# Rotary table tail stock question...



## cathead (Dec 27, 2014)

I have a 12 inch rotary table that has a tail stock for  mounting shafts on centers. 
The tail stock is not a simple 60 degree center but the point is offset upward 
about 1/8 inch from the top of the tail stock shaft.  There must be a reason that
a simple cone center is not used.  I can see no advantage in this but would like
to know the answer as I am building a shorter version to mount shafts using my 
spin index.  What is the advantage in an offset center???ondering:


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## Wreck™Wreck (Dec 27, 2014)

Are you sure that it is offset? Some dead centers are notched to allow the tool to get closer to the center of the part on the tool side.
Also called a half center by some.


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## Reeltor (Dec 27, 2014)

I don't have a tail stock for my RT but I do have one that came with my dividing head.  The top of the center is machined flat for access like Wreck mentioned.  The tail stock is adjustable both in height and for angle.  You said that the point is offset upwards, is there a bolt that you can loosen and change that angle?

I'll see if I have a photo of my tail stock, and add it if I do.

Mike


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## Reeltor (Dec 27, 2014)

I found a photo of my van norman dividing head tail stock and a schematic for Brown and Sharp head and tail stock.  Now, let's see if I can upload them :thinking:
The upload appears to have worked, you can see the curve of the housing, loosen the large center nut and the rear nut to allow the center to pivot.  Loosen all three nuts to move the entire dead center up or down.  This center was so gummed up with old grease that I wouldn't have believed that there was any adjustment possible. Maybe yours is too.
The B & S drawing is a pdf for reference.
I hope this helps you out,

View attachment PAGE 7 brownsharpe-dividing-heads-types012.pdf


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## Wreck™Wreck (Dec 27, 2014)

Like this I imagine, adjusted in myriad ways.
http://www.millerstooling.com.au/cmsimages/Indexing Heads 05.jpg


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## cathead (Dec 27, 2014)

Wreck™Wreck said:


> Like this I imagine, adjusted in myriad ways.
> http://www.millerstooling.com.au/cmsimages/Indexing Heads 05.jpg



The millerstooling.com photo above shows a tail stock with a conventional 60 degree
dead center.  The VanNorman one that Reeltor posted has the offset center.  
I see no advantage in the offset center as either configuration provides equal
access to a machining tool.  

However, there must be a reason the VanNorman tail stock was made that way
offset from center.  

I'm not interested in making adjustments to the tail stock. I am only interested
in finding out what could possibly be the advantage to a non-concentrical center.   



Also for clarity, I am not refering to a half center, only to an off set center.


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## f350ca (Dec 27, 2014)

I believe they offset the centre for tool clearance. If you were say cutting a keyway it gives room to come in from the end without hitting the centre.

Greg


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## cathead (Dec 27, 2014)

f350ca said:


> I believe they offset the centre for tool clearance. If you were say cutting a keyway it gives room to come in from the end without hitting the centre.
> 
> Greg



OK, that makes sense.  I have been mulling this over all day unable to come up with
a reason.  Thanks for the input.:thumbzup3:


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## Reeltor (Dec 27, 2014)

f350ca said:


> I believe they offset the centre for tool clearance. If you were say cutting a keyway it gives room to come in from the end without hitting the centre.
> 
> Greg



100% agree, even more important to have clearance when using a horizontal wheel to cut the keyway.

Mike


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## Wreck™Wreck (Dec 27, 2014)

cathead said:


> Also for clarity, I am not refering to a half center, only to an off set center.



I posted the first picture that turned up on the web, what advantage would be gained with a center with an offset?
I am all ears.


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## 18w (Dec 27, 2014)

It allows you to machine a spline, slot or keyway in a tapered part.  When you tilt the dividing head it allows the center to be in alignment with the head so that the surface of the taper is then parallel to the table surface allowing a cut to be made parallel to the tapered surface. This is if I understand the offset description, ie. tilted uphill or downhill. I edited this to hopefully be a little easier to understand. I knew what I was trying to say, just didn't say it very well earlier.hew:
Darrell


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## Bill C. (Dec 27, 2014)

cathead said:


> I have a 12 inch rotary table that has a tail stock for  mounting shafts on centers.
> The tail stock is not a simple 60 degree center but the point is offset upward
> about 1/8 inch from the top of the tail stock shaft.  There must be a reason that
> a simple cone center is not used.  I can see no advantage in this but would like
> ...



I don't think I seen a center for a rotary table.  I have seen centering plugs for one.  But if you have a center with a flat it is for cutting to or near the center.  

If you have a Dividing Head try to turn the flat toward the cutter so the tool pressure pushes against the rest of the center.


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## 18w (Dec 27, 2014)

Bill C. said:


> I don't think I seen a center for a rotary table.  I have seen centering plugs for one.  But if you have a center with a flat it is for cutting to or near the center.
> 
> If you have a Dividing Head try to turn the flat toward the cutter so the tool pressure pushes against the rest of the center.



Bill, I have a horizontal/vertical rotary table that came with a tailstock. Good advice about alignment of the flat. I have read and reread the ops description and looked at google images. Hopefully he will weigh in here but I now believe the center is just offset above the centerline of the spindle and f350ca had the right answer to his question. Cutter clearance. My post was off on another tangent.:nuts: 

Darrell


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## cathead (Dec 28, 2014)

Thanks everyone!!  I get it!  

Now I think this way:  With it offset to the top and tipped up, one has WAY BETTER
access with a wheel type tool on the tail end.  I was guilty of non outside the box
thinking I guess, only thinking of an end mill.  

OK, I"m off to the shop to machine an offset shaft and finish up on the
tail stock project.  I will post a photo when it gets complete.  

What a great forum, you guys are tops!


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## cathead (Dec 28, 2014)

Here a photo of my home made spin index tail stock.


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