Drill exhaust manifold

[Rabbit TD]

It's me again,  I'm getting ready to drill and tap the exhaust manifold  for the thermocouple when I get it and since it's cast iron I wanted to check with some of you more "machinist oriented" people as far as anything to watch out for.  I don't think I've ever drilled cast iron before that I can remember.  I have a drill press with the vise and all but I was wondering expecially since that looks like a pretty thick area there under the turbo and wonder things like what speeds to use, weather to start with a small hole and step it up or not too and other tricks machinists might know.  I've drilled and tapped before but not cast iron and I sure don't want to crack the thing and I know you can.  :?:  P.S. This is going to be the 1/8 NPT thermocouple.

[Jasonsmack]

Simple high speed drill bits work fine. I usually use a product called Rapid-Tap as a lubricant. It is not nessesary but it does promote a cooler and smoother cut and lengthen the life of the tools considerably. Your hole will fairly small so you can use alot of speed on the tooling. The speed is not going to make alot of difference on the final product, only how long it takes. You should not need to put hardly any downward force on the drill press to make a quick and clean cut in cast iron. The manifold will be a bit harder than a block or cylinder head but it is still one of the easiest metals to cut with simple tools. Overheating the drill bits will be your first and probably only problem if you have any. It is a good idea to use a small drill bit and work your way up to the desired size in two or three steps for a hole that size.

I often use chuck up a pointed centering tool in my milling machine or drill press to aid with the tapping of the hole. Without moving the manifold (assuming you are going to clamp it down somehow) you then remove the drill bit and use the centering tool in the chuck to hold the tap straight while cutting. The drill press will not need to be running to do this. There should be a cone shaped hole in the top side of the tap that you can insert the centering tool into. Again very little downward force from the drill press will be needed, just enough to hold the tools tight together.

[saurkraut]

A plug-in electric drill and two Cobalt drill bits (pilot hole and final) hozed down with WD40 works just fine too.

[Jettagli16v]

I didnt have to drill hardly any material at all...

If you use the preferred mounting location of this board (extra hole for DP support bracket, the one that usually breaks off or falls out)
you will need to remove very little material from that boss.

I drilled my larger hole (21/32 for tapping 1/8NPT, if I recall right) and did NOT penetrate all the way through, just went to the bottom of the hole that was already there. (basically just removing the threads that were already there)
THEN, I drilled a tiny hole in the middle of this for my probe to go through.
(Just a bit less material to remove)
and finally tapped the hole for 1/8NPT.

You should know that the NPT is a tapered thread, you will need to go all the way to the fattest part of the tap before the probe adapter will even start. (unlike tapping straight threads)

I recommend Jarvis USA taps, they cut cast like butter.
**Harbor freight taps are totally worthless and not even worth the $8 I paid for the kit (and thats saying a lot!)

-Brad

[Smokey Eddy]

I drilled mine with a hand drill. I think i went through 5 sizes to be safe. Used lots of oil. Lots of backing out.


Edit: one word of advice, be sure to drill it at an angle such that the tail of the thermocouple doesn't interfere with the block.