Once the set-up procedures and installation are complete, a piece part can be rolled. However, some set-ups such as part change or new set-ups may require some additional adjustments before a part can be rolled.
The headstock center (fig. 1). must be adjusted to achieve the proper length of spline. A line can be drawn on the piece part where the edge of the rack should roll. A six inch scale can then be held along the side of the rack and pushed up to the part that has been put between centers to check the position of the part. If the scale lines up with the line drawn on the part, the headstock center is set close enough to roll the first part. On most machines, clockwise rotation of the headstock adjusting screw moves the headstock center deeper into the machine. Counter-clockwise rotation moves the headstock towards the machine opening. Again, on most machines, one revolution of the headstock adjusting screw moves the headstock center approximately 0.100″.
The situation may arise where the vernier setting of the set-up needs to be checked once the racks are installed. Referring back to our set-up example No. 1, under set up procedures, we can determine that the gap between the racks at the starting end should be 1.853″ (total machine spring back value minus the blank diameter). At this point the racks can be advanced so that the first tooth of each rack are over each other at the machine center. With the machine turned off, an adjustable parallel, or similar checking devise can be used to check the gap between the racks. With the proper gap between the racks, a part can be rolled that will be close to size.
After the first part has been rolled, it can be checked by various different methods to determine proper size. One of the most popular, and in this writers opinion, the most accurate (for setting size on spline rollers) is the measurement over pins. Once the measurement over pins has been determined an adjustment of the machine may be required. The following is a brief outline on the size adjustment procedure:
1. Loosen the vertical set screws (fig. 2).
2. If the measurement over pins is 0.002″ too small, move both of the verniers 0.001″ to a smaller number. This move makes the opening between the racks 0.002″ larger. When making this type of size adjustment, it is a good practice to go past the number you want and then come back to it. This allows the backlash to be taken out of the adjusting screw, which keeps the racks more stable.
3. If the measurement over pins is 0.002″ too large, move both of the verniers 0.001″ to a larger number. This move makes the opening between the racks 0.002″ smaller. The backlash is already in the right direction so there is no need to move past the number you want and come back to it.
4. Tighten the vertical set screws.
In the outline above 0.002″ was used for the M.O.P. size change. This number could have been 0.004″, 0.007″, etc. Divide the size change needed by two and move each vernier accordingly. Depending on the hardness and pressure angle of the part, you may find that a slightly larger or smaller change is required on the verniers to roll the proper M.O.P.. Both the top and bottom verniers must read the same within 0.001″. Otherwise spacing error may develop (see “theory” section).