Tapping - is this just the way it is?

Maplehead said:
It appears that a new Tapmatic tapping head is around $700. Are the used ones on eBay considerable? I usually shy away from used as you never know how much the wear effects operations/results. However, used is $350 down to $75. Your thoughts?
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Be sure to get one that includes all the collets for different sizes of taps. It may be difficult to find those after you buy the tapping head.
-brino
 
I'm concerned about the spacing of the tapped holes.
Do the threads of adjacent holes intersect? In other words, what is the design wall thickness between adjacent tapped holes?

If the threads intersect or if the crest to crest wall thickness can be less than .015", I think I would tap every other hole. Then install a threaded member into each tapped hole, for support. Then finish tapping. If the threads overlap (zero wall thickness) the threaded member should not be harder than the workpiece. If there is a guaranteed wall, I would use socket set screws.

My thinking is that the cutting forces will deform the hole at the thin (or non-existant) wall, resulting in on out-of-round condition and a higher risk of breaking a straight flute tap.

A spirol flute tap should be much less influenced by thin wall.
 
I know nothing about how this will react under power threading. However, I have done a few of these via hand tapping. The holes are super close to each other. After I tap them I then take a 1/16" end mill with a 5/8" cutting length and I slot the columns. This is to allow the strings a space to travel through to where they anchor below. After I slot the columns I re-tap the holes to fix any deformities. So far everything has worked out fine. How this will go under power tapping is anybody's guess right now.
 
UPDATE:
So I bought a used Tapmatic 30X. This afternoon I tried tapping those 48 holes, #6 x 40 with the recommended taps you all mentioned.
Holy Moly!!! This tool has got to be the coolest ever. What used to take 15 hours by hand and was nerve racking wondering if every turn I was going to break the tap has now become an easy peasy quick deal. I did all 48 holes in under 20 minutes. I say to anybody considering one of these - get it, you will not regret it.
Thanks to all that recommended it.
 
Yep, a tapping head is terrific. I have a Procunier 2E, and as Brino mentioned, it can be a hunt to collect a full set of collets. However, it’s an amusing project to make your own, with the only tricky part being an internal square hole holding the end of the tap.
 
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