Square centres

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Tozguy

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When turning between centres, apparently a square centre can be used to drive the work instead of using a dog. The idea makes sense although it is easy to imagine how this approach is limited in the torque it can provide. So my question is put to those who have hands on experience with using 'square centres', could you provide me with a few pointers for starters? It would be much appreciated.
 
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Could you post or point to a pic of one? What comes to mind is the tool used for finding center for something round but those are called center squares. I tried searching for square center & square centre but couldn't find anything.

I probably haven't seen one as I have only used conventional drive dogs for turning between centers. But I'm curious & can't sleep. :)
 
Hi Will,
I have read about square centres in old books on turning but they don't get much attention these days it seems. Sorry I do not have any pictures for you.
They are basically a centre that goes into the headstock on a lathe but that has some 'bite' in the centre divot on the work. More common for turning wood but not so much for turning steel. I am off to brew a second cup of coffee then will try to find poop on the subject for you.
You are right they are not to be confused with centre squares.
 
Are you referring to " cup centers " ? I have cup centers in 1mt along with some that have 4 drive tangs . I believed these were made for wood only .
 
Tubal Cain's book 'Workholding in the lathe' on page 13 shows a picture of a square centre that is a regular 60 deg. centre but with four flats cut in the cone. The flats meet to create four sharp corners somewhat like the point of a nail. After reading the paragraph again it appears that this was used as a crude cutter after the centre was located and punched on the work. If all it was used for was to deepen the punched divot then it is obvious that centre drills have superceded such a crude cutter.
I am probably wrong in thinking that it is intended to provide enough bite to drive the work between centres. Yes my thinking is influenced by wood turning. However it would seem to be an unreliable way to drive steel work. Anyway there is no point in pursuing this approach considering the other options available.
 
They came up here in a discussion about putting work between centers without losing all of that workpiece space to a lathe dog. The idea is that the center drives the workpiece, but you're limited to very light cuts. Making one shouldn't be too bad - take a center, put it in a collet block, grind the four lats using an angle guide.
I searched a bit but couldn't find the thread.
 
I might end up trying something just for the fun of it. If a 60 deg divot is cut very deep so that the edge is rather large in diameter then use a 3 or 6 flute 82 deg countersink as a centre. The countersink should get some bite into the edge of the divot in the work because of the difference in angles.
 
Winging it here... I suppose a different kind of dog might be used to turn the work using a radially mounted but axially oriented hole or two in the end of the shaft, using pins to drive the work without defacing the OD of the shaft. There would be an axial hole or two in the work. A 60 degree center would also be used as part of the tool to center the work, small diameter and used as shallow as appropriate. The tool would have to be shop made, but with mild steel it would be easy to machine, and there would be no slippage of the center of the work. THe pins could be standard hardened dowel pins. If the drive end of the shaft is big enough in diameter so the pins have some leverage, it would probably work just fine. The tool would not be difficult to make.
 
I like the countersink idea. Gonna take a look through the large cheap set of carbide router bits I've got, there might be something in there as well.
 
ThinWoodsman said:
I like the countersink idea. Gonna take a look through the large cheap set of carbide router bits I've got, there might be something in there as well.
Click to expand...
Using a drill bit on a mill with a centered rotary table would be my first idea. To make it even better, drill the hole(s) a little undersize and then ream them for a nice and snug pin to hole fit.
 
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