SQUARING A STUBBORN X2 HEAD

petcnc

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Tramming a solid column mill was always a challenge for me, thus I used the “Long Bolts Method” (full story Here) to achieve best results the easy way.
Although I was able to tram my mill within 0.01 mm (0.0004 in) these results were not permanent and I was always retramming my X2 mill blaming the long bolts, the Chinese designer, my TDI instruments, and my bad luck to buy a cheap mill.

This Christmas holidays I found some time to upgrade the bearings for some angular contact ball bearings that give better results compared to the stock plain ball bearings.
Angular Contact Bearings.jpg


After installing the new bearings I decided to tram the column using a different approach and then to remove the head and square it.

To achieve best results in tramming the column, I used my 6 inch engineers square but as this was (is) my only reference to “square” I tried to eliminate any errors it possibly had by averaging the measurements taken to both ends of the table.

The method goes as follows:

I used two 1-2-3 blocs bolted together and my engineers square side by side. Using shims (alu foil) I adjusted the inclination of the blocks in order to have the same DTI measurements on them (top & bottom) as to the engineers square next to them.

ColumnTramAv.jpg

Next I secured the engineers square at the other end of the table and took measurements for the full height to left side and to the right side of the table moving the head and rotating the DTI.

ColumnTram.jpg

In the process, I recorded the results (bottom & top left, bottom & top right) and made adjustments until I got the same average for right and left side.

ColumnTramAv1.jpg

This way I was sure that the column was EXACTLY PERPENDICULAR to the table.
As I could not follow the same procedure for Y I took measurements putting the engineers square to the front of the table.

Ytest.jpg

Next I started to work on squaring the head.
My mill’s head is bolted on a carriage with 4 bolts that are accessed from the back of the carriage after removing it from the column.

SX2a.jpg

Because of this arrangement it is a time consuming work to make any adjustments to the head.

Head & Carrier.jpg

My head was far from square! In the “X” direction was 0.12 mm (0.005 in) out of square and in “Y” direction was out 0.05 mm (0.002 in) accordingly.

X & Y Adjustments needed.jpg


To make things easier I decided to add some adjusting bolts on the head carriage so I can make micro adjustments for the X directions. For the Y error I planned to use shims.

X Adj.jpg

In order to add shims for Y and adjust the X, I removed the head carriage and the head, separated them and cleaned the mating surfaces on the surface plate.

Surface Cleaning.jpg

Then added the aluminum foil shims

Add_Alu.jpg

I hand tighten the 4 bolts that connect the head to the head carrier, I installed the head on the mill and using a DTI I tried to square the head.

SquaringHead.jpg

To my surprise, when I removed the head and tighten the screws further, the head was ok in Y direction, using the shims, but did not stay square in X direction despite the microadjusting screws that (supposed to) hold it in place!
Several trials later I found the cause of this stubborn behavior! The 4 bolts connecting the head to the carrier had formed seatings to the concave bottom of the hole and as they were tighten they drove the head to the same position! No matter how hard I tried to change this position the head was always off in X direction by 0.12 mm.

PC292002s.jpg

It was time to tackle the problem! As the mill could not mill itself, the only machine available was my mini lathe. Using shims I supported the head carrier on the topslide, secured it with c clamp, and using a 14mm end mill I made the bottom of each hole flat.

PC292008s.jpg


PC292001s.jpg


To play safe and have full control in micro adjustment I added another two micro adjusting screws to the carrier.
So now I could micro-adjust the top and the bottom of the head to achieve a perfectly square head!


PC292016s.jpg


PC292017s.jpg


Tightening the bolts that secure the head to the carrier did not changed the head’s position.

PC291983s.jpg

Measurements with my DTI certified an accuracy better than 0.01 mm (0.0004 in) at any height of the head!
I’m happy with that as I think there is no way to achieve better accuracy due to several other factors (flexibility of the column, flexibility of the base etc.)

PC291980s.jpg


PC291982s.jpg


Thanks for reading this

Petros
 

Zoltan

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Next time use Rolle's Dad's Method to tram the head. It's much faster and simpler and works for the Y axis as well. Plus, it for any runout in the chuck, bore, or spindle bearings.
 

Rimbaldo

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Hi!! How does your micro adjustment brackets are holding with time? Did you ever need to readjust them? Have you tried to do these micro adjustments ... on the fly... with the head mounted on the mill, with all four bolts that attach the head to the carrier fully tightened, without needing to dissasemble it all and reassemble it back?

Did you consider any brackets for correcting the y on the head also?

i’m thinking of doing these brackets of yours in mine! Can you post more close-up pictures and sizes of the brackets, bolts that you’ve used?

Thanks!!
 

Asm109

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I just want to point out that bottom a hole with an end mill does not give a flat bottom. It gives an inverse cone shape. Like the inverted flare fitting used on brakes. Its only a couple of degrees but your bolts will be crushing down on a raised rim at the bolt hole.
 

RJSakowski

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Your X2 is very similar in function to my Tormach mill in that the z axis motion is accompliushed by moving on the z axis ways rather than with a quill. Head alignment is accomplished by first ensuring that the spindle axis is parallel to the z axis ways in both x and y. Then the head can be trammed to the table. The first is done as you have done: the head is rotated slightly on its mounting for the x alignment and by shimming the head for the y alignment. My approach to making precise changes in the head rotation is like this. The head uses two tapered dowel pins to maintain aqlignment. I loosened the lower left pin abd used the upper right pin as a pivot. The mechanism below controls the rotation around that pivot point.
Tram Adjuster.JPG .......... Tormach Tram Adj .JPG
The y direction alignment would be accomplished with shims. One point to note is that any play in the z axis ways will cause head sag so adjusting the z axis gib should be done first. when I finished adjusting the gib, the head sag essentially went away. I used the RDM method for checking alignment, much like would be done with a lathe. It is possible to check alignment in both the xz and yz planes.

Once the head is aligned with the z axis ways, the machine can be trammed using the typical methods. Any adjustment should be done by shimming the base of the column.
 

petcnc

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Since my last adjustment as described above I did not notice any need for another go. The head sits square as adjusted and the only adjustments need from time to time is the gibs!
RJ your method is far more sophisticated than mine! I wish I had seen it before I tried to trim my mill.

Petros
 

Rimbaldo

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Since my last adjustment as described above I did not notice any need for another go. The head sits square as adjusted and the only adjustments need from time to time is the gibs!
RJ your method is far more sophisticated than mine! I wish I had seen it before I tried to trim my mill.

Petros
Thanks! Can you post more close-up-pictures of your brackets??
 

petcnc

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Thanks! Can you post more close-up-pictures of your brackets??
Here you are!

As you can see the brackets are pieces of steel bars that I had available, nothing fancy. I secured them on the head carrier using a single bolt and I used another bolt to microadjust the head by screw in or out the oppisite side bolts on top or bottom accordingly.

This is the right side of the head

PC262459.JPG

PC262452.JPG

PC262453.JPG

PC262454.JPG

PC262455.JPG

Left side bottom

PC262457.JPG
 
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Rimbaldo

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Thanks a lot!! I’ll post my pictures later of my brackets! Just one more thing:

It seems you drilled the cast right on the height where those 4 internal screws attach the front-head cast to the back one, that attaches to the collumn. Did you drill it with the head dissasembled? How did you do it?
 

petcnc

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It seems you drilled the cast right on the height where those 4 internal screws attach the front-head cast to the back one, that attaches to the collumn. Did you drill it with the head dissasembled? How did you do it?
I'm not sure what drillings you refer to.
The only drilling I have done were those to fix the brackets on the head carrier as in the following photo.

PC281960s.jpg

This drilling and threading was done with the head dissasembled.
As you can see in the next photos the head and the head carrier are connected with 4 bolts that go through the carrier and screw in the head.
The brackets are bolted to the head carrier and the bolts that are threaded on them push the head right or left accordingly.

PC292014s.jpg

PC291983s.jpg

The problem was with the head carrier where the holes were drilled with a conventional drill and thw bottom was not flat. For that reason the bolt head was driving the head to the same place everytime you screw the head back.

PC292002s.jpg

So I had to make it flat!

PC292005s.jpg

No other drillig took place either to the head or the head carrier
 
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