Author Topic: Metal choices for conrods, crankshaft  (Read 4096 times)

Offline smfr

  • Full Member
  • ****
  • Posts: 1195
  • San Francisco Bay Area, California
Metal choices for conrods, crankshaft
« on: January 06, 2014, 05:59:42 AM »
It's time for me to think about the moving parts of my Muncaster's engine, and I have some questions about materials.

First, the conrod, which is about 6" (15cm) between holes:



I have some 1018 steel stock for this, but should I consider something with better machining qualities? People seems to use 12L14 quite a bit, but I'm worried about it's habit of rusting. I might be silver-soldering on the yoke too.

Second, the crankshaft. The between-journals distance is 2" (5cm):



I think I'm going to try silver-soldering this, and if that doesn't work, I'll try Loctite and pins. Is drill rod (O-1) suitable for the shaft? 1018 for the journals? Suggestions for US-available silver solders and fluxes is also welcome; I think I want some amount of fillet, and silver color (so maybe Safety-Silv®56?).

Simon

P.S. for those as confused about US/UK metal equivalents, I found this, which is quite helpful: http://dfwmachine.com/2010/07/steel-grade-equivalent/

Offline Jasonb

  • Full Member
  • *****
  • Posts: 6766
  • Surrey, UK
Re: Metal choices for conrods, crankshaft
« Reply #1 on: January 06, 2014, 07:43:56 AM »
The lead in the 12L14 can sometimes cause problems with silver soldering so the non leaded 1215 would be a safer bet and what I would use (EN1A here). Though I would make the conrod from a single piece.

Don't know if you can get it over there but for built up cranks I use precision ground mild steel, thie has a similar finish to drill rod but a lower carbon content similar to 1215.


Offline b.lindsey

  • Global Moderator
  • Full Member
  • *****
  • Posts: 13756
  • Dallas, NC, USA
    • Workbench-Miniatures
Re: Metal choices for conrods, crankshaft
« Reply #2 on: January 06, 2014, 11:35:11 AM »
Simon, as for the shafting, I prefer drill rod for being on size, smooth, and generally a good fit to standard bushing/bearings in its stock form.  Check out the following link for silver solders and fluxes...I have bought from them a few times and always with good service. As you can see, you have a choice of silver content as well. If I recall, Zee put me on to them.

Oops...left the link out....   http://www.contenti.com/products/soldering/420-820.html
Bill

Offline steamer

  • Global Moderator
  • Full Member
  • *****
  • Posts: 10398
  • Central Massachusetts, USA
Re: Metal choices for conrods, crankshaft
« Reply #3 on: January 06, 2014, 12:08:09 PM »
Another choice for cranks is 1144 "stressproof "   It machines pretty easily, and doesn't move around as much as say 1018.   

I have 3 steels in my shop, that pretty much do everything I need them to do  303 SS , 0-1 drill rod, and 1144sp.

For the rod, I'd choose 303 round rod if I was to steam the model to keep it from rusting....pretty much anything you want if it's going to run on air only.

Dave


"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline gbritnell

  • Full Member
  • ****
  • Posts: 2011
Re: Metal choices for conrods, crankshaft
« Reply #4 on: January 06, 2014, 01:09:59 PM »
Hi Simon,
I do find that 12L14 steel has a tendency to rust but not like you would think. Once a part is made and if left unpainted a light coat of oil is all that is needed to prevent most rusting. When I was an apprentice we had to work on the layout plate for a given amount of time. The layout man had squares (large ones), sine plates and height gauges. We had one apprentice that every time he touched the bare metal tools they would rust. What I'm getting at is certain people have more acid in their system/sweat and this along with the environment that the steel sits in has a great deal to do with it rusting. My little steam engines were made mostly from 12L and they have been handled by quite a few people with no visible rusting.
If you want a steel connecting rod I wouldn't be afraid to use 12L. As far as 1018 CRS goes I try to stay away from it as much as possible. It's just crumby steel to work with.
1144 only comes as round stock but for a connecting rod there wouldn't be much waste. It machines nice, holds it's trueness when cut and I haven't noticed any visible rusting on it when left out.
I would also recommend 1144 for t he crank if you are going to make it from one piece. If you are going to fabricate the crank by silver soldering then you could use a piece of 1144 or 1018 for the webs and as Dave said use drill rod for the shafts.
Here's a tip if you're going to silver solder the crank. Chamfer the webs where the shafting protrudes, outside for the throw and inside for the mainshaft. I also cut a small groove on the shaft where it sits inside the web for the silver solder to flow into. Also, drill center holes in both ends of the shaft prior to soldering. The reason for this is because after it's been silver soldered and the piece of the mainshaft has been cut from the center it will spring (warp) but 99% of the time only in the axial direction. Don't worry, mount it between centers on the lathe (dead centers) and true it up by either squeezing the open end in or wedging it open until the shafts run true to each other. If it's a small diameter crank .25-.375 dia. journals you can use the tailstock to apply pressure. If it's large then make up a clamping device. Never bang on the crank when mounted in the lathe!!! As to wedging it open I make a pair of wedges from a piece of flat .125 steel with 2 degrees on one side. I insert them between the webs and then squeeze them until there's a little pressure on them. I can't say how much pressure but initially not much. Prior to wedging or squeezing take an indicator reading then after take another reading. In most cases you'll find that the crank will move much easier than you think. Once you have gone through this procedure you'll gain a feel for how much to squeeze or clamp.
gbritnell
Talent unshared is talent wasted.

Offline smfr

  • Full Member
  • ****
  • Posts: 1195
  • San Francisco Bay Area, California
Re: Metal choices for conrods, crankshaft
« Reply #5 on: January 06, 2014, 05:15:44 PM »
Thanks for the suggestions, everyone! I think I'm going towards 1144 stressproof for the conrod and the other links (thought now I see it has a lower machineability rating than 1215)  :thinking:

Some good tips there for a silver-soldered crank, George!

Bill, I just yesterday ordered some Harris 45% and 56% silver brazing wire. The only place I could find online that had the 1/32" wire was http://www.airgas.com/browse/product_List.aspx?keyword=silver%20braze&CatId=484 so we'll see how that order goes.

This engine also has the piston rods and the crossheads as one forging. For that I'm going to try soldering pre-ground 303 SS to the crosshead, which will be some kind of mild steel.

Simon

Offline tvoght

  • Full Member
  • ****
  • Posts: 930
  • Indiana
Re: Metal choices for conrods, crankshaft
« Reply #6 on: January 06, 2014, 07:19:08 PM »
A heads up Simon, Speedy Metals currently has a 'Fire Sale' on a 24 inch long 2 inch diameter stick of 1144 for $20. A pretty good price if the dimensions suit your needs.  As to machinability, yes it is rated less than the free-turning varieties, but my very subjective take is that it turns like a dream.

--Tim