Did I do it right? and what was the cause - bowed metal!

[Metal Mickey]

I am making a long lever for my Fowler A7 2" scale traction engine and after milling one side of the lever, after releasing it form the clamps it had bowed.

I remember reading somewhere that this could be caused by tension in the metal and heating it and letting it cool down slowly would remove these stresses.

After heating.......

it returned to normal with no hitting with a big or small hammer.......

Did I do the right thing? Did I cause the problem when I milled it? I took light cuts because of the clamping and used cutting oil. I was not conscious of generating a great deal of heat........

Whilst there isn't a problem with the outcome I would like to know what happend, why and what I should do in future......

 

[Jasonb]

Using black bar rather than bright will help keep it straight as there are less stresses introduced into the metal when its rolled.

The other option which is what is suggested in the build manual is to use 3/32 bar or plate and silver solder the various bosses to this which saves all that milling. I did the reversing lever on my minnie this way and will do the same with the Fowler.

Jason

 

[Loose nut]

Your bending problem is a normal "pain in the A....." occurrence.

I will heat the metal up red hot and let it cool slowly before using it, if the part has long thin sections, to keep it from bending from stress. If the part has to be made with a certain level of hardness though that will require a little research and maybe different methods of stress removal.

 

[Metal Mickey]

Thanks for the comments so far......I will see how it turns out before trying the manual method...all is a learning experience so it seems...........

 

[Brian Rupnow]

This is a very common occurance when using cold rolled steel. The "rolling" of the steel to a specific size is done with the metal at a much lower temperature than the forming process for hot rolled bar and plate. This rolling sets up a lot of stresses in the outer "skin" of the part. When you machine the outer few thousandths away on one side, but not the other, the part will bow as thes stresses are no longer equal from side to side. It happens with hot rolled steel also, but to a much lesser extent.

 

[CrewCab]

This is a very common occurance when using cold rolled steel.

So ............ If "one" : ........... is going to make a long, slender part out of cold rolled steel, is it best to heat up the material and let it cool (err..... would that be anneal?) .......... first ........... just a thought

CC

 

[Brian Rupnow]

So ............ If "one" : ........... is going to make a long, slender part out of cold rolled steel, is it best to heat up the material and let it cool (err..... would that be anneal?) .......... first ........... just a thought

CC

I'm not really sure, but I would be cautious of this. If the cold rolled were heated in a furnace, where the heat distribution was equalized over the entire surface, it might work. Heating it with a torch, to a temp high enough to release the stresses rolled into it, might actually cause the warping you are trying to avoid.

 

[CrewCab]

I'm not really sure, but I would be cautious of this.

Thanks Brian ............ I suspect your correct 8) ................ as I said, "just a thought" : ........... but at least it provokes a bit of input

Cheers

CC

 

[rake60]

Metals are a matrix of crystals.
When they are cast or forged internal stresses are formed.
As they are machined those stresses are released.

I can tell you horror stories about that.
We were machining a very large part from a forged casting.
It was crackling and snapping, we knew it was the internal stresses
being relieved. All of the sudden it let go like a grenade.
The casting cracked and threw a 3" diameter chuck of jagged steel flying.

On a hobby scale it's not normally a danger factor but it will show it's
ugly face.

You didn't do anything wrong, it was just the material showing the
"nature of the beast".

Rick

 

[tel]

Thankfully - they still make hammers.

 

[Metal Mickey]

Thanks Rick. Your explanation was very clear. Its amazing what you learn, castings exploding would be something to clear steer off!

Many thanks to all the replies.

Mike

 

[Circlip]

Most Steels should be normalised/stress relieved/annealed before we use them to minimise what you've found out the hard way Mike. If it's a mounting block or something with some weight to it OK, but for smaller and thinner bits "Black bar" is the way to go. If you have a look at some of the destructions for building toy trains written by the masters over here, they ALWAYS specify black steel for the frames.
Regards Ian