# Head nod on a brand new mill with no adjustement



## Fardenco (Mar 29, 2021)

Hi,
I just got a small milling machine from china and I've started cleaning everything up and setting it up for use.
I managed to get a good tramming along the x axis, but my problem is with the Y axis since this mill has no adjustment. I've read that the solution is to shim it but I don't think it's normal to have such a huge error on a brand new machine
I read 0.2mm difference along the 200mm table so that's 0.057° out of square, which seems really huge to me for a precision machine like the mill
I've done some test to find where this is coming from, I'll detail it there so you can tell me if I'm doing it wrong, because it's the first time I'm doing this
First, how I got the measurement : I don't have a tool that goes into a collet to measure this, so I mounted a big arbor into the spindle, and I mounted an indicator on it using a magnetic base. This way I can swing the indicator by moving the spindle. I touch by lowering the head with the handwheel, then I lock the Z axis. The quill is locked too. I swing the indicator front to back, and that's how I get my 0.2mm difference. I'm using a 0.01mm indicator and it moves 20 divisions.
To find whether the problem comes from the column not being square to the table or from the head not being square to the column, I placed a vice on the table and the indicator on a part of the quill that does not rotate. I moved the head so that the indicator is touching the bottom of the fixed jaw, locked X Y and Z axis + quill, took measurement, unlock Z, move up, lock Z and take second measurement. There is not really any difference here. I didn't receive my parallel set yet so I can't do the test along a larger distance, but being that much out of square would have definitely show up here, I think. In fact with the angle I've calculated, aver the 45mm of the jaw I should see a 0.05mm difference so 5 divisions on my dial.
Then I did the exact same thing but moving the quill instead of moving the head. There I got mixed results, when moving the quill down the needle goes crazy, and when I lock the quill it comes back but I'm having troubles getting a consistent result, I don't know why.
I disassembled the head to clean up the meeting surfaces but that did not really help.
I tried to add some shimming at the bottom of the head (because it's leaning towards the front) to see what would happen but I must be doing it wrong, because when I tightened back the screws, I had a lot of drag on the Z axis. By the design of the machine I can't see how this could happen excepted maybe that this induced some kind of deformation that made the gibs tight ? Anyway when I removed the shim everything came back to "normal" but that's not really helping. The meeting surface is about 200mm in height so about the same as my table along Y axes. So the shim should be about 0.2mm. This is quite a lot I think, isn't it ? Wouldn't it impact the rigidity of the machine ? I have a cousin who has a grinding machine, he could adjust the surface on the head to give it the right angle, but I need to be 100% sure that the problem is coming from here, which I doubt since the machine is brand new. Maybe does it come from the quill itself ? How could I test that ?
Sorry for the long story, and thank you in advance for your help


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## Reddinr (Mar 29, 2021)

Precision and "milling machine from China" are not things that go hand in hand much of the time.  I have a bench-top mill, an RF-45 clone that had the same issue with the head not being perpendicular to the table.  In my case it was the column that had to be shimmed.  If I recall, it took about a 5 mil shim to fix it which I thought was pretty significant.  I think it worked out to 0.03 degrees.   Because I was new at everything at the time it took days/weeks to get it figured out and fixed.  One other item to check is whether your table surface is parallel to the y axis ways.  On my mill there is some difference but not enough to worry about as the head perpendicularity was the much larger problem.


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## macardoso (Mar 29, 2021)

Another option is to scrape the mating surface of the head to the Z axis slide. An old file can be used if you only need to do the one surface.


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## Joe-R (Mar 29, 2021)

Fardenco said:


> Hi,
> I just got a small milling machine from china and I've started cleaning everything up and setting it up for use.


Hello, 

One thing that some people new to machine setups tend to overlook when tramming the head or column is adjusting the gibs on the column. 
Try tightening the Z axis gib lock to the point where it is "Tight", do this while your test indicator is swung over the table toward the hand wheel on the Y axis and see if the indicator needle moves much or at all when you tighten or loosen the Z axis gibs. 
I've see mills lose Y axis tram over time because of gib wear and some new machines come with fairly loose gibs or become loose during shipping?

I know you mentioned that the Z axis gib got really tight with the head shim but that may be something different?

The gib can seem tight but still allow for a drooping head which is what you seem to be indicating? There's a lot of weight hanging out there.
You may have already tried this but I thought it was worth mentioning.

Anyway, just throwing ideas from past experience out there.   

Joe


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## markba633csi (Mar 29, 2021)

The junction between the column and the base is nearly always a weak point on these machines. Consider re-tapping the mounting bolts to a larger size in addition to scraping and shims to get the column perpendicular
-Mark


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## Fardenco (Apr 6, 2021)

Thank you for all your replies.
About the gibs, I'm locking them before my measurements so that should not be a problem I think. This is important because as you said, when locking them I can see the indicator moving quite a lot, reducing the node. But not enough, unfortunately.
I never scraped anything so I'm not really comfortable with doing that myself
I'm pretty confident that the problem is not in the alignment of the column.
What kind of surface finish should I expect between the headstock and the z axis saddle ?


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## macardoso (Apr 6, 2021)

Basic scraping (for flat surface and to correct the nod issue) is not hard and would only require an old file, a small surface plate and some dykem hi-spot. Maybe I've warmed up to the idea, but I just recently tried scraping for the first time and found it easier than expected, although definitely tedious.

Shimming is your other option. Perhaps once you get the correct thickness determined, a tiny dab of super glue would hold the shim pack in place.


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## Fardenco (Apr 6, 2021)

What do I do with the file ? I grind it to give it the shape of the carbide inserts that are commonly used for scraping ?
I have a surface plate and some Prussian blue so I could try that


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## macardoso (Apr 6, 2021)

Fardenco said:


> What do I do with the file ? I grind it to give it the shape of the carbide inserts that are commonly used for scraping ?
> I have a surface plate and some Prussian blue so I could try that


Exactly. Doesn't stay sharp nearly as long as carbide but it works fine. Some will say to grind all the teeth off the file and then grind the end to shape the cutting edge. I opted to just wrap the whole thing in masking tape so you don't accidentally file the surface and it doesn't tear up your hands. You don't need any fancy grinding to do a mating surface either. Just a standard grinding wheel. Sure the scrapes will have more scratching due to the rough grind, but it isn't a bearing surface and doesn't matter.

Scrape first to get contact all over and then scrape preferentially on the side which needs to be thinned (if head is nodded down, scrape the upper side, if nodded up, scrape the bottom side). When that is done, make sure to scrape the surface all over again for flatness

Measure often as you go. You could even do a rough shimming job to get an idea of how much scraping is needed. More than a thou or two and you'll have a bit of work on your hands.


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## Fardenco (Apr 6, 2021)

I have 0.2mm to remove on the top side, so about 8 thou
That's a lot, this is why I'm surprised to have that big of an error on a brand new machine, even on a cheap one


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## macardoso (Apr 6, 2021)

Fardenco said:


> I have 0.2mm to remove on the top side, so about 8 thou
> That's a lot, this is why I'm surprised to have that big of an error on a brand new machine, even on a cheap one


Ouch. I mean totally doable with some elbow grease and scraping but it will be some work. 

Any chance you have a buddy with a surface grinder?


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## macardoso (Apr 6, 2021)

Let me question you on something. You comment that you are 0.2mm over the whole table. I'm assuming this was measured with an indicator tramming against the table.

So what is the width of the table in the Y axis? And second, what is the height (along the Z axis) of the mating surface between the head and the Z axis slide?

The reason I ask is that you would need to shim/scrape the interface between the head and the Z axis slide, and that is where we need to know how much material to add or take off.


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## Fardenco (Apr 6, 2021)

The length of the table along the y axis is the same as the length of the mating surface along its height, so the error I measure along the table should be the width of the shim, or amount of material to remove I think
But I might be trying to solve the wrong error, maybe the problem is with the spindle itself, if that makes any sense
I really don't know, all of this is quite new to me
I might have access to a surface grinder and to someone who knows how to use it, but I would rather avoid going through the trouble of correcting this surface just to figure out later that the problem was somewhere else
But I don't know what tests or measurements I could do to confirm that


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## Weldingrod1 (Apr 6, 2021)

Photos please?

Sent from my SM-G892A using Tapatalk


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## homebrewed (Apr 7, 2021)

Relatively inexpensive benchtop mills can have two different issues with regard to tram.  The most obvious is  column-to-table alignment, but the spindle head itself also can exhibit misalignment relative to the column, too (on one or both axes).  You may need to separate the two issues before you can completely solve your problem.  An indicator mounted on a magnetic base, attached to the column, can be used to evaluate the spindle alignment (using a test bar installed in the spindle).

Spindle-to-column misalignment usually is addressed by rotating the spindle head (for X), and shimming it on the bottom (for Y).  Only then can you tram the column relative to the table without seeing shift as the distance between the spindle and table changes. 

When I checked my mill I determined I didn't need to mess with the column-to-spindle alignment to meet my needs, but your machine may be different.


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## macardoso (Apr 7, 2021)

OK, I was trying to keep this moderately simple, but everyone here is right, there are two locations for this potential error. 

1) The axis of the spindle / quill is not square to the table surface. This is a combination of all kinds of errors, but by shimming/scraping the interface between the head and the Z axis slide you can cancel out all the other errors in the *nod* direction.

2) The axis of Z axis motion is not square to the table surface. This is also the column being crooked to the machine base. This can also contribute to head nod. You would typically correct any squareness issues with the column first then tram for head nod later. To measure this, the easiest way is to place a cylindrical square on the table and run a dial indicator on all sides while cranking the Z up and down. There are other methods if you don't have a squareness master. This error is corrected by shimming / scraping the column to machine base interface.


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## Razzle (Apr 7, 2021)

Check out hansw33 on youtube. I don't know what mill you have but hans did a complete measure, scrape in, and rebuild to convert a HF minimill to cnc. His measurement technique may help you find the error.

Sent from my Pixel 4a using Tapatalk


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## Razzle (Apr 7, 2021)

Oh, and oxtoolco on youtube has a great video on right angle reference standards and how to build your own using a parallel, 123 block, dial test indicator and stand. Really neat technique that I plan on using to make a cylindrical square.
Oxtoolco it's hip to be square.





Sent from my Pixel 4a using Tapatalk


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## Fardenco (Apr 15, 2021)

Razzle said:


> Oh, and oxtoolco on youtube has a great video on right angle reference standards and how to build your own using a parallel, 123 block, dial test indicator and stand. Really neat technique that I plan on using to make a cylindrical square.
> Oxtoolco it's hip to be square.
> 
> 
> ...


This is awesome, thank you



Weldingrod1 said:


> Photos please?
> 
> Sent from my SM-G892A using Tapatalk


Here you go


The machine :



The Z axis



The surface which seems to cause me problems. I don't know if it's supposed to be ground or something, but as you can see it's quite rough





homebrewed said:


> Relatively inexpensive benchtop mills can have two different issues with regard to tram.  The most obvious is  column-to-table alignment, but the spindle head itself also can exhibit misalignment relative to the column, too (on one or both axes).  You may need to separate the two issues before you can completely solve your problem.  An indicator mounted on a magnetic base, attached to the column, can be used to evaluate the spindle alignment (using a test bar installed in the spindle).
> 
> Spindle-to-column misalignment usually is addressed by rotating the spindle head (for X), and shimming it on the bottom (for Y).  Only then can you tram the column relative to the table without seeing shift as the distance between the spindle and table changes.
> 
> When I checked my mill I determined I didn't need to mess with the column-to-spindle alignment to meet my needs, but your machine may be different.



My indicator mount does not have enough reach for me to measure from the column to the spindle axis, I'll soon receive a longer one, I'll tell you the result. Thank you



macardoso said:


> OK, I was trying to keep this moderately simple, but everyone here is right, there are two locations for this potential error.
> 
> 1) The axis of the spindle / quill is not square to the table surface. This is a combination of all kinds of errors, but by shimming/scraping the interface between the head and the Z axis slide you can cancel out all the other errors in the *nod* direction.
> 
> 2) The axis of Z axis motion is not square to the table surface. This is also the column being crooked to the machine base. This can also contribute to head nod. You would typically correct any squareness issues with the column first then tram for head nod later. To measure this, the easiest way is to place a cylindrical square on the table and run a dial indicator on all sides while cranking the Z up and down. There are other methods if you don't have a squareness master. This error is corrected by shimming / scraping the column to machine base interface.


This is clear, thank you far the explanations. I'm pretty sure the column is square to the table, but I will do a few more measurements to confirm that.

Thank you all for helping out !


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## macardoso (Apr 15, 2021)

Your head/column side interface looks just like my G0704. They flake the surface for appearance only. The real surface behind those crescent flake marks is likely quite poor.

If you have any Hi-Spot blue, you can blue the head up and rub it against the mating surface. I think you'll be surprised/horrified at how little contact actually exists between the surfaces.


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## Fardenco (Apr 20, 2021)

macardoso said:


> Your head/column side interface looks just like my G0704. They flake the surface for appearance only. The real surface behind those crescent flake marks is likely quite poor.
> 
> If you have any Hi-Spot blue, you can blue the head up and rub it against the mating surface. I think you'll be surprised/horrified at how little contact actually exists between the surfaces.


Yes it really seems poor
The flakes are supposed to be pockets for keeping some oil, but when I see the surface, I already see plenty of space for the oil to stay in


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## macardoso (Apr 20, 2021)

Fardenco said:


> Yes it really seems poor
> The flakes are supposed to be pockets for keeping some oil, but when I see the surface, I already see plenty of space for the oil to stay in


You would typically only care about flaking for oil retention on a sliding surface. Anywhere else would be decorative as best I understand.

I think the manufacturer of the machine just wanted to hide their potential grinding blunders on that surface


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## tkalxx (Apr 20, 2021)

Fardenco said:


> But I might be trying to solve the wrong error, maybe the problem is with the spindle itself, if that makes any sense
> I really don't know, all of this is quite new to me
> But I don't know what tests or measurements I could do to confirm that



Everyone in this thread saying there are 2 main sources of error contributing to the "nod" you measured is correct. Follow what @macardoso said and you should easily determine what is the source of the issue. 

Start with making sure the column is perpendicular to the X-Y plane by running a test indicator up and down a square (do this inline with both the X and the Y axes). Shim the column accordingly front/back, side/side until it is as perfect as you can get it. On my PM25-MV (chinese machine very similar to yours) I had to add nearly 20 thou of shims under the column.... I did however, remove the column from the base at one point which disturbed it's mounting position from the factory. 

Then go back and measure the Y "nod" with a test indicator in your spindle as you described earlier. If you still measure a difference across the table, you can be sure that the axis of your spindle is not parallel to the Z-axis dovetails/slide. This can be temporarily fixed by shimming between the headstock and the Z-axis slide (although more difficult than shimming the column). A more permanent solution would be to scrape the headstock to Z-axis slide mating surface as stated earlier (this is the surface that has been flaked for appearance).


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## Illinoyance (Apr 24, 2021)

Stefan Gotteswinter had a video about tramming the column of his mill.  He used an industrial grade epoxy under the column.


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