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Dividing head tailstock question

Peter.

Titanium
Joined
Mar 28, 2007
Location
England UK
I bought this tailstock to use with a plain dividing head. Commonly they are used on universal dividing heads, this one is typical of the type seen being sold with some universals.

DH tailstock 1.jpg

DH tailstock 2.jpg

Anyway, As you can see in the pics it pivots on the front bolt and the rear bolt works in a slot to allow a certain amount of nod up/down. I am just wondering - what is the usefulness of this feature? This is a 5" centre height tailstock but if you nod it up or down not only does it alter the centre height but the centre height also varies as you advance the quill on the handwheel. You might say that it would be useful when using a universal which is also nodded but then if you nod the DH down you'll need to nod the tailstock up and then the points will be even further apart in height difference. Okay, so you might say that one or the other would need to be packed up on parallels but then the packing height would always be different for different length parts and the tailstock does not have a lot of travel. Seems awful fiddly and the tailstocks with two slots seem to make more sense as you can set both height and angle on those.

Can someone please explain the useage of this feature? Obviously, it matters not for my use since it's being paired with a plain DH so I'll set it level and leave it there but I still would like to know.
 
Well if that's how it is, then that's how it is. I find it difficult to believe that is all there is to it though since someone made a beautiful job of designing and assembling theis part when it's usefulness would have been vastly increased by making both holes slotted.

Who knows?
 
Please excuse the foolish question, but have you verified that the front bolt goes through a circular hole in both parts of the tailstock? Dismantle it and remove the inner part from the outer. There is a small chance the inner part is slotted and maybe it is just gummed up through lack of use.

If it is not slotted, making it so might be a way to convert it to the more standard mode of operation.

The rear slot looks quite wide so it might accommodate enough fore and aft movement.
 
Well if that's how it is, then that's how it is. I find it difficult to believe that is all there is to it though since someone made a beautiful job of designing and assembling theis part when it's usefulness would have been vastly increased by making both holes slotted.

Who knows?
Well some manufacturers did ...
 

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Please excuse the foolish question, but have you verified that the front bolt goes through a circular hole in both parts of the tailstock? Dismantle it and remove the inner part from the outer. There is a small chance the inner part is slotted and maybe it is just gummed up through lack of use.

If it is not slotted, making it so might be a way to convert it to the more standard mode of operation.

The rear slot looks quite wide so it might accommodate enough fore and aft movement.
Yes, already verified. It was all gummed up when I got it so it's been stripped, cleaned and lubed.
 
If you think that's hard to understand, I have a lathe tailstock that allows for adjustment along the lathe axis, same direction as the ram's motion. It even has a nice index mark so you can return it to the "right" position. I tried to move it cross ways as you would for turning a taper, but no go. It just moves along the axis. And it's a South Bend, not some import.
 
Those type of footstocks where used a lot on horizontal mills. It was not at all uncommon to need to cut flutes in parts where a taper was needed. You can't tilt the horizontal arbor or the table.

But if say you were cutting a tapered reamer, and these machines where used to make the blanks before finish grinding, you would need to match the angle of the dividing head.

Remember almost all old high quality dividing heads could have the angle altered. You need a footstock that can match that angle for longer work that needs support.
 
Those type of footstocks where used a lot on horizontal mills. It was not at all uncommon to need to cut flutes in parts where a taper was needed. You can't tilt the horizontal arbor or the table.

But if say you were cutting a tapered reamer, and these machines where used to make the blanks before finish grinding, you would need to match the angle of the dividing head.

Remember almost all old high quality dividing heads could have the angle altered. You need a footstock that can match that angle for longer work that needs support.

I get that, but if you tilt the universal dividing head down, and the footstock up to match, then you will have to raise the dividing head the exact correct amount according to the between-centres length of the part or your taper angle is going to be wrong.
It seems like the kind of thing that someone would attempt if there were absolutely no other choice.
 
Took a quick look in the Treatise on Milling and Milling Machines and found this example. Not sure if there are more the book is 900 pages long. Doesn't seem like it would be used very much anymore like this but I guess there were times it was the standard procedure. Probably more reasons for that tilt, all footstocks seem to have it. I am sure these days it is just done on a CNC.
 

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Took a quick look in the Treatise on Milling and Milling Machines and found this example. Not sure if there are more the book is 900 pages long. Doesn't seem like it would be used very much anymore like this but I guess there were times it was the standard procedure. Probably more reasons for that tilt, all footstocks seem to have it. I am sure these days it is just done on a CNC.
Ok so that makes more sense, a slight nod function with a height-adjustable centre point. I guess that the quill on mine could be swapped out for a more posh height-adjustable one if they offered it as an alternative.

Thanks for posting the pages.
 
For parts held at small angles from the horizontal, whether in a dividing head chuck or between two centers, the angle of the tailstock center doesn't matter much. The critical thing is the height of the center, which is what is adjustable.
 
For parts held at small angles from the horizontal, whether in a dividing head chuck or between two centers, the angle of the tailstock center doesn't matter much.

Would it be correct to say that a bell centre drill should be used in those cases?
 
Not sure that it really much matters.
Turning a piece between centers in a lathe, with the tailstock offset to yield a taper, can be a problem as the center in the tail end of the workpiece revolves on the tailstock dead center and wears as the turning progresses. In this case, though, you are using the dividing head not to rotate the part but to index it so that it may be cut by a milling cutter. You'll get no wear on either the center hole or the center itself.
 








 
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