Center of cold rolled roundstock is always softer right?

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shild
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Center of cold rolled roundstock is always softer right?

Post by shild » Sat Mar 17, 2018 10:00 pm

The center of cold rolled roundstock is always softer isn't it? But how much softer? Is it maybe 25% softer? I've got an allen screw with 5mm .8 threads, I want to replace with a knurled knob made from 3/4" roundstock. If I cut the 3/4" stock down and thread to that size it will be a lot weaker than a normal 5mm .8 allen screw wouldn't it?

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Fender
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Re: Center of cold rolled roundstock is always softer right?

Post by Fender » Sat Mar 17, 2018 10:14 pm

You can't really compare cold-rolled steel to that of cap screws. Most cap screws are made from alloy steel, have higher carbon content, are heat-treated and are tougher and stronger than ordinary cold-rolled 1018 steel.
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John Hasler
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Re: Center of cold rolled roundstock is always softer right?

Post by John Hasler » Sat Mar 17, 2018 10:43 pm

Perhaps make a knurled knob to press-fit the screw into (I assume it's a socket-head cap screw?)

shild
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Re: Center of cold rolled roundstock is always softer right?

Post by shild » Sat Mar 17, 2018 11:08 pm

Fender wrote:
Sat Mar 17, 2018 10:14 pm
You can't really compare cold-rolled steel to that of cap screws. Most cap screws are made from alloy steel, have higher carbon content, are heat-treated and are tougher and stronger than ordinary cold-rolled 1018 steel.
That sure is what it feels like!

shild
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Re: Center of cold rolled roundstock is always softer right?

Post by shild » Sat Mar 17, 2018 11:10 pm

John Hasler wrote:
Sat Mar 17, 2018 10:43 pm
Perhaps make a knurled knob to press-fit the screw into (I assume it's a socket-head cap screw?)
I'm thinking about this, sure would save me on roundstock wouldn't it? How much of an interference fit do you think it should be?

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Re: Center of cold rolled roundstock is always softer right?

Post by John Hasler » Sat Mar 17, 2018 11:21 pm

The usual .001" per inch of diameter of the screw head. I'd also put red Loctite on the screw head before pressing it in.

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Fender
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Re: Center of cold rolled roundstock is always softer right?

Post by Fender » Sun Mar 18, 2018 5:53 am

Instead of pressing the knob on the head of the screw, why not tap the knob for a longer screw, then fasten them together with loctite? You can countersink the hole in the knob if you don’t want the screw protruding from the knob.
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Fred_V
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Re: Center of cold rolled roundstock is always softer right?

Post by Fred_V » Sun Mar 18, 2018 7:08 am

I've done that before but use more than thread locker.
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RET
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Re: Center of cold rolled roundstock is always softer right?

Post by RET » Sun Mar 18, 2018 8:52 am

Hi shld,

I don't know if the center of cold rolled is softer or not. If it is, the amount isn't really significant. What I do know is that ordinary mild steel has a yield strength of about 55,000 psi. while stainless steel capscrews have a yield strength of 120,000 psi. and regular capscrews have a yield strength of 180,000 psi. That is why in my model building, I use capscrews whenever I reasonably can because I know I'm not apt to break them.

Remember, even the regular (180,000 psi.) capscrews can be machined with HSS tooling, so I sometimes will use the CNC mill to cut a hex on the head to simulate a bolt. Its easy to write a little "G" code program to do this. Filling the socket with soft solder will allow you to have a bigger head without the socket showing, especially after the head has been painted.

I don't like making miniature bolts from mild steel because you can easily tighten them to the point where the head comes off. Some safety glasses use #0-80 hex hd. screws in the hinges, so that can be a cheap source of model screws.

As mentioned above, when I need it, I have made a knurled knob and countersunk the center hole to fit the head of a capscrew with the head flush with the top of the knob. Press or Loctite the screw in from the top. Thus, when you tighten the knob, you are pulling the screw further into the assembly. You can even tap the hole to match the thread on the screw and then Loctite the assembly. This is easier to do than making the screw from scratch and you wind up with stronger threads as a bonus. Of course, you can always buy one if that suits your situation better.

Hope this helps a bit.

Richard Trounce.

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Re: Center of cold rolled roundstock is always softer right?

Post by John Hasler » Sun Mar 18, 2018 10:27 am

Fender wrote:
Sun Mar 18, 2018 5:53 am
Instead of pressing the knob on the head of the screw, why not tap the knob for a longer screw, then fasten them together with loctite? You can countersink the hole in the knob if you don’t want the screw protruding from the knob.
Sure. Make the countersink a close fit and put loctite in there as well. Then fill the hole with JBWeld and machine it off smooth. You might want to leave the socket in the screw head accessible, though, for the day when the thing is stuck.

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Re: Center of cold rolled roundstock is always softer right?

Post by Kimball McGinley » Sun Mar 18, 2018 12:01 pm

You can buy plastic knobs that turn an Allen screw into a thumbscrew. Look at McMaster-Carr p/n 91175A063 25 pieces for $10.20 plus shipping

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Re: Center of cold rolled roundstock is always softer right?

Post by tetramachine » Tue Mar 20, 2018 11:00 am

If steel is "Normalized" or annealed the hardness will be the same. If heat treated as most SHCS are then it may be softer by a bit. But not much, and on small screws as you are looking at the hardness will be same throughout.
This I have found from testing materials that I have HT, and measuring the hardness at various points.
If case hardened, then the center will be a measurable amount softer.

Cold Rolled material may be normalized or not, sometimes it is done after some machining has been done, to prevent warping on the work piece.
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