Hi All,
I'm a little confused with specifying a multi start thread. A triple thread in this case. I understand regarding the pitch etc, but cant find any info on how deep the thread should be? Is it just the same as the standard version of the thread just with the bigger pitch?
Hope that makes sense!
Hello lazydaveyt,
You have your terms confused. The Pitch is not bigger than a standard, Single Start Thread, the Lead is.
1. The Lead of a Thread is the distance the mating component (nut) travels axially in one rotation; in other words, the distance between a point of one of the Thread Leads (Crest, Root), to the next corresponding point of the same Thread Lead.
2. The Pitch of a Thread is the distance between a point of the Thread Form (Crest, Root), to the corresponding point on the next Thread Form.
The Lead and Pitch of a Multi Start (Multi Lead) Thread can each be calculated using the Number of Leads (Starts) as a constant and either the known Pitch or Lead to calculate the other. Accordingly, the following applies:
1. To find the Lead of a Multi Start Thread, multiply the Pitch of the Thread by the Number of Thread Starts
2. To find the Pitch of a Multi Start Thread, divide the Lead of the Thread by the Number of Thread Starts.
To calculate the depth that each Thread Start (Lead) should be cut to, the Pitch of the Thread should be used, as is the case with a Single Start Thread. For example:
A Three Start Thread that has a pitch or 3.0mm (the distance from a point on one Thread Form to the corresponding point on the next Thread Form) will have a Lead of 9.0mm. The depth of the Thread will be calculated on the basis of the Pitch of the Thread and therefore, in the case of this example Three Start Thread, the Pitch of the Thread (3.0mm) is the same as a Single Start Thread with a Lead of 3.0mm (3.0mm Pitch)
Thread Pitch for Single Start Thread with a Lead of 3.0mm
TP = L/N
Where:
TP = Thread Pitch
L = Lead of Thread
N = Number of Starts
TP = 3/1
TP = 3
Thread Pitch for Three Start Thread with a Lead of 9.0mm
TP = L/N
Where:
TP = Thread Pitch
L = Lead of Thread
N = Number of Starts
TP = 9/3
TP = 3
You will see that the Pitch of the Thread in both examples above is the same (3.0mm). Accordingly, the depth that each Thread Lead (Single or Multi Start) is cut to is the same, as the Depth is calculated using the Pitch of each of the Threads.
Regards,
Bill
