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Insert drills for CNC turning


Jul 12, 2022
I have been machining longer than I care to admit (37 years) I would like to discuss insert drills for turning (CNC lathe application) I have drilled hundreds of holes with these drills through and blind in 316, 17-4, 304, 303 SS Inconell etc.... I have used Sandvik, Kennametal, Iscar, Walter Titex as well as other brands. Never once have I entered the material at a slower feed rate then increased the feed rate once the drill is engaged. I am specifically referring to insert drills with two inserts a peripheral insert and a center pocket insert which enables the user to offset the drill in the X axis to drill a larger hole. I am also aware that on these drills the outer pocket inserts lead the inner pocket insert by .025 - .030 regarding speeds and feeds I always consult the manufacturer for a SFM and FPT range and given my specific work envelope (holding, mtl hardness, machine torque and HP etc... ) I arrive at a solid RPM and FR so. as I stated previously I NEVER have entered material a slower FR then increased the FR once engaged I have heard from many machinist that this is good practice, I disagree, carbide does not react well to changes in temperature or different cutting pressures. Therefore when using these drills which by the way are solely for removing material fast (not making a pretty hole) you use ONE FR and drill! I s there any one who can convince me I am wrong, I am open to change. Thanks.
A lot of this confusion boils down to terminology IMO. I've noticed on this site in particular that people use the term "insert drill" interchangeably, meaning either actual insert drills like you describe or replaceable tip drills like Sumocham or Sandvik 870.

Here in the UK we have always called insert drills "u-drills" which avoids this confusion.

Anyhow, it is not common practice to reduce the entry feed for "u-drills" specifically, but it can be required sometimes with long replaceable tip drills, and it is common practice on very long solid carbide drills.

Also, I should point out that it is not a hard rule that the peripheral insert leads the centre one, and you need to be aware of that if you're opening up a blind hole with the same drill. I also tend not to use the same feed rate for drilling as I do for boring with these drills.

Also, I would disagree that they are "solely for removing material fast (not making a pretty hole)" - every modern u-drill that I have used is capable of leaving a nice finish and a fairly accurate hole.
I often use a U drill to drill and then bore. Double use tooling is great when you don't have enough pockets.
Seems an odd first post to a thread?
Must be a pet peeve.

I had an app this week that I prolly should have started the entry a bit slower, but I don't think that it was....

I was hand loading new bars, and some of the ends were not square, and I was not facing the whole thing off, I was just facing what would end up being "part", and just starting a bit further out in Z and letting the drill remove it's own "face" material.

The first parts were a bit rough on entry as compared to any others. (sound)


So, if you think that it's poor form to enter slow and then bump up, so you never doo it, how can you be so sure that it's a problem for the folks that doo it?

Personally - I'm not seeing it as an issue.


Think Snow Eh!
I use Kennametal FS drills, and I program a "soft start" at half the feed rate, then accelerate to full feed rate, then program a "soft exit." Works very well.