J & M's High-Torque Retention Knobs

The J&M High Torque Retention Knob Difference

• Made from hot rolled 8620H fine grain steel
  • Improves durability
  • Extends part life
  • Reduces distortion from heat treat
• Shot peened to relieve stress
• Deburred with radius corners for better finish
• Better finishes than required by International Standards
• Written inspection records on every mfg. lot
• Made in the USA from USA manufactured materials
• 2X to 10X less expansion of the toolholder shank
• Laser-marked with month/year of purchase to help determine life span
• Laser-marked with part number, serial number for traceability

All The Qualities You Should Look For In A High-Torque Retention Knob

• REDUCES TOOLHOLDER EXPANSION
• REDUCES COSTS
• INCREASES PROFIT
• INCREASES PRODUCTION
• INCREASES TOOL LIFE
• INCREASES FEED RATES
• INCREASES RIGIDITY
• IMPROVES TOOLHOLDER BALANCE

New Generation High-Torque Retention Knobs
Read An excerpt from CMTA View's June 2009 article.

Using the first generation of our taper shank test fixture, we began experimenting with the actual retention knob design. Using this fixture we found that standard retention knobs inserted into the toolholder with as little as twenty foot/pounds of torque expanded the toolholder shank. Using the newest design of the test fixture, we now know that the toolholder actually will begin to expand with as little as five to fifteen foot/pounds of torque. Even in light of these new findings, we have proven that the new, High Torque retention knobs, when tightened to the same torque value as standard retention knobs, expand the toolholder shank two- or three- times less than standard knobs. The inclusion of a pilot on the high torque ANSI retention knobs greatly reduces the likelihood of retention knob breakage, especially when the Belleville washers are not performing at full strength. The High Torque retention knobs are designed to be balanced dynamically from end to end, which make it much easier to keep balanced toolholders within tight balancing tolerances after installation.

The graph below indicates the growth we experienced while testing using the second generation fixture and the High Torque retention knobs compared to standard retention knobs.



Graph explanation

The vertical axis on the graph on page 11 is based on a toolholder grind tolerance of 0.000080 inch. The greatest deformation reflected by the graph, at 80 ft. /lbs., is approximately 10 times the tolerance, or 0.0008 inch. While this number may seem miniscule, bear in mind that this discrepancy increases by a factor of 3.40 or 0.0027 inch. This number represents the distance that the toolholder moves out of the spindle due to the deformation of the toolholder. The resultant impact is that toolholders that measure 5.400 inches in length from the face of the spindle to the tool tip may run out up to 0.002400 inch T.I.R.

This same graph illustrates that the same toolholder, paired with a High Torque retention knob, may experience tool tip run out up to 0.000576 inch T.I.R., which is a significant difference. Simply stated, the two numbers represent the diameter the tool would be free to move forward and back or side-to-side. Therefore, by implementing lower torque pressure during retention knob installation, along with the selection of the best quality toolholder and use of a High Torque retention knob instead of a standard knob, the distortion problem is solved.

It’s important to maintain retention knob installation torque at an acceptable level. Machines with 40 taper spindles normally have draw bar pressure of 2,500 pounds or less. Lateral force of 1.25 times the draw bar force, or 28 to 33 ft/lbs of torque, is adequate to ensure that the retention knob does not lose contact with the face of the toolholder.

John Stoneback, President
J&M Machine, Inc.

J&M Machine Inc. has manufactured retention knobs for 35 years. Test documentation on this subject is available at www.retentionknobtorquetest.com. Questions call (440) 357-1234, fax (440) 357- 1129 or e-mail info@jmmachineinc.com.