lathe dogs

this may be a pretty stupid question but for being totally inexperienced i thought i still would ask, i see pictures and videos of guys turning between centers and i was just wondering exactly what the purpose of the lathe dog was for, i seen some material in a chuck with the dog against the chuck teeth and i was just curious about this.thanks for any info

jlnak907 said:

this may be a pretty stupid question but for being totally inexperienced i thought i still would ask, i see pictures and videos of guys turning between centers and i was just wondering exactly what the purpose of the lathe dog was for, i seen some material in a chuck with the dog against the chuck teeth and i was just curious about this.thanks for any info

Click to expand...

Normally you don't use a lathe dog with a chuck. You use it with a faceplate. If you look at a faceplate, there are normally some elongated slots in the plate. You put a dead center in the headstock, mount the faceplate, find the appropriate dog that fits your barstock, and mount the dog to the barstock. Then the bent portion of the dog goes into one of the slots on the faceplate. You put a live center in the tailstock and this supports the other end of your barstock. The dog and the faceplate will drive your work. I don't think that too many people use faceplates and dogs today like they used to, unless you have a long piece and it will not go through the bore of the headstock.

I used to have to make camshafts for windshield wiper motors for aircraft when I first started out in the business. That was an experience. You either had to machine a flat area onto your barstock for reference or have it mounted somehow so you could drill each end with a centerdrill, off center. This throwed a wobble in the part when you started machining. And an interrupted cut can wreak some havoc on a cutter if not careful. Nowadays, they just get castings in so using faceplates and dogs are a thing of the past.

stupid question to newbee questions that were answered:

if you don't have a 4-chuck jaw and have a square piece to turn (or an octagonal piece), couldn't you just use a square bracket lathe dog to turn it?

The shape of the hole in the dog doesn't matter, beyond obtaining proper grip on the workpiece with the locking screw. Some dogs have a vee section that keeps round stock centered on the screw, but as long as you have 3 contact points, you can turn it. The screw is 1, and the flanks of the other side of the dog are the other 2.

It's not that critical, as you are controlling the axis with a center in the spindle, not the dog.

jlnak907 said:

this may be a pretty stupid question but for being totally inexperienced i thought i still would ask, i see pictures and videos of guys turning between centers and i was just wondering exactly what the purpose of the lathe dog was for, i seen some material in a chuck with the dog against the chuck teeth and i was just curious about this.thanks for any info

Click to expand...

A lathe dog is used to drive the part to be turned between centres. Since it is not clamped in a chuck or collet, etc, and is only supported between the two centre points, there needs to be a positive contact to provide the driving force to the workpiece otherwise the workpiece would just spin on the centres when the tool bit was fed into the work.

Usually in this case, where there is a chuck mounted to the lathe spindle, they have taken a piece of stock, mounted it in the chuck and turned a 60 deg point on it. this is often easier than removing the chuck, installing a centre and Dog Plate and by doing this, the centre is guaranteed to be "on centre" as it is turned in-situ. The part to be turned is then mounted between centres, with a ball bearing centre or a dead centre in the tailstock. The Lathe Dog is clamped to the headstock end of the part and the tail is rested against one of the chuck jaws as a driver. A rubber band can be used to keep the tail from bouncing around on interupted cuts.

Walter

I turned a piece of 1.75" dia that was too big for my one little lathe dog (you can buy bigger dogs but I just haven't), so I made one out of copper

http://www.youtube.com/watch?v=mCZ6G96h2Ok

It's really a lathe clamp.

I have a lathe plate but at the time of this video (about 3 weeks ago), I didn't have a taper adapter for the chuck (to reduce MT3 to MT2), as an MT3 sticks out too far to be of much use as it sets the dog tail too far away from the dog plate. I've since purchased an adapter sleeve for my South Bend 9A from Tools For Cheap for $15 and now exclusively use the dog plate when turning between centers

You obviously don't want to get to close to a big dog as he's apt to take a bite out of your hand

DaveV

Turning with lathe dogs between centers is the best way to ensure concentricity with the center holes in the ends of the work. Mandrels for holding work with holes(like gears) are held this way for grinding true during their manufacture.

A very old process,but still a very viable method of obtaining great accuracy. Commonly used by watch makers.

this give ya any ideas ? i figure whatever works.. . .