Why "High Speed" drills?

I'm in the midst of complying with SB 14-01-31 on a never-installed and partially completed HS. It's a bear as others who have done it know, but a tameable bear. After reading all the reports of "how to..." it seems that low speed drilling is common advice and I'm finding it works well; no chattering and less wandering about the work place.

Makes me wonder: why do aviation drills have such high rpm anyway? What is the advantage, what is gained?

Speed may be life in combat and on final, but in my experience speed only creates mistakes in the workshop.

I was taught that drilling aluminum you would use high rpm with light pressure and with steel you use low rpm and heavy pressure.

The optimum speed for cutting aluminium is 250 to 350 ft/min. When using an 1/8" drill this means it should turn around 7600rpm - the highest air drills (that are reasonably priced) turn is 3500 to 4000rpm. But that's OK as running that fast in a hand held drill might be rather unmanageable - in a drill press its fine.

When drilling out rivets you aren't really looking for the optimum cutting speed ...

Pete

Does "optimum" mean "maximum speed for production"? If so, who cares?

aerhed said:

Does "optimum" mean "maximum speed for production"? If so, who cares?

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Generally, "optimum" in terms of tool cutting speed is a mix of proper chip development and removal, tool and workpiece heating, tool longevity, and production rate. The right chip size helps carry heat away from the tool/workpiece interface at the right rate to prevent things like welding the chips to the tool, welding the tool to the workpiece, ruining the tool or workpiece heat treatment, or having an undesirable finish on the final cut surface. Because aluminum is such a good conductor of heat and has such a high heat capacity, it can carry heat away from the workpiece and tool rapidly enough that high tool speeds can be tolerated. There can be also chemical reactions between the tool or tool coating and the workpiece and chips that can be limiting factors as well.

My answer would be... Try building a non pre-punched airplane with a 600 rpm drill, and you'll change your tune pretty fast.

gtmule ..... I will second that !

Light sheet metal drilling - light pressure, high speeds AFTER getting the drill started. Makes a cleaner hole.

Drilling

RVDan said:

Light sheet metal drilling - light pressure, high speeds AFTER getting the drill started. Makes a cleaner hole.

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Key word, "AFTER". Get a perfectly centered start then go full blast.