728VT really unhappy!

woodchucker said:
that's not a returnable problem. Shimming is a function of tuning the machine. Should it have been correct when delivered, YES, but is it scrap, no.
Had it been at the manufacturers, or distributors, they would be shimming it. I consider this a minor issue.

edit: but you do have a right to vent about it. It should have been correct from the Manufacturer.
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Ultra Precision Milling Machine​

THIS MACHINE IS A STEP ABOVE ANYTHING CURRENTLY ON THE MARKET!​


Ultra High Quality Milling Machine, Made to Exacting Standards. Nothing Else Compares To The Quality Level Of This Mill. If You Want The Best, This Is It.


If a machine requires disassembly, scraping, and advanced metrology, it's none of the things it's advertised as.
 
Most manufactures provide a a tolerance specification sheet done at the factory which gives the tolerance limits as well as the measurements for the specific machine. It would be nice to know what the level of "precision" is, and when a machine does not meet those specifications as shipped. There is always some level of adjustment needed after a machine is delivered, but I do not see pulling the column and tramming it as something that would be expected assuming the column is tilted. What is unclear is the issue that the quill travel that is not square or the column (Z) head travel is not square. If the gibs are not set correctly or they are slightly off the head could nod when they are locked. Over time the gibs wear on the bottom and you can see nod when locked, also setting the tool height w/o locking the head will cause nod of the head.
 
I am new to this machining stuff. Would pumping the oiler improve head nod?

I have an old dial test indicator and i have a new one on the way, but my head nod seemed to go from top of 2-4-6 block .000 (top) to .010 (bottom) (moving Z up to down). This same .000 to .010 was also shown in the spindle going up and down also. I locked each axis with the hand locks after the movement.

I made two changes like a dummy :). Moved my strap clamp to the middle of the 246 block and pumped the oiler 3 or 4 times. Now my head nod goes from .000 to .001 Same with spindle... could be my DTI also.

So my test is in-conclusive until i learn more and get a better DTI i can trust. THis is my setup

1704146201746.png
 
55fairlane said:
2 weeks ago we set a 728VT in my garage, spent this weekend installing the power feed, traming in the vise, ect.....
Got around to firing the machine up and making chips....went thru the square up the blocks routine, will not square up (in Y ) I tried everything (including getting my text book out from when I served my apprenticeship) finally bolt a 2-4-6 to the table & in the vise....using Z run an indicator up & down the blocks......0055 in 3 inches, the head in nodding at me, crap, call PM.....got thru the details with them, new Kurt vise, new Lyndex collets, used interapid indicator, and started my apprenticeship in 1986....been running machines since then.....3 hours on the phone, try this, they that, thy this.....short answer I get to pull the column loose & shim it....$5722.16 for new machine & I get the privilege of fixing it.....feeling very cheated
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$5722.16 USD is that a lot? I have a similar (smaller) work envelop small mill from 60 years ago, with the documentation was the original bill of sale. Interestingly, my father in law purchased a Corvette convertible around the same time - the mill cost a bit more than 2x the price of the sports car. Granted this old mill is pretty robust in comparison to a machine today, but the point is that relatively speaking these hobbiest machine tools are really inexpensive, and perhaps a little tuning is necessary.

Oh, the above Corvette is long gone (no room for the baby) - needless to say it would now be worth rather more than the little old milling machine.
 
That's one good measurement. You ought to look for repeatability of both the set-up and the measurement.
Remove the clamps and 246 block. Wipe the surfaces. Put it back together, reversed front to back. (so it clamps from the front.). Then measure again. After that, take to apart and reassemble, remeasure, with he clamp in front.

Then you can start to believe numbers as they show themselves to be repeatable in a logical fashion.
 
The setup is good as long as the test blocks are accurately made and square
You can flip it around to double check in case there is any small error in the block
 
Thanks Allen! I will repeat the measurement again like you said.
 
Archer60x said:
(moving Z up to down)
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to me Z is my knee. if you moved the knee up and down and were out by .010 that's not nod.
If you moved your quill up and down, that would be nod.
When moving the knee up and down regardless of nod, you should not have any travel, unless you have worn ways, OR your gib is loose.
if you lock your knee does it change?
if you lift on the table with the X and Y locked, does it move much?
 
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