, ▁or ▁struct ural ▁members ▁like ▁I - be ams . ▁ ▁T rep anning ▁can ▁also ▁be ▁useful ▁to ▁make ▁gro ov es ▁for ▁inserting ▁se als , ▁such ▁as ▁O - r ings . ▁ ▁Micro dr illing ▁ ▁Micro dr illing ▁refers ▁to ▁the ▁dr illing ▁of ▁holes ▁less ▁than ▁. ▁Dr illing ▁of ▁holes ▁at ▁this ▁small ▁diameter ▁presents ▁greater ▁problems ▁since ▁cool ant ▁fed ▁dr ills ▁cannot ▁be ▁used ▁and ▁high ▁sp ind le ▁spe eds ▁are ▁required . ▁ ▁High ▁sp ind le ▁spe eds ▁that ▁exceed ▁ 1 0 , 0 0 0 ▁R PM ▁also ▁require ▁the ▁use ▁of ▁bal anced ▁tool ▁hold ers . ▁ ▁V ibration ▁dr illing ▁▁ ▁The ▁first ▁studies ▁into ▁v ibration ▁dr illing ▁began ▁in ▁the ▁ 1 9 5 0 s ▁( Pr . ▁V . N . ▁Pod ura ev , ▁Moscow ▁Ba uman ▁University ). ▁The ▁main ▁principle ▁consists ▁in ▁generating ▁ax ial ▁v ibr ations ▁or ▁oscill ations ▁in ▁addition ▁to ▁the ▁feed ▁movement ▁of ▁the ▁dr ill ▁so ▁that ▁the ▁ch ips ▁break ▁up ▁and ▁are ▁then ▁easily ▁removed ▁from ▁the ▁cutting ▁zone . ▁ ▁There ▁are ▁two ▁main ▁techn ologies ▁of ▁v ibration ▁dr illing : ▁self - m aint ained ▁v ibration ▁systems ▁and ▁forced ▁v ibration ▁systems . ▁Most ▁v ibration ▁dr illing ▁techn ologies ▁are ▁still ▁at ▁a ▁research ▁stage . ▁In ▁the ▁case ▁of ▁self - m aint ained ▁v ibration ▁dr illing , ▁the ▁eigen fre quency ▁of