Newbie- Form Tapping

[behindpropeller]

I'm looking for some advice on form tapping. What is a good RPM for a TM series mill? What is the largest suggested form tap?

edit: Material will be 6061T6

Thanks

Tim

[Get lucky]

I don't form tap any thing over 1/4 with a form. speed all depends on wear in the machine but most of my tapping cycles are running at about 1400 rpm's with quality taps.

Kyle

[1ctoolfool]

I have tapped up to 1/2-13 with OSG thread formers all day long at 1000 rpm with no problem with a VF-2. Make sure you use the right starting hole diameter and gracious chamfer as the form tap will upset material upward. for instance recommended .460" start hole for 75% thread for 1/2-13. I use .470" (vs. .421" for regular tap)

osg website has a calculator for form tap hole sizes.
http://www.osgtool.com/Technical.asp?tid=1&id=1

I would form tap larger if the taps were available, hard to find larger than 1/2"

also i have thru tapped (normal gun-type tap) 3/4-10 into 1/4" mild steel at 500 rpm with a TM-2 no problem. single pass with slightly oversize tap hole.

[bigbaz]

Use a top quality cutting fluid or you will break taps.