Hole springs open when cut into

[ericc]

Hi. I had an unpleasant surprise when making another Alciatore type tool holder. This is a block with a large hole in it that is clamped around a post. The difference with the Norman tool post is that the post has a flat machined in it. The block has a corresponding section cut on the chord of the hole circle with a steel bar strap and bolt to tighten it around the post. When I cut the chord, the block must have had residual stresses and it closed a tiny bit and would not fit the post. Would it help to do a stress relieve before cutting the chord? I looked up stress relief on the Internet, and it is done well below the austenitizing temperature, like 1100 or 1200 F. Is this enough to avoid the problem? The reason that I never had the problem before while making these holders is that I usually make the hole with a handled hot punch and a striker. This time I just used a boring bar to make it. Forging temperatures must do a lot of good to help prevent the problem.

 

[Illinoyance]

CRS has a lot of locked in stress from cold finishing. Annealing would work. A simpler approach would be to start with hot rolled steel. You can salvage the existing block by cleaning up the hole using a boring head.

 

[RaisedByWolves]

CRS has a lot of locked in stress from cold finishing. Annealing would work. A simpler approach would be to start with hot rolled steel. You can salvage the existing block by cleaning up the hole using a boring head.

This.


I made bananas out of two 48”x4”x6” pieces of cold rolled one time during my apprenticeship.

That was a fun day. Blame got put on the engineer for spending too much for the wrong material in the first place.

Boss asked if I learned anything.

I replied “Yeah, always have a fall guy”.

 

[ericc]

I fixed it. I heated it up to dull red in the forge. It's surprising that this low temperature is supposed to stress relieve steel. I then made a ring out of 3/16" flat bar around a mandrel, then trimmed it to the hole size in the three jaw chuck. This was slid into the undersized hole and expanded gently with a tapered drift until the hole was expanded to the correct size. It overshot by a few thou, but was very easily and predictably pinched down into a perfect fit in a vise. Must be the stress relieving. No metal was removed, since the original hole before springing was the correct size.

 

[RaisedByWolves]

I fixed it. I heated it up to dull red in the forge. It's surprising that this low temperature is supposed to stress relieve steel. I then made a ring out of 3/16" flat bar around a mandrel, then trimmed it to the hole size in the three jaw chuck. This was slid into the undersized hole and expanded gently with a tapered drift until the hole was expanded to the correct size. It overshot by a few thou, but was very easily and predictably pinched down into a perfect fit in a vise. Must be the stress relieving. No metal was removed, since the original hole before springing was the correct size.

We relieve or normalize steels as low as 600* depending on the type of steel and the application.