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Author Topic: Tapping tiny threads  (Read 1260 times)
kvom
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« Reply #15 on: January 25, 2018, 00:42:30 am »

I've been tapping a lot of 2-56 threads in aluminum using a homemade tapping stand  Stik.  My tap wrench is a small jacobs chuck with a straight shank that is guided by a hole in a horizontal bar.  I turn the chuck by hand between thumb and forefinger.  I haven't broken any taps this way, but I sure wouldn't want to do 100 at a sitting.

2-56 is slightly larger than M1 and quite close to M2 wrt the hole needed.
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Bubba
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« Reply #16 on: January 25, 2018, 01:03:36 am »

The one trick I use and it works..
 If the thread is not critical, you can use one size bigger drill bit, this way you wont get 80% thread but in most cases is not needed..
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Dragonfly
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« Reply #17 on: January 26, 2018, 13:33:29 pm »

There is a definite success on the third try.
I made an adapter using what I have at hand - a shaft from a Dremel type grinder with a small chuck which slides and rotates supported on two small ball bearings. I made a copy of the Mach3 PP and modified its canned cycles code so I can use the same MOP as for drilling. But this time it positions the tap over the hole and lowers it the required depth while compressing the spring. So there is a slight force pushing down. And the code stops temporarily with M1. When the tapping is done and the tap is out clicking 'Start' moves to the next hole.
This is the second pass with the finishing tap. The first one was painfully slow rotating it only with two fingers to feel the tool. The critical moment seems to be when the tap cuts through the far end of the hole. After drilling I made a very light chamfer on hole edges to assist the tap initial bite.
I think, based on fingers feedback, that it can be motorized with a stepper and a simple controller which can do movement patterns - forward/backward, something like 1/2 forward 1/4 back- counting the number of whole turns to pre-program the required depth.


* TapGuide.jpg (1364.73 KB, 4160x3120 - viewed 45 times.)
« Last Edit: January 26, 2018, 13:36:01 pm by Dragonfly » Logged

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Bob La Londe
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« Reply #18 on: January 26, 2018, 13:46:34 pm »

I'm glad you got it to go.  I'm not sure I recall reading that they were thru holes.  On a thru hole a spiral point tap is the way to go, and you should not need a finishing tap.  Just go all the way thru.  A spiral point tap seems to be easier on break thru as well.  I know you were doing hand tapping, but that doesn't mean you have to use a hand tap. 
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Dragonfly
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« Reply #19 on: January 26, 2018, 15:01:06 pm »

Bob, I am glad I found a place where I could buy those taps at all.
Such is my reality. Stopping here, otherwise my words will become harsh and political Smiley

Yes, they are through holes and I drilled 2mm further into the sacrificial sheet to make space for the tap tip.
« Last Edit: January 26, 2018, 15:03:52 pm by Dragonfly » Logged

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Bob La Londe
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« Reply #20 on: January 26, 2018, 15:35:12 pm »

I thought the EU was a multi national free trade zone.

I'll email you later.  
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dave benson
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« Reply #21 on: January 26, 2018, 23:47:42 pm »

Hi Dragonfly

I'm glad it worked out for you, with regards  to the Arduino tapping head , this could be done with
something like the motors shown below, they are 100 watt toy scooter motors.

Originality they have a sealed cap on the rear to keep the dust out (the one at the top of the picture)
all I did was extend the armature shaft and connect a generic encoder.

There are various reasons that these kind of motors are not that great as a servo for positioning the axis for cnc machine (I used these as a winch drum for my sons toy crane) where absolute positioning was not an issue, you just needed smooth movement to position without the load  jerking around when the load came to a stop.
 
I just wrote my own PID algorithm and  modified the Integral part of the code, by setting bounds on the accumulator and having a larger than normal following error.

You could use a Battery powered dill motor (some don't have an integral planetary gearbox) I seek out the one's that do.

After saying all this, I wouldn't use an Arduino at all  I'd just get a small servo controller and low powered servo motor and connect to one of mach3's spare axis's .

This has two desirable advantages:

 1: You can program it from your Gcode.
 2: If the tap stalls the motor the servo driver can be wired to output an alarm to mach3 and stop things until you attend to the problem.

If you are going to do a lot of tapping this is far and away the best solution.

Dave






* SUNP0025.JPG (802.07 KB, 4608x3456 - viewed 37 times.)
« Last Edit: January 26, 2018, 23:52:38 pm by dave benson » Logged
Dragonfly
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« Reply #22 on: February 12, 2018, 13:36:25 pm »

To report on my further progress. I added a stepper motor and a coupler between it and the tap driving shaft. The shaft is spring loaded to apply a small downward force on the tap. The tension is achieved by lowering the Z axis which carries the adapter. Besides the modified Mach3 PP I also wrote a macro which is called on each hole by the G-code. The macro does the forward/backward advance, unwinding and lifting up the tap. Currently I chose a conservative approach - half turn forward/quarter turn back. A tapping cycle takes 2 minutes this way but better use more time than end with a broken tap in a hole.
Currently after each cycle the tap is moved and lowered onto the next hole and the program waits (M1) for 'Start' button press. This is to allow me to put a few drops of oil. Now, if I invent a way to automate the oiling it can turn into a fully automated process Smiley
Here is a video how it works.
https://youtu.be/4qKlnTxxg9U
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Bob La Londe
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« Reply #23 on: February 12, 2018, 14:55:57 pm »

WOW!  Very nice.  2 minutes per hole done that way is a huge savings in time over hand tapping I think. 
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Bubba
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« Reply #24 on: February 12, 2018, 18:36:39 pm »

Awesome idea, and even better performance! Cheesy
« Last Edit: February 12, 2018, 18:38:17 pm by Bubba » Logged

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