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

[GeneT45]

I haven't had this exact failure, but I've run across several bolts from big-box stores that broke long before they should have. I've adopted a policy of only getting fasteners that require strength, or those for my stock, from McMaster which still seems to require the expected quality from their suppliers. I'll occasionally buy a few fasteners for something non-critical from one of the local shops, but only for projects where strength is not even remotely an issue. These days, if in doubt, throw it out.

GsT

 

[verbotenwhisky]

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.

I cannot say enough good about the mill and PM is a great group to deal with. I think this was a bad batch of bolts, I sent it to PM so they could see it first hand and after much thought decided to make the bolt out of good material in case these were from the same batch. Holding the head up is kinda important but if all is equal 3 "good M16x2.0 bolts should be more than adequate.

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

Yeah, one of the guys posted earlier in this thread a photo of a set of carriage bolts he bought for his lawn mower where the heads popped off in much the same fashion, makes me wonder if QAQC is being sacrificed for profits...

 

[yota]

what year was your mill made? wondering now if my PM932 has the same bolts.

 

[verbotenwhisky]

what year was your mill made? wondering now if my PM932 has the same bolts.

2022... I hope you do not have the same issue, PM said they had never seen this before, I am hoping its a one off bad batch.

 

[verbotenwhisky]

M16x2.0 T-bolts to replace the head bolts in my mill. I used a die to cut the threads on the first one then decided to single point the threads on the second one with the lathe, to get them tighter, Not my best but it will work. I fabricated both from 4140 pre-hardened 1.5" diameter bar stock.

 

[dabear3428]

M16x2.0 T-bolts to replace the head bolts in my mill. I used a die to cut the threads on the first one then decided to single point the threads on the second one with the lathe, to get them tighter, Not my best but it will work. I fabricated both from 4140 pre-hardened 1.5" diameter bar stock.
View attachment 493066

it almost looks like you knew what you were doing. don't worry i will not spread it around.
nice work BTW

 

[yota]

2022... I hope you do not have the same issue, PM said they had never seen this before, I am hoping its a one off bad batch.

I received mine in September 2021..

 

[verbotenwhisky]

I received mine in September 2021..

If you have trammed yours in without issues you are likely good. Have you checked your column and head alignment? If not, I believe DavidR8 has a great video that outlines how to do so.

 

[yota]

I did Tram it in when I received it and had no issues with the bolts. I think I did look at Davids video at that time.