PM940V-PDF, It broke... Be Aware... (FYI Precision Mathews)

[Jake M]

It's the new way of making bolt heads. I can only speculate, but I think it has to do with "forging" the "head like feature" on the end of the "wire" that forms the bolt. Overworking the metal at the top of the wire, the wrong temperatures, incompatible grain structures forming where the metal has moved too much... I'm speculating, but it's something along those lines.
These are the new (dealer) bolts I bought for my OLD lawn mower deck when rebuilt the spindle. (Rebuilt..... I put two bearings in it. How the heck is that a "rebuild"... The world calls that a rebuild these days. I digress....). You can judge by the condition of these carriage bolts that while the PTO was engaged one time, the mower never touched grass before the heads popped off...

 

[verbotenwhisky]

I received the broken bolt and It is puzzling to look at. I can understand thinking that it was spot welded together now, but why would that be done? I have to agree with making all three. They are likely from the same batch, so I'm not sure I would trust the others. I can also send you replacements if you like. Once again, this is the only example I've seen, so it's probably a fluke, but it's really strange.

Thanks mike, have thought on it long and hard and I will pull the machine down once again this weekend and fabricate the other 2 bolts out of 4140 which will give me 60KSI bolts, I will be more comfortable with those.

Did you see the spot on the head where it appeared a thin tin like coating had pealed up? Strange....

 

[dabear3428]

Thanks mike, have thought on it long and hard and I will pull the machine down once again this weekend and fabricate the other 2 bolts out of 4140 which will give me 60KSI bolts, I will be more comfortable with those.

Did you see the spot on the head where it appeared a thin tin like coating had pealed up? Strange....

Wonderfully, I was just thinking that things were getting boring and what I really needed was a new spectacular failure mode for bolts. Mission accomplished, thanks Verbotenwhisky.

 

[verbotenwhisky]

Wonderfully, I was just thinking that things were getting boring and what I really needed was a new spectacular failure mode for bolts. Mission accomplished, thanks Verbotenwhisky.

Glad I could help, I am to please...

 

[verbotenwhisky]

Well, I bought a stick of 4140 per-hardened, it will give me a good solid bolt with a yield of 95KSI without further heat treating. I know this is a bit of overkill but I plan to own this machine a long time so overkill is okay.

 

[dabear3428]

Well, I bought a stick of 4140 per-hardened, it will give me a good solid bolt with a yield of 95KSI without further heat treating. I know this is a bit of overkill but I plan to own this machine a long time so overkill is okay.

is cutting threads in pre hardened 4140 a good idea? i did not think it was possible to get good threads in that.

 

[L98fiero]

is cutting threads in pre hardened 4140 a good idea? i did not think it was possible to get good threads in that.

You can make beautiful threads in 4140 pre hard, it's not really that hard, only around Rc28/38

Personally, I'd have just gotten some high tensile hex bolts and modified the head.

 

[verbotenwhisky]

is cutting threads in pre hardened 4140 a good idea? i did not think it was possible to get good threads in that.

That is a very good question, all of my book say it machines well with both HSS and Carbide. The reason I chose it was the information I have says you see little or no deformation with it if you need to heat treat and it is at 95KSI yield as is. I will let you know what I discover, I normally use 4140 normalized or annealed.

 

[verbotenwhisky]

You can make beautiful threads in 4140 pre hard, it's not really that hard, only around Rc28/38

Personally, I'd have just gotten some high tensile hex bolts and modified the head.

Thought of that; but, these are M16x 2.0 t-bolts, the head is 40mm diameter with 32mm across the flats. I would rather fabricate them once and be done, remember, the head of the mill is a couple hundred pound so I would prefer it not drop off in my lap.

 

[dabear3428]

You can make beautiful threads in 4140 pre hard, it's not really that hard, only around Rc28/38

Personally, I'd have just gotten some high tensile hex bolts and modified the head.

Pre hard or Pre hardened? i understood him to mean what he said "pre-hardened" but i will state i do not know how to work this stuff, i have just heard (maybe incorrectly) that 4140 after it is hardened is tuff to get good threads, but that is why i'm asking, no personal experience with it.