Torque and it's relation to tramming a mill head

[RSG]

Over torquing the head bolts is almost worse than under torquing them though. Add too much and you can and will distort the head. I've read permanent damage can be done by hammer mechanic types. Mine might be a little in the high range but I usually use about 35 ft. lbs and that seems to work ok.

So this statement caught my eye. Is this something to be concerned about? It never occurred to me when I was tightening the bolts on the head of my new mill and since it is new just how important is it to torque them properly so as to not damage the machines ability to maintain tram? Equally interesting is Pete's recommendation on backing off the worm gear after to lessen any pressure on it.

Pete, I value your input on the forum as you always provide in-depth, clear information. Would you care to elaborate on this topic? I'd love to hear others opinions as well please.-

[SteveHGraham]

If the head doesn't move when I use the mill, I figure the bolts are tight enough. It doesn't take a lot of torque to get there.

I have no patience with guys who overtighten everything. They make life miserable for everyone who comes after them.

[NP317]

Considering that the instructions for my new (2015) milling machine made no recommendations for bolt torque on those head bolts,
I can only assume that the manufacturer does not consider it an issue?

Did/does Bridgeport recommend such torque values?
~RN

[John Evans]

50 f lb's per BP. I do it is a cross pattern in several steps. I have seen over torque or uneven put a drag on the quill.

[pete]

Since I'm no mechanical engineer I can't give proven numbers, so can only repeat what's been stated on the PM forums and mentioned by John. Yes apparently being a hollow casting for the head over torquing the bolts can create enough deflection to cause problems. My opinion is there's a whole lot more precision required and built into the heads on any average milling machine than say a set of heads for a V8 that using a decent torque wrench can't hurt. For myself at least then I know the heads clamped evenly across it's mounting face. A real mechanic could probably do it perfect without one, I can't.However I didn't know up to 50 ft. lbs is ok. I might need to add a bit more now so thanks John. I've seen that tip about backing the worms off to that neutral position a couple of times. Anyone who did mention it seemed to have a lot of experience. From and with my limited experience I think there's definitely something to it. Logically it makes sense that any preload condition in either direction would increase the odds of the head slightly moving under the loads and vibration. Anything that might help keep the head in tram longer for zero cost and a few seconds of attention to those worms is worth trying it I think.

I'm unsure of how your mills equipped RSG or how your mill is built compared to a standard Bridgeport. Since were on the subject then maybe a couple of other tips might help if you don't already know them. If you have the 3 spd powered quill feed Bridgeport states that's not built to be used for power drilling. That feature is meant for single point boring only.The internals for that feed aren't designed to take the higher drilling loads. They are good enough for smaller drills though. Using the standard lever quill feed is just faster and easier anyway so I don't bother. Bridgeport also recommends not running the head in a horizontal position for long periods of time either. The rudimentary total loss internal oiling doesn't properly lubricate the head with it in that position. Short periods are fine though. Apparently some other clones of the Bridgeport design are heavier and better built so powered larger drills and having the head in the horizontal position is less of a problem. That's only what I've read though so wouldn't bet on it for anything I owned. My Taiwan built mills manual doesn't mention the horizontal oiling problem, but does mention about not power drilling. And like NP317's mill it doesn't give a torque value for those head bolts either. For what your doing on your mill I doubt you'd ever need the head in that position anyway but thought I'd mention it. Also when using the back gear it's a good idea to rotate the spindle as you move the lever until you hear the gear drop fully into place. If they aren't meshed correctly you'll not like the noise when you hit the start button. Don't ask how I know that.

[Harold_V]

I have no patience with guys who overtighten everything. They make life miserable for everyone who comes after them.

Such people generally aren't good at all on precision grinders. They require a light touch if one hopes to achieve reliable results.

H

[Downwindtracker2]

A simple rule, if you are tightening with a 3/8" ratchet, Don't Use the Handle, put your palm over the head and use your wrist. Even then, you'll probably over do it.

[John Hasler]

Considering that the instructions for my new (2015) milling machine made no recommendations for bolt torque on those head bolts,
I can only assume that the manufacturer does not consider it an issue?

Did/does Bridgeport recommend such torque values?
~RN

When a manufacturer fails to specify a torque for a bolt I don't assume that it doesn't matter. I asume that I am expected to look up the industry standard torque for that size and type of bolt.

[Rich_Carlstedt]

A few comments on Tramming that may help some here .
There is is "Tilt" which is left / right and "Nod" which is towards you or away.
For tilt you have 4 bolts/nuts and for Nod there are 3 bolts
Always start with Tilt when Traming
Have Two nuts loose and two with some snug which allow movement but not loose.
The loose nuts should be opposite each other and when you get left/Right on the money
Tighten criss-cross to maybe 25-35 pounds, keep the indicator in place ! Then you can go to full tightness ( 50 FtPounds is in the BP manual )
The nod move fix is easy, DO not measure front /back by moving the indicator 180 degrees !
Nod is always a pain for some as they get screwed up easy...since you know the head is square L to R
, only read the indicator moving 90 degrees from the rear point to either side then STOP . It becomes a simple adjust to just match
the two readings, say Left and Rear ! When you have the 3 readings (Left-Rear-Right) you are done - no reason to do front as 3 points make a plane !. As you tighten the nuts/bolts keep rechecking the tram ( L-R ) When tight, back off the worms
Rich

[NP317]

50 f lb's per BP. I do it is a cross pattern in several steps. I have seen over torque or uneven put a drag on the quill.

John: Thank you.
I will adopt that value for use with my own mill.
~RN

[RSG]

Thanks for the responses, all good info. I never even thought about torqueing the bolts. I used the wrench that came with it. As a result from the thread I will pick up a torque wrench immediately and check the bolts.

Pete, thanks for the additional comments regarding power feed. I have read the info you suggested somewhere and as such would never use it to drill. I have done some boring recently for which the power feed came is very handy.

John Evans, thanks for the torque info!

[RSG]

Pete, in case you didn't see my original post when I first got the mill here's a pic of it again to help understand the configuration as it relates to a Bridgeport clone. All the same tramming formalities.