[slammedxonair]

Hello everybody I have a real quick question. What Can I do to drill out a hole I cut on my Dynatorch plasma table? I undersized the cut path Should have used 40 amp setting but I used 60. And I really dont have the extra material to get this prototype done. Drilling normaly is going to take forever to drill out these 4 holes.

Can I take a torch and soften the edges? I really need to get this done tonight. Thanks

[plain ol Bill]

I hope you have or have access to a carbide drill in the size you need. If not run to the neighborhood hardware store and get a concrete drill and use it.

[slammedxonair]

do the concrete bits hold up better on steel than regular dill bits?

[HuFlungDung]

If you intend to what amounts to step drilling the plasma cut hole, it is likely better to bore it than to drill it. A masonary drill can be sharpened so that it will drill hardened material from solid quite well, but it needs to drill the complete hole in one go because the drill point gets stabilized at the center of the hole.

When you try to skim out an existing rough, crooked, uneven hole, the masonary drill will not likely be stiff enough to drill in true position, and the vibration will be extreme and immediately knock the corners off the carbide.

If you began with mild steel, it is likely that the hard skin is very thin. You could grind that out of the hole with a carbide burr or small stone in a die grinder. Then you may be able to drill it with normal HSS drills.

I'd still advise boring the hole though, because I've seen some fairly awful holes cut with a plasma, but I'm think of thicker material that was difficult to pierce. A boring head in a mill will do the job. Interpolating the hole on a cnc is another quick way to fix the plasma cut hole.

[Torchhead]

Drilling hard material can be done with really slow RPM, heavy pressure and some thick lubricant. There is an old hand drill sold in the 1930'2 and 40's that used a crank and ratchet system called a Cole Drill. (http://www.rustyiron.com/engines/coledrill/index.html) You could drill any steel softer that a HSS Drill bit. The key is not to let the material get hot...that just makes it harder. A hand drill can't be slowed enough. You can anneal carbon steel by heating it very hot then cooling it slow. Old timers stick the hot steel into ashes or sand and let it cool over several minutes. Even soft the steel will work harden if you attack it with too high an RPM.

Depending on the hole size I have found milling holes with an end mill is sometimes better than drilling BUT you have to have a rigid spindle and clamped workpiece since milling is not self centering. Carbide mills have more shank meat than a similar sized twist drill. I don't think masonary drills would work very well in Steel.

Those of you that are fans of the "Machinist's Bedside Reader" will know what I'm talking about (:-)

TOM CAUDLE
www.CandCNC.com