Motors Minimum RPM ( wrt rigid tapping )

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cut2cut

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I'm just getting into rigid tapping and wondering if my motor can go slow enough. Yeah, in a world where we want to go fast or go home... I'm asking that question! :)

I have a 1.5hp Marathon inverter motor and Delta VFD ( link to the motor below ). I don't know if its bad to run this motor at too low an RPM. Currently I'm running a pulley at 2 to 1 for added rpm for general milling and its not possible to change pulleys.

So if the minimum rpm of the motor is say 300 rpm, that means to get 300 rpm at the spindle I have to run the motor at 150 rpm. Is this bad for the motor ? I suppose it depends on the VFD frequency a bit. Largely I would assume that tapping doesn't require tons of torque but since I'm new to rigid tapping, I don't know enough and want to go cautiously. Thanks for any help !

note, I can't remember where I saw it, but I thought I read somewhere 300 rpm is indeed the minimum rpm for this motor. I could have dreamed this, because right now I can't find that designation anywhere.

Marathon Motor # 145THTR15540

http://marathonmotorsupply.com/inde...osure-tenv-phase-3-voltage-230-460-hz-60.html

Jake
 
the motor is inverter rated that's a good thing,
it won't have a lot of hp at 150 rpm, but you can certainly operate the motor at low speeds.
you may wish to add additional cooling provisions if you are going to operate for long periods of time at very low speeds
 
Ulma Doctor said:
the motor is inverter rated that's a good thing,
it won't have a lot of hp at 150 rpm, but you can certainly operate the motor at low speeds.
you may wish to add additional cooling provisions if you are going to operate for long periods of time at very low speeds
Click to expand...

Thanks for the reply! Basically I shouldn't be using it at low rpm except for tapping 1/4 20, 10-24 etc, relatively small stuff at least initially. I'm sure that will change over time and I'll push it harder but just getting my feet wet, so to speak.
 
biggest pain with power tapping and a VFD is long deceleration times. EXAMPLE: You want to stop, decel time is set to three seconds, it will not stop for three seconds and so on. Then decrease the decel time and you get over voltage alarms on decel. The answer is a brake resistor so you can have fast decel times
 
Karl_T said:
biggest pain with power tapping and a VFD is long deceleration times. EXAMPLE: You want to stop, decel time is set to three seconds, it will not stop for three seconds and so on. Then decrease the decel time and you get over voltage alarms on decel. The answer is a brake resistor so you can have fast decel times
Click to expand...

I worried about this aspect and have to admit I wondered if the spindle encoder would curtail this issue alone. The current settings in my VFD are allowing a lot of coast to avoid the associated over current fault, but that has to change for the rigid tapping or the tap could easily coast / over shoot and bottom out ? I'm installing a brake resister too, so that hopefully isn't going to be a problem. I don't know how far I can push the decal time, however, so if anyone has advice on how far that can be pushed I'd appreciate it. I suppose its a bit of trial and error though for each motor / resistor / vfd combination ?
 
Yep trial and error. I have looked ALL OVER for a VFD that would have a decel rate parameter, or some other decel option with no joy. These things come with 100s of un needed options :(

Pretty sure I got 0.5 second decel time on my two mills. This works OK when used to it. Not sure I would let anybody else power tap on my mill.
 
I suspect that the manufacturer of a machine capable of rigid tapping would have included a spindle drive capable of doing it.

We have a new Trak mill without the rigid tapping option, it costs a bit more for the spindle encoder and board for the C axis so the boss didn't go for it. Floating tap holders work well but are a gamble tapping close to the bottom of blind holes.

As much as I dislike How Too videos this is a rather straight forward explanation of rigid tapping and its programming.

Good luck.
 
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Karl_T said:
Yep trial and error. I have looked ALL OVER for a VFD that would have a decel rate parameter, or some other decel option with no joy. These things come with 100s of un needed options :(

Pretty sure I got 0.5 second decel time on my two mills. This works OK when used to it. Not sure I would let anybody else power tap on my mill.
Click to expand...

bummer. The Delta VFD-e has these settings :

Delta VFD motor parameters .jpg
 
Wreck™Wreck said:
I suspect that the manufacturer of a machine capable of rigid tapping would have included a spindle drive capable of doing it.

We have a new Trak mill without the rigid tapping option, it costs a bit more for the spindle encoder and board for the C axis so the boss didn't go for it. Floating tap holders work well but are a gamble tapping close to the bottom of blind holes.

Good luck.
Click to expand...

This is something I'm adding to my cnc mill conversion. I'm adding the spindle encoder myself :)
 
I see you have decel time 1 and decel time 2. Look the detail up on these. Just maybe a VFD input can switch decel times
 
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