Gunn Machine & Tool Co.

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Specialist in on-site spindle taper seat grinding for repair and restoration of precision to your machine spindle.

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In-Place Spindle Taper Grinding

Breathe new life into your machine tool with minimal downtime. Gunn Machine & Tool Company restores the precision and accuracy of machine spindle taper seats. We use special precision equipment, designed and built by us. By choosing our on-site spindle grinding service, you'll benefit from less downtime and lower costs. We also offer spindle inserts and conversions, face drive key repair, and PM program setups and consultations.

CNC, Manual, Vertical, Horizontal, Mills, Lathes, Hobbs, Machining Centers, Grinding Machines and more can benefit from our service.

Tapers Cat1

Tapers BT1

Tapers MT1

Tapers HSKc1

Tapers NMTB1

We recondition CAT, BT, HSK, Big Plus, Morse, Kwik-Switch, NMTB, and other taper seats, in-place.

TG Tool
New TG Tool

Proven Methods

When accuracy matters, choose Gunn Machine & Tool Company. Rotating the machine spindle as we grind ensures the seat will be concentric to the spindle's rotation within its bearing center line, just as in the machine's normal operation. This method eliminates the error of tolerance stacked up upon assembly and is the most accurate method of grinding the taper seat true to spindle rotation. We have even used this method on warranty issues and new spindles for machine and spindle manufacturers who require extremely close tolerances.

In-Place Grinding

Grinding your spindle taper seat in place offers many advantages over other methods. Because you don't have to disassemble your machinery, alignments are unaffected, which results in greater accuracy. Machine downtime is limited to a few hours instead of days or weeks, making in-place grinding far more cost-effective.

The Spindle Grinding Process

  1. Inspection & Testing:
    • Visually Inspect the Spindle for Damage
    • Determine the Amount of Contact Area Using Precision Taper Gauge & Bluing
    • Test for Run Out Using Precision Test Bar & Indicator
    • Test Drawbar Clamping Pressure Using Draw Force Test Gauge
  2. Setup & Grinding:
    • Set Up and Grind Taper Seat for Proper Contact & Runout
    • Perform In-Process Inspections to Ensure Minimal Material Is Removed
  3. Inspection:
    • Perform Final Inspection of Contact, Run Out & Drawbar Clamping Pressure
    • Document & Discuss All Inspections with Customer
    • Present Inspection Report to Customer

Spindle Inserts

Gunn Machine & Tool Co. has designed a spindle taper insert to repair machine spindles, such as those found in large horizontal boring mills, when damage is more severe and cannot be repaired by grinding alone. Inserts can be made for drawbolt or pull-stud type retention systems. The insert is repairable and replaceable, should damage occur in the future. Inserts may also be used in spindle conversions, to change form older-style Morse tapers to CAT-style tooling.

  1. We travel to customer's plant to inspect spindle and see if it is a good candidate for this type of repair.
  2. Dimensions of spindle are taken in order to custom manufacture the insert.
  3. Dimensions are used to design the insert and make a set of prints for manufacture.
  4. The insert is manufactured at our facility.
  5. We travel back to customer's plant for installation.
  6. We machine your spindle in place to accept the new insert.
  7. We install the insert.
  8. We finish grind the insert's taper seat in place.
  9. Test cuts are made with the machine.

Repair of Face Drive Keys

Gunn Machine & Tool Co. can, in some cases, repair the damaged spindle drive keys without spindle disassembly, on-site. However, in some cases the spindle would have to be removed. The process depends several factors:

  1. Whether or Not the Keys Are Integral to the Spindle or Separate & Located in a Keyway or Pocket
  2. The Size of the Spindle Taper
  3. The Top Spindle RPM
  4. Machine Type, Make & Model

The Key Repair Process

In most cases, machines — such as Horizontal Boring Mills with NMTB, CAT, or BT tapers — can be repaired on-site. This is done by machining the keyway in place. We use our special equipment to machine the keyway as needed and make new step keys to fit.

In the case of integral keys, there are a number of different ways to carry out the repair. The spindle face can be altered to accept new keys by machining pockets. These pockets will locate new keys that are then held in by screws. Careful consideration is given in choosing a method of repair that best suits the application.

In high-speed spindles, which require a high degree of balance, we prefer the spindle be removed. We can then make sure the balance of the spindle is not changed.

Spindle Conversions

Gunn Machine & Tool Co. can update your older-style Morse or NMTB spindle taper to accept newer CAT-style tooling. This is done by installing a special insert that utilizes an OTT drawbar system. The insert is similar to the ones we use to repair severely damaged spindles. We complete the job by adding safety switches that will only allow clamping cycles when the spindle is stopped and a hydraulic system to facilitate unclamping.

Tool Holder Reconditioning

Tool holder wear is a big problem when it comes to getting the most out of your hard-working milling machinery. Wear reduces the life of your spindle and the accuracy of your work. Gunn Machine & Tool Co. can recondition your machine's tool holders.

Take a good look at the tool holders. Do they show signs of wear? Is there fretting on the taper shank? If so, you should consider replacing them or have us recondition them.

Tool Before Tool After