Newbie- Initial thoughts on tapping

[LuckyStrike]

I was wondering if anyone could put up a really quick "thread tapping 101" for a 3 axis CNC lathe covering tools, types of tapping, adaptors needed etc? We're considering moving to cnc from hand tapping but don't know to much about how to implement it with CAM and the machine. Cheers everyone! =)

[LuckyStrike]

Genius here forgot to put materials. We'l mainly be tapping aluminium but might work with plastics such as PMMA and PTFE occasionally.

[DareBee]

Does your lathe have rigid tapping capabilities?

[LuckyStrike]

I don't believe so, no. I'm assuming I'll be looking at one of the geared attachment jobbies I've seen about, but I'm not too sure hence this post

[Crashmaster]

I tap on my CNC lathe, which does not have rigid taping. We bought this Tap holder from Somma, and couldn't be happier...

http://www.sommatool.com/catalog/too....floating1.asp

[LuckyStrike]

Looks pretty good but 'm still not too sure as to the actual basics of cnc thread tapping. Once I know what's actually involved I'll look into buying an adaptor, but I'll definitely bear that one in mind

[Geof]

"thread tapping 101" ?

First drill the hole, the correct size is preferred.

Then run the tap in and out.

Okay, I admit I am being a smart ass; but really that is it. Most lathes have one or more tapping canned cycles, G84 is the one I use on a Haas machine.

For the G84 you program the starting point, final depth and the feed rate, with Z zero at the end of the part an example for a 1/2" deep 16 tpi hole would be:

G84 Z-.5 F.0625 R1. (Sorry I don't think in metric, brain is too old)

The R value is the location at which the machine starts the feed and gets it synchronized with the spindle rpm. Because this can take a short distance it is a good idea to have R several pitches away from the end of the work, although 1" is a bit of overkill.

The feedrate F has to match what the machine is using, feed per rev or feed per minute; normally on a lathe feed per rev will be used.

The spindle rpm is somewhat flexible; aluminum taps better in my experience if the rpm is in the high hundreds or a thousand or two with plenty of good rich coolant. But there is a limit; it is possible if the rpm is too high the machine will not be able to feed fast enough.

Obviously the machine has to stop the spindle and feed and then back things out and during this operation synchronization may be lost a little bit unless the machine has Rigid Tapping mentioned below. To allow for poor synchronization the tap is held in a floating holder which is balanced between springs and can move axially a small distance to allow for poor synchronization during reversal.

On machines equipped with Rigid Tapping synchronization is NAD perfect so the tap can be mounted rigidly in a collet holder; which must hold the tap straight and on center otherwise it will make an oversize or tapered thread, or break.

When Rigid Tapping is available on the machine Repeat Rigid Tapping may also be possible; this allows a deep hole to be tapped in a series of pecks that permit chip clearance.

[LuckyStrike]

Perfect! I suspected it would be something as straightforward as that, so thanks for clarifying everything. I think we'll probably end up getting a tapping system if it's going to be this easy to implement. Cheers for the heads up about the heads up about a synchronisation distance too - sounds like the kind of thing that could have led to me milling several buggered bits of aluminium before working otu what was going on

[Geof]

Originally Posted by LuckyStrike ..... Cheers for the heads up about the heads up about a synchronisation distance too - sounds like the kind of thing that could have led to me milling several buggered bits of aluminium before working otu what was going on

BTDT

[LuckyStrike]

Haven't we all? I still remember trying to catch a piece of perspex that climbed the spindle at 10,000rpm...

[Geof]

Originally Posted by LuckyStrike Haven't we all? I still remember trying to catch a piece of perspex that climbed the spindle at 10,000rpm...

If you are lucky and survive such an experience with all body parts intact your learn that the best procedure is heading down behind something as the material goes up.

Sometimes I think there should be a secondary Estop button at floor level so you can hit it on the way down.

[LuckyStrike]

I like that floor estop idea. Thankfully I was only machining a tiny piece, about 1 by 2 inches. Still, smarts a bit when it zips your fingers a few hundred times a second