thread engagement for screws
thread engagement for screws
(OP)
if ý waold like to use steel screw in a threaded hole on alumýnum plate and alos steel plate , how much thread engagement do ý have to obtain for safety? I s there any book abour screws and thread engagement?





RE: thread engagement for screws
J=[(ext. thd. shear area)x(tens. strgth. of ext. thrd.)]/[(int. thd. shear area)x(tens. strth. int. thd.)]
If J is less than or equal to 1, the length is adequate to prevent stripping. If J is greater than 1, then multiply the length of engagement by J to find the req'd. length of engagement. This will force the bolt to break first.
RE: thread engagement for screws
RE: thread engagement for screws
Also, if you are using aluminum plate and steel plate with steel bolts, beware of corrosion problems. Additionally, fastener seizing and galling are problems when using steel bolts in aluminum plate.
RE: thread engagement for screws
THE source is John H. Bickford's "Introduction to the design and behaviuor of the bolted joint".
This is the definitive work on the bolted joint. It is a fantastic book. Understand what is between these pages, and you will a much welcomed engineer indeed.
RE: thread engagement for screws
I'd watch out for that metal combination, your mechanic will possibly strip the tapped hole if you don't get a longer engagement. I, too, predict galvanic reaction, though threadlock or something like that might prevent it.
I fixed my Dodge last weekend, I find Chrysler prefers to design a thread engagement more like 1.5d to 2d especially when there's only enough room for a wrench!
RE: thread engagement for screws
Most thread former manufacturers recommend 70% - 80% thread engagement for their thread formers in aluminum with 1.5d - 2.0d (d=screw diameter)length of engagement and will provide tables that will tell you what taper, hole size and length of engagement you will need for various size self-tapping thread forming screws.
A side benfit of using the self-threaders is that if you are using an English thread such as a #6 and you strip it out, you can sometimes move up to the metric M-4 for repair purposes, if it strips, move up to the English #8 and so forth. It is not recommended procedure but it does work, and reliably so in many cases. But, it is always best to test it out first.
You did not say what alloy aluminum you are using but sometimes in soft aluminum you can use a self thread forming tri-lobular body with wide spaced threads fastener such as the Plastite or other trade name with a dry to touch lubricant and get along fine.
Bill P.
CSFT, Inc.
RE: thread engagement for screws
They have software (demo available) that might be of use.
Ron