Pm932 Pdf Column Bolts Question

JR49

JR49

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I just finished reading a long running thread on a Grizzly G0755 mill, started in 2013 ( "New Grizzly G0755 is set up and running"). This mill is basically the same machine as my 932. One of the posts in that thread said that the specs for torqueing the 4 column bolts is 121 ft. lbs. That seems really high to me. When I first got my mill, I used a torque wrench to loosen my bolts so that I would know how tight they were, and it only took around 45 ft. lbs. to loosen them. HOWEVER, I'm not sure if the loosening torque is directly proportional to the tightening torque. All advise on my mill as well as advise on correctly torqueing appreciated. Thanks, JR49
 
What is the thread size and pitch of the bolts and do they have grade markings (like 8.8, or 10.9) on the heads?
 
The grade of the screw isn't as important as the material they are threaded into. Grade 8 torque specs would play billy hell with gray iron. Your 45# sounds reasonable.
 
T Bredehoft said:
The grade of the screw isn't as important as the material they are threaded into. Grade 8 torque specs would play billy hell with gray iron. Your 45# sounds reasonable.
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You are correct, Tom. I was trying to find out what is there, because I have no knowledge of that mill. Is there a specification in the manual? If not, JR49 will need to come up with a number that makes sense based on thread size and a gut feeling of how good the castings and the threaded holes are...
 
Bob and Tom, thanks for responding, not sure where all the PM 932 owners are, this is the second question specific to 932's I've asked with no response from owners. Thank God for you guys, Bob, I believe it was you that answered the last one. Anyway, the column bolts are M16 X 2.0 and 60mm long, the bolt head has two markings on it DN, and 4.8. What do ya think? JR49
 
I think you will find most PM932 owners have not removed the column and would have no reason to need to know the torque specs.

I had the same dilemma when I did the CNC conversion to mine but my column bolts were not tight from the factory so there was no real torque value to compare. I tried to research it but the grade of cast iron is not known so it makes it difficult to determine from published tables. I've seen torque specs from 35 to 120 ft-lbs.

As I recall I did my best "guess" based on experience by tightening by hand with a box wrench and then checking with a torque wrench to see what the values were, then tightened all to the highest value. Not perfect but it has worked so far.

This calculator works pretty well but the yield strength Mpa for cast iron ranges from 100 to 280 so what do you choose?
 
jbolt, thanks for the response, but you never actually said what torque value you ended up using. Also, about your first sentence "I think you will find most PM932 owners have not removed the column". Unless they all get delivered with the column perfectly trammed in the Y axis, then these bolts would have to be at least loosened to fit a shim or two under the column. Actually, having said that, I must admit that my mill did not need any tramming. The reason I asked is from reading the thread that I referred to in my OP, but I'm sure that eventually I will need the spec., so wanted to find out. If I don't get an answer I will E mail Matt, and if he knows, I will post it here so we all will know. Thanks, JR49
 
JR49 said:
jbolt, thanks for the response, but you never actually said what torque value you ended up using. Also, about your first sentence "I think you will find most PM932 owners have not removed the column". Unless they all get delivered with the column perfectly trammed in the Y axis, then these bolts would have to be at least loosened to fit a shim or two under the column. Actually, having said that, I must admit that my mill did not need any tramming. The reason I asked is from reading the thread that I referred to in my OP, but I'm sure that eventually I will need the spec., so wanted to find out. If I don't get an answer I will E mail Matt, and if he knows, I will post it here so we all will know. Thanks, JR49
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I'd love to tell you what the torque was but that was two years ago and I don't remember.

The tram on my mill was not bad with the head gib tight. Under CNC I have to keep the gib snug so there is a little nod to the head which I shimmed.
 
I torqued my column to 90 ft. lbs. My approach was not very scientific. I tightened them using a box end wrench and stopped when it felt "tight enough". Then I used a torque wrench to tighten them equally. 90 ft. lbs. happened to be slightly tighter than the tightest bolt before torquing.

Tom S.
 
I loosened the bolts and installed some shims when I trammed mine, I torqued it to the following specs...

Wrench + cheater bar + as tight as this old man could go!;):D
 
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