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By rronald

February 22, 2023, 10:12 am

Spot drill feed rate

Greetings. I'm trying to determine speeds and feeds for spot drilling. I have a spindle with limited power, so the spindle HP is a factor for me.

I've got about 700 holes to drill. Half of them are to be threaded M6. The other half will be drilled and then reamed to 6mm. Accuracy probably calls for doing a spot drill operation. And, since there are so many holes, I'd like to have the spot drill also cut a chamfer. So, I've ordered a 10mm 120 degree spot drill. The plan is to drill down 2mm, which will create an effective diameter (which will be the outer ring of the the chamfer) of 7mm.

When I enter these parameters, I'm dubious that the calculated spindle load is correct. The calculator backs off the feed rate to 21% of nominal to get the load down to .72 HP. But, I'm not inserting the whole 10mm tip into the part. So the load should be no higher than what I would get if I used a 7mm spot drill. If I leave all other fields alone and set the Tip Dia field to 7mm, the load drops to .3 HP.

But believe that a 7mm spot drill inserted 2mm has the exact same cutting surface and loads as a 10 mm sport drill inserted 2mm.

If I then click on "Feed" to recalc feed rates, the spindle HP is increased to .72 HP and the feed rate doubles.

Shouldn't the calculations for a spot drill take the depth of the operation into account?


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Eldar Gerfanov (Admin)

February 22, 2023, 6:02 pm


It doesn't calculate the exact forses for situations like this.

In fact it doesn't consider the tip at all.

So in your case you should set the diameter of the drill to the size of your countersink.

Hope this helps.

Best regards.

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