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13. Introduction to Thread Forming Taps (Roll Taps)
Shape of internal threads and ratio of thread engagement aff ected by bored hole diameter
Compared with the basic height of thread engagement, the actual height of the thread engagement is called “thread engagement ratio” in SP percentage. Depending on the bored hole diameter, internal thread and thread engagement ratio will change. The tapping condition must be chosen by referring to the thread engagement ratio. The portion of material to be formed can be reduced by selecting the largest possible bored hole diameter. In this way the load on taps is
reduced, decreasing tap’s wear and damage. SL
PO
Ck45, minor diameter of thread (cutting process) Aluminum, minor diameter of thread (forming process)
M24x3 M25x2 minor diameter tolerance of internal thread minor diameter tolerance of internal thread Ø 20.752 - Ø 21.252 Ø 22.835 - Ø 23.210
ST
| Internal | External | [Aluminum, internal thread formed] | Internal | ||
| [Ck45 internal thread cut] | |||||
| thread | thread | M25x2 | thread |
M24x3 bored hole size: Ø 23.903 bored hole size: Ø 20.652 minor diameter of finished internal thread : 22.723 mm
minor dia tolerance of internal thread NG minor dia tolerance of internal thread NG
thread engagement ratio: 103.1% ROLL
thread engagement ratio: 105.2% [Aluminum, internal thread formed] [Ck45 internal thread cut] M25x2
M24x3 bored hole size: Ø 24.042 mm bored hole size: Ø 21.000 minor diameter of finished internal thread : 23.067 mm
minor dia tolerance of internal thread: CARBIDE
minor dia tolerance of internal thread : Middle Middle thread engagement ratio: 92.4% thread engagement ratio: 89.3% [Aluminum, internal thread formed]
[Ck45 internal thread cut] M25x2 M24x3
bored hole size: Ø 24.240 mm LONG
bored hole size: Ø 21.352 minor diameter of finished internal thread : 23.462 mm minor dia tolerance of internal thread NG minor dia tolerance of internal thread NG
thread engagement ratio: 81.5% thread engagement ratio: 71.0%
HAND
Example of thread engagement for M6x1 cutting and forming tap TAPS
Boring before tapping - Check 1
EG (STI)
PD PD
MinMin
MinMin 100%
100%100% SPECIAL
MaxMax 78.2% THREADS,
GAUGES
MaxMax THREAD
Min MILLS
Max 74.1%78.2%
Internal threads made by roll taps are different from those made by cutting Length of taps on the shape of minor diameter. engagement=9.1mm DIES Engagement classification Engagement length Engagement Internal threads Unit : mm length classification Unit : mm D1
| S | Short engagement length | 4H | 5H | — | S≤3(mm) | External threads | *Hole size for thread forming taps | |||||||
| Drill size | ||||||||||||||
| Min | Max | |||||||||||||
| M | Normal engagement length | 5H | 6H | 7H | 3<M≤9(mm) | (ref.) | Min | Max | CENTER | |||||
| L | Long engagement length | 6H | 7H | 8H | 9<L(mm) | Bored hole size | 5.0 | 4.917 | 5.153 | |||||
| 5.49 | 5.59 | DRILLS | ||||||||||||
| Length of engagement | Engagement ratio | 92.4% | 100% | 78.2% | *Forming condition changes depending on | |||||||||
| On "middle" engagement class, 7H class can be chosen in | workpiece's Material and shape. Above is for | |||||||||||||
| case of "L" engagement length. | P=1.0mm | D1 is minor diameter of 6H internal threads | customer's reference. |