I don’t mean to be contentious about this, but if your tap pulled out, it’s because it came loose in the collet, which is pretty easy to do. Now, these tapmatic style heads are “ball drive”, they engage, or they free wheel, there is no middle ground. When being driven into the hole, you stop Z feed, the tap continues for say .140” (whatever is specific for that head), then the balls driving the tap release and the unit free wheels…. it could set there indefinitely spinning happily (the machine) and doing nothing (the tap). Now, as soon as you start to move up the balls drop into the reverse engagement dog and drive the tap up out of the hole.
If your feed rate is too slow, going in or going out, you will get intermittent feed, spin, stop, spin some more, and so on as the feed rate catches up with the taps pitch. If your feedrate is too fast, going in you’ll probably break the tap, there isn’t a lot of cushion in these tap holders, maybe a couple hundred thousandths, depending upon the unit. If you try to feed out of the hole too fast, you can pull the tap out of the collet, which is probably what happened in your situation.
This dead band idea is of no consequence, you don’t care how much Z it takes to reverse the spindle (as long as it’s not more than the R level you start at above the part). You feed in a set Z amount and the tap pulls out a set Z amount before it hits neutral… those are the only parameters you really need to be concerned with. Once your machine hits the Z depth, you dwell for 1/2 a second or so, so it has time to pull the tap out and go into neutral, and then feed back Z plus at 1.75 or 2x (whatever your head reverse ratio is) your feedrate going in, as long as you are feeding high enough in Z so the tap comes free of the hole and springs back up to “starting” position on the tapping head, you are good to go.
Programming wise, there is not much difference using a ball drive vs. cone clutch style tapping head. The only real difference is that the ball drive you will feed the Z depth you want minus the pull out amount. With a cone drive, you will feed the Z depth you want plus whatever compression amount it takes to start turning the tap. Other than that, the process will be the same.
Brian Lamb
blamb11@cox.net (blamb11@cox.net)
On Jun 4, 2014, at 3:43 PM, Art Eckstein art.eckstein@gmail.com (art.eckstein@gmail.com) [sheetcam] <sheetcam@yahoogroups.com (sheetcam@yahoogroups.com)> wrote:
Brian,When I first tried to use Sheetcam with a tapping head, the first problem was the recognition that the tap would continue to go down as you have noted. The next problem was that with THAT tapping head, was (and I don't remember why now as that was several years ago) that the tap was driven down to a point that when reversed, it actually pulled the tap out of the head a slight amount. After a couple or three holes, the tap was still in the hole when it tried to move to the next XY position and that = broken tap. As Don has stated, not all of these tapping heads are created equal and you need to know what parameters that need to be adjusted and how to adjust them.Back when I was trying to learn how to set mine up is when we had a discussion on the group about the "deadband" where the head was turning in neutral (neither up or down on the tap) and found this to be a major variable. I also think this is where the dwell factor came in. Remember, the spindle is always turning so if you stop the down feed AND you have not reached the end of travel (of the tapping head), the tap will continue down. Especially if your doing blind holes, this can be disastrous. So based on your contention (which is mostly correct), you need to drive the tap down, stop before you have reached full depth, dwell until the tap has stopped rotating and then start the up feed which must also include a necessary amount cover the "dead band" area IF one is present and then make sure you have the tap out of the material before you continue to the next hole. ArtCountry BubbaAt 06:19 PM 6/4/2014, you wrote:Why is there a problem? When your Z axis stops feeding the tapping head continues to feed until it disengages. Then you reverse your Z axis and it engages the reverse feature of the tapping head, and the tap follows the Z axis up and out of the hole. Programming is as simple as knowing the amount of Z pull out and decreasing your overall depth call out by that amount.Brian Lambblamb11@cox.net (blamb11@cox.net)