Mastering Thread Rolling – Material Preparation

Why is material prep important with thread rolling?

 Thread rolling is a cold forming process and the material goes through a state change. With Axial rolling tools this change normally occurs in the first 2 pitches.

 Material is prepped at the mean of the Pitch based on the class of thread.

 The state change occurs by compressing the material down to the Minor dia then it flows up the roll form and creates the Major.

 The chamfer must start a least .010” below the Min. Minor

 Improper prep results in too much material and risks breaking the rolls

REVIEWING PERFORMANCE OF A THREAD ROLLING TOOL

The long-term performance of a thread rolling tool is directly related to wear of the spindles, bearings, backing plate and face plate of the rolling head. Wear of any components will present initially in pronounced taper of the finished thread.

Older style heads were equipped with needle bearings while newer style heads utilized carbide bushings. The carbide helped to maintain parallel form for longer life cycle than the needles.

Correcting taper generally requires replacing one or more of the contributing components. In a pinch, the straightness is achieved through preparation of a counter tapered part prep. This can squeeze additional life out of the tool without the time and cost of immediate repair or part replacement.

We inspect, evaluate and quote repair cost and time when tool performance becomes questionable, and the inspection is scheduled regarding production needs.

You can teach an old dog new tricks!

For many years in manufacturing the multi spindle screw machine was the dominant metal working tool available worldwide. With short cycle times attributed to several different machining processes occurring at the same time each on a different spindle. The machine technology generated specialized tooling to integrate within the individual spindle cycle time. The machines demanded highly trained specialized set up technicians and because of the set up demands the set-up time required practical lot sizes to make them cost effective. During their heyday most manufacturers offered apprentice programs and controlled training cycles to ensure that talented people were available to support their manufacturing plan. Many of these machines are still in use and still productive. Done right they still offer the lowest cost per piece in the machining industry.

In today’s world the programmable CNC has become the dominant tool for metal working. Skill sets have transitioned from hands on tooling changes to computer literacy. Small lot sizes pose no problem to cost per piece. Cost per piece can be influenced by design of the part to be produced. Threaded parts and long journals can add many passes to a single point turning tool. Journal lengths greater than 6 times diameter require several passes to machine and become even more difficult in smaller diameter parts.

Every second of cycle time has an associated cost and cycle time is the highest cost when compared to tooling. Bidding for work within a job shop atmosphere is directly tied to cycle time. Quoting a job requires careful attention to cycle time if you want to garner a contract and maintain profitability. Some of the tooling technology developed for automatic screw machines has had a natural transition to the CNC world. Thread rolling is an example, the ability to produce threads typically at 1 inch of thread length in 1 second of cycle time is common. Turning of journal lengths up to or greater than 10 times diameter is easily achieved. While there are a variety of tools commonly called “Hollow Mills”, one stands out.

Genesee Tool Co. offers a multi flute, indexable carbide hollow mill that easily and accurately adjusts to part diameters. A three-flute tool, for example, feeds at three times the speed of single point turning. Long journals can be machined in a single pass. Multiply the seconds saved per piece by the number of pieces to be produced and you can quickly calculate the value. It may prove to be the difference between a bid and a contract. Talk to us about your needs, we may be able to offer a solution to optimize your process and improve your bidding results. 

Procedure for 1/2-13 UNC Roll On Roll Off® Thread Rolling System, Patent Pending

Tool setup

  •  Mill a .250” to 375” flat on the shank within .500” of the head if not already there.
  • The tool is assembled and setup.  The rolls are set with a gauge pin to the max Minor less .002”. see below

Machine setup

  •  Mount tool and sweep faceplate OD with an indicator – TIR total .005”

Process setup

  • Use sacrifice material-  program a .600” length to test roll a .500” long part,  Insure the material will not hit faceplate.
  •  Pre-turn for rolling = Mean of the Pitch or __.445”__
  • 30’ chamfer starting at  .015” under min. Minor. ___.372”____
  • Feed rate is Pitch less .0005” or ___.0764”__ Roll on and off at the same federate.
  • Sync tap (G84, G77) works best.   G34 with M03,04 spindle reverse- no dwell.
  • SFM- 125 SFM for low carbon steels, 100 SFM for SS and hi-nickel.  Increase after good part.  Call for confirmation.

Call before you hit cycle start.     704-849-9209  

Adjusting after first test roll-

Step 1- Minor Dia. and Pitch Adjustment-

  • Loosen 3 nuts and adjust tool +/-.  One witness line is .004”on Minor.  Center Pitch. 

Step 2- Major Adjustment-

  • Adjust pre-roll dia to the mean of the Major.  .001” change in pre-roll dia. = Major dia. change of .003”

Step 3- Adjust chamfer

  • Adjust for desired result.  Keep chamfer min of .010 under min Minor.  Material will “rollup about 15’. Alternative- cut after rolling.

Thread Rolling Tool Performance

The long-term performance of a thread rolling tool is directly related to wear of the spindles, bearings, backing plate and face plate of the rolling head. Wear of any or all these components will manifest initially in pronounced taper of the finished thread. Older style heads were equipped with needle bearings while newer style heads utilized carbide bushings. The carbide helped to maintain parallel form for longer life cycle than the needles. Correcting taper generally requires replacing one or more of the contributing components. In a pinch, the straightness is achieved through preparation of a counter tapered part prep. This can squeeze additional life out of the tool without the time and cost of immediate repair or part replacement.

We inspect, evaluate and quote when tool performance becomes questionable. Call us.