T-slot cutters

[ths]

I need to make a couple of t-slot cutters for use in cast iron out of silver steel. They are both 5/32" thick by 1/2 and 5/8 diameter.
 
I was wondering if quenching in oil from red heat would obviate the need to temper them. I have always quenched from red heat in water in the past, then tempered to the appropriate colour, but am a bit nervous about getting an even result.

Cheers, Hugh.

[steamer]

A tough one Hugh,

I'd make up two....leave one untempered...only temper the shank on the second one and start with the tempered one.

Dave

[MuellerNick]

but am a bit nervous about getting an even result.

I would be more nervous to break the cutter at the first cut, because it is too brittle.


Nick

[jonesie]

no mater what you quench it it, it still needs to be stress relieved. you can look up the steel and there is a min. temperature to draw them at that will still keep them hard.jonesie

[steamer]

Agreed Jonsie....the problem is the typical process we use to do this is far from accurate....In the past I've used the cutters dead hard, and I've gotten by just fine.

I'd be worried about the shank on this breaking....but that's JMHO

Dave

[Ramon Wilson]

Hi Hugh,
 You should have no problem quenching silver steel in oil and getting sufficient hardness to successfully cut cast iron providing theres no hard spots.

Many cutters have been made over the years and this is my preferred method as quenching in water can cause brittleness even when tempered. I have made comments on this in the past at the relevant points on the Eta engine build and the Tigre build over on HMEM.

Biggest cause of brittleness to the home user is probably down to overheating - it needs be no more than a just on the bright side of a dull red - if it's getting toward orange it's far too hot. If in doubt cut a thin slice and do a test piece.

If you really feel the need to temper it then all traces of black from quenching require polishing off and all traces of oil removed. Heat a small tray of dry sand then, once the sand is nice and hot, place the part into and under the sand turning constantly to ensure even heating - you will have far better control of the temperature this way.

You may be able to make the cutters separate to the shank and hold them with a countersunk screw which definitely makes heat treating far easier...


This cutter is used radially to cut the exhaust ports but is in actual fact just like a teel slot cutter.

Finally you could always make two cutters too- one to rough the slot and the other to size it which would ease things on the cutters.

Hope this helps you some - Ramon

[MuellerNick]

Judging the right temperatures by color is a reliable way to do it wrong.
I assume, you have no temperature controlled furnace. But I'm sure you do have a magnet somewhere. If you heat the steel and check with a magnet, you do have the right hardening temperature if the work is no longer attracted by the magnet. Curie-temperature.


For tempering, the method with the color is also quite unreliable. Because the color is also time dependent. The longer it takes, the higher the faked temperature-indication is.
If you slowly let creep the color up from the shaft, it works out OK. Heat the shaft slowly and wait until the right color creeps up to the cutting edges.
 


Nick

[steamer]

Also agreed Nick....but I don't have a furnace...just a torch.....as do most.

If you have the gear...by all means use it!

I,  like Ramon does,   quench in oil...I have a little baby food jar with some used motor oil...additionally I use 0-1 tool steel...not W-1 which is water hardening.

Dave

[MuellerNick]

Sure, if it is a oil-hardener, quench it in oil. And if it is a water-hardener, quench it in water (oil works too sometime with small X-sections).
Depending on the alloy-content, you need a minimum cooling-down speed for the steel to get hard. And sometimes, only water is fast enough. Other steels get hard if you quench them in molten salt.


The point is, "dark red" is no temperature indication. You see different colors, depending on the ambient light. Almost everybody will say, that molten aluminium doesn't glow. It glows! I have casted enough times outside in the dark (when our casting sessions took a bit longer).


For tempering, you could use Termochrom sticks. Temperature indicating "crayons". The baking furnace is a good substitute (if wife is out).
Also, tempering isn't done in a minute, it takes half an hour or more. The color you get from that is completely different what you think it should be.




Nick

[ths]

Thank-you all for all the advice. It is a water hardening silver steel that I believe to be Stubs. My hardening and tempering equipment is a Primus torch. I'll probably do what I always have, that is to use water and temper by colour, but I have heard people here tell of using cutters that have been left in the hardened only state, or oil quenched only.

My nervousness has been to do with the spectre of catastrophic cutter failure in use. I've never had it before, should be OK.

Thanks again, Hugh.

[Ramon Wilson]

Hi again guys,

In light of some of the issues raised perhaps I could elaborate a little more on this subject ?

Fundamentally there are only two ways of going about heat treating metal. Firstly would be the correct way - using proper temperature controlled ovens capable of the temperatures required for the initial heat treatment and a separate and different type of oven for the tempering.
Given that virtually all of us would not have access to such kit in the home workshop the only alternative is indeed the humble torch and a brazing hearth and sand tray. The object of course is trying to achieve a result with the latter to that which is obtained by the former and one which, as far as 'hardening' and then 'tempering' something with such kit and the variables involved is concerned, is nothing more than a compromise.

That said there has for many many years been sound advice as to how to achieve this using 'colour' as a guide, both in heat treatment and in subsequent tempering. Though this obviously has pitfalls - not least an individuals perception of degrees of colour and more importantly the ambient light in which it is viewed this can provide a reasonable degree of consistency if done with care and uniformity.

I think it would be fair to say that virtually none of us would have the means to measure the degree of hardness achieved by flame hardening but were it possible it would soon be apparent that not much temperature change - in degrees of colour that is - before quenching would give quite variable degrees of initial of hardness. Consequently, tempering such variable parts to a given colour will also give the same inconsistency.

Hugh's initial question re oil versus water hardening on Silver Steel is a valid one as SS is usually stated as water hardening. That does not mean it cannot be hardened in oil just that it can be hardened in water. Personal experience both at work and at home shows water quenching SS even if carried out in controlled circumstances (work) can lead to brittleness. Oil quenching eliminates that possiblity to quite a high degree.

Where the initial heat treat is concerned, the colour - if that is the only means at ones disposal - is important if brittleness (certainly something not desired in a cutter) is to be avoided. Taking it too high before quenching can lead to making the steel brittle despite subsequent tempering.

All the cutters made at home so far have varied - some being left as hardened and some also tempered. The hardened ones have all stood up to the reqirements without degrading though some of the tempered ones have at times given up quite quickly.

Tempering using a direct flame really does not 'do the business'. Even with a soft flame the heat goes into -or rather onto - the part too quickly and if the colour is allowed to creep only the tip is tempered to the degree required given that it's quenched quick enough as the desired colour reaches the tip. There's also the fact that due to the direct heat the inner material is nowhere tempered to the same degree. Using a hot sand tray will give a much slower, much more uniform heat where the colour can be carefully controlled at a considerably slower pace as well as giving an overall temper both dimensionally and through the core. That said the temperature of the sand is not controlled and can still take the part beyond what is required if not carefully watched. If the temperature can be strictly controlled however eg in an oven the colour will remain constant depending on temperature

All this said though this is still a compromise ....

At work many many small components were heat treated in a controlled environment on a near daily basis. Mainly tool steels of varying sorts and differing heat treatment requirements  but many from GFS and Silver steel too. These would be hung in cages and heat treated, temp 850F (if I remember right) then quenched in whale oil. They would be tempered to manufactures guidelines which was usually two hours per inch of ruling section and twice at that. After an initial grinding they would all be batch tested for hardness which was usually Rockwell 58-60 for the GFS. This process was gradually worked up from a basic flame heating of the odd 'get you by' component to full in house manufacture. The only type of steel not dealt with was HSS as the ovens could not quite reach the temperature required though we used to do the Sverker tool steels which at 1000F plus would come out of the oven quite 'yellow'.

The first time the GFS and similar steel parts came out of the oven from it's controlled temperature was when the somewhat surprising low level of actual redness was observed (this was in average daylight conditions) Tests were done on some flame hardened parts which showed initial Rockwell to be far higher than recommended - since then I have always kept this in mind when flame heat treating and tried to convey this to others as a factor to take consideration of when doing the same.

Heat treatment, like most things is a vast subject, but like most times too we only just need to know enough to tackle the job in hand. It's nice to make a tool to last but most times they are just made for the one job and will soon sit languishing once used for that initial task.

Sorry for the long post but hope that will be of further use. Good luck however you tackle it

Regards - Ramon

[steamer]

Agree Ramon!   the only real way is to use the right equipment.

As it was described by me by a master watchmaker, if you polish the cutter all over, and heat the cutter from the shank, you can watch the colors change up to straw yellow, which it has been said is the "ideal" temper at which point you should quench in oil.

that said...I've been pretty successful using the small cutter I've used...AS IS   I think what happens is in use the cutting edge gets heated to the tempering temperature and it has always seemed to hold up OK...


works for me.

Dave

[Maryak]

Back in the dim dark days when Adam played fullback for Jerusalem, we made our own chisels in the blacksmith shop using a coke forge,  fitted with a hand blower i.e. the faster you wound the handle the more intense the flame, and a 3lb hammer plus anvil. After shaping and heating to what was a dull red in the shops ambient light, the tool was quenched in water.
Next came burnishing with a lump of broken grinding wheel followed by running the colours to the tip and quenching in fish oil, (smelled something rotten). I still have some of those chisels and they still work just fine.

I agree with Ramon that to be absolutely correct then the correct temps are a must and who would want it any other way if it was for the international space station. For what we do with our home made cutters the only sweat needed is that generated by the fire and IMHO 99/100 times it will do the job OK.

Best Regards
Bob

[tel]

And not only chisels et al - back about that era we used to do all the custom points, guides and cutters for the auto spring coilers from silver steel and/or gauge plate - all hardening and tempering by hand torch.

[Ramon Wilson]

'Morning Guys,
I was afraid, after I read my post that it might be seen that I was infering that the only way (for 'us') was the correct way. I assure you that is not so - completely on the contrary in fact. Carrying it out in a controlled fashion however simply served to show that what we do is simplistic by comparison. And though 'simplistic' it may be it can still be just as effective if done with a degree of care.

My first experience of it Bob was like you when as a young apprentice welder asking the blacksmith to harden the point on chipping hammer made from an old file - they lasted soo much longer than any commercial item. Far to many cutters etc have been heat treated over the years for the basic info not to be effective but the old adage 'Heat to cherry red and quench' is far to open for interpretation. What colour is a cherry for a start  Letting the colour run up when tempering is a tried and tested method too but doing it in sand is far easier with a better outcome for somone with little HT experience

No, what I had hoped to show was that heat treatment at home can be overdone particularly on the initial heating which will lead to brittleness which if so may then lead to someone on their early heat treating attempts being disappointed in their results.

The work I referred to began just as you describe Tel, all flame heat treated and sand tempered for parts that were required 'today' - all other heat treatment of tooling made being sent 'outside'. It was only after we began to do it ourselves that the differences and subsequently the potential for the uninitiated to overdo things by flame (including myself up to that point) that it became apparent.

Despite having this facility at my disposal I never did use it for any heat treatment of my own save for one item (a largish Acme thread tap made to cut the nut for the mill) still continuing to flame heat treat at home but at lower temperatures (colour) than before.

I think I may have said before - but personally I don't think theres a better satisfaction in our hobby than making a cutter and seeing it work effectively 

Regards - Ramon