Mill Tramming Complications - Debugging Help Required

Interesting. I'll try to remember that for next time.

I came to the same numbers using trigonometry in just a couple of minutes too.

... and I ended up with a pretty diagram.

Yes that definitely looks like a consistent "lean" on the vertical column, tested both ways with the square.

On the one hand its too bad its out of warranty but on the other youve used the machine for 18 months without this fault causing you problems. It does not wreak too much havoc if you machine each job with the head in the one position and use the quill for many operations. It is only when you say drill a hole with the head down low then move the head upwards to fit a tapping head and then the head is out of line with the hole. Or machining one part of a large casting with head in one position and then moving head up or down to machine another level of the casting and you find the head has moved half a millimetre along the x or y axis etc.

I was struggling to see why this would be an issue for me, as the head would still be trammed to the table.

But you are right. With every move of the head (to say, insert a larger twist drill) the head moves laterally.

Thanks for taking the time to write that.

You're welcome. Of course, you could just work around it by moving the table to bring the job back into alignment but that can get to be a PITA on complex jobs and the one time you forget to do it will be the critical last step in a complex job you just spent days on...

Yes, that Murphy is a swine!

I'll try to rectify it - probably by shimming, as I have no means to remove the column completely.

I considered machine epoxy, but that stuff is super expensive!

It might be a combination of shimming and ordinary epoxy somehow injected into the gap could work, maybe. But it would be best to remove and inspect/rectify column if at all possible. Looks like a fair lump of iron for a guy on his own though.

Edited By Hopper on 07/12/2020 11:37:00

And the hoist I used to install it has been returned to its owner.

From the photo of the tramming set up holding the dial gauge, I would be very careful about quoting very small dimensions read by the gauge, the rods holding the gauge need to be much more substantial,to stop deflection affecting the readings.the rod in the mill spindle should be much shorter and larger in diameter to make the set up stiffer, the rod holding the dial gauge should be around 15 mm diameter min.My old boss have gone bananas at the set up.

I think you're looking at the old set-up, no? The one with the brass rod?

The new set-up uses one of THESE and a 0.01mm DTI.

I've got to go through this again with the SX2P soon - plus now I've got to do a vertical alignment check which I never thought to do previously - I thought that rotating a dial gauge around four points of the bed would get everything right,

OK I've not thought this through at all, but no doubt someone can explain it: Would it be possible to un-shim the column, tighten it all up, shove a fly cutter in the collet and fly cut the entire bed and be done with it? Wouldn't that at least guarantee that the tool axis is perpendicular to the bed?

The bed is much flatter than you will get with a fly cutter.

Also, that won't get rid of the lean. It will only help to avoid tramming the head, which is quite trivial really.

A fly cutter on the bed could produce a wedge shape or a scalloped top if a small fly cutter is used. The top of the table needs to be parallel to the sliding surfaces in both X and Y directions, best not to start on that. The ideal setup is that the quill movement is parallel to the head movement on the column before anything else. If you can't adjust that then you have to decide which movement you want to tram, quill or head. There is also some assumption here that the spindle rotation is correctly aligned to the quill movement.

For heads that have a rotating joint it should be possible to adjust alignment of the quill to the column. This may require some scraping of the joint faces otherwise a wedge shaped shim between the two parts could be considered. Lots of time and effort whatever.

You can adjust one thing and find errors somewhere else start to show up as a result. These hobby machines are made to a price and it may not be possible to achieve the near perfection that an expensive machine aims for.

Martin C

Surely the first thing to do, is dismantle it, take the column from the base and have a look, there could have been some machining chips on the base that got stuck between the two parts on assembly, or rough machining that could possibly just need a light stone over to correct.

Worst case, I'd go with scraping to correct if needed, it's a slow process that removes small amounts of material.

I'd have thought referencing the sole of the column to check for flatness would be a good idea, it might be a high spot that needs knocking off to bring it right.

I wouldn't go running a flycutter over your table personally.

I think the flycutter comment was for someone else.

Popping the column off and scraping would be no mean feat on a 400kg machine.

I would have to acquire lifting equipment from somewhere and learn how to scrape (it is on the list!).

The thought of doing so for the first time on my milling machine does leave me feeling a little nervous.

It completely depends on whether you want to cure the problem, or fully understand what the problem is and fix it, to work on the column, it would mean removing all the things attached to it so it would be feasible.

If you can't be bothered, buy a dirt cheap feeler gauge off ebay and try shimmering it.

One thing that was mentioned was possible movement in the gib as the head is moved up while taking a reading.

With your square bolted to the table, and your indicator set up properly, you could try setting your dial to zero with the gibs locked securely, unlock, move the head up 20mm, lock the gibs again, take your reading, keep repeating, this should help remove possible inconsistent readings from gib movement rather than the column being out of square.

It's not question of being bothered, or not. It's one of capability

If you don't feel confident enough to tackle it, dismantle it, take the column to a machine shop, how much would the column weigh? I've never seen that model in person, maybe 40kg? Should be manageable, explain the problem, they'll machine the sole of the column so it sits a perfect right angle to the Z axis ways.

The whole thing weighs nearly half a tonne.

I'd be surprised if the column weighs less than I do!

And scraping is not the appropriate method for removing the 0.75mm the base is out by. It's a finishing process, and an advanced skill level that takes a long time to learn correctly. Base would need to be machined to remove that much metal sensibly.

And you are right about not flycutting the top of the table. That would only take a cut parallel to the existing surface so no gain. It is the relationship between the dovetail ways on the vertical column and the horizontal ways on the machine base that the table slides on that is critical.

Of course, we are assuming that the top surface of the table has been machined parallel to the table's lower slideway surfaces at the factory. Perhaps a risky assumption on cheap Chinese hobby machines. I suppose you could check that by holding your dial gauge in the spindle as in your video but with the plunger reading off the surface of the table. Then run the table full length back and forth along the X axis. It should give 0 variation over the full length, or a few hundredths of a mm at most. Then do the same for the Y axis, maybe with a ground plate or parallel laid flat on the table to bridge the T slots. Any variation on the dial gauge indicates the top surface of the table is not parallel to the way surfaces on the bottom of the table.

The other assumption, as someone pointed out above already, is that the spindle axis is parallel in both planes to the quill axis and thus the quill movement. Hard to imagine it being half a millimetre out though. You could possibly check that by tramming the mill as you have done, which sets the spindle axis square to the top surface of the table. Then maybe use a square to eyeball that the extended quill is also square to the table top in both x and y planes. Or with your dial gauge mounted in the spindle, run it up and down the square as you did in the video, but by extending and withdrawing the spindle, not moving the whole head. You should get a 0-0 reading or within a few hundredths mm if the spindle and quill axes are in line.