Which oil for quenching ?

I've just finished making handbrake parts for a 1947 Humber Hawk Series 1, the toothed quadrant and the mating pawl, from 1/4"gaugeplate. After much careful measurement (not easy, given the badly worn state of the originals) I knocked up milling jig No. 1 and set to work producing the quadrant shape.

Jig No.2 then produced the teeth ....

using a carbide tipped routerdovetail cutter, which worked suprisingly well.

Then jig No1 was re-used to check the pawl shape, using a piece of bar drilled at the correct centeres to represent the handbrake lever ...

Now I have the machined components and it's time for hardening and tempering. Data on the gaugeplate wrapper suggests 780 - 820 degrees for hardening (held at temperature for 15 - 20 minutes, Tubal Cain), then quenching in oil. Tubal says engine oil gives variable results, so which oil is best ? I don't do much hardening so don't need gallons of the stuff, and I'd like it to be very reasonably priced. Any suggestions ? Your help will be much appreciated,

Thanks,

Ken.

I'd be inclined to try a heat treatment company, who will have the correct oil. In my apprenticeship days it was whale oil but I would guess that is difficult to obtain nowadays!

I use brine; seems to work fine. Provided you vigorously agitate the part when quenching it results in a hardness measured as greater than Rc65. Tempering as detailed by the manufacturer results in reduced hardness, in line with the manufacturers data.

Andrew

Edited By Andrew Johnston on 02/08/2015 21:08:34

I would agree with Brian - after taking the effort to make it, I would be miffed if it bent or cracked when I tried treating it. The problem with sub con HT is the minimum charge they normally have (circa £50). Perhaps you could get it done by a local machine shop who get regular treating done and bung them a few beer tokens?

If you do try DIY then think about the best way to quench, I would guess it needs to go in bowed edge first with teeth at the top - on it's back so as to speak but certainly edge on, not flat side first.

Mark

Ken,

Gauge plate is formulated to minimise distortion. Quenching in oil has a reduced cooling rate compared to water (or brine) which also helps to keep distortion at bay. I've successfully used straight SAE 30 oil (new!) but there are several references on the web to using vegetable oil. I think the cheapest cooking oil in the supermarket will do the job admirably. I don't suppose there was anything magical about whale oil - before the mineral oil industry took off I believe it was the only none gumming commercial oil available in bulk, much used in oil lamps. I would imagine that the most important part of the formulation for commercial hardening oils is to give a long life - something that is probably not relevant to our usage.

Nice bit of machining by the way,

Rod

Some useful tips there chaps, thanks. Commercial H.T. companies are out; too expensive, so it's a DIY job alright. I like the idea of using cooking oil; I'll look for web references, as Rod mentions, before jumping in. And yes, edgewise immersion too. All good thoughts,

Thanks again,

Ken.

I tried veg oil once on a D bit around 3/4in dia with a reduced shank. Not very good as I don't think there was enough of it to cool the metal quickly enough. Personally I would use a lot of water, get it all in quickly and be sure to wave it about.

Thanks for the idea of using a router cutter. I have used them on aluminium a few times but not steel and if they will cut gauge plate it widens their use.

Next time I harden something I am going to try the clock makers method again. Soap. One I talked to reckoned it didn't matter which type but when heating blacken it all first - my way of putting that - it should all fly off when quenched.

John

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All British gauge plate I've ever seen is oil hardening to minimise cracking /distortion. Quenching in water/brine is asking for trouble. Gauge plate is not a plain carbon steel & is an alloy steel formulated for oil quenching.

The D bit round stock mentioned is probably "silver steel" which is a plain carbon steel & is water /brine hardening. I've never oil quenched silver steel so cannot voice an opinion on this.

The more exotic "tool steels" have various additives to give high hardness/toughness/min distortion to allow for oil quenching.  

Edited By Dinosaur Engineer on 03/08/2015 02:14:15

Used to harden hundreds of inch square by eighth thick gauge plate guides with a v cut out in old engine oil that gave a black finish, all came out ok.

Had good results with canola (rapeseed) oil from the grocers, preheated to about 35C in a slow cooker for quenching oil-hardening stock. It certainly smells better than old motor oil, and when it's cooled, just pour it back in the jug. The domestic authority knows that containers in the shop are not safe to put in the pantry.

In the past our local Blacksmith/Engineering Shop used Castrol R oil for all Quenching/hardening/tempering jobs - Will always remember the resulting smell (like being at a motor meet) - sort of follow along the lines of a vegatable based oil

You should weigh the cost of heat treatment firms against the cost of failure if the part breaks in use possibly damaging the car or possibly killing a bystander if it fails while parked on a slope.

Then professional heat treatment may be the better option.

I have used old engine oil,it works ok,just do it out doors ,its a bit smokey and can catch fire. I usually harden gauge plate in water,Last tool I made from 3/8 gauge plate was a curved tapered gib head key extractor about 7 inches long,this was hardened and tempered with a Calor gas torch and water quenched, and has taken a few beatings since,its now on the A32 somewhere after I went to help a full size traction with a troublesome flywheel key,and one of the crew must have dropped it.

Silver steel is an alloy tool steel. At one time or the other I have seen it mentioned for both water and oil quenching.

I have quenched items at work in oil - it was in something the size of dustbin and nearly full and plenty of room to wave the item about.

The main difference really is the cooling rates. Water is about 3 times faster than oil also boiling temperatures.

As an aside last time I handled one of these things it was pressed steel so why harden and temper it anyway? It's likely to be a lot stronger and more hard wearing than the original anyway. Heat treating the pawl would make mores sense as it has a much harder life but I feel that it would need tempering into the blue so also questionable really.

My driving instructor used to do his nut if I just pulled up the handbrake without pushing the button first. Just shows how quickly they can wear out.

John

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Old engine oil is the one I have heard mentioned as much as whale oil. The carbon deposits must make the difference

The oil water choice is down to cooling rates. Water is something like 3 times faster but spoiled by boiling to some extent which is why in both cases the parts need waving about. Taking an extreme HSS is likely to crack if quenched in water due to it's hardness and differential cooling through the section. Even more extreme stellite can crack due to quenching because it gets too hot while grinding it.

Where people at home get away with quenching oil hardening steels in water may just be down to none optimal conditions and simple sections. Relatively low amounts of water and space to wave it about etc.

People shouldn't forget over heating can cause problems as well.

John

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i seem to recall most hand brake quadrants I have seen (and I have seen a few over the years, but never taken much notice of their manufacture) have had just the ratchet hardened - most likely induction hardened. That's not something you can do at home easily!

Mark

I stand corrected Silver steel is an alloy steel - normally contains Chromium and Manganese in addition to the carbon.

Gauge plate is similar in composition but contains further additions such as Vanadium & Tungsten to give improved properties.

You can probably get both formulations in bright drawn or black.and save money if they are to be machined all over.

Don't ask me what numbers - I'm an animal I just ask the supplier for what I want. A silver steel equivalent is available in round black bar so probably available in other sections. After all they have to be made out of something in a more raw state.

John

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Edited By John W1 on 03/08/2015 12:54:10

The Mondeo auto-adjusting handbrake won't auto adjust if the push the button in!

Am I the only one impressed that a router bit will mill gauge plate? I thought the received wisdom is that one would chip if used like that.

Neil