Quick and Easy Thread Rolling Setup
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May 6th, 2008- RSVP Tooling, Inc. announces quick and easy setup on their axial thread rolling system with the use of a setup plug. Some customers, who have a sample part to produce, make the mistake of trying to tighten the head down onto that in order to get an approximate initial setting of the head. Unfortunately, the head rarely closes down enough in such cases and needs plenty more adjustment.
Therefore, it is easier to use a plain diameter plug that has been turned down to about .002" below the minor diameter of the thread to be rolled. For example, on a 7/16 x 20 UNF 2A class thread, the maximum permitted minor diameter is 0.3749". With the rolling head in the closed condition but the nuts loosened, a plain plug turned or ground down to 0.373", can be inserted between the 3 rolls and then the head can be adjusted down until the rolls grip the plug.
The 3 locking nuts at the back of the head can then be re-tightened up. To remove the plug just pull the head open. The actual ideal diameter of the plug will depend on how tough the material is to roll and where in the tolerance band the customer wants to operate. If the material is tough then the plug may need to be .005" to .006" below the minor diameter (0.369" using the above example) in order to roll size. Even using a plug to pre-adjust the head as close as possible to required size, the customer will invar iably have to make one or two small downwards adjustments to get it exactly right.
Once the head is producing good parts (where the pitch diameter and major are both on middle limit) the customer may then need to turn or grind down his plug by a few thousandths in order for it to once again fit in between the rolls. Using the above example, the plug may start off at 0.373", but could need reducing to 0.371" to fit into the head again after adjustment in the machine. Once this plug diameter has been established, it can be used in all future setups for that part and its diameter noted on the process sheet (along with the ideal blank diameter of the part).
It should be noted that a plug diameter suited for rolling 7/16 x 20 UNF 2A fit on a tough material may not be ideal for rolling 7/16 x 20 UNF 3A in a softer material; there could be a .003" difference in the plug diameters. This is the same principle as the tangential setting gauge, which the customer uses to set the gap betwe en the rolls; it is just ground to the nominal maximum permitted minor diameter, with the expectation that the customer will need to make subsequent downwards adjustments in order to achieve final size. If the customer always has to adjust the head down by .004" after each use of the setting gauge, then he could just grind .004" off the gauge so that it is closer to actual size on each use.
Finally, as a general guide to preparing a setup plug, the customer should take the nominal maximum minor diameter (available in most thread charts) and subtract half the pitch diameter tolerance for that thread.
Contact Name: Steven T. Nero
Organization:
Title: Sales Manager
E-mail: steve@rsvptooling.com
