Mini-Mill Spindle-Column Alignment

[rudydubya]

Spectre, welcome to the forum. I'm still a newbie too, but here's my understanding of Rollie's Dad's Method: Average the minimum and maximum readings at the collet end (just add the two readings together and divide by 2), and then average the minimum and maximum readings at the far end. If the averages are different, then the alignment is off by the amount of the difference. In your case, the average at the collet end is zero, while the average at the far end is 0.005, so the far end is 0.005 off-center. If it were perfectly aligned, the average of the minimum and maximum readings at the far end would be the same as the collet end, zero in this case. Hope this helps.

Regards,
Rudy

 

[chester179]

Thanks for posting this rudy. Very helpfull.
One thing that i would add is to check the adjustment of the column/carriage assy for correct fit - mine had discernable movement that interfered with reliable measurement and adjustment of the spindle.
Simple adjustment of the 4 adjusting screws corrected this problem.

I torqued the 4 spindle housing bolts to about 20 lb.ft probably a bit on the low side but i didnt want to risk damaging the threads.

 

[dgjessing]

I'm so glad this thread was resurrected - this explains what's wrong with my mini-mill! I'd get the thing trammed just perfect so a fly cutter would make the nice "()()()()" pattern, but when drilling, changing from a short center drill to a long drill bit would throw the center off... WTF? I thought. This explains it!

Mine is .025" off over 4" in the X axis, but good in the Y axis. Off to do some minor surgery...

:bow: to the OP

.... after surgery... ;D Much better!!!

 

[rudydubya]

chester179 and Dave, glad this old thread was still useful.

chester179, thanks for the feedback. I see that was your first post here on HMEM. Welcome. When you get a chance, stop by the welcome section and tell us about yourself and your shop and your equipment and your projects and your interests. Great bunch of folks here, and they would all like to meet you. And you probably already know we love pictures.

Regards,
Rudy

 

[chester179]

Thanks Rudy.
Your method got the spindle head lined up with the column.
Trammeling the mill revealed that the column/spindle was not in perpendicular alignment to the table/base. It was discernably tilting forward - presumably a natural consequence of the front heavy spindle head weight on the column.
The method i used to remedy this was to build a wooden brace with a steel bolt between the brace and the top of the spindle column. The mill was the trammeled and the adjusting bolt was tightened up to counter the forward stoop.


This corrected the alignment to acceptable levels.

 

[rudydubya]

Interesting solution to correct the tilt, chester179. Thanks for sharing. I corrected the tilt on mine with a small plate and some bolts at the bottom of the column while I was trying to minimize the column flex. You can see what I did and see some other solutions here: http://www.homemodelenginemachinist.com/index.php?topic=6075.msg64571#msg64571.

I see from the picture that you've installed the air-spring mod as well, or did that come with your lathe? Any other mods that we would be interested in? Lots of folks here on the forum with mills like ours.

Don't forget to stop by the welcome area and start a hello thread so all the members can meet you.

Regards,
Rudy

 

[chester179]

Very interested to read the link to how you solved the problem of column flex in your mini mill rudy. Seems we both had the same problem ; forward tilt due to top frontside weight on slightly flexible column. You opted to strengthen the column while i opted to counterbalance the topheavy weight causing the stoop. I guess combining both methods might get the best results.
My mill is standard as it came from the factory , ive only recently got it and up to present have just been trying to get it all aligned with sufficient accuracy for use. Now i can start using it but will keep a close watch on the forward tilt as things settle into place , particularly with the wooden construction. Have you found the alignment on your mill has remained stable or have you had to adjust it subsequently?
Mines a Chester Conquest (UK) btw.

 

[rudydubya]

chester179, my setup appears stable. I checked the tram this afternoon to see how much it might have changed over the last several months, and it was only off about 0.0005", about like it was when I last trammed it, as I recall. It hasn't seen much use over that period, and most of that was light work. It will be interesting to see how your wooden brace holds its tram over time. What kind of projects are you planning?

Regards,
Rudy

 

[chester179]

Rudy well a week down the line and it seems stable. One thing i did notice was that my x axis trammel varied on the lhs depending on if the spindle head was tightened or not indicating the carriage was fitted loose enough for it to move on tightening. I tightened up the carriage adjusters. Fortunately the x axis alignment still seems ok.
Originally i noticed that the forward lean on my mill could be corrected by leaning on the spindle housing so rigged my setup as a permanent way of counterbalancing this tendency to lean.
All ive done with it so far is milling retaining bolts and drilling holes. Originally it was an expensive response to needing to do some precision drilling but subconsciously maybe i was also ready for a new hobby.
Rob

 

[rudydubya]

Rob, glad your mod is working for you. As for the head movement when locking the gibs, I saw that also while I was getting used to my machine, especially when setting or adjusting the head height. I now keep the gib screws adjusted tight enough to offer a bit of resistance when cranking the head up or down. But even so, I always assume the head may move a thousandth or so when I lock the gibs, and watch for it if I'm trying to do something that requires that kind of accuracy. Adding my cheap DROs have made that a lot easier to monitor.

When you decide on a project be sure and keep us informed. I only wish I had started on this hobby many years ago.

Regards,
Rudy

 

[Goldigger]

I tried aligning the spindle to the column tonight...I should have started at 6am then I might have got it finished..
For my test bar I used a bar from w printer, thinking it would be perfectly straight and round.
Seems not, rotate it 180 degrees and its off by 0.20mm
If I measure at the top and set the dti to 0, move the spindle to the bottom of the z axis...its now reading -0.60 on the x axis...

So my spindle appears to be pointing to the right on the x axis. That might explain my issue on my rotary table.
With the rotary table centered and spindle aligned to 0.0 x and y..move the x to the left say 20mm and drill a hole..then move the rotary table through to -20mm on the x axis and drill another hole.
I should end up with a hole 20mm either side of the centre of the work piece..the hole to the left is always a shorter distance..

I have a problem with taking the head off to get to the 4 bolts..I have to loosen my gib just to move the head off the end of the column..

 

[Goldigger]

Can someone confirm im doing this correct please...
Im pretty sure my Y axis is only off by 0.03mm so I'm going to just adjust the X axis

I have my test bar from a printer in a 1/2" collet..
With the head at the top of the column, i take a reading off the DTi at the bottom of the bar...I have 0.15mm runout
With the head at the bottom of the column, i take a reading off the DTi at the top of the bar (just below the collet)...I have 0.02mm runout
(When i move the head from top to bottom the DTI goes from 0 - 0.50mm)

With the head still at the top of the column, i rotate the spindle and zero the dti so that when i rotate the spindle and read the dti it will read -0.01 through to +0.01
Rotate the spindle so that the dti reads zero
Move the head to the bottom of the column, rotate the spindle and if my X axis is square my readings on the DTI when rotating the spindle should be -0.07 through to +0.07
?

edit..if my method is correct then the Y axis is out by 0.07mm
Where can i find shim stock in the uk? i was tempted to use kitchen foil?

I've found shim stock on ebay, is there a reason why some people have used brass rather than steel shim?
how about this shim tape?
http://www.ebay.co.uk/itm/Stainless...938?pt=LH_DefaultDomain_3&hash=item2314e83e22

 

[rudydubya]

Hello Goldigger, hope your day has been a good one. I'm not sure I understand exactly what you're aligning now, and maybe I'm misunderstanding your axis references, so maybe a question or two before I give you my opinion. First, I think you are still working on aligning the spindle with the column, and not the table, is that correct? Second, when you say adjust the X axis, do you mean adjusting the head slightly from side to side when looking at the front of the mill, or is it back and forth? I was thinking it was side to side, but then your question about shim stock made me wonder (the older I get, the easier I am to confuse). As far as shim stock, I think either brass or steel would work, I used brass because I had some I found at a hardware store, but I think steel would have been fine. As a source, have you considered sacrificing a simple feeler gauge, which should be available at an auto parts or tool store, for their thinner leafs?

Regards,
Rudy

 

[Goldigger]

Hi Rudy..
Yeah sorry my explaination wasn't to clear..
I'm trying to align the spindle to the column..when i referenced the X axis i mean spindle side to side/left to right..when looking at the head from the front

The shim stock was for the front to back adjustment, or the Y axis as the spindle is pointing backwards by 0.07mm
I found plenty of options on ebay, some cheap shim from modelling shops
http://www.ebay.co.uk/itm/BRASS-SHI...UK_Crafts_Other_Crafts_EH&hash=item2c5e23cf45
Hopefully me pic helps..

Im tempted to buy a test bar from Chronos in the UK for £39..3MT 250mm long
http://www.chronos.ltd.uk/cgi-bin/sh000001.pl?REFPAGE=http%3a%2f%2fwww%2echronos%2eltd%2euk%2fcgi%2dbin%2fss000001%2epl%3fpage%3dsearch%26SS%3dmt3%20test%20bar%26PR%3d%2d1%26TB%3dA%26search%2ex%3d0%26search%2ey%3d0&WD=bar%20test&PN=XMAS_GIFT_IDEAS_6%2ehtml%23aGX13#aGX13

 

[rudydubya]

Hello Goldigger, yes, now I understand, thank you. That brass shim assortment is similar to what I found at a local hardware store. Always handy to have some around. As far as a precision test bar is concerned, I always thought one would be nice to have, but I haven't gotten to the point where I felt I really needed one yet. Granted, I'm an amateur with no practical experience, but I used Rollie's Dad's Method with a bar from a printer and got satisfactory results. My bar was fairly straight, but not exact, and the diameter was consistent along its length. A straight test bar is not required for Rollie's Dad's Method, but to keep the procedure simple it should be the same diameter at the points you use for measurement. By its nature, Rollie's Dad's Method eliminates the need for a bar that's exactly straight.

I went back and re-read your post of 11/11 and it sounds like you're on the right track. If I understand your procedure correctly, you secured the DTI on the column and measured the runout of the bar at a point close to the spindle when the mill head was at the bottom of the column and got 0.02mm runout. You then adjusted your DTI dial so that it read from -0.01 to +0.01 as you rotated the spindle. You then moved the head up to the top of the column without moving the DTI and measured the runout near the bottom of the bar. I don't think you mentioned the maximum and minimum readings you got there, but if you added those two readings together and divided by two the result should be how much out of alignment your spindle is from the column. For example, if your measurements at the bottom of the bar ranged from -.05 to +.12 as you rotate the spindle, then your alignment is off by +.035. If your measurements ranged from +.05 to +.12, then your alignment would be off by +.085.

I assume you put your DTI so you were measuring the front (or the back) of the bar for the measurements when checking your Y axis alignment. Repeating the process with the DTI touching the side of the bar should give you the X axis alignment error.

I'm no expert, but that's what I did when I aligned my mill. Hope this helps.

Rudy

 

[Goldigger]

Hi Rudy, sorry for not replying sooner..
I shimmed the housing to align spindle to the column in the y axis, pretty much the same as yours..tightened everything up and checked..
0.01mm out so happy..
Aligning the spindle to the column in the x axis (left to right) took ages, but got it pretty much spot on.
After torqing the bolts up and checking, the spindle alignment to the column is 0.04mm out in the y axis.
Spindle to the column in the x axis (left to right) is still spot on..

Do you think the 0.04mm mis alignment is Acceptable?

I've modded my column so that I can adjust column nod with two bolts at the bottom of the column brace..but I believe that doesn't solve the problem, spindle to column needs to be adjusted in the way outlined in your thread first..

 

[rudydubya]

Hello Goldigger. Yes, your bolts at the bottom of the column brace should help with the alignment of the column with the table, but not the spindle with the column. As far as 0.04mm mis-alignment being acceptable, you'll have to decide if trying to reduce that 0.04mm is worth the time and effort needed to re-shim and re-align, based on your projected use of the mill and what you're going to accept for accuracy. One consideration in your decision might be the distance over which that 0.04mm was measured. If the distance over which you measured the error was, say, 8 inches, then that's only 0.005mm per inch (sorry to mix those mm and inches).

Personally, if I knew or suspected what might have caused my initial alignment to go awry, I'd try again, but I'm probably more obsessive than most... If you do decide to re-align, make sure your gibs are locked tight during your measurements and be aware that any paint or filler at the joint between the spindle housing and the carriage could get into the joint while the housing is being moved about and confound the shimming adjustments.

Hope this helps. Let us know what you decide and how you make out.

Regards,
Rudy

 

[Goldigger]

Hi Rudy,
I pulled the mill apart again today..
I atempted to align the spindle in the y axis (front to back)..tigened it all up and still out.
So i unbolted the spidle housing completely, and removed all paint from the mating surface..
Shimed and tightened it all up and 0.01mm out

So loosened it so i could align the left to right X axis alignment..
Same thing happened again when i tightened it all up..alignment in the Y axis is thrown out..0.04mm.

I've put the mill back together and tramed it..tramming the y axis was a bit of a fiddle, but just used the bolts on the column mod to pull the column back.

 

[smarston]

Could someone please check my math from the spreadsheet?
I don't want to show how I've arrived at the answers (just yet). I'd like for someone to come up with their own answers by whatever means they deem necessary and compare to mine.

Hopefully this will be of some use to us down the road.

View attachment Shim Calculator V3.xlsx

 

[SilverSanJuan]

I haven't had a chance to go through all the math yet, but I'm confused by some of your measurement definitions.
Specifically the "NEAR spindle" and "AWAY from spindle" measurements. What is the base of those measurements? Is it the bottom of the head? Your dimension lines seem to indicate that the measurement is taken from the top of the head. It's just confusing the way it is drawn.

I'm looking forward to testing it out though as I'm still trying to get my alignment trued up.

Todd