Heatless grinding wheels?

[kb9tke]

I have come across a site that sells grinding wheels for the small rotary tools that claim that they do not heat up the metal as they cut. How is that? They were called Mizzy's and they come in various coarsness. I saw 80 frit and 320 grit. These, if they work as claimed would be ideal for making picks. Does anybody know why or how they do what they claim?
Thanks
r3jar

[Kaellman]

Interesting! Have no idea really. Isnt heat needed to be able to grind?

[Chucklz]

Heat isn't needed, it just happens to be produced through friction. Its physically impossible to not produce heat. Now, how much, and at what rate... those are variables that you can control.

[Mad Mick]

The amount of heat produced in the material can be reduced by regular quenching. I.E.
Grind 1, 2, 3, quench. Grind 1, 2, 3, quench. Grind 1, 2, 3, quench...

[kb9tke]

I have heard many people talk about the series of quenching you mention,however, when your using a rotory tool like a Dremel and you have the metal you are working on clamped in a vice. By the time you set the dremel down and then unclamp the metal to quench it has already cooled down somewhat. I would be very leery of hitting the metal with freeze spray after grinding. OR would that be a viable alternative? Any other suggestions anybody have? I bought my first set of picks from Southord but after seeing them and making a few, I beleive that I can make them much cheaper and then I can also add my own twist or ideas to them. Sure do appreciate the replies, though.

[Mad Mick]

An alternative to removing the workpiece from the vise, then quenching, is to have a wet rag handy. Work on the piece for a few seconds, then SWITCH OFF THE ROTARY TOOL & PUT IT DOWN BEFORE TOUCHING THE RAG (or have someone else hold the rotary tool), then quench the piece with the wet rag. If you're not comfortable with this, mount the rotary tool (securely but lightly, otherwise you could damage the tool) in a vise and use it the same way you would a bench grinder, quenching the workpiece every few seconds.

I recommend the latter for anyone who is new to powertools. And don't forget to protect your eyes when using any powertool!!

[NKT]

Nice double post there...

Anyway, a heatless grinding disc for steel would be impossible. The action of ripping little bits of steel off the bit bit of steel takes lots of energy - that's why steel is so tough! So you will always get heat.

If you want to make your picks nicely, practise quenching a lot, as in, grind for a few minutes, then quench, then grind for a minute, then quench, then grind for a few seconds, then quench, then grind for a second, then quench, with the grinding time dropping as you wind up working on smaller and thinner bits of steel. You can lengthen the time a fraction by wetting the resting plate on your bench grinder with each quench, so it sucks out some of the heat when you resume.

The other way, which I sometimes use, is a wet wheel grinder. You put about a pint of water in it, and it turns the wheel round quite slowly, running it continuously through the water, so that it picks it up, and you grind rather slowly, but it is totally cold. However, it is still heating at a local level, it just isn't allowed to build up and affect the temper.

I made my first pick like this from an allen key, and it is insanely strong. I defy even the clumsiest beginner to break one. It's overkill for the others, though.

[Mad Mick]

I defy even the clumsiest beginner to break one. It's overkill for the others, though.

Hurry, hurry! Step right up! Here is the challenge for May. If you can break this wrench, then you can be considered noob_of_the_month!!

[rayman452]

I use a grinding attachment thingy on my drill press, and hold the hacksaw blade in my pliers. Its very effective, I can dip it in water quickly, but I dont do it too often, which I dont know if it is tempered or not...its not springy, but its not hard...its inbetween, a springy hard.

[NKT]

Better to dip too often than not often enough.

You want the steel to be hard on the outside and springy in the middle, so it doesn't wear, but doesn't snap or bend either.

If you keep it below 250 C you will not ruin whatever temper the steel already has. Once you reach 300 you will start to change the microscopic structure of the steel a little, until you reach the various temper colours. Fortunately, the lower temperatures are the softer, springy levels (yellow and straw oxidation colours, heading to light brown) while the higher temps are harder and more brittle (blue, dark blue, almost black).

Grinders tend to leave a hardened surface that is very thin, due to the micro-scale melting when material is removed. This is good for picks. What you must avoid is getting the metal hot enough that it is coloured blue anywhere, as it will have lost most of it's strength, and be very hard. This means it will crack at that point, and eventually snap.

Whole books have been written about tempering, hardening, and general effects of temperature on steels of all different blends. Look it up, there is acres of text, but for a lockpick, just find some steel that you think is good, and keep it cool, so it stays like it was to start with.