"DoN. Nichols" wrote in
:

On 2010-01-10, Doug White wrote:
snip
For a home shop with a smallish mill (Clausing 8520), could someone
in the know help recommend a specific Tapmatic model?. I've been
thinking about getting one for a while, but I'm unclear on the
practical differences between the Rx, TC/DC & X models. I'd be
looking at a size 30, and all models seem to be about the same
length. The TC/DC has an "adjustable self-feed", which the others
don't, but I have no idea what that means. The TC/DC also has
"adjustable depth control for blind holes", which sounds useful.

Should I be looking for a TC/DC, or are the others just as good? I'm
looking for maximum flexibility & idiot-proofness.

O.K. I would have to dig up the listing of what is what to be
sure. (Or -- go downstairs to a far too cold shop far too late in the
day. :-)

No rush, and I can sympathize. My shop is already getting too chilly
even for brief forays when it's not worth turning on the heat. The temp
in the Boston area isn't supposed get above freezing until Friday.

But the features on the two which I have (one a 30 size and one
a 50 for larger taps) have the following differences which I consider
important:

1) The smaller one (I think a 30X, but I am not sure) has a collar
at the top which sets a torque limit. The advice for using it
is to start with it set to the lowest torque, and put a brand
new tap in the head, and try tapping the workpiece material and
size which you are using. Keep increasing the torque setting
until it goes through with no trouble -- and adjust it just a
tiny bit higher.

Now -- keep tapping using these settings until it starts to slip
again. At this point, the thing to do is to remove and discard
the tap which you are using, and install another brand new one.

This, obviously, is for production, and is the best way to avoid
broken taps.

This sounds fine, except for blind holes. Do you have to rely on a
depth stop, fast reflexes, or just not doing them?

2) The larger one does not have the torque limit, but has an
adjustable collar on the tap chuck which sets how far the chuck
has to travel before the dog clutch releases and the tap is free
from the spindle. This is important when you are tapping
shallow blind holes. You need to have the tap head set so the
dog clutch will release from a starting point where the tap just
touches the workpiece (so it *can* self start) and yet can
release before touching the bottom of the hole. You need to set
the drill press or mill spindle stop so the dog clutch will
release before the tap jams against the bottom of a blind hole.
And you need to adjust the collar to start the tap reliably.
Normally, there is quite a bit of free feed before the dog
clutch disengages and stops the tap from turning. This is fine
with through holes, but is a problem with blind holes. Note
that this larger one does not have the torque limit, but it
handles taps from 1/4" (IIRC) up to 1/2", which are harder to
break in the drill press. (It would still be nice to have that
torque limit to set for the tap which I am using. :-)

Hmm. I thought they all had a torque limit. I'll be curious to here
which model is which.

Now -- the "adjustable self feed" may be for tapping in a CNC
mill which does not have spindle thread feed capability, so once it
starts to cut, it pulls the tap down as needed, and your CNC counts
the turns of the spindle and then stops and reverses it. (This may
not have a reversing gear inside it the way the two which I have are
set up, depending on the CNC to reverse the spindle instead.

The Tapmatic website has stuff broken into two areas, one for CNC & one
for manual stuff. The TC/DC is firmly encamped under manual tapping.

Essentially -- you need to download and read the manuals for
each to see what it is intended to work with. Mine are for manual
Mills and drill presses. Others only work on CNC mills, or something
like an automatic screw machine (lathe), so you need to get the right
one for what *you* will be using it with. Unless you have the CNC
mill with the right spindle programming, you probably don't want the
"adjustable self feed" version. And you certainly don't want a "rigid
tap holder" (which is probably a lot less expensive).

And -- remember that the 30 series can only go up to 1/4" (or
some only to #10 screws) -- and the torque limit is assuming thread
cutting taps, not thread forming taps which need more torque, so you
may not be able to use them up to the full size of the tapping head's
claimed range.)

The size 30 would be fine for my needs. I rarely go above 1/4-20, and
I'm very unlikely to have enough larger holes to warrant getting a head
that won't do 4-40 & 2-56. Eventually, I might get both sizes, but I
should definitely start with a #30. They are limited to #10 for thread
forming, which is fine for my needs.

But -- my larger one was really nice when I had about 40 1-4/20
holes to tap in 1/4" thick mild steel. The main trick was modifying
the drillpress table to hold the length of the workpiece. I did that
with two 2x4s secured from below by lag screws through the slots in
the table. And I was always careful to clamp it down with a
Kant-Twist for each new hole -- and position the stock so if the
Kant-Twist slipped, the column would keep the workpiece from rotating.

I assume you used the bigger one because A) you had it, and B) you knew
it would be trivial for it. Given that the size 30 is rated for 1/4-20,
did you think it wouldn't actually handle it? I've been assuming that
their capacity specs are accurate.

Thanks for the info.

Doug White