tapping cast iron & other stuff

I'm out in the garage right now converting a set of small block heads to screw in studs and I'm at the tapping stage, using Goodson's guide and all. I got thinking about what tapping fluid I should use, I've got Rapid-Tap, etc. and know some use Marvel Mystery OIl, etc. Just wondered what you guys have found that works well. Thanks

 

I was taught to tap cast iron dry, always have, and never had a problem.

Bob

 

Cast Iron is usually done dry.

 

cut with saw dry, tap dry, old grey iron is not tuff....

 

Thanks guys, I appreciate it.

 

Cast iron can be tapped dry or you can use a cutting fluid such as tap magic.

 

Good Tap is very needed to get good T,and never use fine T in soft metals,run in 1/2turn and back off 1/4turn,repete,every 3 full turns clean [air]out trash.

 

i always use lube helps prevent rusting in the thread , it also saves wear and tear on the tooling , cast iron can be abrasive RAPID TAP is my choice and then spray it down with WD40 to prevent rusting i used to do rotory spools for logging equipment and there would be 20/25hrs of machine work

 

Winner

 

Goodson makes a little kit for this, a pretty nice tapping guide/stud puller, a drill bit, a spot facer for the stud boss, and a tap that actually is laser etched with "cast iron" on the side along with the size. It went really well, one head is now done and I'm going back to my "slapping and shrinking" on the rear fender of the 50 Pontiac. Currently, it looks like lumpy oatmeal from a long ago repair, but I'm learning how to make this shrinking disc work and it's pretty interesting.

 

i was always taught to tap cast iron with compressed air only

 

We use tap magic on low volume proto-type work. We use TapFree 2 on our production machining, smaller taps, 5/16-18 and below. On the larger sizes, above 3/8-16, we just run the castrol clear edge coolant already in the machine.

We tap somewhere on the order of 70-90,000 holes a year in cast iron. Check damned near all of em with go/nogo gages. Mistakes cost money

For tool steels, castrol moly dee is great, but expensive, and it will severely stain yellow metals. Tap magic is always the fall back