Hello

Thank you for reading my question

I would like to know what is your preferred method to drill dowel holes

On the job I am machining now I have 2 blind dowel holes Ø3 x 8mm deep on aluminium

The tolerance about positioning, is not stated on the drawing, we only have a general tolerance box in which it states +-0.1

These 2 holes are not aligned and they are also on 2 different heights (surfaces) one is about 5 mm higher than the other

Since we do not have a proper tolerance on the positioning, I think these 2 holes are independently from one to an other, I mean I do not think we have a part that fit on it, with the same holes positioning, but this is only my guesswork (deduction).

In my company they always interpolate this kind of dowel holes with a 2.5mm carbide slot-mill, and we drill it 2.8 first, even on holes deeper than 8mm, the reason why they do in this way is because they are worried that with the reamer we will not get the right position.

What is your preferred method to drill dowel holes?

I did drill the same kind of dowel holes, on a steel 14mm deep through.

Even in this case they had programmed with interpolation with 2.5mm slot-mill, and I decided to do it with the reamer instead, and it worked very well, and in this case we also had a proper tolerance on the positioning, 0.02mm circular rad.

I think if you check the run-out of the spot-drill and the reamer, regarding the drill even though it will not run very through, should be ok, since it will follow the spot-drill.

And also make sure the spindle inside and the holders are properly clean, with the reamer should always be ok to machine this kind of dowel holes.

What sort of holders do you use for the spot-drill? Do you use collets?

What sort of run-out would you consider ok to machine this kind of holes?

Any suggestion according this matter will very appreciative

Thank you in advance for your help