Hi guys,
Have a Hurco VM10 (quite a small mill) and need to drill 20mm x 40 deep into 140 off Mild Steel billets.
Would you guys use a series of drills working up to 20mm or just spot and then straight to it?
It’s a good quality HSS bit but have no through coolant on machine.
Thanks in advance.
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most important thing is length of drill bit stickout and length of tool holder. obviously depending on part and setup you might need a long drill to reach even when hole is not that deep. or you might only have long length drill bits available
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longer drill bends easily obviously so hole not straight and drill can break easier
if you use 364 rpm at 75mm/m feed you will need about 1.8hp, obviously if you use higher feed you have to think about
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1) spindle stalling or rpm slowing down or unstable rpm
2) drill bit bending
3) drill bit vibration increases with drill bit length usually
4) hole oversize amount
5) hole straightness
6) sudden tool failure and part damage and machine damage
7) drill thrust or force on the part can bend part or move part depends on setup
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chips wrapping around drill bit can be a problem, if you cannot stop and manually pull them off the flutes. pecking helps but stubborn chips often require a backwards CCW rotation and strong coolant flow after drilling to help unwind chips off drill bit. that is if you want chips removed automatically rather than manually pull them off
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usually many create a database of a standard tool setup that is tool length tool holder length etc to standardized tolerances then record part material and feeds and speeds tried and record any sudden tool failures over the years and 1000's of holes drilled. then you can see what feeds and speeds cause more sudden tool failures and massive costs of part damage and machine damage. that is if going faster trying to save 2 minutes a hole is causing 20 hours extra rework a year or adding 6 minutes a hole in rework than often going slower is actually faster
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many a long drill or a deep hole needs maybe different feeds and speeds for higher reliability. most start with moderate settings rather than take a chance with even a 2% sudden tool failure rate. 2% is like every 100 car trips you get into 2 car crashes requiring towing the car and $10,000's in repair costs. 2% can be a lot. obviously if part cost over $10,000. and a week of labor into it you have to be more concerned about not damaging the part if sudden tool failure occurs. or would boss be upset if part was scrapped. telling the boss you scrapped a part trying to save 2 minutes drilling time usually doesnt go over very good.