"Bob La Londe" wrote in message news
"James Waldby" wrote in message news
On Sat, 01 Dec 2018 19:56:13 -0700, Bob La Londe wrote:
On 11/29/2018 2:18 PM, Bob La Londe wrote:
On 11/29/2018 1:24 PM, Bob La Londe wrote: I bought a commercial
tension compression tapper for use on my
non-C-axis CNC mills. [...] lately I've found myself
tapping three different sizes commonly. [...]
My solution. Make a couple more TC tappers. The first two blanks I
destroyed on the lathe by trying to shade tree it. Nothing is
really critical except that the bore for the tap holding collet
chuck and the shaft of the TC tapper are concentric. Well on the
third one I had some success, but I failed to get the proper
alignment turning concentric. [...]
Mine is in front:
http://bbs.homeshopmachinist.net/attachment.php?
attachmentid=4017&d=1543523014
Anyway, I thought about my steps and processes and I know how to
make the next one better. Now I am thinking about materials. The
first ones were all made out of 304 stainless except the straight
shank collet chuck which [...]
I was busy cutting molds and inserts all day today for customers, so I
didn't have time to make another TC tapper. I did modify the first one I
finished. All I did was bore out the nose and let the collet chuck slop
around a little more. CNC tapped 20 holes to 10-32 holes with it.
Looked a little sloppy, but as soon as it entered the hole it was nice
and straight. The threads look good, and it didn't waller them out any.
Maybe next week I'll have time to make a couple more. I bought some
1144, but that stainless one looks so pretty I'm tempted to make more of
them out of stainless even though it is a little touchy to work with.
Just changed one of my processes and order them a little better.
I hope you can post some more pictures, eg of the TC tapper parts before
you assemble the others. My impression (or possibly misunderstanding) is
that having a spring with the right spring constant is important to how
well a TC tapper works -- how did you pick out what spring to use?
**********
I have a pegboard on the back wall of my shop where I store salvaged parts.
Springs, hose clamps, etc. I walked back to where I have springs, and I
designed the tapper around a spring I just happen to have six of. I have
one commercially made TC tapper, and I compressed the spring until it felt
like it took the same amount of force to move it. Then I designed the TC
tapper to have that much preload. I dropped the spring in the tapper body
and pressed it in with my thumb to about the same preload, and marked it
with a Sharpie marker. I snapped the spring at the mark. When I installed
the springs I reversed the pieces so the flat ends ride against the cross
pin. The pin wound up pretty close to where I wanted it.
I don't think spring selection is that critical. I mean I wouldn't use the
spring out a self inking stamp pad or the coil spring out of a truck, but if
you look at springs that are close to right size for the collet chuck and
you have to start to load up the tendons in your hand to compress it you
will be close. Worse comes to worse, if your spring is a little light you
can tap the holes twice. Assuming it isn't so light that you use all the
compression of your tool before it reverses. Once the tap is started in the
thread, all the spring does is allow the tap to follow the thread if your
synchronization isn't perfect. Unless you have a C axis spindle its never
perfect, and it takes time to reverse the spindle at the bottom of the
stroke. This is where selecting the right dwell time and a little planning
is helpful. Steel might not be as forgiving as aluminum. This is one place
I'd just have to run some tests and see.
I have two styles setup in my styles library for that machine in CAM now.
Its pretty easy to do. My speed feed calculator (HSM Advisor) will do it,
but it tends to want to suggest RPMs that are to low, or to high for my
comfort level. Since I mostly run my machines in inch mode its pretty easy
to calculate myself. Pick an RPM and divide by the TPI. Of course I had to
semi script a "custom" the "drill" operation for dwell and reversal, but
somebody else had already done it and posted about it on the CAM software
forum. I only had a couple details to work out.
I set up my first test of the new homemade TC Tapper after the latest
modifications running 20 holes with 10-32 threads in 6061-T6511 aluminum. I
had only three holes where I could see movement as the tool exited the work
piece. It looked to be about 1 thread. I'd say the TC tapper did the job.
I'm not brave enough to tap blind holes with it just yet, but it does a
passable job on through holes using a spiral point tap.
I'm considering making a video of the process, but making a video, setting
up cameras and planning shots makes any job take twice as long.
***********
If you make one, plan on breaking some taps and run tests on pieces of metal
off your scrap pile. I ran one test, modified the tool, and then used it on
a real work piece. Well, sort real. It was the backing plate for a full
profile glue and tape mounted job where I drilled holes, flycut to proper
thickness, and then screwed down through all the holes before cutting 360
degree profile parts full thickness. I guess it was a real fixture plate as
opposed to a real part, but the results were passable. So far I have not
broken a tap. I had used the commercially made tapper on one similar job
before deciding I wanted atleast three of these tools in my tool rack for
this machine.