Cutting & drilling gr8 bolt

[historicalarms]

Morning fellows, I have a "bucket list" project in the works that will require machining, drilling (prob. 3/8 hole) and milling a Gr 8 bolt. I wanted a gr 5 but the wife came home from town with a g 8 (1 1/4-7) for me. I thought any course tread would be gr 5 but I guess not.
Anyhow I googled the problem and am even having trouble finding a Brinell # of gr 8, lots of "stress" properties but not much that a red neck hillbilly can use.
Guess I'm asking what would you guys use to do all the operations I listed with 13-40 light horsepower & a mill-drill....is it even possible.
I did try to machine some 4140 in it's hardened state ( dont know the Brinell # difference between the 4140 & gr 8) and it was more or less a waste of time with the tooling I tried (carbide inserts).

 

[RobinHood]

HSS will work on a GR8 bolt. Just go slow. Lots of lubrication.

I have made boring bars, drilled the length of them all with HSS drill bits. The material is not that “hard” it is “tough”. Like 4140 pre-heat.

 

[Chip Maker]

4140 PH (pre hard) is 28-32 RC (Rockwell C scale). It will work harden if the cutter rubs instead of cuts. Good quality high speed steel will cut it as Robin Hood mentioned using a slower speed and lubrication. 4140 can be made harder, but it will be case hardened. Carbide should have no problem machining 4140 PH or a gr 8 bolt. A cement drill will drill hardened steel, even D-2 60-62 RC if sharpened properly.

 

[historicalarms]

Thanks guys , ya I contacted a friend of mine that has a Power Engineer degree yesterday and in our discussion, I found out that all my fretting & apprehension for cutting Gr 8 was unfounded.
I will pass on one of his statements that might interest the forum. He makes the claim that tough unhardened steel and hardened steel of the same alloy will have the pretty much the same tensile strength in either state , the major difference after hardening is that it will have a much more robust abrasive resistant property afterwards. He claimed at engineering school (NAIT) that they were shown test of a certain tensile strength steel being sheared in its annealed state and then the same steel after heat treating. the experiments showed the metals coming apart at the same tensile limit...the difference being the softer steel cut & peeled apart, the hardened piece shattered in a small explosion of the two pieces.
Gord claims he had the same discussion years ago with Ron Smith, somewhat world renowned Alberta rifle barrel maker. Ron claimed that is why 4140 is so renowned as a suitable barrel steel. In its soft state it is very easily machined to absolute critical dimensions and then it can be heat treated to stress-relieve after all the machining process but then drawn down to a state that pressure shattering is reduced to the level that any rupture will more likely result in a tear into a couple pieces rather than hand grenade of shrapnel in its hard state.

 

[whydontu]

I use B7 4140 bolts to make punches and dies for my sheet metal punches, and I do it on a 3/4hp Busy Bee lathe. Machines easily, heavy cut and lots of cutting fluid.

 

[PeterT]

4140 can be made harder, but it will be case hardened.

Can you elaborate. Do you mean 4140 alloy doesn't lend itself to through hardening vs case hardening for some reason? I thought you could do either/or just depending on the HT process, but I haven't worked with it much.

 

[Chip Maker]

Can you elaborate. Do you mean 4140 alloy doesn't lend itself to through hardening vs case hardening for some reason? I thought you could do either/or just depending on the HT process, but I haven't worked with it much.

4140 can indeed be hardened thru. In my trade (metal stamping) it's not that common for thru hardening of 4140 as there are better tool steel choices for thru hardening for die applications whether piercing, blanking or forming. Die set guide pins are 4140 which have a hard case depth and the core is ductile. 4140 is induction hardened as opposed to nitriding to achieve the hard skin.