Nut and bolt grabbing

[Mr blindbird]

Hey there,last night i made a tread M27x1(i know,it's not on any table,came up with it cause it was the only one i could make for the pieces i wanted to join),wich were a alu tube diameter 30mm,functioning as the nut,and a standard steal piece wich was the bolt,now they worked perfect,infact i was so proud of it i was screwing and unscrewing it multiple times just to feel it glide.
This evening,i went back to make another steal bolt to close off the other end of the alu tube...and just for the feeling,i unscrewed the other steal bolt again,still went smooth like babyoil but when i wanted to screw it back in.... :bang:it jamed,after like 3 treads deep...the two wouldnt move anymore forward nor back,in an attempt to put the steal bolt in the vice and force the alu tube to unscrew,it came appart but the whole tred was hopelessly dammaged,even when i tryed the bolt in the othe end of the tube,wich worked just fine yesterday also,it wouldnt get even 2 treads deep.
Now,i know that 2 unlubricated stailess steal nut and bolt eventualy grab in eachother but i didnt know it was the same with alu and steal,does anyone of you guys know about this? just to make sure and be able to stop myself accusing for turning the 2 parts bad together??
 

[bogstandard]

Mr B,

In English, what you have experienced is called GALLING, pronounced 'gor-ling'.

Aluminium and stainless steel are renowned for it. When the two surfaces rub together, especially if they are slightly rough. The high spots between the two parts 'weld' to each other, and you end up with what you have been trying to get apart.

I hope this helped to explain it.

John

[sbwhart]

Yes Johns got it spot Galling is what you got I've experienced this to my cost as part of my day job, when it happens it just won't shift without damage to the parts.

You usually get it with dry parts a little bit of oil helps to prevent it.

Cheers

Stew

[Mr blindbird]

Thx for the feedback guys,now i know for sure what it was,and it makes completely sence,the night before,the treads probably still were lubed by the cutting oil,today,i remember cleaning the treads before rejoining them,what made them run dry with known concequenses,up till today i only knew stainless steal would do that,i'll be more carefull in the future and keep the alu lubed.
O well,i'll have to do it over right away...like murphy says;there's never time to do it right but there's always time to do it over  
Thx for the help

Danny