Lathe Dogs

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Hukshawn

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you know, ive never understood the purpose of a lathe dog and turning between centers. why not just put it in the chucks? if youre worried about chuck damage, youre still putting a set screw from the dog and risking damage from that...
in my mind, i cannot think of a single reason to use a dog. (im sure this is very ignorant of me... i await the onslaught, but im being honest!)
 
Turning between centers is the most accurate method for maintaining concentricity. The lathe dog provides the "crank" to turn the work. It clamps to the work and the dog leg engages a slot in the face plate.
 
Turning between centers allows you to take the arbor and work off the lathe to measure or do other work to the job, and then return it to exactly the same position it was in previously. The center also locates the work precisely, and lets it line up with the tail stock without any bending from chuck clamping pressure. A chuck can be used in the same way, by turning an accurate 60 degree center on a piece of stock chucked in the jaws. As long as the center is not disturbed it will remain perfectly centered on the spindle, and the work can be removed and replaced into the centers as needed without loss of accuracy. The dog must continue to be driven by the same driving feature if you are doing threading or other indexed work. Less work is done today between centers than earlier, but it is the correct way to do many jobs that are now being done incorrectly.
 
Turning between centers also allows the workpiece to be removed for inspection or secondary operations and reinstalled in the lathe without loss of concentricity.

Edit: sorry Bob, yours came in while I was typing.
 
#3 Turning between centers also permits turning a taper by offsetting the tailstock.
 
A little old fashioned research(reading comes to mind) like Machinery Handbook, will supply the reasons for lathe dogs.


Hukshawn said:
you know, ive never understood the purpose of a lathe dog and turning between centers. why not just put it in the chucks? if youre worried about chuck damage, youre still putting a set screw from the dog and risking damage from that...
in my mind, i cannot think of a single reason to use a dog. (im sure this is very ignorant of me... i await the onslaught, but im being honest!)
Click to expand...
 
If it's an odd shape, or you can't grab the center in your chuck, but you can put something like a live center into it to hold it on center, and then use the dog to put power to the object.
 
Ah, I understand. thanks for the explanation, guys.
I have a bunch of dogs and a plate that doesn't fit my lathe (came with an old lathe I bought) never really took the time to figure them out.
 
No need for a drive plate either, just use a chuck jaw to drive it. For Some weird turning I've
even used muffler clamps for dogs. Then if you ever get involved with multiple start threading
you will become friends real fast with this method which is fast and requires no math. What I
mean by that is, there are times when a part has to be removed and brought to the job site to
be altered some and will always be returned exactly the same when removed, instead of dialing
in a 4 jaw and a 3 jaw is totally out of the picture at least for me.. sam
 
If you don't have a centre for the spindle you can turn a 60 degree point on a bit of steel held in the 3 jaw and simply re cut it each time you use it, which meens you can get drive off the chuck jaws and will give good concentricity since you have re cut it each use.

Stuart
 
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