Doubts about deep drilling in metal with an HSS drill

[Wesley souza]

TL;DR Summary

Doubts

hello my friends, the other day I read that the barrels of firearms before 1930 (the birth of gundrills) the barrels were forged from plates until they became a tube and later, they were made from steel bars that were drilled with welded HSS drill bits. Does anyone have experience with the deep hole process with an HSS drill? Would it be possible to recreate this process nowadays, inside a garage?

 

[DaveE]

You want to make firearms in your garage? Maybe buy one of these:
https://www.grizzly.com/search?q=gunsmithing+lathes

 

[jrmichler]

I have, from time to time, needed to drill deep holes in steel. Hence my collection of welded twist drills:

Yes, it's possible to drill deep holes in steel with welded HSS twist drill bits. Some things to be aware of:

If you read old gunsmithing books, you will find extensive discussions of how to straighten gun barrels. That is because twist drills inherently drill curved holes. It is a result of the design of a twist drill.

Drilling deeper than the length of the flutes requires peck drilling to get the chips out.

Twist drills have large tolerances on hole diameter, even if the drill is properly sharpened. Reaming is necessary.

It's difficult to make straight holes with a gun drill. Gravity makes the drill shank sag, which causes the hole to curve upward. But a gun drill will make straighter holes than a twist drill, the diameter tolerance will be much tighter, and peck drilling is not necessary.

So, yes, it is possible. But do not expect to make match grade barrels.

 

[DaveE]

Reamers too. Yes HSS can cut steel, if you do it right.
https://www.grizzly.com/search?q=gun+reamers

 

[Baluncore]

The key to drilling barrels is to turn the barrel, not the drill. When the barrel rotates there can be no up or down. That way the long drill can sag, but it will straighten inside the hole, and so still drill a straight, but slightly oversized hole.

Hold the drill in the tailstock of a lathe, while the barrel is turned in the headstock. You will need a cats-head to support the barrel where it extends through the head bore.

Extend the drill with a thinner tube, (not a solid bar), so you can force coolant up the drill stem to the cutting edge. The coolant will flush the chips back, outside the drill and tube.

Make a flat drill, sharpen it a bit like a negative rake tool, so it produces crumbs or small chips. Make sure there is a path for the chips to be flushed continuously back from the cutting edge. Above all, avoid normal drill profiles that are designed to produce clean cut helical turnings.

 

[anorlunda]

If you begin with a barrel forged on a mandrel, there is much less material to remove by drilling.

 

[Averagesupernova]

The key to drilling barrels is to turn the barrel, not the drill. When the barrel rotates there can be no up or down.

^^^^This. I've found drilling the center of a shaft in a turning lathe is the only way to go.

 

[Baluncore]

If you begin with a barrel forged on a mandrel, there is much less material to remove by drilling.

There is a rotary way of forging on a mandrel. To make a blank barrel you can pierce the centre with a mandrel. Then finish bore and ream the tube.
https://en.wikipedia.org/wiki/Rotary_piercing

You can make longer smaller bore tube by drawing a thick tube to progressively reduce both the outer and the inner diameters.

200 years ago, the wooden wind shafts of windmills with patent sails were bored to house the sail control rod. A "bullnose" auger was used that produced small shavings. I cannot help thinking the same technique was not used later by gun makers.

To make a long auger drill with a pair of coolant holes, flatten most of a thick walled tube. The centre hole will close except for a thin line on each side that will become the coolant channels. Twist the flattenned tube to make the auger, then weld on the HSS cutter material.

 

[Wesley souza]

The key to drilling barrels is to turn the barrel, not the drill. When the barrel rotates there can be no up or down. That way the long drill can sag, but it will straighten inside the hole, and so still drill a straight, but slightly oversized hole.

Hold the drill in the tailstock of a lathe, while the barrel is turned in the headstock. You will need a cats-head to support the barrel where it extends through the head bore.

Extend the drill with a thinner tube, (not a solid bar), so you can force coolant up the drill stem to the cutting edge. The coolant will flush the chips back, outside the drill and tube.

Make a flat drill, sharpen it a bit like a negative rake tool, so it produces crumbs or small chips. Make sure there is a path for the chips to be flushed continuously back from the cutting edge. Above all, avoid normal drill profiles that are designed to produce clean cut helical turnings.

thank you my friend for being so helpful. I would like to know more about the flat drill. could you bring some drawing or something that makes it clearer for me?

 

[Wesley souza]

If you begin with a barrel forged on a mandrel, there is much less material to remove by drilling.

thanks for your support

 

[Wesley souza]

De tempos em tempos, precisei fazer furos profundos em aço. Daí minha coleção de brocas helicoidais soldadas:
View attachment 297439
Sim, é possível fazer furos profundos em aço com brocas helicoidais HSS soldadas. Algumas coisas para estar ciente:

Se você ler livros antigos de armeiros, encontrará extensas discussões sobre como endireitar canos de armas. Isso ocorre porque as brocas helicoidais perfuram inerentemente furos curvos. É resultado do projeto de uma broca helicoidal.

Perfurar mais profundamente do que o comprimento das estrias requer furação para retirar os cavacos.

Brocas helicoidais têm grandes tolerâncias no diâmetro do furo, mesmo se a broca estiver bem afiada. A fresagem é necessária.

É difícil fazer furos retos com uma furadeira. A gravidade faz com que a haste da broca ceda, o que faz com que o furo se curve para cima. Mas uma broca canhão fará furos mais retos do que uma broca helicoidal, a tolerância do diâmetro será muito mais apertada e a perfuração de pico não é necessária.

Então sim, é possível. Mas não espere fazer barris de grau de fósforo.

Thanks

I have, from time to time, needed to drill deep holes in steel. Hence my collection of welded twist drills:
View attachment 297439
Yes, it's possible to drill deep holes in steel with welded HSS twist drill bits. Some things to be aware of:

If you read old gunsmithing books, you will find extensive discussions of how to straighten gun barrels. That is because twist drills inherently drill curved holes. It is a result of the design of a twist drill.

Drilling deeper than the length of the flutes requires peck drilling to get the chips out.

Twist drills have large tolerances on hole diameter, even if the drill is properly sharpened. Reaming is necessary.

It's difficult to make straight holes with a gun drill. Gravity makes the drill shank sag, which causes the hole to curve upward. But a gun drill will make straighter holes than a twist drill, the diameter tolerance will be much tighter, and peck drilling is not necessary.

So, yes, it is possible. But do not expect to make match grade barrels.

thanks for your support

 

[Wesley souza]

The key to drilling barrels is to turn the barrel, not the drill. When the barrel rotates there can be no up or down. That way the long drill can sag, but it will straighten inside the hole, and so still drill a straight, but slightly oversized hole.

Hold the drill in the tailstock of a lathe, while the barrel is turned in the headstock. You will need a cats-head to support the barrel where it extends through the head bore.

Extend the drill with a thinner tube, (not a solid bar), so you can force coolant up the drill stem to the cutting edge. The coolant will flush the chips back, outside the drill and tube.

Make a flat drill, sharpen it a bit like a negative rake tool, so it produces crumbs or small chips. Make sure there is a path for the chips to be flushed continuously back from the cutting edge. Above all, avoid normal drill profiles that are designed to produce clean cut helical turnings.

I was looking for flat drill sharpening and found this video. the sharpening of the drill bit in this video, if I'm not mistaken, looks like the sharpening used on gundrills. would it be correct?

 

[Baluncore]

The rake angle of a twist drill is set by the helix angle of the drill. As a twist drill cuts, the swarf is coiled and rides up the inside of the flute at the rake angle.
See; https://en.wikipedia.org/wiki/Rake_angle

A low or zero rake will push the material away, sheared into chips, rather than produce a long helical turning that cannot be flushed out of the hole.
By using a flat plate, (like a spade bit without the point), and grinding a slight relief angle on the end, you can make a cutter with a low rake angle. The feed rate will be very low.

A negative or zero rake would require a carbide cutting edge, which would be hard to drive. A HSS cutter could have a low positive rake. A good flow of coolant would be needed, which would also flush the chips out of the hole. You will need to experiment with different rake angles until you find the angle that makes small chips, without getting too hot, or wearing too fast.
Consider making a gun drill with a HSS tip;
https://en.wikipedia.org/wiki/Gun_drill