Deep hole drilling on an engine lathe

[biednick]

I need to drill a deep, straight hole in a piece of stainless and am seeking advice on the best way to do it on an engine lathe. I haven't decided on the grade yet but I'm leaning towards 416. It'll be 15" deep, just over 1/2" in diameter, and a through hole. The final diameter isn't critical. A few thou off one way or the other is fine, but straightness and consistency is fairly important.

I do have the option of buying some proper gun drilling equipment, but I'm hoping to avoid that if possible. No round tube is available close to the dimension I need.

Since it's a through hole I figure my best chance of success is drilling from both ends so I'm doing 2- 15d holes instead of a 30d hole. After drilling I'll ream to final size from one end. As far as drills, I'm not sure what my best option is. I'm leaning towards starting with a jobber and drilling the rest of the way with an short flute extended length carbide bit. My thinking is the short flutes and carbide will provide better stiffness at the expense of chip clearing ability.

 

[Martin W]

Use a single flute gun drill.
Martin

 

[biednick]

Use a single flute gun drill.
Martin

Do you have any suggestions on chip clearing/coolant? I'm hoping to avoid using high pressure coolant, which is why I was shying away from gun drills.

 

[Jim F]

Joe Pie.

 

[Martin W]

I think you pretty much need flood coolant. That’s a pretty deep hole.
Martin

 

[Smithdoor]

I need to drill a deep, straight hole in a piece of stainless and am seeking advice on the best way to do it on an engine lathe. I haven't decided on the grade yet but I'm leaning towards 416. It'll be 15" deep, just over 1/2" in diameter, and a through hole. The final diameter isn't critical. A few thou off one way or the other is fine, but straightness and consistency is fairly important.

I do have the option of buying some proper gun drilling equipment, but I'm hoping to avoid that if possible. No round tube is available close to the dimension I need.

Since it's a through hole I figure my best chance of success is drilling from both ends so I'm doing 2- 15d holes instead of a 30d hole. After drilling I'll ream to final size from one end. As far as drills, I'm not sure what my best option is. I'm leaning towards starting with a jobber and drilling the rest of the way with an short flute extended length carbide bit. My thinking is the short flutes and carbide will provide better stiffness at the expense of chip clearing ability.

A deep hole is a pain
416 is also a pain.

I look at 300 series ss steel.
I take drill bit in and out lot so do not loose the drill


Dave

 

[Chipper5783]

How many pieces? Obviously you’re aware that chip management is the issue. If it is just a couple pieces, get a long twist drill and go for it - a lot of back and forth, clear the chips, blow them out (don’t get greedy and let the chips pile up in the drill bit deep in the hole). I’ve cut quite a bit of 316/416 - I’ll take 416 any day (look up the machinability index).

 

[biednick]

A deep hole is a pain
416 is also a pain.

I look at 300 series ss steel.
I take drill bit in and out lot so do not loose the drill


Dave

I've cut plenty of stainless, and I'll take 416 over any 300 series other than maybe 303. It'll either be 416 or 17-4. I still need to crunch some numbers to see if 416 is strong enough, but my gut and some quick hoop stress calculations say yes. H1150 will be more than strong enough and machines beautifully. It's just more expensive and I have less experience with it and thus less confidence in my ability to successfully drill it.

 

[biednick]

How many pieces? Obviously you’re aware that chip management is the issue. If it is just a couple pieces, get a long twist drill and go for it - a lot of back and forth, clear the chips, blow them out (don’t get greedy and let the chips pile up in the drill bit deep in the hole). I’ve cut quite a bit of 316/416 - I’ll take 416 any day (look up the machinability index).

Just 1. I think going slow and using the tips in the video above should work well. I'm not considering any 300 series due to the machinability, but may end up with 17-4 for strength.

 

[Charles scozzari]

I have had success drilling coming in from both ends ( flipping the work end over end ) by using a smaller diameter bit first then the finish bit at full length in one shot.