most grinders have a small trough to fill with water to regularly cool the HSS – otherwise years of soldering makes finger tips fairly impervious to heat!

.

Be sure to clean the fur off … it smells awful when it gets hot

MichaelG.

I have a pair of holders comprising simple slots in square bar with some small hex socket grub screws to hold the HSS tool stock. Bar is about 1/2" or 5/8" square with, obviously,1/4" deep slots. Came out of one of the handy stuff boxes I've hoovered up over the years.

I suspect they were actually adapters to allow small square stock to be used on a large lathe without shimming or other tool height issues. The small grub screws are much closer together than the screws in a noraml QC hlder which would support the hypothosis. As would a couple of baccy tins worth of short ends ground to special purpose shapes.

But they work just fine for holding when grinding.

Rough shaping the tool with a thin angle grinder blade is much quicker and cooler than taking it all the way down from square on a bench grinder.

Clive

Yes just keep dipping in cold water & everything will be fine.

Steve.

Instead of seeking a confusing array of varying opinions on the internet, you should read any good book on beginner-level lathe work. They will tell you straight up to frequently dip your tool bit in water while grinding it to prevent overheating of the edge and softening there of.

I would recommend LH Sparey's "The Amateur's Lathe" as a starting point. For your milling work, Harold Hall's Milling A Complete Course would answer most of your questions.

Don't let the edge go blue

It occurs to me that if a person's finger nerves do not work well enough to send the brain a signal to dip a tool being ground that is getting warm in the water pot, maybe they should not be grinding tools or doing other hot work. Burns are no joke if they happen repeatedly in the same area.

Given that HSS like stainless, which is often surprisingly similar in composition, has a fairly modest rate of heat conductivity by the time your fingers get "ouch" hot the part actually being ground will be far hotter. With tooling its only the first few tens of thou at the business end that really matter.

I can easily see that vital bit getting heat soaked warmer than it likes if you take too long over grinding. Hard, fast, quick grinding with the right sort of wheel kept in good condition puts surprisingly little heat into the tool blank if you only do it for a few seconds. Most of the heat seems to go away with the ground off debris. Bit like using good quality carbine inserts "in the zone". Chips come off blue but the work stays relatively cool.

But most folk are using an affordable grinder with either the wheel(s) that came with it or an affordable alternative. Usually grey and intended for general purposes so optimised more for durability under unskilled, careless or frankly risky handling than getting the best edge on machine tools. Instructive to see the difference if you show the tool blank to a proper tool & cutter grinder with appropriate wheels. T&C grinder wheels on a bench grinder might be considered something between a tadge risky and an accident waiting to happen. Yup, I've done it and probably shouldn't have.

Keeping grinding wheels in the best condition isn't that easy for the home shop person. Especially if working without training or mentors advice. Getting to some acceptable degree of OK isn't too difficult but, as ever that last bit that really makes things sing is harder. Seems the last 20% takes more effort than the first 80%. A universal rule I think.

Clive

No they were weren't. They commonly refer to HSS.

Edited By Hopper on 01/10/2020 23:17:24

The most common cause of the hss getting hot is either the wrong grade of grinding wheel, or it has dulled and needs to be re dressed and sharpened. CBN works very well for hss , but again the wrong grade for roughing out and it all just gets hot. They have cbn dressing sticks as well. When roughing out a new tool I keep it cool by dipping the blank into the water often. When the water starts to bubble or boil, dip again. When the time frame to boil the water near the cutting edge happens inside 10 seconds of grinding, the wheel needs to be de glazed or re dressed again. An open 36 grit wheel is great for roughing out tools, while a 80 to 100 grit is great for the finishing and light touchups. Many just by the finer 40 or 60 grit and try to make that 1 wheel do everything. I only make form tools from hss or tools that the standard shape carbide tools do not cover. I try to grind all the tools with the hss not getting to a light straw colour anywhere. Good hss has red hardness, so can be dull red hot and not have the hardness reduced. For small internal radius on a tool, I use either the desic diamond burs, or dress a mounted point to create that geometry. I find with the dremel stones or the desic diamond points, that a smear of cutting oil helps it cut a lot longer before clogging or going dull. The better the front or cutting surface finish on hss tools , the better the finish on the part, and the longer the tool will last as well. A mirror finished tool will last more than 3 times longer than a just ground tool from a 60 grit stone.