Mill tram

Hi,

I have just finished tramming my milling machine and have got it to less than 0.01mm at a full rotation [the circle swept is 230mm] the only thing is, that no matter how tight I do up the bolts on the head [there are 3] it will eventually move off tram. I usually have to do this about 3/4 times a year. Would it be expected to move slightly off tram with use? It never moves much, maybe at most 0.03mm on the x axis none in the y. Although it does'nt take long to get it back to tram, I would prefer not having to do it at all.

Thanks,

Raymond.

If you are brave you could drill it, ream and fit a dowel pin. Or just drill and fit a roll-spring pin like in a car door hinge.

Neil

To start with make a record of which way and by how much it moves every month and plot it. It may be going back and forth due to temperature, or it might be sagging in one direction only as the head weight or cutting force pulls it over.

Thanks guys,

Michael, the machine in question is a Chester LUX dovetail column. and this is the only problem I have had with it in almost 7 years [if you could call it a problem] but to me "it's a problem" and it needs to be addressed.

Regards,

Raymond.

Hi Raymond, from experience in industry and at home this does seem to occur with turret mills. Even if you haven't had a 'bang' they do seem to move without any apparent reason.

Tony

Thanks Tony,

Like I said it does not take me long to get it back in tram, but I feel that it shoud'nt move unless I want to to move it. especially when it is as tight as the proverbial, and I am never guilty of taking massive cuts or feeds. I might end up changing the bolts grade 8.8 just now, for maybe 12.9 and put a Norbar on to them, as long as I don't go overboard with the torque setting. If it still moves after a period using the 12.9s then I will do as Neil suggested and use a hardened dowel into a reamed hole probably 2 [one at each side]

Regards,

Raymond.

Have you checked the flatness of the mating faces ? (against a blued surface plate)

May not be in contact over the full mating surface ?

Regards,

Nigel B.

I agree with Graham in that dowelling in theory may work but in practice will not be the answer. Just an aside on this subject, I once managed to scrap a job on an early shift because one of the so called skilled night shift men had put my mill head over at an angle and then put it upright again using only the scale and no tramming, I was not best pleased with the sheer laziness of it !

Tony

Another approach to dowelling is to drill & ream a taper pin hole once the head is set true.

The pin is not left in the hole, but is used to re-align the head if it moves - loosen the securing bolts, insert pin, tighten the bolts, remove pin. The double-angle universal head on a Correa mill at work has all the basic positions set using this method & it is frequently used to re-align tool discs on CNC lathes. Note not to leave the pin inserted during use, as a bump will damage the pin & it's seating - accurate re-alignment will not then be possible.

Nigel B.

Nigel,

From experience with the taper pin fitted as standard to a Boxford VM30, its only use is to hit "0" rather than looking at the scale, you still have to tram it if you want to be accurate. As Graham has said even a Bridgeport moves, however hard you bolt up. If in use you watch the cutter pattern on the job, you can see when it has crept too far.

K

I am with you on the doweling.

Work with Hardinge Cobra 42.

used to go out of true daily.

made an alighment tool and even supplyed sample to Hardinge.

Funny .Since we had the tool; takes minutes to realign and check and almost never need it now....aint life odd.

its only use is to hit "0" rather than looking at the scale

My experience using this method to align tool discs on CNC lathe indexing turrets after bumps or overloading has been that it re-aligns those components very accurately - I have not yet had to "adjust" the position set by the pin(s) to get correct alignment.

Nigel B.

I have worked in aircraft industry manufacture and some of the tolerances would make most people get put off from engineering for life. I would state that with the head of your machine being out of tram by 0.03mm is nothing too much to worry about (of course, I don't know what tolerances you are working to!!!!). You have stated that 'no matter how tight you do up the bolts' - this would need to be quantified by an amount as previously stated here by use of a torque wrench. I shoot small bore and torque settings on bedding screws make a massive difference in accuracy, so this may be worth a look see? Drilling and pinning could be a very good answer to a problem of time to reset the head, I just wouldnt leave the pin in situ once the head is square.

I think that if you were to check more frequently, that your head is more out of tram than in! Don't be too paranoid, just be aware, as you are, and if extreme accuracy is required then check and reset where required.

Thanks guys.

I have decided to just check the tram every day that I use it, and adjust if needed.

I am still going to change the 3 bolts to 12.9's and torque up slightly more than at present.

Raymond.

Andrew, Yes, I will investigate the torque settings, and keep each one the same and check the effect.

Have you tried schnorr / nordic washers? WIll prevent the bolts loosening due to vibration.

On my combo horizontal/vert. mill, just behind the head there is a tapered hole which lines up with another in the main casting and a removable taper pin is fitted. Pin has a black knob-handle to grip it and is threaded under the knob with a nut which can be wound down against the casting to force pin out of hole, if stuck. Very quick alignment!

I appreciate the frustration - I spotted that mine was very slightly off after facemilling (2.5" what was about a 3" square piece of 1/4" plate. It had the very smallest 'dish' in it which was only visible on blueing it onto a surface plate, which I realised meant the mill head wasn't 100.00% square to the table. It was a thou and this means about 0.046 degrees error in my case.

Needless to say, spent a lot of time fiddling with it - probably striving for unnecessary accuracy - and as the OP and others note, after all maner of careful setting (mine has a dowel pin for location) it still 'slipped' on being tightened up.

What i ended up doing was nipping it then carefully use a dead blow rubber mallet to get it spot on as i progressively tightedn it all up. Else no matter how careful I was, it 'slipped' ever so slightly if I just did it up in one go from the point it was supposed to be square.

Personally, 0.01mm over 230 sounds more than good enough - that's 0.0025 degrees.

One 'idea' I have seen is a small block bolted tightly to each of fixed and movable parts of head (as far from pivot as possible obviously) and an 'adjusting' screw to force them slightly apart to true up small errors that appear as you tighten. A bit Heath Robinson but esentially a mechanised method of what I do...