Z Axis DRO on The head vs Spindle

speedybtx

speedybtx

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Maybe a dumb question... but why on the head travel. I see this as the Z axis on the DRO over at PM. How usefull is it being on the Head vs Spindle.
I see the Zaxis small readout on the head for the Spindle, yes. But...still..
thanks much
 
On the Grizzly G0755, I mounted the z axis on the spindle quill. Perhaps coming from use of a round column mill/drill for 25 years, I see the head adjustment as a coarse movement and try to set up work so the job can be done without moving the head if possible.
 
For what it’s worth, I just finished installing a DRO on my RF30 clone.
Went on the spindle because I can use a tape measure for the gross measurements done with the column. ;)


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A lot of mills have a simple readout on the quill already. As long as it isn't a round column, I'd prefer the DRO on the head or knee. That way I can keep the quill retracted as much as possible. But that is my opinion.
 
It goes on the head/column because that's what you move to adjust the z height. When milling a part "properly" the quill or spindle should be fully retracted and locked in place and the z height is set using the head or the knee, depending on what type of mill you have. The quill should only be used for drilling, boring, or reaming. You can of course adjust it for milling but you'll lose rigidity, put more stress on the machine and lose accuracy and surface finish quality.

FYI, I also put my z axis scale on the head and not the spindle of my 833TV.
 
M.T. Pockets said:
It goes on the head/column because that's what you move to adjust the z height. When milling a part "properly" the quill or spindle should be fully retracted and locked in place and the z height is set using the head or the knee, depending on what type of mill you have. The quill should only be used for drilling, boring, or reaming. You can of course adjust it for milling but you'll lose rigidity, put more stress on the machine and lose accuracy and surface finish quality.

FYI, I also put my z axis scale on the head and not the spindle of my 833TV.
Click to expand...
I hope I didn't mislead anyone here with my comment. I have a round column mill so I put the scale on my spindle because I don't move head of the mill once I start an operation. As @RJSakowski mentioned, small changes in depth happen with the spindle.
 
M.T. Pockets said:
It goes on the head/column because that's what you move to adjust the z height. When milling a part "properly" the quill or spindle should be fully retracted and locked in place and the z height is set using the head or the knee, depending on what type of mill you have. The quill should only be used for drilling, boring, or reaming. You can of course adjust it for milling but you'll lose rigidity, put more stress on the machine and lose accuracy and surface finish quality.

FYI, I also put my z axis scale on the head and not the spindle of my 833TV.
Click to expand...
Thank you, and that is interesting as that is the first time I have heard of such operation method on a dovetail column Mill. Granted I only have a a few years experience, though as someone who reads and internet browses a lot, I am suprised to not have run across this, except knee mills. :)
 
I had three bench/bed mills, and had the Z-axis on the head on all three. The only time I moved the quill was for touching a part/zeroing the Z-axis, drilling, or pocket milling (which I did very little). Works better when you always move the head 'up' to your final number. This keeps the screw/nut loaded and is repeatable. Worked for me anyway. :)
 
For those who put the scale on the head, I am curious as to how you accomplish fine movement in the z direction. My experience with a square column mill was with the Grizzly G0755. Z axis movement was either with the the side crank or with the column motor. Neither one of which is amenable to thousandths movements. The quill could be used for those adjustment but that seems to me to defeat the purpose of the DRO.

Additionally, there are issues with head sag,and backlash,. Locking the head will invariably lift the head slightly as it tends to remove head sag. If the scale is located near the z axis ways, the amount of movement is less than the movement at the spindle. If wear of the ways is uniform and the locking torque is the same each time, the sag correction should be close to the same each time. However, as the ways wear, sag increases so the areas where the head most travels are likely to have more sag than the unused areas.

My first DRO install was on a round column mill with the scale on the quill. The reason for installing a DRO was to enable machining of features of a few thousandths in size. Tooling included 00000 center drills and .009" drills which would snap if you looked at them wrong. Work was to .0002". I would have hated to do that project using a scale on the column.
 
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