375 forum posts
Hi, I am building a 3" scale Allchin, The crankshaft and first drive shaft are in mild steel, I made the bearings from phos. bronze PB102 because I had some available. Now I am wondering if it was a good choice, I am worried the phos.bronze may only be good for hardened steel shafts and my mild steel shafts will wear more than the bearings. I am thinking I should bore out the bearings and fit a SAE660 leaded bronze or LG2 gunmetal liners
I would appreciate anyone's advice or experiance.
|1008 forum posts|
Unwise to ignore the BS recommendation for use.
Still it isn't going to wear that quickly, so you could finish the machine, get it into steam and have some fun and then order the 660 bronze. I've done the same on my 3" LS and that's my plan, and I'm not planning on a new crank! (Nor do I have the slightest intention of calculating the loads, nor of case hardening)
A lot depends on the load in the bearings and the highest load will be imposed by the water feed pump probably, if you are simply doing a bit of light steaming to run it in. Use the injector, shove a bit of proper teflon based grease in there, keep them clean and and keep an eye on them?
I'll let you know when mine pack up!
If you are really worried get crank and shaft nitrided?
375 forum posts
Hi Meyrick, thanks for your reply, very much appreciated, you have confirmed my fears but as you sugest there is no need to panic now, As you suggest I will finish the engine and get steaming then line the beraings with 660 bronze during winter workshop hibination.
You mentioned BS recommendations, do you know where I can find info on BS recommendations for bearings and shaft combinations?
|duncan webster||05/07/2009 20:24:50|
2643 forum posts
If you've got room you could bore out your phos bronze bearing and line them with white metal. It's not that difficult, you tin the bore with soft solder, then warm up the bearing and white metal to the appropriate temperature ( a cheap non contact thermometer would be a good investment), then pour the molten white metal into the bearing, let it cool and remachine. You can fit a sooted steel plug in the middle to reduce the amount of white metal, or just use newspaper to catch the swarf as you machine it and save it for re-use. Then of course, next time you need to fit new bearings, just melt out the old stuff and cast in some new.
We used to gauge temperature with pine sticks, like skewers, dip it in the molten metal and if it chars it is hot enough. there must be better ways!
375 forum posts
Thanks Duncan for your suggestion to use white metal, that sound interesting and will be a new experience, I think I will give that a go, in a year or two though.
|6 forum posts|
I am building my 7th. traction engine,I always fit cast iron bearings to mild steel shafts.
My first T/E a 3" burrell is still running on it's original cast iron bearings,after 32 years.
Why any one uses any other material for bearings I fail to understand.
The only brass based material in my models is if water is in contact .
Edited By Albert on 15/07/2009 09:26:21
|calder percival 1||16/06/2011 22:31:50|
|19 forum posts|
|Iron has around a three to one life span over bronze and if the lubrication is present it works much the same as a sintered bronze bearings as the iron "soaks " up the oil for slow release. We use cast iron bushes in our wire straighteners at work and they have saved us so much work instead of the old bronze ones which i might add were scraped in by hand everytime we changed them .|
|450 forum posts|
Duncan, do you know a source for White Metal in small quantities? I'm searching that stuff since years, but with no success. I'm sure it is still used in full size railways, but they need larger amounts I think.
|David Clark 1||17/06/2011 10:56:00|
3357 forum posts
Whitemetal for casting models is available from Alex Tiranti of Reading.
They do various tpyes.
|duncan webster||17/06/2011 11:07:24|
2643 forum posts
|I scrounge mine from a friend, what you are after is Hoyt's white metal, I'm not sure this is the same as is used for making lost wax castings. It comes in quite small ingots. You might find someone who reconditions old engines who would be prepared to sell you a lump|
|26 forum posts|
Try this company for white metal:
You need to make sure you get the correct grade though. White (or Babbitt) metal is an alloy of tin, lead, antimony and copper; the proportions determine it's melting point and its characteristics as a bearing metal. The more tin, the higher the melting point and the price.
You shouldn't really use second hand whitemetal, chiefly because of the risk of it being contaminated however there is also the need to know what grade it is and how it has been treated. If it has been over heated there is the possibility that it might have become "spoiled" which results in it becoming gritty and unfit for anything but scrap.
Whitemetal was used extensively for bearings during the steam age and is still used in some modern internal combustion engines today. It's a very good bearing metal and is vastly underated in my personal opinion.
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