Feeds and speeds for gundrilling

gregormarwick · Nov 11, 2020

I'm about to drill a 5mm hole 400mm deep in a piece of 4140QT @235Bn.

I have a new gundrill here for the task.

A couple of weeks ago I did a similar part in the same material, with the same series of gundrill from the same manufacturer, but it was 280mm deep.

In that part I used 2800rpm (44m/min) and 33mm/min (0.012mm/r), which was right at the very low end of the recommended cutting data.

Running soluble semi synthetic coolant (Hysol XF at 5-7%), obviously not ideal but I can't swap the whole machine over to oil every time a need to use a gundrill...

It is 1000psi though.

Looking at the old drill, the edge is not in very good shape, and I'm concerned about the new drill getting the hole completed in the longer part.

Thoughts?

edit: clarified old vs new drill...

TeachMePlease · Nov 11, 2020

80xD in steel with a questionable edge?

Doesn't sound fun to me. Have you talked to the drill vendor about a quick resharp? I know DrillMasters Eldorado Tool will do re-sharps on their own drills for very little cost, and very quick. I'd think the peace of mind would be worth it.

I also work in a different environment from many here, so if that's not feasible, ignore me, as always.

atex57 · Nov 11, 2020

Touch up the face with a diamond file. Use some Dykem or similar to check progress. I have known guys that can hand grind and go right back to it. Look on Youtube or similar to find a vid showing this.

Ed.

gregormarwick · Nov 11, 2020

Thanks for the replies, just to clarify, I have a brand new drill. The one in the picture is from the last time with the shorter hole, it was also new before it did that. I was hoping for advice on how to prevent the new drill looking like that before it's finished the hole!

One part, one hole, new drill, just need to get through it without any problems!

Hardplates · Nov 11, 2020

gregormarwick said:
Thanks for the replies, just to clarify, I have a brand new drill. The one in the picture is from the last time with the shorter hole, it was also new before it did that. I was hoping for advice on how to prevent the new drill looking like that before it's finished the hole!

One part, one hole, new drill, just need to get through it without any problems!

Just a theory but being you are at the low end of the feed window maybe the material is work hardening and the drill isn't getting under the harder layer. Maybe try a test piece being a little more aggressive?

CAMasochism · Nov 11, 2020

I agree with hardplates. I have a part that is 4340HT that I used to drill with a 5mm gun drill at 2400 RPM and 1.5 IPM, ~38mm/min. The hole depth was only about 178mm, but I could reliably drill 20 of these holes before thinking about replacing the drill.

Though we have moved away from gun drilling it to using a Mitsubishi solid carbide drill at 3878RPM and 29.5IPM, while being able to drill the whole order.

Though they don't make them as long as you need right now.

camhead420 · Nov 11, 2020

Hi,

I work at a company that works in the gundrilling field. My question is what is your approach for starting the hole. Are you doing a pilot? Just enough to get the drill to the shoe, or wear pad.

gregormarwick · Nov 12, 2020

Well, there is a hole in the part, I won't know if it's wandered much until I machine the other end.

I just copied CAMasochism's cutting data as it wasn't a huge departure from what I used previously.

Drill has a bit of wear again, but better. I guess the soluble oil is just a limiting factor.

CAMasochism · Nov 12, 2020

gregormarwick said:
Well, there is a hole in the part, I won't know if it's wandered much until I machine the other end.

I just copied CAMasochism's cutting data as it wasn't a huge departure from what I used previously.

Drill has a bit of wear again, but better. I guess the soluble oil is just a limiting factor.

That's pretty much how my drills would look, and yea the soluble coolant just doesn't work as great as oil would, but you work with what you got.

Also that there is a right purdy machine you got!

gregormarwick · Nov 12, 2020

CAMasochism said:
That's pretty much how my drills would look, and yea the soluble coolant just doesn't work as great as oil would, but you work with what you got.

Also that there is a right purdy machine you got!

Yea, the machine certainly is a joy to look at! And for the most part a pleasure to use, although I do have some occasional disagreements with the Celos Fanuc control...

Thanks all for the help.

cpifer3 · Nov 13, 2020

Just did some .250 holes , 17.5 deep in 4140PH . I was at 1600 rpm and .00045 IPR. Could get around 8 holes before re grind. This was with drill stationary and part turning, using sterling gun drill oil , and air mister around 180 to 200 psi I think .?

BSCustoms · Nov 16, 2020

if youre in the habit of sticking your drill intentionally deep in your parts I suggest getting a copy of the gundrillers handbook. Very much worth the money.

Jashley73 · Nov 16, 2020

Also, nothing wrong with spiking the concentration to get a richer, slipperie-er coolant for this.

gregormarwick · Nov 16, 2020

BSCustoms said:
if youre in the habit of sticking your drill intentionally deep in your parts I suggest getting a copy of the gundrillers handbook. Very much worth the money.

I'm not familiar with that book, and google returns a few possibilities. Can you provide a link?

Jashley73 said:
Also, nothing wrong with spiking the concentration to get a richer, slipperie-er coolant for this.

That will be a backup plan I suppose, I'd rather not unless I absolutely have to, this machine doesn't have low pressure CTS, only full high pressure or flood, so very rich coolant means foam.

BSCustoms · Nov 17, 2020

The Gundrilling Handbook

here yarrr bud.

Jashley73 · Nov 19, 2020

BSCustoms said:
The Gundrilling Handbook

here yarrr bud.

Worth every penny. Bought this for the boss in the past, while we were gearing up for a big & new to us gun-drilling job.

TeachMePlease · Nov 19, 2020

BSCustoms said:
The Gundrilling Handbook

here yarrr bud.

Just ordered my copy today. Thanks!

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Feeds and speeds for gundrilling

gregormarwick

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TeachMePlease

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atex57

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gregormarwick

Diamond

Hardplates

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CAMasochism

Stainless

camhead420

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gregormarwick

Diamond

CAMasochism

Stainless

gregormarwick

Diamond

cpifer3

Cast Iron

BSCustoms

Cast Iron

Jashley73

Titanium

gregormarwick

Diamond

BSCustoms

Cast Iron

Jashley73

Titanium

TeachMePlease

Diamond

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