Thread: grinding high speed steel

For metal lathe tools I always grind holding the tool steel in my hand Thus water cooling is necessary Accuracy not speed in grinding tools is I feel more important
If speed in getting a tool into operation is important then use throw away tipped tools
I have not yet had to grind my woodwork lathe tools as I don't do much wood turning just a few knobs handles etc and so far have been able to sharpen the tools with stones

Being an old fella I was always taught never to grind so hard as to get a colour change .



The trouble with life is there's no background music.

I've never had any problems grinding it hot.....HSS being designed I think for high speed (which means high heat....what I've always assumed....could be wrong) would mean I guess it can get hotter in your hand without loosing its temper.....

They work well with my setup to sharpen jointer blades......I just grind them square to renew a straight edge then bevel it on the AlO wheel off a tool rest then.... buff the tip on a hard felt buffing wheel.......the point being I found I can be quite relaxed about heat buildup with HSS on both wheel types.....unlike regular tool steel........

Its interesting how quickly some blades can loose their temper though..... I sharpen my straight razer on the buffing wheel......its taken me years to do it right........ I would get the razor sharp enough to shave but then the edge would crumble very quickly in a way that implied it had lost its temper.....when sharpening I had expected to feel a heat buildup first, but it always felt cold in my hands.......what the problem turned out to be was that the blade was just so thin it would burn up on the tip without my fingers even feeling any heat............suppose its obvious, but it took a while to work out......now its just a couple of very light passes and its done....ready to go back to the bathroom and cut my throat...

I think the most important thing when it comes to grinding hot on your grinding wheels is to dress it very frequently, more often than one might think.....I use a diamond stick in a jig that works off the tool rest.....with a light hammer tap to drop it slightly I then make one quick truing pass .......I might do this every couple of minutes......its just so obvious to me how much an improvement it makes......grinds far quicker with the same amount of heat buildup.......

I'll get some pictures

I sat down last night after getting off line & read the whole thing all 12 pages of it.
Very interesting. There seems to be a bunch of accepted wisdom that not realy based on fact. There alsoseems to be some detail a lot miss.
Seems to me that a lot of people havn't got their detail right & are confusing different acceptable methods for different types of steel.
I wouldn't be surprised if a lot of people don't know what is made of what steel & therfore how it should be treated.
check out the ariticle. I'll be doing some further investigation of my own.
cheers

Don't know how you managed to get through all 12 pages.......I got through about 3........has me looking twice at my ravings ......do see what you mean by lack of fact.......there would be some contradictory findings in that lot for sure, despite each party being adament their right...........

one thing that I'd like to find the truth on is the use of water to cool a blade, from what I've read you shouldn't use water to cool any kind of blade because the sudden compression it brings causes small fractures at edge that are invisible to the eye yet contribute to a faster rate of wear when the blades in use...........is this true ?

anyway it would be interesting to see what you can find out on the topic.....maybe wise up a few on their grinding methods.......including myself.

Originally Posted by apricotripper

one thing that I'd like to find the truth on is the use of water to cool a blade, from what I've read you shouldn't use water to cool any kind of blade because the sudden compression it brings causes small fractures at edge that are invisible to the eye yet contribute to a faster rate of wear when the blades in use...........is this true ?

.

For quality steel (30 years ago) I was taught to use oil to cool the steel as water cauld cause fractures

Have never seen any real printed evidence either way but a lot of blokes who said that they had read this or that but could never show me the article
I honestly don't know but being set in my ways usually use oil unless there is none handy then I use a substitute water


The trouble with life is there's no background music.

Ta Ashore,,,,,,never tried oil......I'll give it a go,,,,,,the only thing that puts me off the idea is that I'll probably end up getting oil everywhere..........but, if it works I'll do it....... the approach I usually take is to sharpen blades in pairs, that way while one is cooling I can grind the other.

Originally Posted by apricotripper

Ta Ashore,,,,,,never tried oil......I'll give it a go,,,,,,the only thing that puts me off the idea is that I'll probably end up getting oil everywhere..........but, if it works I'll do it....... the approach I usually take is to sharpen blades in pairs, that way while one is cooling I can grind the other.

Use a thick 30 grade oil gearbox oil then wipe it clean it only costs the bottom foot of a sheet and shmbo may not even notice.
but as I say have never seen anything in print just what I was taught 30 odd years ago


The trouble with life is there's no background music.

Our profile grinder at work has a pump set up where it cycles cutting fluid past the knives being shapped. We use High Speed with abour 18% carbon, and some of our knives are tungstan.

What I remember from when I used to be a machinist using carbide and HSS tools for machining various metals.

We used to grind our HSS tools by hand but didn't have coolant feed on our grinders. The purpose of the soluble oil solution is to cool (really stop the job from overheating) and lubricate the wheel to aid the cutting action.

HSS is hardened and tempred steel. If you heat it up too much you will damage the heat treatment allready applied to the HSS. Likely it will become soft and even brittle. When grinding you can keep it cool enough by having a container of water to dip the job in every so often as you go. Clear signs of overheating are when it starts to get straw and then blue colours. If it goes red hot you will really have to grind a lot off to get rid of all the damaged material.

To have ultimate sharpness and a long lasting tool it is important not to overheat it when you grind it.

Stevo

I say again. If your HSS tool is getting too hot you are being to enthusiastic and grinding too hard, trying to remove too much too rapidly!
As one very experiencerd turner said to me. "When I buy a new chisel I grind it once, after that I sharpen it".

The 12 pages is definitely worth the read there are some interesting twists in the plot toward the end.
main points that I can confirm from other sources.
1. DO NOT quench high speed steel it causes fine cracks in the metal.
If you are goint to use cooloing it must be from the "get go" & the tool must remain "cool".
2. high speed steel is not the same as ordinary tempered high carbon steel like used in hand chisels & plane blades. High speed steel is not hardened & tempered steel. It is a completely different & specific alloy and its metalurgy, hardening & tempering is a complex business.
3. high speed steel will stand high temperatures in both cutting & sharpening, well past the oxidising coliours & into dull red glow.
4.Ordinary high carbon steel will not stand anything like high temperatures.
5. some of the posts here confirm the misunderstanding in the detail concerning high speed steel.

I continue to seek more info.
cheers

Here's my fimble results (from experience)

- Carbon steel heats up faster and easier to lose temper on a dry grinder than HSS.
- I now grind all my turning tools by hand on the dry grinder (sure it wears them down faster, needing to be relaced faster, but its only a 3-4 second touch up job on the grinder to get them "sharp" again - I leave the burr.
- I use water to cool (if needed), and no problems so far.