[mhackney]

I'm interested in any experience, products and advise folks have regarding tapping small (2-56, mostly 4-40, 8-32) holes in primarily brass and aluminum. I mostly tap through holes up to 5/8" and blind holes 3/8" deep.

regards,
Michael

[rowbare]

Check out these threads: http://www.cnczone.com/forums/tormac..._question.html
http://www.cnczone.com/forums/tormac...ds_advice.html

In particular, check out the posts by Don Clement. He does a lot of small hole tapping and has shared a lot of good information about his approach to it.

bob

[mhackney]

Thanks Bob. I saw that Tapping Question post but not the 2nd one. I've done a bit of research here and on the web. Seems to be a fair amount of info on tapping aluminum but not much on small (4-40) in brass. Brass is a PIA - it grabs the tap and snaps it right in half. When I hand tap, it is 1 turn in, 1/2 out, 1 in, 1/2 out. I have tapped 1000 holes that way with no tap breakage but I am not sure how that would translate to a tapping head or CNC process. The constant in/out seems like it would be a problem for automation.

Cheers,
Michael

[samco]

I don't know the actual specifics of tapping those materials - but taking your point about going in 1 turn - back out - in 1 more turn - back out. This could be done with EMC2 and rigid tapping. The spindle encoder with an index would start the threads the same way each time. so if your spindle could stop decently - you could setup a gcode program that would in effect peck tap - in, out, in further, out, in further yet.. and so on. I would think any commercial control with rigid tapping capability would also do the same.

Edit - with emc - you cannot do the 1/2 out thing. It would have to go all out - then back in say - 1 more turn. (unless you made the spindle an axis... )

sam

[hoss2006]

You could set up a tapping attachment and write your own programs to have mach 3 tap the holes.
Projects 8
This a one of the programs I made to do a partial retract for a 16 tpi thread.
I tested an 8-32 tap in aluminum without breaking.
The springs in my tap holder were so stiff that it was, for all intents and purposes, rigid tapping with taps that small.
Hossmachine Store
Hoss

[mhackney]

I like that setup Hoss and have been considering it. Just wanted to do one last check for info before diving in!

cheers,
Michael

[hoss2006]

With 2-56 or 4-40 you'll need zero mechanical backlash on your Z axis to lower the risk of snappage.
We had good luck at work using one of the small Procuniers with 2-56 taps 3/8 deep in aluminum and brass.
Had it in a small drill press and the operators could go for hours before snapping one.
Hoss

[mhackney]

I've been looking at the procuniers and tapmatics (used of course). The smaller versions of each look to be about right. I just don't have experience to know if you need to back out every turn with these or if using a spiral tap might help. I suppose I could experiment. I like the idea of using my drill press since that would free up my mill to make the blanks that I would need to drill and tap. I suppose if I found a good deal on a tapping head I could try it and always get my money back if it didn't work.

My G0602 is due to arrive today so I am going to be busy for a while getting that set up!

Cheers,
Michael

[LongRat]

Thought about thread milling? I recently tried it on my BF30 with very good results. If the tap tends to grab the thread mill might be a nice way around that.

[mhackney]

I'm not familiar with thread milling. I'll look it up, thanks

Cheers,
Michael

[hoss2006]

The smallest size procunier would be best. It has more feel to it since it depends on how hard you push
down on the quill handle.
You control by hand how deep you go and can retract as much as you want.
The drill presses depth stop can be used for final depth.
If you stop pushing midway in it will just stop turning and reverse when you lift up on the handle.
I'd love to get ahold of one sometime too.
Spiral taps work great since they pull a long curl of a chip that comes up out of the holes,
much less chance to clog up.
Hoss

[keebler303]

Thought about thread milling? I recently tried it on my BF30 with very good results. If the tap tends to grab the thread mill might be a nice way around that.

Break one 4-40 thread mill that cost you $150 and you will quickly switch back to taps.

Form taps on the handle would probably work well here, just make sure to use the right drill bit and a good oil.

Matt

[thedave]

Depending on how many holes you need to tap at a time, a tapping arm might do the trick. I built one and have had good success with it. I have around $ 175 in to the tapping arm, including the tapping tool. I am still running a manual mill so I don't get the full benefit out of it. I tapped 80 1/4-20 .75 deep and 60 8-32 .5 deep blind holes in less than an hour using forming taps, not including waiting for battery charges. I get 20ish taped holes per charge on the 1/4-20 and 40 ish on the 8-32. I am going to figure out how to hard wire the power screwdriver to solve that issue. I used the general design on the arm from CNC Cookbook, and a Dewalt cordless screwdriver. I am using 1/4" socket tap adapters to hold the taps. I doubt the power screw driver has the torque to tap anything larger than 3/8. I will run some tests. I had to tap 4 1/4-20, /5 deep through holes last night, 45 seconds. Total tapping time from mill, including setup, 92 seconds.

CNCCookbook: Tapping Arm (scroll to the bottom)
DW920K-2 1/4" (6mm) 7.2V Cordless Two-Position Screwdriver Kit | DEWALT Tools

I will post images and a build log in the next week or two.

[rowbare]

I think form taps are the way to go for these small holes. You don't have to worry about chip evacuation or cleaning chips out of tiny holes and the taps are stronger to begin with. Google "using form taps on brass" and see what people have to say.

bob

[thedave]

The forming taps have been great on aluminum. I have had good luck with OSG forming taps. If you use forming taps, remember that the hole sizes are different. I think you tap at 50-65%. I found this out the hard way. Check with the manufacturer.

[hoss2006]

FWIW it's been my experience that roll form taps wear out sooner than spiral cutting taps
especially in the brass parts we made.
We had to meet a thread gage tolerance but you might not need to be as critical.
Hoss

[mhackney]

I do not have critical tolerances to maintain. "Kentucky windage" should be fine. I have a lot of stuff to check in to now! Thanks everyone!

I will be making parts in 100 unit batches. One part starts as 1/2" x 3/8" x 2 1/2" brass bar. It will have 2 holes tapped 4-40 on its narrow face (3/8") on 3/4" centers. So the tap is through 1/2". Other parts are much simpler and not as deep.

cheers,
Michael