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Deep hole drilling, it means there is a big draw ratio of the drilling hole diameter and drilling depth, at least 5 times. But in deep hole processing, sometimes it can reach to 150 times. And normally when the hole draw ratio is bigger than 5 times, we can call it deep hole. When the drill bit enter into the drilling area, it’s difficult to judge the processing condition. And it must be forced to coolant the cutting oil. The drill shank needs enough rigidity so that we can get a good processing precision.
Drill shank of the gun drill is empty inside. The cutting oil enter into the drilling bit, and there is a v shape groove ,which use to remove the chips. Gun drill can be used in the normal processing center, but it will need the high pressure cutting oil
There are 3 holes: two 4mm hole, one 5mm hole, both of them the drilling depth are deeper than 700mm. For a normal machine, it can’t process such a deep hole, and under such condition, we have to use the deep hole drilling machine. When the draw ratio of drilling hole diameter and drilling depth is bigger than 100 times, a normal machine can’t process that. 
A deep hole drilling machine will apply for three-step processing method: positioning drilling, guide drilling and normal drilling. For different drilling hole diameter and drilling depth, we’ll apply for different drilling speed.
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