Call Us: 248-960-5891

Don’t throw away those expensive, special taps – ReSharpen

No Comment
Tap Saver L.L.C.

TapSaver, LLC

Don’t throw away those expensive, special taps…..Re-sharpen !!

Tapping……..For many of us it’s our least favorite machining operation, for good reason.  You have one specific tool to use to hold many different dimensions, at high production rates, without breaking the tap in the part.   The high production rates necessary today for manufacturing internally threaded fasteners have created the nib tap design to maximize tap life.  There are many styles of nib taps available, but the key features are usually a PVD coating to add surface hardness and lubricity, a long chamfer length to have as many threads on the tap cutting as possible, and maximize the number of flutes, usually 5 or 6, to also reduce chip load.   Tap manufacturers design and manufacture  these nib taps to incredibly tight tolerances,  utilizing the latest technology in HSS and coatings to maintain dimensional consistency of the pitch diameter and  threads, to have these taps produce  thousands of fasteners per tap.

To maximize tap life and get the most production for your  tooling dollars, it is possible to re-sharpen these nib taps, one, maybe two times,  and achieve close to the original production quantities with each re-sharpening.  The key to maximizing tap life and utilizing re-sharpening is managing tap usage.  Running a tap until it is worn out usually creates too much wear on the cutting edge and thread flanks to allow it to be re-sharpened, rendering it scrap.  Many manufacturers will attempt to re-sharpen a worn out  tap “by eye”, or have their guy who is the best at tool grinding re-sharpen the tap, and get a pretty good, but not consistent results.  There is a better option.

TapSaver, LLC specializes in re-sharpening taps, and under the new ownership, is poised to expand operations, and work closer with our customers to improve tap application and management maximizing their tooling dollars.  We have been re-conditioning taps since 1964 and that is all we do.  We have specially designed tooling and fixtures on dedicated equipment to tightly control all of the grinding operations necessary to re-condition taps from 1/4″ to 4″ diameter in all styles and types.

Controlling Tap Wear

Most taps for fastener tapping are of the Nib style, either a 1 piece bent shank style for small diameters, or a tap that is detachable from the shank for sizes generally larger than M10 – 3/8″.  These tools typically tap thousands of nuts before they are pulled from service because it will no longer produce a gageable thread.  The reason the tap no longer produces gageable threads is excessive wear and dulling of the cutting edge and thread flanks (Pic  #1).  Re-sharpening  the tap by grinding the flute face creates a new, sharp cutting face, but taps with excessive wear do not completely “clean up” leaving dull cutting edges on the threads.   (Pic  #2)   Grinding more off the cutting face introduces many issues that may prematurely reduce tap life  such as reduced pitch diameter, grinding burn, or weaken the land width

Excessive Tap Wear                                                             Excessive Wear After Re-Sharpening

Pic  #1                                                                                                          Pic  #2

 Excessive Tap Wear  tap-wear-after-sharpening

The breakdown of coating and tap steel at the cutting edges accelerates  after the initial breakdown.  The absence of the PVD coating allows accelerated wear and galling of the HSS creating excessive tap wear.  Monitoring maximum number of nuts produced per tap when the thread gage fails establishes the number of  nuts per tap, at failure.  By setting a production limit, less than the maximum producible,  before the wear gets to severe, allows pulling  the tap to save it for re-sharpening.         (Pic  # 3)  This wear can then be ground off during re-sharpening creating a new, sharp cutting edge restoring the tap to like new condition (Pic # 4).

Controlled Tap Wear                                                                        After Re-Sharpening

Pic # 3                                                                                                      Pic # 4

Controlled Tap Wear After Resharpening Tap

*Tap photographs are compliments of metallurgical and fastener testing lab, Midwest Testing Laboratory, Troy, MI.

Controlling Tap Size

The concern that taps loose size as a result of re-sharpening is a fact.  When taps are manufactured new there are 2 features ground in to minimize drag during tapping. First, there is back taper, on average .001″ reduction of diameter per inch axially, secondly there is radial thread relief of the pitch diameter to reduce wear on the thread flanks.   These 2 features vary slightly by manufacture and tap design.  At  TapSaver we take these features into consideration when re-sharpening to minimize size reduction when  re-sharpening.  For nib taps the flute face or rake face is ground.  The stock removed from re-sharpening  is a balance between many factors but the most important is to maintain rake and minimize stock removal to minimize size reduction.   On average the pitch diameter size reduction is .0005″,  or  ”1 GH” limit per re-sharpening.  Fastener manufacturers specify a “GH” size limit for taps to achieve desired size results to compensate thread sizes for heat treating or plating.  Other than the loss of a “GH” on a tap that slightly reduces the number of fasteners produced, the re-sharpened taps function as well as new taps, and maintain successful gaging results.

Illustration of Radial Relief illustartion-of-back-taper

Cost Savings

At TapSaver, all we do is re-sharpening, or modifications to existing taps, to improve tap performance.   This provides us the opportunity to re-condition taps efficiently and accurately keeping tooling and manufacturing costs for our customers to a minimum.   Below is an example of typical cost savings utilizing re-sharpening  for a nut manufacturer.  This is a very conservative example, making assumptions for tap unit cost and the number of nuts / tap.  So your actual results should be much better.

New taps only

New Taps

Qty

Cost Ea.

Total $

Nuts / Tap

Total Nuts Tapped

Comments

Cost / Tapped hole

1/2-13 Nib

200

45.00

9000.00

20,000

4000000

Taps worn out

0.00225

1/2-13 Nib

174

45.00

7830.00

20,000

3470000

Taps worn out

0.00225

Totals

374

16830.00

7470000

0.00225

New taps with re-sharps

1/2-13 Nib

200

45.00

9000.00

18,000

3600000

To re-sharp – 25% scrap

0.00250

90% tool life

150

9.00

1350.00

16,200

2430000

To re-sharp – 25% scrap

0.00056

80% tool life

100

9.00

900.00

14,400

1440000

Taps worn out

0.00063

Totals

11250.00

48600

7470000

0.00151

5580.00

33.16 8% savings

Tap re-sharpening, when done properly, can directly yield significant results in tool cost savings.  We at TapSaver can work directly with your production personnel  to improve tapping operations, better manage tap usage to take advantage of tap re-sharpening, and supply a guide for operators help assist them with managing tap wear as well as tool management.

For more information on tap re-sharpening of all types of taps contact:

TapSaver, LLC

Brian Mann

bmann@tapsaver.com

TapSaver.com

 

*About the author:

Brian Mann is the new owner of TapSaver, LLC  Walled Lake, MI.  He attended Lawrence Technological University and has over 30 years of experience in the cutting tool industry.  His extensive experience in tap applications in automotive, aerospace, petroleum and medical industries provides a comprehensive background for your difficult tapping jobs.