tips on modifying a tap for mill

??? Didn't you say you already basically ruined as a regular tap ???

I have made taps out of bolts before. They work good for chasing a thread, but only fair for tapping a smooth hole. I have made taps out of acme threaded rod before. They work awesome in plastic, and horrible in aluminum. Ok. I have some threaded couplers made out of aluminum I tapped with one, but it was a nightmare.

For tapping with the mill I have a small 3/16 right hand boring bar and a

3/16 left hand boring bar that have a nice 60 degree point. I use these with Mach 3 NFS threading wizard, or if I am being anal I create a helix in CAD, and then tool mops relative to it in CAM.

I've never used an actual tap on one of my mills. I do use a small tapping head on one of the drill presses though. Nor have I deliberately broken a tap... the truth of which is not necessarily born out by the number broken taps I have thrown away...

If any of that helps... Yeah! I am a hero. If not, then I'll waive the consulting fee.

"Bob La Londe" fired this volley in news:1HU0r.8235$I% snipped-for-privacy@newsfe16.iad:

Yeah, but it's my only one, and it's "sort of" working as a threading mill right now. Just don't want to make it worse.

I started out with a 3/16" boring bar, Bob. It was too flexible, and just sang to beat the band. The tap cuts quietly.

I'll try making up a LH boring bar, and cutting in climb.

Lloyd

You can always make a much bigger boring bar.

You beat me to it. With nearly 3/4 of an inch of hole to play with, you should be able to make a nice stout boring bar and use an insert for the sharp part.

Not, mind you, that I've ever done this myself -- I've ground tools for inside single-point threading out of tool steel, but I haven't made an actual monotonous rod.

Tim Wescott fired this volley in news:KNKdnUT2QqhGgNnSnZ2dnUVZ snipped-for-privacy@web-ster.com:

Yeah... I'm going to have to run the trig on the point. Obviously, since it's cutting a little on the lagging bottom shoulder and a little on the leading top shoulder, then unlike a regular 60-degree point, it's going to have to be a smaller angle.

And that may very well be why my tap isn't giving a decent cut, yet.

Lloyd

have you heard of the Devlieg microbore line?

A very rigid bar holds a brazed carbide insert. Grind the insert to a

60 degree angle but with a lot of relief on the bottom (for threading right hand going down)

You really need a good baldor carbide grinder and preferably an optical comparator to check your grinding. Given all this, single point thread milling "werks grate"

Karl Townsend fired this volley in news: snipped-for-privacy@4ax.com:

Karl,

I can't even imagine how an adjustable boring bar would help in this case. I have an adjustable boring head of the off-set slide type.

But insert-style (indexable carbide, and not) internal threading tools are a LOT cheaper, and in this case, more flexible than that... those cartridges are outrageously expensive.

The grinding of a healthy relief on the bottom is important, but more important would be grinding the angle to less than 60-degrees to make up for cutting on the lag and lead.

A single-point threading mill would give its best profile when as small a cutter radius as possible, commensurate with enough stiffness and thread depth.

LLoyd

I have a single point one I made up by off-hand grinding an old 5/8 many years ago that I still occasionally use for 3/4 and larger npt--it takes several minutes to actually machine a thread this way as opposed to only taking a few seconds when an actual thread mill that has multiple teeth is used....

Also, where a single point tool is used, you're still probably better off to finish by chasing with an actual tap afterwards.

A modified tap is NEVER going to give you a decent cut unless you completely grind away all but one flute, then grind all but one tooth off of the remaining flute, and THEN grind a portion of the upper face of the single remaining tooth away in a manner that provides a proper primary clearance angle on BOTH sides of the resultant 'vee' tooth form.

END MILL

ya, you want about 1/2 or at most 2/3 diameter from single point tool to bore on thread mill. I scored a whole set of micro bores real cheap, also drawers and drawers of inserts. I like to grind the form on just the brazed insert with the baldor and then put it on the optical comparator. I've done threads, timing pulleys, and gears this way. Works a treat.

Probably a case of use what you have.

karl