Build Thread- NT 30 ATC using a VFD

[small_toys]

Well, I bit the bullet and ordered the IH Mill manual version. Still waiting on it to arrive. I will be converting it to cnc but woul like to see what ideas ya'll would have about an ATC for the NT 30 taper. I will be using a VFD on the motor and will want to use the tangs on the NT 30 spindle. Question is how accurately can I stop the spindle if I used an index pulse from the spindle. In order to switch tools I need to stop the spindle exactly the same each time. This will allow the spindle tangs to line up every time otherwise I will have problems.

Any thoughts on this.

EDIT:
I will be using MACH software with a smoothstepper and Gecko drives for the servo motors on the axis. Spindle will be 2 or 3 HP Hatachi with AC motor.

[Al_The_Man]

For spindle orientation using the spindle motor itself usually requires a more sophisticated control that can be only be offered with the basic flux vector controlled VFD.
You also require an encoder on the final spindle shaft.
It is usually either done with the appropriate VFD with feedback or a separate small C axis motor to rotate the spindle.
Although in the case of C axis motor, this is mainly fitted to a lathe where live tooling is used with C axis rotational positioning.
With a VFD you will need a 3 phase spindle motor, if not already fitted.
Al.

[small_toys]

So it could be done with a Index pulse from the spindle using a VFD. I will use a 3 phase AC motor. This is the drive I am looking at.

http://www.driveswarehouse.com/Drive...7b9bc0378f087a

[Al_The_Man]

I very much doubt you will be able to make a repeatable stop with this unit.
The very lowest controllable rpm with a 4 pole motor appears to be 15 rpm.
Al.

[BobWarfield]

SmallToys, I went looking for cheap VFD's that could be setup for spindle positioning and wound up with nada.

The two alternatives I looked at in the horsepower range you have are:

1. The auxilliary motor Al mentioned. A small stepper will do. Biggest issue is to decouple it so it doesn't act as a generator when spun by the main motor and fry your drives.

2. Run a big servo as your spindle motor. You can convert any motor into a servo with an encoder and the right drive. You may find it easier to find a 2-3 HP servo drive that will work with your motor.

Here is an adaptation of a DC motor:

http://www.truetex.com/dcdrv.htm

AC servo drives may be a better bet for you.

The option of changing your spindle motor to a servo is probably the "right" way, but the aux motor seems the easier lower risk way.

Best,

BW

[small_toys]

Yea, I know the servo would be the correct way but also the most expensive way. Before I buy the AC motor and drive I may take time to search ebay for a 3HP servo with a controller. But it would have to have single phase 220 input. I currently have a 2 HP 4300 rpm DC brushed motor from a tread mill. Not real sure how reliable this motor would be. Its real light weight.

Still waiting on the mill.

[Runner4404spd]

i think your over thinking this. the mill is small enough that you shouldn't need the guid dogs engage to cut the material. if your taking that large of a DOC i think you'll exceed the mill capacity. i have a fadal 3016 and it uses drive dogs but its a 10 HP spindle on there. with 3 hp and a hobby machine i think you could get away with just the nmtb 30 holder.

[NEATman]

Smalltoys-
Are you planning on using an impact wrench on an vertical air cylinder (like a kurt power drawbar)? If so, you may be able to add a cam profile to the top of the spindle that would take advantage of the downward motion of the air cylinder to orient the spindle to the same position or 180° from the same position (either would work, as there are two drive tangs). Perhaps something like in the attached picture. If you have a cam roller come down on this, it would rotate the spindle into alignment, plus it would hold the spindle in postion for torquing the drawbar.

Alternately, if you have an inpact wrench that has enough power to rotate your spindle if the brake isn't on, you could have a pneumatic shot pin that engages a hole in the spindle, and a spring to disengage it. So every time the wrench tries to tighten or loosen the drawbar, it will rotate the spindle until the shot pin engages, locking the spindle in position. The shot pin could be tied to the same air supply as the impact wrench, so it engages when air is sent to the wrench.

I have a bridgeport with NMTB-30 tooling with drive tangs, and I have had this thought for a while, just never had the need to do more than manually change the tool, as it is just a hobby machine.

Keith

[atvracer]

one option

use a normal AC motor to drive the spindle but put a gear next to the pully on the spindle with a small servo/stepper on a pivet and a air cylinder to dis/endgage the spindle servo then mount a prox/hall on the spindle for the timming or do the same but use a clutch and belt to dis/endgage the stepper/servo this will also work for boring hole with a shft to pullout boring bar

[BobWarfield]

NEATman, that's a clever solution, I like it!

Cheers,

BW

[HimyKabibble]

I have a very hard time believing the drive dogs are required for machines with single-digit horsepower spindles. The taper alone should be MORE than capable of driving up to probably 5+HP and more. I've run up to 3HP through a little Tormach holder for hours on end with no signs of slippage, and a 30-taper will grip one helluva lot better than a little Tormach holder.

I am going to swap my spindle to a ISO 30-taper. ISO 30 does NOT have drive dogs by design.

Regards,
Ray L.

[philbur]

Here's some numbers for an ISO 30 taper based on a cone clutch calculation taken from machinery's handbook. As you can see low drawbar force looks OK for relatively high rpm's but if you have a geared head mill then you might be in trouble at low rpm. It's torque that is the potential problem not HP.

Phil