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

verbotenwhisky said:
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.
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you can get your workout in as you machine, mill some, pick up the head off the floor 20 reps and you will be a beast!
 
dabear3428 said:
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.
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You are correct, my wording is bad it is pre-hard at Rc28 to 32, 95KSI Yield.

No, I was correct....
 
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Hi Guys,
If you want a bolt with a thin flat head you might try making one from another bolt. Just turn off the portion of the head you do not want.

I did this to lower the profile on my clamping bolts for my backer board. Here are some pictures of what I did and how I recessed the bolts away from the surface of a backer board that I made from a 1 inch thick piece of Nylon board that I found in surplus. In this photo you will see a bolt before and after it was turned. If you want the head to be rectangular to fit into a slot, just grind off two sides to make them flat(er) on those sides.


I turned these down on my old SB10.

B2 said:
on a backer board that I made
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B2 said:
Hi Guys,
If you want a bolt with a thin flat head you might try making one from another bolt. Just turn off the portion of the head you do not want.

I did this to lower the profile on my clamping bolts for my backer board. Here are some pictures of what I did and how I recessed the bolts away from the surface of a backer board that I made from a 1 inch thick piece of Nylon board that I found in surplus. In this photo you will see a bolt before and after it was turned. If you want the head to be rectangular to fit into a slot, just grind off two sides to make them flat(er) on those sides.


I turned these down on my old SB10.
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this would be a great way to insure post #31 happens, these are to hold the head on his PM940V PDF probably weighs 400# and is subject to a lot of dynamic loading, I do not see him doing this.
 
dabear3428 said:
is cutting threads in pre hardened 4140 a good idea? i did not think it was possible to get good threads in that.
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Nothing is impossible until you've seen the carnage to prove it so.

B2 said:
Hi Guys,
If you want a bolt with a thin flat head you might try making one from another bolt. Just turn off the portion of the head you do not want.
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I'd recommend highly against this in all but the least demanding applications. Commercial hardware grade hardware is NOT consistant through and through. you won't be saving the percentage of the strength that you think you are. Bolts are not rated as a material, or required (or even expected) to be consistant throughout, they're rated by bolting properties of the finished bolts.

Nothing wrong with "customizing" bolts, you've just got to keep them out of areas with consequences.
 
why forged bolts guys, a grade 8 would be more than enough. I am sure 80 ft/lbs is enough? What are you torquing to?
the 4140 or 1144 would be fine... hardening probably not necessary, as they have enough tensile unhardened.
 
verbotenwhisky said:
So, I wanted to fine tune the tram on the head of my mill. I loosened the three bolt, adjusted it then as I tightened the lower bolt, M16x2.0 when I hit 20 Ft/Lbs of torque I heard a ting... Me: "what was that? did you hear that?" Wife: "yeah, What was that?.." I reached up under the head after realizing the bolt was no longer turning and pulled the piece of it out attached to the nut... Wife: "thats not suppose to come out".... :rolleyes: ... Me: "Nope, not like that"...:confused: ....

Wife: "Now what?"... Me: "we have to take it apart to replace that"...

View attachment 490209 View attachment 490211

What broke and the surprising way it broke:

View attachment 490213

What it is suppose to look like...

View attachment 490217

My wife said, "how long will it take to get the part?" and my answer was "I have 4140, I'll make a new part".. I have to admit I forgot to take a picture of the new bolt but it looked a great deal better than the one in the photo. Take a look at the one in the photo, see the dish in the end of the bolt? Additionally there should have been 2 long bolts and 1 short but the one on the right side was a short as was the one on the bottom which broke, the one on the right, when tight, didn't fully engage all of the threads in the nut, there should have been at least 2 threads above the nut.

With all of this said, any of you Precision Mathews guys feel like chiming in on this? that break is like this bolt was 2 parts not one, clean, not a shear. Take a close look at the head it appears as though the case hardening pealed away from a base material, very odd....

PM940 guys, be aware if you are tramming or otherwise adjusting your machines....
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So sorry to see this happen sir, that could have lead to a dangerous situation - glad nobody was hurt. Wow.. while no doubt you'll solve this, it does not make me feel confident about these inexpensive PM mills that i'm currently looking into, PM 728VT, PM 932M and the PM 833T...

The PM 932M is the little brother to your lathe I believe, I was looking at it last night with all the bells and whistles DRO and all $4,500... I was thinking that it would make a great starter mill...

Other than the 3 bolts is there anything else keeping that head from detaching from the mill while in use, I know this would make me gun shy, and worried for a while..! what about you? I am guessing it doesn't bother you much, one time event, its a fluke, not the norm... unfortunately Murphy's law was written specifically for me, so I pay attention to events like this....

Anyways, hope you get this solved to your liking and it never happens again, have a great rest of your day. Mike.
 
Well it's not something unique to our mills at least:

Interesting bolt failure.. - The Home Shop Machinist & Machinist's Workshop Magazine's BBS

Dad had a pretty eclectic selection of bolts and nuts. some new - some old. I needed a 5/16 bolt for the fender on the 42 and found a bag of 1" long ones. Grabbed a bolt and nut and went to install it. Used a crescent wrench and a short ratcheting open end/box end wrench. (so not much torque). I...
bbs.homeshopmachinist.net
 
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