Drill Question - Difference between usable flute length and flute length?

In my shop, there's ongoing discussion as to what is considered "flute length".

My boss defines it from the full diameter, to the end of the gullet.

Another guy defines it by the usable length.

If you look at the following Mitsubishi drill, there is a major difference between the Usable Length, and the Flute Length:



They're saying the Usable Length is 22.5mm (23.3-.8 for the tip). Which makes sense, since it is a 5xD. However, the flue length is 40mm down to the gullet. That's almost a .700" difference.

So, what's the difference between usable flute length, and flute length?

If you bury that drill 40mm deep (without pecking, and you shouldn't need to peck with thru-coolant), the chips will no longer evacuate and there will be a kaboom.

But, if you peck the last 10mm or so, you can get away with it.

Regards.

Mike

You are confusing flute exit point with usable.
The wheel that ground it has an arc so this callout on print but it gets shallow quick and one is not transporting chips though it.
Normally the primary ends sooner.

Finegrain said:

If you bury that drill 40mm deep (without pecking, and you shouldn't need to peck with thru-coolant), the chips will no longer evacuate and there will be a kaboom.

But, if you peck the last 10mm or so, you can get away with it.

Regards.

Mike

Click to expand...

...and that can be a real life saver, at the expense of time.

Programmed via Mazatrol

:-) As far as I'm concerned, if it isn't "usable" it isn't part of the "flute" . It was just necessary machining to do the job. :-)
...lewie...

A wise man once said that most questions are answered by refining the question itself.

In this case, if you refine the meaning of "usable" you should have the answer or a clear path to that answer.

The only real reason for having flutes that are longer than what is strictly needed to form the rake angle of the cutting edges is for chip evacuation. And if the chips are packed into a moving mass that has the same cross-sectional area of the flute just behind the cutting edge, then when the flute becomes smaller than that cross-sectional area, then the chips are in danger of backing up and the drill may break. But, that is my definition of "usable". Yours may differ.

Again, going with my definition of "usable" as being used for chip evacuation, I would disagree about the sloped/ramped part of the flute being "just necessary machining to do the job". That final, ramped part of the flute prevents the chips from backing up when the bit is before or at the "usable" depth in a hole. The ramp directs the chips away from the axis of the bit and into the air. If the flute abruptly ended at the last point where it was at full depth (with an impossible to machine shoulder), then the chips would back up there and the "usable" length would be even less. In fact, an abrupt shoulder would start to cause the chips to back up far sooner as longer chips would strike it and buckle and tangle almost as soon as the drilling starts.

So, that final, ramped part of the flute has it's own purpose and if it were absent the drill would not function as well as it does.

Call it a deliberate feature or a happy accident, but the use of an abrasive wheel with a definite radius/diameter almost a required tool in the drill making industry. And the flute shape, including the ramp at the end, is an almost universal feature of all drill bits.

Lewie said:

:-) As far as I'm concerned, if it isn't "usable" it isn't part of the "flute" . It was just necessary machining to do the job. :-)
...lewie...

Click to expand...

The final ramped part of the flute is there due to the size of the grinding wheel used.
A 3 inch wheel and a 10 inch wheel make a different length arc here.
Why worry or call it out in the specs? Because you do not want to clamp on the fluted area so this determiners how deep you can set a bit into the holder.
EPAII is so very correct that you not drill this depth even if the primary went all the way.
The flute area cross section is getting smaller and smaller and would pack.
Much here is not a design feature for chip transport as it is the machine and wheel size/shape used.
One needs to think about how to make a drill flute economically. You can go down to 0.500 diameter wheel or cutter and the chips will exit just fine.
Bob