Plugged and Re-tapped Holes
Plugged and Re-tapped Holes
(OP)
Our inspector has rejected some parts with 8-32UNC helical thread inserts located 1.4 to 1.7mm out of position. He has just asked me if these holes can be plugged an re-tapped. The material is aluminium 6061-T6.
Does anybody know how strong holes are when they are plugged and re-tapped?
Does anybody know how strong holes are when they are plugged and re-tapped?
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JHG





RE: Plugged and Re-tapped Holes
RE: Plugged and Re-tapped Holes
If welded you lose the T6 temper, likely going down to T1. Ultimate goes from 42K psi to maybe 16K psi.
Could you drill out and tap a much larger hole encompassing the right and wrong locations, then install a threaded "blank" and finally redrill and tap your 8-32 hole in the right place?
RE: Plugged and Re-tapped Holes
I am looking into installing Keenserts, those screw-in thread inserts with the opposite side hammer-in pins. These are big enough the cover the existing holes completely. The only problem I have is that the local vendor has the worst telephone answering system I have ever encountered.
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JHG
RE: Plugged and Re-tapped Holes
Since the OD thread is much bigger than the original thread it will be correspondingly much stronger than the original.
RE: Plugged and Re-tapped Holes
I freeze the plug, heat the part, then plug the hole. You can also use a threaded plug and tack weld it.
Chris, CSWA
SolidWorks '15
SolidWorks Legion
RE: Plugged and Re-tapped Holes
I don't think it will work.
Drill a BIGGER hole that cuts out the bad hole completely. Helicoil THAT hole with a 1 inch plug of aluminum stock the right thickness. Then drill and tap the new nbr 10 hole where it is supposed to be in the big Al plug.
RE: Plugged and Re-tapped Holes
If the holes are only 1.4-1.7mm out is there not sufficient clearance in the mating part to cope with this?
Also why not consider elongating or making the holes in the mating part bigger if they are not large enough now.
RE: Plugged and Re-tapped Holes
The offending holes are 8-32UNC. The keensert of interest has a 5/16-18UNC outside thread. This is a semi-production part going into an aircraft. Structurally, it is rigid enough to keep optics aligned, so it is grossly over-designed from the point of view of outright fracture. Still, MS27039 pan head screws into tapped holes in solid material are good.
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JHG
RE: Plugged and Re-tapped Holes
Also, since this application is for a "semi-production part going into an aircraft", you will likely need to get MRB approval for this type of rework.