# Rotary Table Alignment



## Jmccrack (Aug 20, 2019)

Hey guys. All the conventional wisdom says to align a rotary table you put a dial or a coaxial indicator or a rod in the spinal and swept the center hole of the rotary table. Than rotate the spindle and 0,0 your table. OK..........After you do that put the dial on the rotary table top and sweep the spindle preferably the inside of the spindle. I would be interested in what you get. I have an 8” Taiwanese Vertex table. When I do what I suggested above i am .003” out. I suggest the best way to align a rotary table is to put the indicator on the table and sweep the spindle. Thoughts??


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## rlo1 (Aug 20, 2019)

I always thought that if you center the rotary table with with a center finder to the mill spindle you are good.


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## Jmccrack (Aug 20, 2019)

So did I and maybe some of the more expensive ones are. But just for giggles put a magnetic dial on the Rotary table and run the indicator around your spindle or better yet inside your spindle,you might be surprised


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## BaronJ (Aug 21, 2019)

If you centre your RT properly, why should I be surprised by dial indicator readings taken against the spindle bore !


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## Jmccrack (Aug 21, 2019)

On some or a lot of tables you will find the center of the RT centered off the spindle will be different than if you center the RT off the table. Check it out


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## BaronJ (Aug 21, 2019)

If the mill head is out of tram I can understand that there may be a difference.


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## Jmccrack (Aug 21, 2019)

Hey guys check out this video from Joe Pi. I think most of us know him from his you tube videos Go to minute 12 and watch from there.


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## BaronJ (Aug 22, 2019)

Whilst I agree that he shows in the video that there is a slight difference, he doesn't make any mention of why.  There are two points that will cause a difference, the tram of the mill and the parallelism of the table surface to the bed.


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## clockworkcheval (Aug 22, 2019)

A couple of years ago I purchased a Vertex HV-6 150 mm diameter Rotary Table. After some adverse results I checked the whole thing out. I found that the MT2 bore diameter at the top of the rotary table was concentric within 0,02 mm with the outer diameter of the rotary table - what is good enough for me. But the other end of the bore was 0,4 mm out if center, what is definitely not good enough for me. So the whole bore sits slanted in the RT. Mounting an ER25 collet arbor in the MT2 bore only increases the eccentricity, making the whole RT worthless as a carrier for cutting horological gears. The RT is now slumbering in a corner of my workshop waiting for me to muster the courage to fully rework the bore. I think I must do a straight re-bore and insert a push-fit cilinder with a nice concentric MT bore.
I also found a typo in one of the Dividing Mechanism tables. To divide the circle into 13 equal parts with Plate C on row 39  the handle should be turned 6 36/39. In 36 is a typo, which took care of another gear. I now always calculate the number of handle turns by hand.


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## BaronJ (Aug 22, 2019)

Hi clockworkcheval



clockworkcheval said:


> A couple of years ago I purchased a Vertex HV-6 150 mm diameter Rotary Table. After some adverse results I checked the whole thing out. I found that the MT2 bore diameter at the top of the rotary table was concentric within 0,02 mm with the outer diameter of the rotary table - what is good enough for me. But the other end of the bore was 0,4 mm out if center, what is definitely not good enough for me. So the whole bore sits slanted in the RT. Mounting an ER25 collet arbor in the MT2 bore only increases the eccentricity, making the whole RT worthless as a carrier for cutting horological gears. The RT is now slumbering in a corner of my workshop waiting for me to muster the courage to fully rework the bore. I think I must do a straight re-bore and insert a push-fit cilinder with a nice concentric MT bore.
> I also found a typo in one of the Dividing Mechanism tables. To divide the circle into 13 equal parts with Plate C on row 39  the handle should be turned 6 36/39. In 36 is a typo, which took care of another gear. I now always calculate the number of handle turns by hand.



I also own a Vertex HV6-6 RT.  I've not found a problem with mine, however I've not yet used the dividing plates, so I've not come across any errors in the dividing tables.  This is actually the second one I've had, the first one came with a bent shaft and was replaced by the supplier.

I completely stripped mine down and cleaned it checking concentricity of the base and table as I went.  I didn't find anything that worried me other than the taper in the centre was not deep enough to allow the Myford chuck arbour to seat properly.

A few turns with a MT2 reamer sorted that one quite easily.  If your taper in the bore is out then machine reaming it using the mill should correct it, though you will have to take great care that you don't over do it and don’t make the taper too deep.


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## fcheslop (Aug 22, 2019)

I had the same problem as clockworkcheval on the 4inch version and it cleaned up easily using a taper reamer
The dividing paper work also has the same error so always do the maths first just to check .It saves getting those gears with the half tooth not always guaranteed though
The paper work with the table is probably the same as the 6inch
For the money and the amount of use my little one has had its been well worth it. Iv cut around 30 gears  using it and more than one duffer. I find the 4inch version easier to get onto the machine and set up than a 6inch I used to have 
cheers


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## Jmccrack (Aug 22, 2019)

Have you fellas dialed in both ways? From the spindle to the bore then from the table to the spindle? On the subject of dividing plates I never use mine anymore. I put together the Rotary Controller from “World of Ward” and have not looked back. Check out his web site. The unit is a snap to build and costs very little. I cut gears and splines and have never been stumped.


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## petertha (Aug 22, 2019)

BaronJ said:


> There are two points that will cause a difference, the tram of the mill and the parallelism of the table surface to the bed.



I agree. The spindle axis first has to be perpendicular to the RT axis before one can commence the RT test, meaning the mill head must first be trammed . If the spindle is pointed L/R or In/Out (or worse yet some amount of both) you will get different DTI readings purely from that discrepancy alone because the ball would be traversing around a 3D path on a cylinder. If the spindle is perpendicular but the centers are non-coincident (ie. displaced) then the DTI is now only traversing in a 2D plane. The DTI should pick this up & alignment achieved. Crude sketches hopefully illustrate.

Now where it gets interesting is if the DTI ball is traversing an inside taper. For example if the DTI is mounted to an arbor in the RT & table rotated & the DTI ball is traversing inside the tapered seat of the spindle, which is normally what we do. Again,  assuming the spindle is trammed, I think you can still zero the axis together but the DTI deflection amount cannot be relied on because its being exaggerated by the taper. But you should be able to move the RT until the DTI settles to some stationary value indicating the axis are co-linear. We dont care about how many thou on either side, just that the needle isnt moving. Sorry harder to draw this scenario without getting out the CAD tools but hopefully it makes sense.  

Now if you flipped the DTI test around so it was attached to arbor in the spindle & measuring the inside taper of RT, maybe the only difference between DTI-up and DTI-down tests is you are just picking up the relative angle of say an MT3 taper in the RT vs the R8 taper of the spindle? (which is meaningless). Otherwise I cant see that either test would make a difference if aligned.


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## Cogsy (Aug 23, 2019)

BaronJ said:


> There are two points that will cause a difference, the tram of the mill and the parallelism of the table surface to the bed.


 I think there's a third (which I also think is what Joe was suggesting when he mentioned the RT bearings), the centre hole of the RT may not be 100% central to the axis of rotation. This should be fairly east to check, just by setting up an indicator in a fixed position to indicate the centre hole and rotating the RT through 1 revolution.


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## tornitore45 (Aug 23, 2019)

Is a matter of geometry.  With the indicator in the spindle you find the center of the RT hole. The indicator placed on the RT revolves around the RT center of revolution which depends from the bearing concentricity and  may or may not coincide with the hole center.


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## BaronJ (Aug 24, 2019)

Hi Guys,

Petertha,  Your post describes exactly my view.  Thanks for the drawings, well illustrated. 

Cogsy,     You have picked up on the one thing I didn't mention !  Simply because if the table is turned and the bearing spindle is co-axial with the edge they should be in line.  It didn't initially occur to me that a bit of swarf under the surface of the plate when turned would cause bearing misalignment.

Tornitore45, Agreed.

Thanks for all the comments.


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## Richard Carlstedt (Sep 19, 2019)

First, The Table OD and ID must run true. 3 of my tables run true ( 2 -8" and a 12" ) However, the 6" unit was off, so I chucked it up (table only ! ) in the lathe with a DTI indicating the WAY surface, then I re-bored the center hole concentric with the ways.  You could also bore the hole in the mill by rotating the table with a small cutter ( Boring head could make error).
Once you have a good center-bore , whether straight or taper (ie M.T.) , then just chuck a piece of stock in your collet and bring it down into the center-bore  AND then fasten the RT to your mill table - Done !
No DTI needed and it is super fast.  In other words, let your spindle C/L locate the RT C/L 
Rich


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## Bruce R. (Jan 21, 2020)

I never indicate my rotary table,  I made a stepped steel dowel, one end fits tightly into the hole in the center of my rotary table and the other end fits the half inch collet in my mill. I mount the table loosely with the dowel in the collet, then bring the quill down and fudge the table around until the dowel seats in the center hole, then I tighten the table bolts. Once the bolts are tight, I’ll run the quill up and down to make sure nothing moved.  I’ve been using this procedure for the past 30 years and never had any problems with turning out good parts.


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## BaronJ (Jan 22, 2020)

Hi Bruce, Guys,

One of the things that I discovered was that with my mill (BF20L) it is very difficult to get an accurate tram of the head.  I actually set the table up on the lathe faceplate and very lightly reamed the bore to square it up.  The bearing and bearing surface have obviously been machined at one setting and are dead square to each other.  Once the RT is on the mill its no problem to use the bore to set the table in line under the quill.









This is the device I use.  It allows for a slight misalignment in tram.


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## Bruce R. (Feb 2, 2020)

I don’t know what you mean by “tram”. But I’m gonna go ahead and assume that you mean the vertical axis of the head of your mill is off.  Mine is adjustable in 2 directions and I use a 12” parallel and  a holder for my indicator that is bent on 90 degrees in my spindle. I adjust the indicator on the holder so that it swings in a roughly 10” circle, with the parallel on the mill table at 12 o’clock and 6 o’clock I bring the indicator into contact with one end of the parallel, get a reading, and twist the spindle by hand to swing the indicator to the other end of the parallel. Adjust the mill head until you get the same reading on both ends of the parallel. Then turn your parallel to 9 o’clock and 3 o’clock and repeat the process. Sometimes you have to go back and forth between the 2 directions until it’s perfectly vertical, you also need to watch when you tighten the mill head fasteners as it could move and throw the reading off.  An easy way to tell if the head is off is to use a flycutter, it should cut all the way around in a circle, if it only hits at one spot then the head is off kilter.


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## RM-MN (Feb 2, 2020)

You just described tramming the head of the mill perfectly.  Now you know what tram is and that your mill is in tram.


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## Wallen (Feb 2, 2020)

This may not effect this problem, but I have came across a bent shaft of the pinion gear and it was giving me a problem with accurately indexing with the rotary table, because of being put away without being careful not to bang the handwheel, they should be resting on a board to where the hand wheel is not touching anything.


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## Richard Carlstedt (Feb 2, 2020)

Bruce, You got it !
If I may ,I think I can speed up your process (60 years in a shop) 
Always do the X axis first ( L & R) ( 9 and 3 O'Clock) ( We called it Twist or Rotate)
Then do Front to Back (called Nod or Tilt) .....but know this 
Many guys try to do it at 6 and 12  O'Clock,,,..don't !
Too easy to get confused ( Had many Journeymen even get lost) 
Use your Dial indicator at 12 and 3  O'Clock  only while adjusting the Nod.
You Nod the headstock to get the two readings the same - discard what you had when doing X axis readings as it means nothing , you want 3 and 12 the same - and when  they are the same, then go to 6 and 12 to tweek 

Rich


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## awake (Feb 3, 2020)

Rich, this is interesting - I'll give it a try next time. Up to now I have found it best to set the nod first, then do the rotate. Just have to remember that the nod motion is out on a cantilever, and take that into account ...


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## SpringHollow (Feb 6, 2020)

I do X first (9 and 3) but when doing the Nod, I do 6 and 12 and never have had a problem.  Why would you want to do 3 and 12?  Are you worried that they will get confused by the direction of the indicator and turn the wrong way?  These days, i use the dual indicator setups which is easy and fast.

Joe Pi's YouTube videos using a rotary table are quite good


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## Richard Carlstedt (Feb 6, 2020)

_Why would you want to do 3 and 12?_
Speed , is the essence of working on setups.
Setups do not pay bills, so in most all machine shops , it's  the tricks of the trade that can make a job profitable or not. Fixing Nod is a pain in the butt for most machinists, as evidenced by your purchase of a duel indicator tool ( no offense meant, just most shops do not have them )
With 12 & 3 , no "zeroing" of a indicator is needed- just balance the reading
No Worry about what the reading should be, just the same.
No changing of the machinists position is needed to read the dial as it's easy to view a indicator in a 90 degree arc . (ie, lean over the table on the right side) 
Faster as a 90 degree move takes less time than a 180 degree turn .

Many of the Youtube Video's that folks watch show these tricks of the trade.
They are huge time savers. In the Old days, shops did things that are unknown today. Things like .....never use a center drill to start a hole (Lathe) and have a more accurate center for the drill... or never use a height gauge or the dead center for setting tools in a lathe, but use your pocket scale.. .making your 3 jaw more accurate .....and on and on. 
Rich


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## awake (Feb 6, 2020)

Rich, what is the issue on using a center drill to start a hole in the lathe?


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## Richard Carlstedt (Feb 6, 2020)

You do not need a centerdrill.
Centerdrills are for making centers in a shaft in order to use a live or dead center, but it's "convenient"  for some to use for drilling, but sometimes even centerdrills are off . Also they are 60 degrees and not 118 like a drill.
Do what machinists have done for 100 years, before they had easily obtained centerdrills.
*Process*
When ever you want to drill in the lathe,  _always  _place the bit in the chuck with the cutting lips/edge of the drill in a horizontal position. Bring it up to the work face ...then using your tool bit and cross-slide ,( raise the tool bit up about 1/8 ")  and then move it in maybe 1/4" to 1/2 " behind the cutting flutes and push the drill off center about .010"  ( the above depends on the size of the drill-) . Now this is a two hand operation advance the drill so the divot in the work piece is about 1/2 the drill size and when that point is reached -keep feeding the drill in  and at the same moment retract the crossfeed !
Now you have a perfect centered hole start !
*Technical Data explanation*
So here is what is happening . Pushing the drill away from you makes it cut only on the far side cutting lip( it becomes like a boring bar in miniature)  The result is a conical shaped hole with a tit in the middle and is a true centered machined surface ( like a boring tool).  Now what you want is a cone length longer than the tit length - when this is reached ( 50 % to 90 % diameter) and the drill forced in (without side cross-feed pressure !) the hole forces the drill lip inward as the force needed to cut the tit is less than allowing the drill lip to cut the cone .
*A few notes*
Doing the above saves setup time . The machinist immediately goes to his drill , no swapping chucks or using the Jacobs key.
With Aloris Tool Posts , it easy to raise the tool bit and then drop it back into place as I suggested here, but when the old guys used Lantern Posts, they just made sure the tool bit's cutting edge did not touch the cutting flute of the drill bit and used the "Heel" of the toolbit when touching the drill bit.
In fact, the old guys did not even "face the end" of the work before drilling, and used the above method to "mini-face" the saw cut stock with the drill a small amount before proceeding  as noted.
All the above is for those who wish to expand their skills .
It also adds to satisfaction at using your skills in new ( or old ! ) ways

Rich


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## SpringHollow (Feb 6, 2020)

The double indicator method is so fast - no changing positions, etc - that I am surprised shops do not use it more.   But I do realize it is another piece of "kit" that you have to have hanging around.  In my opinion, the Starrett/SPI style of spindle square is the best because calibrating it is so easy - just rest on a surface plate and set dials to zero  One really nice seldom mentioned feature is that the same spindle square can be used with a sine bar to set an accurate tilt to the head if needed.  Practical Machinist just published a brief article on tramming. In the linked video, he is using the double style that I do not like as much because of how it has to be calibrated - takes longer.  
https://www.practicalmachinist.com/...edium=email&utm_campaign=2020Chatter_February

Rich, I really like the description for drilling that you gave -I will have to try that.  Thank you for taking the time to explain it so well.  For the same reasons, I like Joe Pi's videos - just like you, he takes the time to not only tell you what to do but why.  That added knowledge makes me much better at machining and adapting techniques to new situations.  How he used spacer blocks on a recent video where he was using a rotary table to make some parts for the cannon is a good example.  It was not something that would have occurred to me but now I can add it to my repertoire.  Unfortunately, lots of the cumulative machining knowledge gathered over the years is going to be lost, I am afraid.  So I appreciate whenever I see someone passing it on to others.  I just purchased Tom Lipton's Metalworking, Sink or Swim where it looks like he has tried to document some of that knowledge.

I have asked this question on another forum and never got an answer:  Why do people always tram their table and then mount a vise and assume the tram to the vise is good?  Shouldn't you always tram your work holding device, the table if clamping to the table and the vise if using the vise to hold the material?  It seems like tramming just to the table potentially adds error when using the vise.

Ken


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## awake (Feb 6, 2020)

Rich, thanks for the explanation. That's a technique I've not encountered before!

Ken, here's my thinking about the vise: the key issue is that the movement of the work piece past the tool in the spindle is going to be controlled by the table, not by the vise. Thus, if one trammed to the vise and not to the table, one will wind up with results other than what are expected.

The answer, of course, is to square the vise to the table - typically along the X axis (though could be along the Y) unless one needs to cut at an angle, but equally important is that the bottom of the vise clamping area *must* be parallel to the bed - if it is not, no amount of tramming will correct the problem; the vise must be replaced or repaired.


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## SpringHollow (Feb 6, 2020)

Thanks.  I was not referring to indicating the vise to the table travel but making sure it was perpendicular to the spindle in the x-y plane (parallel to the bed as you mentioned).

I think I understand what you are saying, it is the "cosine" problem.  If the vise is not parallel to the table, the dimension of travel on the dial/screw will be different than the amount of travel of the cutter on the surface of the part as well as the depth of cut varying. Tramming to the vise will give you perpendicular sides but inaccurate dimensions.  Tramming to the table will give you known travel distances but your sides will not be perpendicular if the vise is off relative to the table.  I will indicate the height of the vise holding area after tramming to the table and see if there are any differences across the vise.  I have always trammed the table until the last couple of times.  The projects I have done since are not ones where I could see the error if I created one.  If the vise is good, there would be no difference.  Worth checking because if the vise is parallel to the bed, then tram can be checked without removing the vise.  Saddle wear on a heavily used mill could add error if tramming to the side of where your vise is located.  I would surprised if most vises are off significantly enough to notice.

Or I still have it wrong 

Ken


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## Richard Carlstedt (Feb 6, 2020)

Discussing vises is a good way to start arguments
I have had a 5 inch Kurt in my shop for 43 years and it is as close to perfect as they come. I was given a 4 inch Kurt imitation made in India and it was a piece of garbage. Took about 30 hours of rework to get it square and flat. I would say 60 % of my work is done without a vise , so I do not worry about vise tramming as I use the table  and clamps. When you talk about Vice tramming , I assume you mean tramming the top of the vise  where it is flat  ?
A quality Vise like a Kurt is very flat  and is only required to be checked once .

Should have mentioned this earlier
Always tram with the quill fully extended and clamped ( Most accurate tramming ) and then fully retracted and recheck to determine if quill wear has affected the tram 
Rich


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## SpringHollow (Feb 6, 2020)

Fortunately, I have a Kurt. I trammed the bottom where one's parallels would sit.  My spindle square just fits inside the fully open vise.

Excellent idea to compare extended vs retracted.  I try to keep the quill retracted for stiffness and have always trammed that way because that is how I use it but I can see where tramming extended would make any "errors" more noticeable.

Ken


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## chrsbrbnk (Mar 7, 2020)

we always center drilled a spotting drill nicer but kinda rare  the most accurate cdrill technique was to just barely start the tip the stub tip  is the right angle    don't go deeper than the tips of the first set of flutes the idea is to have the drill engage on the cone shaped hole, not a sharp hole edge. the work surface  was as smooth as possible surface ground often    even surface lay direction made a difference , the idea was to load each flute evenly right from the start and not get anything that would deflect the drill tip like a groove or ridge      drilled  hole locations were on the order of  +-.001 if they were in a hurry and +-.0002  as measured on the CMM  if looking for accur.


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