Drill speed

[steve garro]

What speed would be ideal for drilling 1/2" holes through heat treat 4130 3mm thick?
Not milling, but just straight up punching big vent holes type of thing?
Can't recall, my shop teacher would be PISSED.
Thanks - Garro.

[Andrew R Stewart]

Steve- My Atlas lathe manual says 70 feet per minute for 4140, cromo. At 1/2" that's 500rpm. Don't know if this is the best but it's where I'd start. Andy.

[vulture]

around 300 rpm. 40 x 12 / .5xpi = 305ish. That would be: surface feet per minute of alloy steel(40)times twelve divided by the tool diameter times pi= rpm.

[Alistair]

What speed would be ideal for drilling 1/2" holes through heat treat 4130 3mm thick?
Not milling, but just straight up punching big vent holes type of thing?
Can't recall, my shop teacher would be PISSED.
Thanks - Garro.

Steve,

are you freehanding this with an electric drill or using a drill press?

In theory you're looking for about 60 surface feet per minute, so for a 1/2" bit that'd be 450 rpm. Drilling HT 4130 is a bit like drilling stainless though, if you don't cut a deep enough chip with each rev. of the bit you run the risk of work hardening the material. At that point I don't think even a carbide bit would work.

I would cut the theoretical drill speed in half, and press down hard to get the heavy feed that will get you good chip depth.

If you do end up work hardening the material around the hole you'll have to get the die grinder out and remove enough material to get back to stuff that's drillable. Or you could anneal it with your O/A torch.

Here's a link to a more detailed description, Drilling 4130 ("Johnny")

Good luck!

Alistair.

[Jacques]

3mm is practically nothing. Use a good center drill and rpm won't matter (500 is probably ideal).

[steve garro]

Steve,

are you freehanding this with an electric drill or using a drill press?

material. At that point I don't think even a carbide bit would work.



Good luck!

Alistair.

A brand new Grizzy heavy-duty drill press - I want to set it up as a dedicated venthole/big hole work station, freeing my mill to be permanently set up to well, mill.
I have been using nothing but either the mill or handdrills for ten years (go ahead, point & laugh)
and, since I have a 12-speed drill press now I was windering what the ideal speed is, since I can optimise that........
Great discussion, thanks guys!
- Garro.

[Eric Estlund]

I'm scratching away with a #2 96 Grobet for a good chunk of today, no one's laughing Steve!

If it's a dedicated vent hoe machine, you may want to consider stepped center drills (or possibly a unibit if its of great quality).

I use these in a hand held air drill for my vent holes.

[Willie1]

Last week I drilled a bunch of 1/2" holes in 3/8 1080 steel at 400rpm. Used a lot of tap oil and it worked really well. Not quite the same as what you are doing though.

[Bobqzz]

I'd be very inclined to drill a pilot hole then use a unibit

[Zimmermanbicycle]

+1 on this setup same thing I'm doing to good effect
-Eric

I'm scratching away with a #2 96 Grobet for a good chunk of today, no one's laughing Steve!

If it's a dedicated vent hoe machine, you may want to consider stepped center drills (or possibly a unibit if its of great quality).

I use these in a hand held air drill for my vent holes.

[bellman]

I know we are just talking about holes in tubes here but I want to second what Eric E said about the centering drills.
I use a 7/16" (smaller for chainstays) centering drill and it cuts the smoothest, roundest, fastest hole hole for me.
A 1/2" normal drill can go sorta choppy tri-corner on you without a pilot (especially on a tube )but the centering bits take it to full size really smoothly

The down side if it matters is that the shortness of the bit puts the chuck or spindle nose right down in the work.