Keeping the X on a round column bench mill

Could you explain why if I had a laser pointer mounted on the head by the spindle . If I pick the point up say on the vice and Mark it if I raise the head and align the pointer to the spot it wouldn't be close within a few thousandth. Be like using a plumb Bob .
 
I'm asking this question out of ignorance since I don't have a round column mill, so please forgive me. Are all these hoops being jumped through to realign the head to its previous X-Y zero easier than using an edge finder to set a new X-Y zero? Would that not give you a more accurate tool-to-work piece alignment/realignment than a dot on the wall, etc.,? That is the point of the exercise, no?

Tom
 
I'm asking this question out of ignorance since I don't have a round column mill, so please forgive me. Are all these hoops being jumped through to realign the head to its previous X-Y zero easier than using an edge finder to set a new X-Y zero? Would that not give you a more accurate tool-to-work piece alignment/realignment than a dot on the wall, etc.,? That is the point of the exercise, no?

Tom

Hey, Tom. This is usually an issue when we have a work piece already in the vise and we find we don't have enough space in Z for some operation that must be done on it. If we move the head, we lose our orientation on that specific piece. I would imagine that most of us who own these contraptions have learned to allow for the longest tool and get set up to accommodate it before starting work but sometimes it happens ... and then we have to move the stupid head.

This is the one big irritant on a round column mill, which is otherwise a rather good machine.
 
Hi Mikey,

I understand the need to re-establish the spindle to work piece orientation after you move the head up and down, but I’m just wondering if re-establishing it by resetting the X-Y zeroes with an edge finder wouldn’t be more precise than, for instance, trying to realign a fuzzy laser dot with a spot on the wall. Maybe it’s not. Or, on the other hand, is the laser dot (and other methods discussed) precise enough for our typical hobbyist needs? Like I said, I don’t have a round column mill, so I’ve never tried to re-align one. Just curious.

Tom
 
A typical laser pointer has a spot size of 1/8" or more at 20'. That's .125"@240" or .005"@10", a typical distance of the spindle axis from the column center. When all the other sources of error are factored in, it would be difficult to realign the head to .001". Add to that, for these tired eyes anyway, I would have to walk over to the wall to check the alignment, then go back to the mill bump it slightly, then back to the wall to check again, etc.

An edge finder would be more precise providing you had a enough travel in the quill to reach your reference point. If I knew that I would have to readjust the head, I would mount an separate reference point on the table that I would be able to access with an edge finder from both head heights. A cylinder is a good reference for X and Y as there isn't a need for alignment with the X and Y ways. If a Z axis reference is desired as well. a sphere could be used instead.

For a quick and dirty alignment, usually good to within a couple of thousandths, I would use a dowel pin in the chuck or collet. I would have a hole machined in the work or in a separate piece and fit the dowel pin in the hole, moving the table appropriately. I would then move my head as required and move the quill to engage the hole again. With the pin in the hole, I then tighten the head bolts.

A round column mill doesn't change the Y position materially as long as the plane through the spindle axis and the column center is parallel to the Y axis. For example, a 1º error in the column orientation will result in a .0015" error in the Y position while the error in the X position would be .175"

I struggled with the alignment problem for many years. I had a total of just over 5" of quill travel and I could have as much as five inches of tool length difference. I reduced the problem significantly by getting a set of R8 collets and using them instead of the chuck for mounting drills and reamers. I use the Tormach TTS tool mounting system on my round column mill and I can hold my tool length differences to less than an inch in most cases. This greatly reduced my need for moving my mill head.
 
Could you explain why if I had a laser pointer mounted on the head by the spindle . If I pick the point up say on the vice and Mark it if I raise the head and align the pointer to the spot it wouldn't be close within a few thousandth. Be like using a plumb Bob .

You could do it that way but the laser would only show the error 1-1, it would be near impossible to align a typical laser dot within a thousandth on an inch by eye. If you have the laser pointing horizontally away from the pivot point (center of the column) with the dot on a wall several away the error will be magnified. Say its magnified 100x, so 1/1000" of movement on the head will show 1/10" on the wall, it's easy to align a laser dot within 1/10" of an inch. The further away from the pivot point, the greater the magnification or error.

Hi Mikey,

I understand the need to re-establish the spindle to work piece orientation after you move the head up and down, but I’m just wondering if re-establishing it by resetting the X-Y zeroes with an edge finder wouldn’t be more precise than, for instance, trying to realign a fuzzy laser dot with a spot on the wall. Maybe it’s not. Or, on the other hand, is the laser dot (and other methods discussed) precise enough for our typical hobbyist needs? Like I said, I don’t have a round column mill, so I’ve never tried to re-align one. Just curious.

Tom
The problem is the work that must be aligned is often out or reach of an edge finder, also it may require moving the table x or y to get the finder to an edge, then you got to move it back again. See above for why its not so hard to align the laser dot.
 
I'm asking this question out of ignorance since I don't have a round column mill, so please forgive me. Are all these hoops being jumped through to realign the head to its previous X-Y zero easier than using an edge finder to set a new X-Y zero? Would that not give you a more accurate tool-to-work piece alignment/realignment
Tom
Your right but if you have to raise and lower you table on a Bridgeport do you want to brake down the cutter to realign just to make room between the work and spindle. Its like that to change cutters or drill bits. If you have to move the head just after you center drilled it's that way . Extra time and labor. I have a brand new drill mill not even out of the crate. But I'm gonna try setting it up just to mill 80% ars . I found an old enco mini type Bridgeport mill that will be my using mill for most work but if I can come up with a laser set up it'll get used more. Lots of projects I want to build even a niche tool to sell .I'm saying the dot would line up on the mill it self not the wall . On its own axis straight is straight like using a plumb Bob on a straight line to the point of the laser dot it has to be close.
 
Why not set up a vertical reference point that is parallel to the column, make a bracket to hold a dial indicator and use that as the reference to reestablish zero?
 
Your right but if you have to raise and lower you table on a Bridgeport do you want to brake down the cutter to realign just to make room between the work and spindle. Its like that to change cutters or drill bits. If you have to move the head just after you center drilled it's that way . Extra time and labor. I have a brand new drill mill not even out of the crate. But I'm gonna try setting it up just to mill 80% ars . I found an old enco mini type Bridgeport mill that will be my using mill for most work but if I can come up with a laser set up it'll get used more. Lots of projects I want to build even a niche tool to sell .I'm saying the dot would line up on the mill it self not the wall . On its own axis straight is straight like using a plumb Bob on a straight line to the point of the laser dot it has to be close.

Yeah, it's finally dawning on me that if you use an edge finder to simply establish a new zero, you will lose THAT zero when you move the head to replace the edge finder with the tool that you moved the head for in the first place. (Hey, I'm old, cut me some slack ;))

I also didn't think you lost X-Y zero when you raised and lowered the table on a Bridgeport. Learn something new every day.

Tom
 
Why not set up a vertical reference point that is parallel to the column, make a bracket to hold a dial indicator and use that as the reference to reestablish zero?
That's what I'm saying use the laser, Mark the spot before cranking the head then realine to that spot and lock up the head. It should be close. It would be straight up + down in the same plane. Parallel.
 
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