that's _exactly_ the sort of thing I was hoping for! I wasn't thinking about powered wheels, but 'wheel cement' has opened up a whole new route. It should work for an manual stone, and I might just look at some sort of rotary tool too. The various instructions imply a grit range of 60 to 320 or so; which is pretty much the range I was looking for a shaped stone at.

Just knowing I'm not _totally_ nuts [0] is very helpful.

[0] Well, not for this idea, at any rate…

 

[nanscombe]

I remembered finding that before for someone who wanted something similar.

Aha, here it is. A thread by walney col.

"Making your own abrasives with aluminium oxide powder"

http://forums.ukworkshop.co.uk/viewtopi ... 0&p=894326

 

[JakeS]

Always possible, but there's a minimum and maximum radius of curvature to which you can bend paper. In particular, one of the plans has a pretty sharp 60 degree corner, and that sort of bend never comes out right with sand paper, and is worse at the coarser grits. (The 3M might be better for that? I've mostly used local store wet'n'dry papers)

The 3M 'papers' I've had from Workshop Heaven have been plastic films - they form a fairly good corner, certainly better than wet'n'dry, but I wouldn't rely on such a fold to sharpen something to a precise 60-degree edge, if that's the point. If you'll excuse the pun.

(My concern for those, however, would be that the self-adhesive back probably isn't self-adhesive enough to stick reliably down to a non-flat surface.)

 

[adrspach]

For more round shapes you can use hard felt wheel impregnate it with glue wait for it to harden, shape it as required and impregnate it with with yor grinding medium. I am not sure how it would work with sharp corners. However if you want that for mechanical power then I would worry about overheating and stone falling appart due to centrifugal force.
For hand sharpening I know that guys on one of the razor forums tried different glues as bonding with different grits either in form of chromoxide or other oxides which you can get for tumbling.
In my opinion far easiest way is to get a piece of decent sandstone or slate and shape it to your liking.

 

[sdjp]

I picked up a tub of the Coldax adhesive that Nigel mentioned; and have done some preliminary studies. I've held off posting anything, due to missing a cable to get the photo's off the camera - all I've got to hand is the photomicrographs (which were captured directly).

I took a piece of brass, left half 'polished', there other side got textured with a 240 grit flap wheel (on a dremel like tool). Then I took various abrasives, and applied them at right angles to the texture. The 240 flap disc; a 320 non woven block; 320 Al2O3 bonded with coldax on a hard felt; and finally 400 SiC bonded with shellac on wood. (There's nothing like changing only one variable at a time … and that's nothing like changing only one variable at a time!). The first three were on the dremel, last one by hand.

That Coldax adhesive is pretty phenomenal! It's a little thicker than it looks, I left too thick a layer on, meaning that it sagged a little bit on the drying - however, it worked fine, despite being a tiny bit off centre. Roll it in the grit, and it picks up just the right amount. Easy to use, and seems to be forgiving go my poor technique on the first go.

I used a 10g per litre (1lb cut) blonde shellac, and it didn't hold the grit well enough - ablated away too fast. Still, worked to a degree. I've some 20g per litre (2lb cut) dissolving, so I'll have a second go with that, at higher concentration.

In all honesty, the wider photo's are more interesting, but here's a photomicrograph of the 320 on the coldax - the 320 is vertical, initial texture was horizontal. You can just see the remains of the 240 grit initial texture - that's just about 10 seconds worth of lowest speed on the dremel.View attachment 320

Basically, looks good enough to try in anger - I've some stock on the way, and I'll go about forming a round gouge (12mm No 9), and see how well the coldax works on rounded felts, and an actual job. Proper photo's to follow, once I locate the cable...