Lathe Dog and Turning between the centers:
Turning between the centers is the most accurate and repeatable method of turning on the lathe. If accurate work needed and the operation may not be completed without removing or repositioning the part for whatever reason, turning between the centers is the way to go. A round stock or generally the work, since it may be an irregular shape other than round, is center drilled at both ends. In some cases the work piece it may have more than one center, a crankshaft for example.
The chuck is removed and we set a drive plate in place and a dead center at the spindle. We will need a dead center or a live center on the tailstock to hold our work piece in place also. If a dead center is being used must be lubricated often since it stays stationary as our work piece rotates.
So now that we have center drill our work piece and we have set the centers on the spindles we will need a lathe dog to transmit the rotary motion to the work piece. Two types of lathe dogs are available on the market, the one with the straight leg and the other with the bent leg. So for that reason there are two types of drive plates. The one with the drive pin that used with the straight leg dog and the second one with a slot machined into that fits the bent leg dog. The bent leg type is considered safer as there are fewer protruding parts to cause accidents.
As an alternative to the drive plate we can use any type of chuck. A round stock may be used and be turned at a 60 degree taper as a dead center with a bent leg dog driven by the jaws of the chuck. The disadvantage of this method is that we need to true up the taper each time that we remove it and reposition it to the chuck. At the other hand, we don’t need a drive plate or to remove the chuck.
Turning between the centers notes
A very important note, turning between the centers it may be a dangerous operation. It’s obvious that the work piece is not clamped securely and the only thing that holds it in place is the pressure from the center of the tail stock. For that reason avoid turning big pieces or taking heavy cuts. Another factor that must be taken into account is that heat building on to the work piece as the work progresses. The work piece will expand from the heat a little bit, so check the tension often and readjust the center of the tailstock.
We spoke earlier for accurate work between the centers but we need to clear out that accuracy, in that case as any other case of lathe operations, it mostly depends on the good condition of our machine and the proper setup. The lathe must be properly leveled and the tailstock must be aligned perpendicular to the spindle.
Lathe Dog Project
I decided to make mine lathe dog, because I could not find one that fit to my needs in the market. The project is simple and I used the milling attachment since I don’t have a milling machine yet. The idea and the design are actually stolen from the Rudy’s Kouhoupt video “Advanced Aspects of Machine Lathe Operation”.
click on picture for slide show