# Z Axis DRO on The head vs Spindle



## speedybtx (Apr 13, 2020)

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


----------



## RJSakowski (Apr 13, 2020)

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.


----------



## speedybtx (Apr 14, 2020)

that is also what I did on my previous PM45


----------



## DavidR8 (Apr 14, 2020)

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. 


Sent from my iPhone using Tapatalk


----------



## macardoso (Apr 15, 2020)

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.


----------



## M.T. Pockets (Apr 15, 2020)

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.


----------



## DavidR8 (Apr 15, 2020)

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.


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.


----------



## speedybtx (Apr 17, 2020)

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.


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.


----------



## wrmiller (Apr 18, 2020)

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.


----------



## RJSakowski (Apr 18, 2020)

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.


----------



## DavidR8 (Apr 18, 2020)

I have to admit that I have the same question. Precision Matthews mills such as the PM25 have a quill DRO not to mention the number of people mounting digital calipers on the mill quills.


----------



## speedybtx (Apr 18, 2020)

I had always moved the Head pretty close to the work.  I probably extended the quill .25 or .5 inch as well.  So that I can clear the work when or if I needed to move the work.  Using the quill for end mill work, typically never exceeded more than an inch.  If moving the spindle/quill that much would result in a poor operation, then that is a machine problem.  Head was always moved in a manner to take out any backlash and then locked down.
The handle on a column mill is to me, an awkward location as well... as opposed to a Knee Mill.   I may just save up a bit more so I can consider a knee mill. Hard to justify the extra money.. it's a hobby lol.
Wish I knew someone with one so I could get first person experience.


----------

