Author Topic: radial engine cam material choice  (Read 1825 times)

Offline Ramon

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Re: radial engine cam material choice
« Reply #15 on: February 23, 2018, 09:03:40 AM »
Hi Petertha,

Tool steels - through hardening, oil quenched variety - do not usually react in the way you see it with a propensity to crack and distort - because of the temperature shock of quenching providing temperatures are in the right area for the specific metal. Flame hardening can be a bit hit and miss in this direction - it is easy to over judge the degree of heat required for basic GFS or Silver steel (Drill Rod) As mentioned previously there are ways to ensure the distortion of thin parts are kept to a minimum ie virtually nil if not completely nil. Cracking will usually occur if the temperature is taken to far and the material becomes crystallised and brittle on quenching which no amount of tempering will change.

Thin sections created by 'cut outs' as in your part are difficult to deal with from an uneven temperature aspect and using side plates (heated to the same temperature) will help a great deal to overcome this. Ideally if those holes can be reduced in size or moved away from the edge (or both) or as you suggest eliminating them entirely that will improve the situation considerably.

I've carried out a lot of heat treatment of small components in tool steels and have a lot of patience so ask away if you need to

Regards - Tug
"I ain't here for the long time but I am here for a good time"
(a very apt phrase - thanks to a well meaning MEM friend)

Offline petertha

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Re: radial engine cam material choice
« Reply #16 on: February 23, 2018, 07:29:00 PM »
Thank you Tug. I think that's worth an experimental shot then. Buy a stick of A2, make some test 'washers', one with peripheral holes & the other without. As mentioned I cant really see an obvious requirement for the holes & why they couldn't be eliminated. They add up to negligible weight savings which isn't an issue anyway. If its a complete flop I guess I can use the rest to make a kitchen knife :)

Just a general question to tap your obvious experience. If air & oil hardening steels are about the same price, machine similar to one another in annealed form (that's a guess on my part), similar temperatures involved, both achieve similar hardness levels post heat treating... why as model engineering hobbyists do we use O1 often & muck about with oil as opposed to make things from A2 & just let it air cool?

Offline Ramon

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Re: radial engine cam material choice
« Reply #17 on: February 24, 2018, 06:58:30 PM »
Hi Petertha,

I've no experience at all with air hardening steels so afraid I can't answer your question.

I can say that over the time I've been modelling I've heat treated (at home) using GFS (01) and Silver steel without too much problem overall though there has been the odd failure. I have a part not dissimilar to your own that I am concerned about distortion - the gear ring in the Bentley - but it has yet to be H/T. Made from GFS I intend to have that between two plates as described. If you go about it as suggested the distortion will be very small if any but the potential is there.

I made the thrust race rings from EN40b and had them Nitrate Hardened as this is virtually distortion free but then I was at work  ;) EN40b is not a very nice material to machine to a good finish so wouldn't suggest that option.

A while back I was cleaning down a couple of diesel engines after their run at Forncett. One of them had run backwards and that action had unscrewed the rear rotor pin. Checking other the other engines pins I removed one and it broke apart in my fingers. Made from Silver Steel these pins had been heat treated with real care because of their function but I would guess the undercut for the screw thread reached a higher temp due to the smaller diameter and became crystallised. All engines are due for a replacement pins made from EN24t which is a very tough but machinable high tensile steel in it's supplied state. Whether that would be an option for a cam ring I have no idea - perhaps Mike could comment on that.

Regards - Tug
"I ain't here for the long time but I am here for a good time"
(a very apt phrase - thanks to a well meaning MEM friend)

Offline john mills

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Re: radial engine cam material choice
« Reply #18 on: February 25, 2018, 07:02:43 AM »
i have  mostly worked as a machinist mostly hot work die steals for things like your cam ring I'm no expert but i would have housed m200  and nitride  m200 like 4140 can be supplied heat treated not to bad to machine
then nitrided a hard surface with little distortion can grow in size i believe 4140 can be done the same.I have not done much with steels that can be done properly at home.