# Keeping the X on a round column bench mill



## Canuck75 (Jan 10, 2014)

*I have posted some information on this forum before about my machinery and have made many modifications to the mill, but this article is specifically about addressing the problem of keeping the X on a round column bench mill when changing the head position.

My particular "King" mill has a 19.2" X, 8" Y and 5 3/4" quill travel plus the head travel on the column. This capacity meets all my hobby machining needs. I dreamt of having a universal turret/ram/ knee mill but space and money dictated my choice. I saw this used bench mill on Kijiji and within driving distance. Mill looked a little scuzzy so did a full teardown, cleanup, repaint. Also started plans to make improvements.

During operations I find I often raise and lower the head to keep everything as short as possible for rigidity sake and to get room for the boring head, chuck and drill etc. Redialing or edge finding after each head change was required. The question of keeping an accurate X during these changes kept bugging me. Other owners of this style mill have posted opinions on this subject indicating we all want to make one of these basic mills do more than they were originally designed to do - in other words make a silk purse out of a sows ear - well why not! I went through a lot of "what ifs". I established several parameters relative to what I needed my mill to do. First: I don't do work big enough that I need to rotate the head to reach far corners of a work piece, or, even to get it out of the way; Second, if you do rotate the head you relatively loose some of your Y travel range not having a "ram" to compensate (even in a commercial machine shop I seldom had to rotate the head and when I did I always needed to use the "ram" to offset the change in Y reach): and, Third, I do have to raise and lower the head often during machining operations thus a desire to control the X accuracy setting if possible.

Having accepted this, it was just a matter of what way to do it. Others have made made very good stand off frames to control the X which also retain a head swing capability but I'm not sure what guarantee of accuracy you will have when you swing the head back and clamp everything up again. Based on my personal "parameters" I chose the non rotating head solution. I know others have thought of fixing the gear rack to the column and using guide blocks (I presume) on the head, so thought I would give it a try. It could always be undone with no harm done. Also the whole mod is basically invisible so the aesthetics of the machine are not altered which is a personal preference.

The attached series of photos shows the results of my effort. Subsequent up and down tests show an accuracy of .001". If on occasion I am really paranoid, I can always edge find or dial indicate for that particular operation.

First photo shows the purchased condition just for interest. Photo 2 - pinning the rack moving up the column with the assist of a dial indicator as in photos 3 and 4. Photos 5 and 6 show the top and bottom guide blocks bolted to the head - this was done with the head on the column, in position, and using the pre drilled holes in the guide blocks to drill the head and then tap. The last 3 photos show the test results. First with the head at the bottom and after a X and Y edge find setting the DRO to zero. The second to last photo is with the head raised 5.5",quill extended, and table brought back for X and Y edge find to see how it would compare to the DRO - .001", and last photo is with quill retracted and head back down and another edge find comparison to the DRO - .001".

I,ve added one photo of the top guide block showing the slightly modified middle pulley bracket to accommodate the movement of the bracket when loosening and tightening the belts. 

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I welcome any comments.










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## Shepherd (Jan 10, 2014)

VERY nice! Question...you pinned the rack in the middle?  This doesn't interrupt the operation up and own, presuming the bolt head is sufficiently countersunk....more pics, if you have them, would be great!


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## brasssmanget (Jan 11, 2014)

That looks very interesting. I've been giving some thought to trying something like that with my RF31 - now you have revived my interest in doing it. Thanks! )


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## Canuck75 (Jan 11, 2014)

Shepherd said:


> VERY nice! Question...you pinned the rack in the middle?  This doesn't interrupt the operation up and own, presuming the bolt head is sufficiently countersunk....more pics, if you have them, would be great!



Yes, x4. I figured where I wanted the roll pins to go and pre drilled the holes in the bottom of the gear teeth on the drill press first, thus keeping their size and being square. The bottom 1/4"-20 bolt hole had already been drilled and tapped by the previous owner which put the the head 90 degrees to the table which is what I wanted anyways. Yes the heads are flush. The top 1/4"-20 hole was pre drilled at tap drill size and countersunk part way. Put the rack in place and tightened the bottom FSHCS in with locktite. I advanced up the column using the dial indicator to keep a zero on the rack at each pin position, temporarily clamping it, drilling thru the column, installing a roll pin, and advancing again. When I got to the top, a roll pin next to the c-sink hole was driven home first, then the FSHCS hole was drilled, tapped, and c-sunk to be flush. I did this to ensure that the FSHCS would not draw the rack off even a thou. The FSHCS was the put in with locktite.

Dialling the rack as I went gives a .000" error the full length of the column.


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## Canuck75 (Jan 11, 2014)

Shepherd said:


> VERY nice! Question...you pinned the rack in the middle?  This doesn't interrupt the operation up and own, presuming the bolt head is sufficiently countersunk....more pics, if you have them, would be great!




Thanks for your comments. Rather than trying to lump all my efforts into one article with the limit of ten pics per, I will break it up to cover each mod. It's the photos which really help one understand. The next one will cover gib locks.


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## Silverbullet (Mar 25, 2017)

Makes sense to do it this way , arks of a circle cut in different degrees. Should even make it shift able to do circle cutting on larger work pieces. Could add a sprocket and chain drive to do it . Like the up and down only around . Think this one in mine when I do it.


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## Mark_f (Sep 5, 2017)

Is the sides of the rack straight and smooth enough for the accuracy?

How tight are the guide blocks fit on the rack to eliminate any error?

I thought about doing something like that to that style mill in my friend's shop, but these questions have stopped me.


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## RJSakowski (Sep 5, 2017)

I have had a round column mill for forty years and had to deal with the problem of losing registration whenever the head was moved.

The issue with registering at the column is the registration point is only about 2-2.5" from the column center whereas the spindle is about 4-5 times further.  This means that any error in registration will be magnified 4 - 5 x.  There will necessarily need to be some clearance in order for free movement to occur.  Clearance would need to be less than .0002" to insure .oo1" accuracy at the spindle.

Another issue with using the rack as a registration device is that it was not meant for that use.  There is no need for or guarantee of consistent width or straightness.  The rack could be ground but even so, it doesn't compare to the dovetailed ways and gib system of a square column mill.  In the square column mill, any movement is linear so a .001' at the column is .001" at the spindle.

Finally, at least on my round column mill, the head is split and is secured by tightening three 5/8" bolts.  As you start to draw the bolts tight, friction will grab one side or the other first and subsequent movement will be from the other side which will slightly distort the alignment.


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## Mark_f (Sep 5, 2017)

RJSakowski said:


> I have had a round column mill for forty years and had to deal with the problem of losing registration whenever the head was moved.
> 
> The issue with registering at the column is the registration point is only about 2-2.5" from the column center whereas the spindle is about 4-5 times further.  This means that any error in registration will be magnified 4 - 5 x.  There will necessarily need to be some clearance in order for free movement to occur.  Clearance would need to be less than .0002" to insure .oo1" accuracy at the spindle.
> 
> ...


Those are exactly the points I was referring to. My friend is going to give me his mill but the round column bothered me as far as losing X When the head is moved. I couldn't see any way to reliably fix that problem.


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## Eddyde (Sep 5, 2017)

This issue has come up here before. The best solution is to securely mont a small laser, such as a from a laser level, pointer or gun site, onto the head of the machine, aim it at a spot on a wall as far from the machine as possible, draw an accurately plumbed, vertical line on the wall where the laser dot is. Then whenever you move the head, you simply align the dot to the line. Since the error is greatly magnified, it is easy to get alignment within a thousandth of an inch or so. Of course, the mills column should be accurately plumb and the machine securely mounted. I have used this method on a drill press, it works very well.


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## Silverbullet (Sep 5, 2017)

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 .


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## higgite (Sep 5, 2017)

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


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## mikey (Sep 5, 2017)

higgite said:


> 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.


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## higgite (Sep 5, 2017)

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


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## RJSakowski (Sep 5, 2017)

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.


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## Eddyde (Sep 5, 2017)

Silverbullet said:


> 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.   



higgite said:


> 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.


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## Silverbullet (Sep 6, 2017)

higgite said:


> 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.


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## tweinke (Sep 6, 2017)

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?


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## higgite (Sep 6, 2017)

Silverbullet said:


> 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


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## Silverbullet (Sep 6, 2017)

tweinke said:


> 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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## tweinke (Sep 6, 2017)

Silverbullet said:


> 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.



Yes I definitely get that. Was just thinking if a guy had a nice flat and straight bar set up parallel with the column and an indicator mounted to the head as long as you do not swing the head it would be easier to get back to zero. Although if you swung the head to one side it could be limiting the swing. The laser would certainly eliminate that issue. The creativity here certainly makes this a good place to be combined with the fact no one flames you for adding your thoughts!


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## Eddyde (Sep 6, 2017)

Here is some more discussion on the laser approach, relating to vise alignment:
http://www.hobby-machinist.com/threads/milling-vise-alignment-in-13-seconds.39171/
However, the concept is the same.


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## This Old Lathe (Sep 12, 2017)

tweinke said:


> 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 do. Very straightforward and as-accurate or more so than the more-involved methods described in this thread. I do understand the desire to have some 'built-in' feature to accomplish it though ....


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## Canuck75 (Sep 16, 2017)

Hello Mark F, Tom and R.J.  ,-

Sorry, I've away from the site for awhile and have just now read your comments.

First of all the rack on my mill was within .001 to .002" in width originally and with some buffing was close enough (10ths) that the guide blocks could be moved end to end by hand with some friction. The fit needs to be snug.

Secondly, I agree with the comment about the ratio of column centreline to the rack and the column centreline to the quill centreline, that is why nothing can be sloppy.

Third, and because my mill has a split casting and two bolts, experience showed that if the top bolt was tightened first, the head would retighten in the exact same manner each time, thus, in my case, would return to the same X reading within  .001" each time.  I posted a video showing this to be the case.

I am confident enough under normal circumstances, that I can move the head up or down without having to reset the X. If I'm doing work where there is a "pucker factor" involved, the only thing to do is recheck - that's life.

Thanks for the comments.

Canuck75


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## Uguessedit (Jan 20, 2020)

Seems to me that a pair of bearings at the top and bottom snug to the rack would keep it well guided and friction free. I have a round column with hiwin rails on the base with extended axis and a 10000 rpm capable spindle. I haven’t had any issue with the rack myself since I don’t use that much z to cnc and was able to get a solid 5” out of the spindle though I only use about 3.5”. Really if you use a probe or edge finder it’s probably not that big an issue if you need to machine the same part at different heights. Typically for myself if I’m changing parts it don’t matter since I reset zero and home anyways so it’s been a moot point. Perhaps manual use that’s different. Neat seeing different ideas. I use mine as a backup mill and to do drill arrays where the z height isn’t something that’s critical for the application.


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## Garryloy (Jan 20, 2020)

In about a month I plan to post a new solution to this problem - if my idea works.  I have a RF-31 that I have modeled in 3D (SW) and I have completed all the design work on the new approach.  It looks really good on paper.  I have all the materials and I am in the process of making the parts now.  It's hard to find time for it with 14 grandkids.


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## minsk (May 8, 2022)

Canuck75 said:


> *I have posted some information on this forum before about my machinery and have made many modifications to the mill, but this article is specifically about addressing the problem of keeping the X on a round column bench mill when changing the head position.
> 
> My particular "King" mill has a 19.2" X, 8" Y and 5 3/4" quill travel plus the head travel on the column. This capacity meets all my hobby machining needs. I dreamt of having a universal turret/ram/ knee mill but space and money dictated my choice. I saw this used bench mill on Kijiji and within driving distance. Mill looked a little scuzzy so did a full teardown, cleanup, repaint. Also started plans to make improvements.
> 
> ...


how are you doing dro on your computer?


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## Canuck75 (May 23, 2022)

minsk said:


> how are you doing dro on your computer?


minsk,-
Thank you for your interest. Am still pleased with my DRO setup after nine years. New glass scale systems are now very cheap but won't change unless my system fails.


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## minsk (May 31, 2022)

dro pros is really nice...but  my mill is not nice enough to warrrant it


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## Canuck75 (Jun 12, 2022)

minsk said:


> dro pros is really nice...but  my mill is not nice enough to warrrant it


Yes, budget is always a concern, and at the time the system I have cost ~$500 Cdn, which was a very big expenditure for me. However, Using a DRO, even on these mills increases your capability many fold. I like to build model engines and cannot see doing it without one. Highly recommended.

Thanks


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