[How-To] Bolt torque for milling head "nod" bolts

[blaser.306]

I have a New . not even new to me 9x49 bridgeport J head clone milling machine . I am attempting to tram the head, I have the Tram done in the "X" axis and it is holding. The three bolts run thru the ram and are threaded into the opposite side of the casting to hold the nod setting. I had it set up and trammed to within .0005" over 8" and mad a test cut it cut with a .007" bevel? Head lifted up... I had tightened the bolts just using a 19mm (3/4") combination wrench and it appears to not be enough to hold the adjustment, Perhaps I will try using a torque wrenck to verify the actual value ? I am lead to beleive the number is 50 foot lbs. Can anyone expand or enlighten me on the subject?

 

[Eddyde]

Hard to understand exactly what's going on. What were the parameters of your test cut? did you check the tram after the cut to rule out deflection of the ram?

 

[FOMOGO]

There a bolt size and thread type torque charts on line, or in many other sources, i.e. engineers hand book, auto service manuals, etc.

 

[blaser.306]

The head definately moved ! When trammed back in , the adjustment bolts tight. I can use the flat wrench and just remove the preload from the worm gear and the head will fall... Like the bolts arent holding anything at all?

 

[davidpbest]

I have a New . not even new to me 9x49 bridgeport J head clone milling machine . I am attempting to tram the head, I have the Tram done in the "X" axis and it is holding. The three bolts run thru the ram and are threaded into the opposite side of the casting to hold the nod setting. I had it set up and trammed to within .0005" over 8" and mad a test cut it cut with a .007" bevel? Head lifted up... I had tightened the bolts just using a 19mm (3/4") combination wrench and it appears to not be enough to hold the adjustment, Perhaps I will try using a torque wrenck to verify the actual value ? I am lead to beleive the number is 50 foot lbs. Can anyone expand or enlighten me on the subject?

You have found one of the Achilles heels of the Bridgeport/clone mills. ACRA and Wells-Index J-head mills have a different knuckle mounting systems that are far more rigid. A 4” face mill diving into steel at anything over 0.010” DOC will throw off the NOD on my Bridgeport clone. Sounds to me like you should take the knuckle system apart and diagnose of releasing the NOD gear causes it to droop. I have actually scuffed up the surfaces of the knuckle and replaced the bolts with higher grade replacements which has helped. But the design is more oriented to head mounting flexibility than to rigidity.

 

[blaser.306]

The "Bolts" in this mill run straight thru the ram and are threaded directly into the casting on the opposing side ear. I just do not wish to go all ham fisted monkey on it and strip out a thread or do some other irreparable damage. The cut I made was .010" deep wit a 2.500 " face mill using spg inserts, The cut started off with a mirror flat surface and finished up with a step. I am not doubting the indicators, but do find it difficult to beleive that these machines are not capable of holding tolerance on all but light cuts!

 

[Shootymacshootface]

I have a large Clausing/ Kondia FV1, a Bridgeport, and at work I use a Lagun clone. I tighten either with a 1/2 drive ratchet, or an extended length 3/8" drive ratchet, TIGHTLY.

 

[Just for fun]

What's the manual say? There is probably some backlash in the adjusting bolt, so once you have the head tight snug the adjusting bolt the other direction maybe that will help with the head lifting up.

 

[blaser.306]

Thanks for the replies. Actually the manual has nothing noted for "suggested" torque values. The head isn't lifting , it is falling forward. I did some other searching and found that even the Bridgeport manual indicates the head is designed to have the forward edge of the table indicate .0005" higher than the back edge. I re trammed , tightened with the same wrench , then using the same approximate force applied to a med length 1/2" ratchet achieved a solid lock down with no movement. Now to making chips.

 

[akjeff]

Tramming a mill table a thou high in the front is pretty common. It's done to account for some measure of the knee sagging in the front when the weight of the vice, rotab, workpiece, etc are loaded on the table. So, your head may not have nodded forward, it may be that your table moved. You could also see a change in the tram when your knee locks are on or off. Becomes really apparent if the knee gib is sloppy, and in need of snugging up.