What is the strongest indicator of spatial depth?

Thread Depth and Percentage Engagement?

• Hi there, I really hope someone can help me answer this question. I am very rusty on my lathe work and the maths that goes with it. I am making a part that require a very precise fit as any wiggling or loose fit could be catastrophic. Ok here goes. The thread I have to cut is a ISO Metric Thread and has a 2mm pitch. According to my understanding the thread depth should be 5/8 x the pitch, thus 5/8 x 2 = 1.25mm 1. Is this the correct way to calculate the thread depth, if not how to do it please? 2. Is this thread depth the depth as measured perpendicular to the axis of the work piece (as would be measured with the cross slide) or as would be measured (cut) with the compound set to 29 degrees? I have read that when you cut the thread you use 5/8 as the depth along the flank with the compound, when it is set to 29 or 29.5 degrees.... But when I am looking the profile for a ISO Metric Thread up on wikipedia http://en.wikipedia.org/wiki/ISO_metric_screw_thread is shows the thread depth as 5/8 perpendicular to the axis. 3. Because I need a very close fit, the engagement would be 75% or better. Thinking back at question 2. cutting the thread peth 5/8 the pitch perpendicular to the axis of the work piece might be 100% engagement and along the flank something less than 100%. How do I work out the relationship between the cut depth (cross slide vs along the flank) and the percentage engagement? Any assistance with this would be greatly appreciated. Oh, and I don't know if it is relevant, I am working with aluminium. Please help as I am having a brain fart at the moment...

• Answer:

  Well!!!!! You are basically wrong...... First on how to calculate the thread depth... Refer the link you provided for the proper definition and derivation Height of Thread H = P cos 30 = 2 cos 30 = 1.732 mm Now, Thread Depth td = H - H/8-H/4 = 5H/8 Thus, Thread Depth = 5/8*(Pitch * cos 30) {Not 5/8*Pitch] Hence, Thread Depth = 1.083 mm Answer to your Questions: 1. NO.. Correct Method as explained above 2. The Depth is measured Perpendicular to the axis. But, when you are cutting the thread, you will have to set the flank to a slight degree lower (i.e) 29.5 degrees 3. Percentage of Thread Engagement refers to the cross sectional amount of thread available in a tapped hole/ screw. It is the ratio of thread overlap against the reference overlap. It is dependent on the mating element size (i.e) for screws, the hole size For tapped holes, the cylinder size Refer The second link for a detailed calculations and you can find the efficiency!!