[vroemm]

Hi.

New cast iron is not yet stable.
If you machine it, it will change shape after a while.
With old cast iron this is not the case.
Thats why sherline makes its routers with old cast iron.

Is this the same for new and old steel ?
Suppose you make somthing very accurate from new steel.
Will the stressesin the new steel reduce after time ?
And will it change the shape of the steel ?
Causing the accurate surfaces to become inaccurate ?

Thanks..

[Mcgyver]

yes. steel, cr more so than hr has a lot of internal stresses and moves. worse if you weld it. in industry fabrications that require precision are stress relieved or even normalized. I've done this and it works well - sending fabrications out to be normalized.

most of the stresses are concentrated towards the surface so most of the time you deal with it through design & process. for example, if you are taking a .500 Cr say 4"x6" and drilling a few holes it will be fine, however if you fly cut 50 though off one side it would warp....you've removed the stress from one side and it moves to find a new equilibrium....in those case you start with something over sized and remove similar amounts from each side...progressively, paying attention to how you are clamping etc so that it ends up flat when un-clamped (ie if its bent like a banada, and you clamp it straight and mill, its going to spring back afterward). for round work, i usually take 30-50 thou off overall before you start turning individual dia etc.

its the subject of books, lots content here as well, tough to completely explain in a post

[CountZero]

Is cr= cold rolled?

Sorry if this is an obvious question...

[Mcgyver]

Count, is me that should apolgize, i forget people from all over read these posts and I assume everyone will know my shorthand...yes CR short for cold rolled, HR short for hot rolled

[vroemm]

yes. steel, cr more so than hr has a lot of internal stresses and moves.

How fast or slow does the stress get less by its self over time ?

I remember a story about BMW racing cars.
They toke a motor block of a very old normal road car.
They left it outside for a long time.
Then the stress was gone.
They made a high quality racing car motor from it.
And beat the pants of everybody in the race :-)

[NC Cams]

Both steel and iron "relax" over time as the residual stresses containted thereing either are relieved or generated as a result of either cold and/or hot working.

Normalizing is one of the many ways to anneal the stresses out of a part. However, there are vibratory methods (metalax) as well as low and high temperature stress relieving that accomplish the same effect.

"Seasoned" blocks can be generated by simply letting them sit. Another and some contend better method is to subject the block to normal operating temprature conditions over time via "normal" operation. Repeated thermal and mechanical cycling at well below the fatigue limit of the material will often times "seasson" a block much better than simply letting it sit.

It is not uncommon for race blocks to actually seal up better on the 2nd or 3rd rering once the block has been heat and mechanically cycled. This is aso why racers do NOT like to lose a well seasoned block that they've prepared and massaged over time. Like a good vintage wine, seasoned blocks and/or fabrications often improve with "age"....

[svenakela]

My old dad has a uge pile of steel behind the barn, maybe I should pick it up and use it for the chassi of my next machine. Not a bad idea after all...

[vroemm]

Both steel and iron "relax" over time as the residual stresses containted thereing either are relieved or generated as a result of either cold and/or hot working.

Any idea how long it takes for the stress to be reduced to a acceptable level by just waiting ?

[vroemm]

My old dad has a uge pile of steel behind the barn, maybe I should pick it up and use it for the chassi of my next machine. Not a bad idea after all...

Very good idea.

With questions:
Do get long bars stress when it is not lying flat ?
Maybe your dads steel has created new stresses in itself by the way is was piled up ?

Or am i taking it to far ?

[Zumba]

Normalizing is one of the many ways to anneal the stresses out of a part. However, there are vibratory methods (metalax) as well as low and high temperature stress relieving that accomplish the same effect.

I took a quick look at the Metalax website out of curiousity. How much does one of those units cost?

[RICHARD ZASTROW]

Zumba, Carefull on the vibratory stress relief. It does stress relieve but does not remove or reduce hardness induced thermally (welding etc.). When machined after vibratory or thermal stress relief, mechanical stresses are introduced. Additional complications from hard spots NOT removed during vibratory stress relief. I actually prefer (2) stress relief cyces. One after all welding etc. one before final machining if very close tolerances require. On really close work, .0001"s tol., I prefer cryogenic treatment. If tolerances aren,t so extreme, the vibratory method is ok.

[RICHARD ZASTROW]

oops

[LUCKY13]

There use to be a Old Mopar racer that would buy new motors ( when they where much cheaper and available) and he would run them in his Wreaker (truck) for 100,000 miles. Then he would take them out and sink them into a pond (emty blocks) behind his shop for several years. He keep quit a few motors in that pond. When the time was right they would be pulled out of the pond & machined to go in his race car. He held many records for many years as I remember. Its funny the things you can do to metal.


Jess

[vroemm]

Its funny the things you can do to metal.

Yeah.
But it makes it all much more complicated to make a frame for a router.
Which i find not funny at the moment :-)

[Mcgyver]

Then he would take them out and sink them into a pond (emty blocks) behind his shop for several years. Jess

I've been told that Standard Modern (my lathe) would bury the bed castings for a few years when then came from the foundry. Other than time to season, not sure of the, or if there is, an advantage to the constant temp. I'd always been told to hold/cold cycle numerous times to work stress out of hardened parts (young T&D apprentices building their tools would drive mom's crazy with stuff in the freezer and the filling the oven every time it was in use.)

[vroemm]

I've been told that Standard Modern (my lathe) would bury the bed castings for a few years when then came from the foundry. Other than time to season, not sure of the, or if there is, an advantage to the constant temp. I'd always been told to hold/cold cycle numerous times to work stress out of hardened parts (young T&D apprentices building their tools would drive mom's crazy with stuff in the freezer and the filling the oven every time it was in use.)

I was wondering the same.
I also always thought many time changing from hot to cold relieved the stress faster.
(O, nice, firefox 2 has real time spell checking, great)
In the documentary about the BMW motor block they put the motor block outside, and encouraged personnel to pee on the motor block, to induce temperature changes.
If i remember correctly.

If have a sort of greenhouse, which gets real hot in the summer. +/- 36 degree and more.
If i put a frame in this greenhouse, and the cool the frame down with water a few times a day, would this remove the stress within a year or so ?

[walter]

In the documentary about the BMW motor block they put the motor block outside, and encouraged personnel to pee on the motor block, to induce temperature changes.
If i remember correctly.

I have to say... those Germans are VERY crafty

[Geof]

..If have a sort of greenhouse, which gets real hot in the summer. +/- 36 degree and more.
If i put a frame in this greenhouse, and the cool the frame down with water a few times a day, would this remove the stress within a year or so ?

This will relieve some stress but I think you could skip the cooling with water. If you decide to do this do rough machining first to within about 0.5mm of your finished dimension, maybe as small as 0.2mm. If you do not rough machine before relieving the stress you will probably still get enough movement to notice. Even so you will probably still get some movement after final machining but it will be reduced.

[budP]

I dont know about those Germans, Did they have 2 blocks to pee on? one for men and one for women?

budP