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Shim-free tramming of mini mill

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petcnc

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#1
I thought I had posted this a year ago but I cannot find it anywhere on the site!

So I re-post it for anyone interested in a shim-free method to tram solid column mini mill.


After some months from the initial tramming of my mini mill (see it here: http://www.hobby-machinist.com/showthread.php/10788-Tramming-my-Sieg-SX2P-mini-mill-(identical-to-LMS-3960)?p=89448#post89448) I discovered that the drill chuck I was using initially, has an unacceptable play, driving the whole procedure on the wrong side.
When I used collets and rechecked verticality of the column I noticed that it was far from vertical.
So same procedure followed again, and again, and again, to manage some 0.10 mm @ X and 0.08 mm @ Y direction. Far from happy!
Last Christmas having some free time, I searched thoroughly the Internet and plan a more systematic approach on the matter.

My approach started from testing that:

a) the head of the mill stands parallel to the column and
b) the column stands vertical to the table.

Part A. Head to column tests.

The drawing below shows my test setup.

Head test.jpg

I have mounted in a collet a steel shaft 20 mm thick (salvaged from an old shock absorber), and used Rollie's Dad's Method (explanation follows) to do the measurements. For the X-axis checks, the DTI point was set on the side of the shaft. Then, two sets of measurements were taken, one set at the collet end of the bar, and the other set at the far end of the bar. I started my measurements at the collet end. I locked the carriage there, rotated the spindle 360 degrees, wrote down the minimum and maximum readings from the dial indicator, and then found the average of the two measurements [(max + min)/2]. Then, without changing anything about the indicator, I unlocked the carriage and wheeled the head back up the column, so that the indicator was at the other end of the bar. I locked the carriage, got the maximum and minimum readings there, and averaged those two measurements. Then I compared the averages. The difference between one end's average and the other end's average was the total misalignment for the distance along the bar. (That's Rollie's Dad's method.) The beauty of Rollie's Dad's method is that the test bar doesn't have to be perfectly straight, and runout of the chuck or collet won't affect the results either. I repeated the procedure for the Y-axis, with the indicator point behind the test bar, as shown in the right side of the drawing. Results were X = 0,05 mm misalignment and Y = 0,01 mm over a distance of 200 mm. That means if I drill a 20 cm deep hole, moving the head down from top to bottom end, the holes will be out of alignment by 0,05 mm. I can live happily with it!

Part B. Adjusting the column verticality (tramming)

I don’t know about you, but I am the kind of guy who feels very frustrated if, lets say, after a dozen of trials fails to achieve the results he aimed for. That was exactly the case when I tried to tram my mill. As I was putting a shim on one corner I had to put another one at another corner otherwise the readings were far from correct. With the new shim I had to calculate again and put a new one and so on. I have repeated this procedure a dozen times and I decided that there is something wrong with the method as there are 4 corners and in order to achieve ultimate results you have to put different thickness shims in at least 3 of them.
Scratching my head for days I could not find a better method. Internet had nothing to suggest either. Suddenly last night I found the solution. I will use long bolts screwed to the base and I will support column with nuts below & above each corner.
So sleeves up and off we go. I prepared 4 long bolts with their nuts and washers (see next photo the short black bolt is the original).

PC250330.JPG

I removed all shims and cleaned thoroughly base and column. I put the bolts, nuts and washers to column (see next photos).

PC250334.JPG

PC250335.JPG

Then, leaving nuts loose, secured bolts firmly to base (That’s why I did not trim the heads of the bolts initially).

PC250343.JPG

Next step was to screw lower nuts fully down and to secure column by screwing the top nuts tight.
I was ready then to mount my DTI, a piece of glass from an old scanner (measured to be flat) and start tramming.
The procedure was easy. If you wish to lift a particular corner(s) unscrew the lower nut (after making provision that the top had been loosen as well so the column could change inclination).
To make corrections and fine-tune any corner follow next photo!

Procedure.jpg

Then using a scanner glass (as the flattest thing in possesion) I tested and fine-tuned X and Y axes.

PC250341.JPG

Piece of cake! In 5 minutes job finished.
Results: X= 0.00 Y= 0.00
PERFECT!!
That is X+ and X- readings

PC250336.JPG

PC250337.JPG

And thats Y+ and Y-

PC250338.JPG

PC250339.JPG

Finally, holding the magnetic base I rotated the spindle 90 degrees (in case there is a misalignment in the spindle) and tested again. Results same as before.

That’s how the base looks now. I never choped the bolts to achieve a more professional look (as I should have done).

PC250346.JPG

Thank you for reading

Petros

Head test.jpg PC250330.JPG PC250334.JPG PC250335.JPG PC250343.JPG Procedure.jpg PC250341.JPG PC250336.JPG PC250337.JPG PC250338.JPG PC250339.JPG PC250346.JPG
 

thomas s

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#2
Great idea when I need to tram my mill I will give this a try. thomas s
 

brav65

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#3
Great job! That is how I have installed many steel posts in re-model situations that required a large beam and we did not have room for a wood post. One question I have is, have you noticed any increase in flex on the column? Code requires that we grout the space between the floor and the plate to preven any flex on the bolts. I guess you could grout the base of the mill as well to provide support for the column. Thanks for the post.
 

petcnc

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#4
Great job! That is how I have installed many steel posts in re-model situations that required a large beam and we did not have room for a wood post. One question I have is, have you noticed any increase in flex on the column? Code requires that we grout the space between the floor and the plate to preven any flex on the bolts. I guess you could grout the base of the mill as well to provide support for the column. Thanks for the post.
No sir, I did not noticed any increase in flex on the bolts. It is probably due to minimum length of bolt been exposed between base and column as you see at next picture.

PC250343.JPG

Thank you for your kind remarks

Petros

PC250343.JPG
 
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Wireaddict

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#5
Besides cutting the bolt heads off or turning them round & possibly knurling them you could also use allen setscrews that size. I've got my mill pretty close by shimming but I like your idea so next time I tram it I'll try doing it your way only using setscrews if I can find them that length here.

Another thought I had: if one corner needs to be raised then the 2 adjacent corners should be raised by about half that amount to continue providing support under them & to avoid distorting the bottom of the column slightly.
 
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petcnc

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#6
Besides cutting the bolt heads off or turning them round & possibly knurling them you could also use allen setscrews that size. I've got my mill pretty close by shimming but I like your idea so next time I tram it I'll try doing it your way only using setscrews if I can find them that length here.

Another thought I had: if one corner needs to be raised then the 2 adjacent corners should be raised by about half that amount to continue providing support under them & to avoid distorting the bottom of the column slightly.
Good thoughts both of them!

Thank you
 

Zoltan

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#7
It seems to me that you want two nuts between the column and the base: one to lock against the column and one to lock against the base. Unless, off course, you went the route of using permanent thread locker to secure the bolts/studs into the base.
 

Wireaddict

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#8
It seems to me that you want two nuts between the column and the base: one to lock against the column and one to lock against the base. Unless, off course, you went the route of using permanent thread locker to secure the bolts/studs into the base.
That would work but the second set of nuts would raise the column more which would make the column slightly less rigid & increase vibration. Unless the bolts bottom out in the base I think thread locker is a necessity here.
 
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petcnc

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#9
It seems to me that you want two nuts between the column and the base: one to lock against the column and one to lock against the base. Unless, off course, you went the route of using permanent thread locker to secure the bolts/studs into the base.
Thread locker was the solution I have used. It was not a necessity though as the two nuts tighten to the column base secure the bolt firmly. I never had an issue of loosing the head alignment no matter how rough the cut was (with all the chattering involved).
 

MaverickNH

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#10
This method seemed to work well for me. I had tore down, cleaned and reassembled my HiTorque 3960 mini-mill and was sufferring grief trying to tram with shims.

After installing the nuts & bolts, as directed above, I elevated the column by 1 full turn, then backed down as necessary to measure within 0.0005 on a Pro-Tram 5" unit oriented in both X and Y directions. I picked up a 1/2" x 9" precision steel shaft from McMaster Carr, straight to within 0.002 per foot, and laid a 6" square against the rod and found less than a 0.0015 gap - my thinnest feeler gauge - as I rotated the shaft. There is detectable wobble at the end of the rod when spun, but just barely.

I'm calling this pretty good.
 

petcnc

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#11
Happy to hear that another hobby machinist found my method useful.

Petros
 

yendor

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#12
I have an RF-30 Clone and wonder if this method would transfer over to that machine, it is a round column and the column is bolted to the base traming involves shimming the column to the base.

I just wonder if it would be at the expense of rigidity?
 

petcnc

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#13
Well that depends on a number of factors: I would suspect that the thickness of the bolts and the new distance of the column from the base are the main ones. I did not notice any difference to the column rigidity to my mill but mine is a mini mill... I'm not familiar with yours and I cannot say.
On the other hand it doesnot harm the mill to try this method and let us all know of the results. If not rigid enough you can always go back to shims.

Petros
 

petcnc

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#14
UPDATE

As I was never happy with the head of my mill, it was not exactly square as I would like it to be, I followed a completely different approach to make it square. Full story here.
In a few words I added micro adjusting screws to the head carrier and milled flat the holes where the bolts sit in order to make the micro adjustments needed.
Petros
 

Mjohnson

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#15
I used the method shown in this video. It has worked very well.
 
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