Category: No Go Too Loose

Tap Troubleshooting

12/15/2010

Troubleshooting problems with new taps.

Taps are very free cutting and will easily cut oversize threads if overfed or pushed. For the best results use a Tap Holder with built-in tension, compression.

Always utilize your holder's tension feature by programming spindle feed to 95-98% of the calculated feed rate.

Most drill size charts are based on using standard job drills which can drill over size by approximately .003". The charts are based on .003" over size condition to achieve the proper percentages of thread.

With today’s high precision drills, they are now capable of drilling to near net size. When using a high precision drill or a “G” drill you should refer to the drill size formula’s in the “Tapping Formulas” section of the catalog.

Tapped holes deeper than 1.5 diameters often call for a larger tap drill.
Blind holes often require larger tap drills to reduce loads on the tap caused by chip build up in the hole.
Materials that tend to gall when tapped or when fasteners are installed should have larger drilled holes.
Under tapping pressure, soft materials tend to extrude and enter the root area, necessitating a larger drilled hole.
Materials that don’t readily dissipate heat, should have larger holes to reduce the tooth contact area and minimize heat build up.
When making threads with high helix angles using a larger tap drill will help reduce tap breakage.

Possible Cause	Possible Remedy
Problem: Tapping oversized threads (no-go gage too loose)
Improper tap for material and thread application.	· Use a suitable tap for the hole style and material being tapped.
Cutting speed to high.	· Reduce cutting speed. · Improve coolant/lubrication.
Cold welding on the flanks of the tap (loading).	· Use a new tool. · Use surface treated taps. · Improve coolant/lubrication. · Grind away chipped and damaged teeth.
Chip packing in flutes.	· Use tap with different flute geometry/angle. · Possibly use set of taps.
Grinding burr.	· Remove burr with soft wire or fiber brush.
Incorrect fixturing or positioning of part.	· Use tap holders with axial and parallel floating. · Check clamping of part for correct alignment.
Inconsistent feed of tap.	· Tap with controlled feed. · Check CNC programs. · Check lead screw for backlash. · Use compensating tension/compression tap holder.

Problem: Tapping oversized threads (no-go gage loose)
Possible Cause	Possible Remedy
Tap selected too large for class of thread fit required.	· Review markings on tap and determine if it is suitable for the class of fit required. · If in doubt, contact us!
Improper reconditioning of tap.	· Reconditioning of tap requires that all ground surfaces maintain the original geometry put on by the manufacturer.

Problem: Tapping bellmouthed hole (first few threads gage oversize)
Possible Cause	Possible Remedy
Wrong initial starting pressure.	· Work with controlled tap feed.
Axially hard working spindle.	· Use a tap holder with length compensation.
Incorrect fixturing or positioning of part.	· Use a tap holder with axial and parallel floating. · Check clamping of part for correct alignment.

Problem: Torn and rough threads
Possible Cause	Possible Remedy
Improper selection of tap for material and thread application.	· Use a suitable tap for the hole style and material being tapped.
Cutting speed too fast or slow.	· Select proper cutting speed. · Improve coolant selection to assist the effects of tap speed.
Cold welding on the flanks of the tap (loading).	· Use a new tool. · Use surface treated taps. · Improve coolant/ lubrication. · Find away chipped and damaged teeth.
Chips packing in flutes.	· Use tap with different flute geometry/angle. · Use set of taps.
Grinding burr.	· Remove burr with soft wire or brush.
Tap drill too small.	· Use correct size drill. · If in doubt, contact us!
Insufficient coolant/ lubrication.	· Selection of suitable coolant/lubrication for material being tapped. · Use adequate amounts of coolant lubrication.
Tool overloading due to coarse pitch, hard materials or short chamfers.	· Use a set of taps.

Problem: Tapping undersized threads (go gage won't enter/binds up part way into hole)
Possible Cause	Possible Remedy
Tap selected too small to do multiple regrinds.	· Limit the number of regrinds a tap has. · Use a new tap.
Area of wear not removed when tap was resharpened.	· Grind tap again. · Use a new tap.
Improper tap for material and thread application.	· Use suitable tap for the hole style and material being tapped.
Go gage binds up part way into hole.	· Tap is dull - recondition or replace tap. · Avoid too much axial force during tapping operation (this caused the tap to cut out of lead) · Use tap holders with length compensation.
Tap selected too small for class of thread fit required.	· Review markings on tap and determine if it is suitable for class of fit required.

Problem: Tap life too low
Possible Cause	Possible Remedy
All reasons stated in torn and rough threads.	· See torn and rough threads.
Loss of tap hardness by excess hear during regrinding.	· Change the specification of the grinding wheel. · Use coolant while grinding.
Loss of surface treatment from regrinding.	· Retreatment of the tap surface. · Check suitability of surface treatment for material being tapped.
Work hardened drill hole and hole chamfer.	· Change or regrind tap drill more frequently. · Check proper drilling speed and feed. · Anneal part before tapping.

Problem: Torn and rough threads
Possible Cause	Possible Remedy
Improper selection of tap for material and threading application.	· Use a suitable tap for the hole style and material being tapped.
Tap drill too small.	· Use correct size drill. Note that cutting and roll form taps use different size tap drills for same size thread.
Tap hole not deep enough.	· Check actual drill depth, drill may have slipped back into holder.
Missing tap drill hole.	· Ensure tap drill hole is present. Common problem in multiple spindle applications on transfer lines.
Chips packing in flutes.	· Use tap with different flute geometry/angle. · Use a set of taps.
Cutting speed too high or low.	· Select proper cutting speed. · Improve coolant/lubrication to assist the effects of the tap speed.
Cold welding on the flanks of the tap (loading).	· Use a new tool. · Use surface treated taps. · Improve coolant/lubrication. · Grind away chipped and damaged teeth.
Overload of the chamfer teeth.	· Use longer chamfer. · Increase number of tap flutes to provide more chamfered teeth.
Incorrect fixturing or positioning of part.	· Use tap holders with axial/parallel floating. · Check clamping of part for correct alignment.
Tap hitting the bottom of hole.	· Use tap holder with length compensation and torque overload system.
Tapping hard or high tensile materials.	· Check selection of tap, carbide tap may be more suitable then high speed steel taps.

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