Author Topic: Silver Steel or Free Machining steel??  (Read 640 times)

Offline bpudney

  • Full Member
  • ****
  • Posts: 13
Silver Steel or Free Machining steel??
« on: March 09, 2019, 06:10:02 AM »
My main interest these days seems to be 2.5cc compression ignition engines.  In the past I and many others have used 12L14 or similar steel to make cylinder liners.  In broad terms they are cylinders with a hole up the middle, typically about 15mm inside diameter, 19mm outside diameter and 35 to 40mm long, with exhaust and transfer ports.  Ideally these cylinders should be hardened, case hardening seems to be one method suited to "one at a time" manufacture.

For another task I recently got some 20mm diameter silver steel.  It machines well, not as well as the 12L14 but pretty good and takes a beautiful finish with a bit of care. 

In one of those light bulb moments I wondered about making cylinder liners from silver steel, because of the relative ease of hardening and tempering.  The only potential problem I could think of was distortion when quenching.  Not having any grinding capability distortion would mean the part becomes scrap.  After hardening/tempering the liner would only have to be lapped to produce the internal bore that the piston runs in.

I haven't done a lot of silver steel hardening and tempering, so what do others think??  Each cylinder takes me a few hours to make, so material cost isn't really an issue, free machining steel about $1, silver steel about $5.

cheers
Bill

Offline Jasonb

  • Full Member
  • *****
  • Posts: 6300
  • Surrey, UK
Re: Silver Steel or Free Machining steel??
« Reply #1 on: March 09, 2019, 08:12:51 AM »
Bill whats the difference between the risk of distortion from quenching Silver steel and the same risk when quenching the case hardened liner?

I've not hardened the steel liners I have made in the past but only made a few engines of this type.

Offline bpudney

  • Full Member
  • ****
  • Posts: 13
Re: Silver Steel or Free Machining steel??
« Reply #2 on: March 09, 2019, 09:19:45 AM »
Jason asked..........
Bill whats the difference between the risk of distortion from quenching Silver steel and the same risk when quenching the case hardened liner?

I've not hardened the steel liners I have made in the past but only made a few engines of this type.

Jason,   I don't know, probably not much!!  I have a few concerns about case hardening, one is the depth of case with modern (not as poisonous??) C/H compounds, such as the stuff I have.... Cherry Red.  Another is the stink and mess made.  With silver steel the likelihood is that the part will be through hardened and tempered and the bore, which is the critical bit will be nice and evenly hard and able to be lapped to a very fine finish, possibly better than the case hardened steel.
I suppose I'm flying a kite really!!
cheers
Bill

Offline Ramon

  • Full Member
  • ****
  • Posts: 1713
  • Suffolk in the UK
Re: Silver Steel or Free Machining steel??
« Reply #3 on: March 09, 2019, 10:11:18 AM »
Hello Bill,

On the basis of carrying out a lot of heat treatment at work I would agree that your biggest potential - indeed more than likely - issue to overcome will be that of distortion. As you rightly say if that occurs then grinding is probably the only option not only internal to true the bore but probably external too.

The first two 5cc engines I made - the Racers - had differing liner materials, one was cast the other from a very tough but easy to finish steel. I have no idea of the material spec save that it began life as a high stress stud coined form working offshore. It was stamped on the end CR 8 which I believe may refer to its tensile strength. As said it machined beautifully but it proved a real tough job to cut the exhaust slots with a home made carbon cutter. Just after these engines were finished I found squirrelled away in all my old C/L aerobatic stuff a long article by George Aldrich on using a CIS system - 'Cast (iron) In Steel' and leaded steel at that. His view was that up to 1 inch diameter a cast iron piston could be made light enough and the leaded steel gave an excellent wear combination with cast - and there was no need to harden :)

Since then all the engines I've made have done just that - I do run them but nowhere near enough to assess if wear is a long or short term problem but George was involved on the engine side of things with some pretty 'higher echelon people' in the competitive aeromodelling world in his day so can only assume that it was not such a big issue.

Dick Roberts - another well known engine builder over here told me that he did (case) harden his cylinders but these were also made from free cutting  En1a for ease of machining - not exactly a first choice material for hardening in this manner I thought but he assured me he had had no failures and that it did provide a hard surface. He told me that he stood the liner on end and filled it with case hardening powder then heated it up as evenly as possible before quenching . Needless to say my first question was that of distortion but again he assured me that it had been extremely minimal and that it had easily been dealt with using a home made lap.

With Dick's reputation as an engine builder I'm certain that that is a potential way forward for you but as you rightly comment it can be a rather messy and definitely smelly affair.

Silver steel however is a different matter - this is a through hardening material and as such if not heated perfectly uniformly and even more importantly - quenched absolutely uniformly - then given the thin section involved it would, with out doubt, distort and in all likelihood quite excessively too.

Personally Bill, I would not use Silver Steel or any other through hardening tool steel for a liner other than leaving it in it's soft state. Whether any would have as good wear characteristics as leaded steel I have no idea. Others may have differing opinions and it would be good to hear them but that said, given the point already made about the potential problems of having to cut ports with home made cutters, for me, it's full circle back to good old George ;).


Hope that helps some Bill, good luck with it what ever way you go and .... you won't forget to tell us all about will you ;) ;)

Regards - Tug

PS - the liners in the Oliver's will be from En1a free cutting steel too :)
« Last Edit: March 09, 2019, 10:27:42 AM by Ramon »
"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 Neil-Lickfold

  • Full Member
  • ****
  • Posts: 57
Re: Silver Steel or Free Machining steel??
« Reply #4 on: March 09, 2019, 11:12:22 AM »
Silver steel with varying section thickness like a liner,is not very stable at all. Even case hardening steels are not really dimensionally stable at all when chopped into with porting.  A2 or Calmax is a very stable material , even though it is heat treated right through. I have not made liners from A2 , but have made parts with detail quite similar to that of a liner that was quite stable. Keep in mind that a diesel engine can get to 200 to 210c. So get the liner tempered to this temp range. Allow a few thou for od grinding/hard turning and a thou or so for I'd lapping.

Offline Jo

  • Administrator
  • Full Member
  • *****
  • Posts: 12188
  • Hampshire, england.
Re: Silver Steel or Free Machining steel??
« Reply #5 on: March 09, 2019, 02:34:26 PM »
I was told by Eric Offen that unless I was thinking about taking up racing my engines, when I might want to consider chrome plating them,  to stick with Cast Iron or En1a liners.

Jo
Usus est optimum magister

Offline Allen Smithee

  • Full Member
  • ****
  • Posts: 867
  • Mordor, Middle Earth
Re: Silver Steel or Free Machining steel??
« Reply #6 on: March 09, 2019, 03:27:30 PM »
I was told by Eric Offen that unless I was thinking about taking up racing my engines, when I might want to consider chrome plating them,  to stick with Cast Iron or En1a liners.

John used to offer a "hard chrome" option on Oliver Tigers, but most people were of the view that running in the chromed liner took longer than the life of the piston!

AS
Quidquid latine dictum sit altum sonatur

Offline Ramon

  • Full Member
  • ****
  • Posts: 1713
  • Suffolk in the UK
Re: Silver Steel or Free Machining steel??
« Reply #7 on: March 09, 2019, 07:15:05 PM »
Bill, been thinking on this off and on through the day - a couple of questions of interest if I may.

I'm wondering if your reason for thinking about heat treating liners is based on that you are finding the previous cast iron in leaded steel set up is wearing unacceptably or is it you just fancy having an attempt at H/T? How often do you run your engines or do you actually use them for flying?

Also - how did your Nalon Viper perform, did it live up to expectations? I have two 5cc version cases made though made a slight error on one in drilling the cylinder bolt holes too deep. Once the 'waist' on the case is finally turned it's going to expose those  ::)


Neil -  A2 and Calmax are new tool steels to me but having looked them up I see the low distortion claim for the A2 and the fact that it is 'air hardening'. I have no experience of that process but always thought that the air need to be a blast. However from the info I found, though it didn't say it straight out,  it implied that just allowing it to cool would work too. Can you confirm that?
The info on the Calmex found did state that a blast was needed - if that's not very controlled on a thin walled cylinder would that not potentially give rise to distortion?

I was surprised to see that Calmex is an 'Uddeholm' steel - we used quite a variety of their steels but as said Calmex is a new one

I'd be interested to hear more about 'air hardening' ;)

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 bpudney

  • Full Member
  • ****
  • Posts: 13
Re: Silver Steel or Free Machining steel??
« Reply #8 on: March 10, 2019, 02:15:29 AM »
My interest in using silver steel was really because I have some, and as I mentioned the light bulb flickered on and I thought "why not".  However the responses seem to suggest that sticking with free cutting steel and persevering with case hardening may be a reasonable way to proceed.  I'm planning on using whatever I can make so having some sort of increased life expectancy might be a good thing.  Having said that I certainly haven't experienced any increased or excessive wear in my "soft" steel liners.  Thinking about it didn't most US motors use a soft liner?  Thinking Coxes here.
Onwards and upwards!!
Nearly missed Ramons questions....
I've always been interested in H/T as part of my apprenticeship involved making (literally) hundreds of small routing/drill templates from gauge plate.  I certainly hope to use any engines, at the moment I'm trying to make up my mind what to build for my #2 Sugden.....possibly an Ambassador.
I made two Vipers a Mk1 and a Mk2.  They both run quite well, not quite up to an Oliver though!!  But they are both heavy, the Sugdens weigh 147 and 141 grams for #1 and #2, the Vipers weigh Mk1 - 183 grams and Mk2 -197 grams.  Those steel fins on Mk2 Viper make a difference!!  I used to fly competitive free flight, so EVERYTHING got weighed!!
Thanks for all the help and advice, I think I'll stick to free cutting steel for now, with maybe an excursion to silver steel if I'm feeling adventurous one day!!
cheers
Bill

Offline Neil-Lickfold

  • Full Member
  • ****
  • Posts: 57
Re: Silver Steel or Free Machining steel??
« Reply #9 on: March 10, 2019, 08:15:53 AM »
The A2 is easy to heat treat at home. Just need to get it to bright cherry red, and let it air cool, ie take the flame away. If wanting to air quench, you need an air nozzle that creates a fan of air, like one of those augmenter heads or a vacuum cleaner in reverse, or if it has wire mesh on it, just draw air through the part.
Then temper in the oven . I find that tempering a few times is way better than just tempering once.
Although it is quite stable, changes in the   0.01mm range is normal. But us a whole heap less than the movement of either silver steel or O1 tool steel.
Another thing I have always though to try was getting a liner nitrided instead of the hard chrome route.
Where ever possible, I try and heat treat in a vertical as possible setup. With A2, I try and continuously heat the part as even as possible without it cooling.
In my view only the area above the transfer ports needs to be hard. That is the area that gets all the work out etc.
Neil
« Last Edit: March 10, 2019, 08:22:47 AM by Neil-Lickfold »

Offline strictlybusiness1

  • Full Member
  • ****
  • Posts: 203
  • ME., Tool Maker
Re: Silver Steel or Free Machining steel??
« Reply #10 on: March 10, 2019, 12:15:52 PM »
Does the A-2 benefit  from being wrapped in stainless steel to prevent decarburization?  Has anyone attempted to use any one of the Maraging steels such as C-350 which can be hardened at 900* to 925* F without any distortion or decarburization?

Jim Allen