cleaning up drilled holes

[markw]

Similar times. They go through rotors like butter, used them to re-drill 5x4.5 into WJ rotors with 5/8" holes. Depends on the angle of the hole, you center punch the center of the hole, then lightly apply pressure. The video shows them punching holes in tubing pretty quickly. I've used them for punching through 1/4" and 3/16" plate all the time. The small set which goes from 5/16" to 3/4" was about 60 bucks, once you get a set you won't go back to twist drills, and if you do, you'll want to get a good set of twist drills like norseman or something.


Here's 7/16" hole in .250 plate I did for my bumpstops. Bit hits the plate at 48 seconds and is through at 54 seconds. I love these things.

https://www.youtube.com/watch?v=wxzPwu2JUgc

 

[md21722]

I was thinking of my experiment in drilling 1/2" holes through cast iron differential housings. The drill guide I looked at said about 450 RPM for drilling 1/2" through cast iron ...

 

[Original_MudButt]

If you plan on doing more fab work, keep this formula: R.P.M = 3.8 x (S.F.M./Drill Diameter).
S.F.M. = "Surface Feet per Minute" which is different for every material and can be found in the machinery's handbook among other places.

In your case the S.F.M. for grey cast iron using a HSS bit is 100, so:
3.8 x (100/.5)=760 R.P.M

1) Slower is better than faster. It will take longer, but you (probably) won't dull the drill bit.
2) There are other factors such as machine rigidity, tool bits and/or coatings (ie; titanium nitride, cobalt, carbide, etc.), type of lubrication... So on.
3) Experience is a very good teacher, but the above formula will get you started.
4) In life, in all things, lubrication is the key. Just about anything will be better than nothing, although WD-40 sucks as a cutting fluid. I like Tapmatic Edge gel.