Machine tapping

[shell70634]

I've been watching videos of machine tapping and understand how it works. My question is reversing the machine. I have a Bridgeport clone, Clausing Kondia FV-1, and I'm hesitant to reverse the motor as quickly as shown in the videos. Do I need to turn off the motor and take into consideration the continued rotation and reverse after the chuck stops? Would reversing immediately cause damage to my machine?

 

[mmcmdl]

On a thru hole ,no , instant reverse the machine . On a blind hole , turn machine off , when fairly close to desired depth , downward feed will still feed down as spindle rpm slows . You will be able to see your depth of tap when running slow , then reverse . If you're power tapping a blind hole , it's better to have that tap slip in a cheap chuck than snap it if you accidentaly bottom it out .

 

[shell70634]

Thanx. I've always treated machinery like a car transmission. Wait for parts to quit moving then shift into reverse.

 

[mmcmdl]

No need to !

 

[Bi11Hudson]

While not exactly relevant, it does have a connection.

With a fractional horsepower 3 phase motor, instant reversal (plugging) is acceptable. It's hard on the machine but is done regularly. A machine like a Bridgeport is probably reinforced to accomodate this. A clone I couldn't comment on.

If the motor is single phase, it should be allowed to spool down, at least to where the centrifugal switch drops out. Reversing at speed will not reverse a single phase motor. It must be near or at zero speed.

.

 

[tjb]

I had the same hesitancy several months ago when I power tapped for the first time. Scared me to death to go from forward-to-off-to-reverse in one fluid motion, but I was assured that was the right way to do it. I needed to tap about a hundred (no exaggeration) 1/4-20 through holes on a piece of 3/4" aluminum. The first few holes, I did it like I was dancing on egg shells. By the time I finished that project, I was moving through them pretty quickly. The one caution I was given was to make sure to use two-flute taps. Regular taps evidently will have a tendency to break when power tapping because of swarf buildup. I've never tried to power tap blind holes, so as noted above, recognize that the method is different.

I've been told power tapping is a relatively common practice, so it seems to me that the full sized mills are designed to handle it. Mine is also a Bridgeport clone. Any seasoned veterans out there, let us know if that's not right.

Regards,
Terry

 

[mmcmdl]

Most all BP clones are 3 phase and accomodate instant reversing . As Bill stated , single phase aren't made to reverse full load .

 

[Lo-Fi]

Worth mentioning that most VFD's brake the motor to a stop quickly (mine does DC shunt) before ramping back up into reverse. Soft start is also soft reverse. Also, as tapping isn't a high horsepower op, I've never been shy to turn the motor speed right down and leave it on one of the mid/higher range pulleys. Otherwise you're into low range or back gear territory and massive torque available at the spindle, which would be scary. This does assume you've got a VFD running a 3 phase motor, though it's a fair assumption for a home shop where a VFD is used as an easy and affordable single to 3 phase inverter for old industrial kit.

I did a bunch of M4 holes through 6mm steel plate like this today with a standard 3 flute, it was really quite civilised.

 

[tjb]

While not exactly relevant, it does have a connection.

With a fractional horsepower 3 phase motor, instant reversal (plugging) is acceptable. It's hard on the machine but is done regularly. A machine like a Bridgeport is probably reinforced to accomodate this. A clone I couldn't comment on.

If the motor is single phase, it should be allowed to spool down, at least to where the centrifugal switch drops out. Reversing at speed will not reverse a single phase motor. It must be near or at zero speed.

.

Didn't know that. Mine's 3-phase, so I had no problems.

 

[shell70634]

My machine is 3 phase on a rotary converter. No longer worried about it.
Thanx to all

Shelly