VFD - Do I understand this correctly???

[Tom Kitta]

The bigger motor rule is for running slow & needing power. Milling unless you work *hard* and hog does not use that much power - this is why old BP machines were fine with 1hp motor.

A new BP clone with 40 taper has 5hp motor - which is a LOT of power. With sharp cutter in mild steel == 5 cubic inch of metal per minute (say 4 counting in machine friction) at full power. That is HUGE metal removal - there is no way my machine could remove that much without walking out the shop. That is cutting with 1" end mill 1" deep at 4 inch/ min rate - that is very aggressive and you should not cut more then 50% of the EM diameter.

so if you only use VFD for fine tuning speed +- 20% on a mill that has originally 1hp motor there is little need to go bigger unless you want to hog material (which may be more then the mill can handle depending on size). If you use VFD to go +- 80% you should think of bigger motor or you will be only able to take lighter cuts at the extremes - most of the problem will be at low range - low range == big end mill or big drill == lots of power.

 

[DavidR8]

[QUOTE="Brent H, post: 30628, member: 1269" most VFD speed controlled machines will have a larger motor fitted to make sure there is good low speed power

That is my understanding as well, and why I'm thinking growing to 3HP from 2HP. On the other hand @David_R8 has the same mill and his was only fitted with a 1HP motor? So far this is looking to be an affordable way to achieve variable speed provided I get a used motor and an offshore VFD.[/QUOTE]

Actually I have a 1.5 hp motor.
It came with 1 hp.
I bought from e-motorsdirect. Very happy with the product.


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[YYCHM]

That is my understanding as well, and why I'm thinking growing to 3HP from 2HP. On the other hand @David_R8 has the same mill and his was only fitted with a 1HP motor? So far this is looking to be an affordable way to achieve variable speed provided I get a used motor and an offshore VFD.

Actually I have a 1.5 hp motor.
It came with 1 hp.
I bought from e-motorsdirect. Very happy with the product.
[/QUOTE]

My point was why the 1 HP discrepancy between the two machines in the first place?

Did you get a VFD approved motor?

What speed range(s) have you successfully used?

What speed range did you set your pulleys and belts for?

Craig

 

[Dabbler]

So there is a lot to digest from the above responses. I use the same VFD for 2 mills and the surface grinder. None of these are VFD rated motors.

I have wired my big mill for 1720 RPM, and never run it below 200RPM, shifting the belts to get lower speeds if required, which is seldom. That seems to be sufficient for cooling, as I hardly ever take a big chip. Taking light cuts, and those being at low duty cycle: 10 minutes on, 1-2 minutes for repositioning or measuring, the motor never gets above room temperature.

I could just as easily use a 3/4 HP motor on that mill and be happy.

I run another mill off a 2HP single phase motor. there is no detectable difference in performance. They are both belt driven heads.

The other mill is 2 HP 3PH, with the variable speed head. So for really slow rotating, I use the low range, spin the mechanical speed control down and run the motor at 1000 RPM. I get huge torque with no heating. I can go down to 1/2 of the lowest speed (15 RPM?) with enough torque to break a HSS cutter (ask me how I know!)

So there are many approaches to getting what you want, but real question is, what do you want? speed control? If you do, get a 1HP 3600 RPM motor, set your belts to a lower speed setting, say 40% of the maximum speed. Use a 1 KW VFD (for head room) and run your VFD from 20-70 HZ. That will give you ample torque at speeds below 100RPM, and give you the same tops speed, around 2000RPM, if I recall. There will still be ample torque to break a 1/2" cutter if that's your desire.

If you think that you'll get smoother cutting out of 3ph, it doesn't work that way for a mill, the speeds are too slow, and the cutting geometry means that 1PH and 3PH perform identically. It is probably my imagination, but it seems like the 3ph gives slightly less vibration the 1ph, but that might be the difference between a 3000lb mill and a 1900 lb mill...

I did all this before I bought a rotary phase converter. I now own a 15HP rotophase, which I'm in the process of wiring up. Soon most of my machines will run off that, because the speed control thing isn''t that important for me right now. I'll still use the VFD on the big mill, as the belt change is a little high and inconvenient to change.

I may get a little roasted by saying this, but you can't take big enough chips to justify bigger HP on the round column mills - the deflection leads to chatter and deterioration of the cutting edge, or worse, breaking the cutter. I think that @David_R8 uses a roughing mill in his, and that reduces the cutting forces a lot, allowing faster removal of material. (I don't own a roughing mill - yet)

I know the 3 pulley system is a pain - my first mill had it - but if you go 1HP/VFD, you will only need to change belts on extreme cuts. Unless you are planning to use a 2" facing mill on a regular basis, this shouldn't be needed very often.

 

[DavidR8]

As @Dabbler mentioned I do use roughing end mills to remove the bulk of material. I then switch to regular end mill for finishing passes.

Im perfectly happy with the 1.5 hp motor on my mill. 3 hp would be overkill as the design of the mill would not allow for deep hogging type cuts.


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[Tom Kitta]

I use roughing end mills rarely b/c I usually need better surface finish & don't like switching EM - I usually don't tons of material to remove and HP never is an issue but rigidity is. As I mentioned before newer milling machines come with way, way too big motors to actually use all the power they provide.

None of my machines use painful pulley system for speed control (OK except one baby sized mill - but here belt change is ultra fast) so there is no need for VFD speed control.

Since motors are cheap nowadays their sizing is more of a marketing department gimmick then actual engineering need.

On lathes this is a bit different.

 

[YYCHM]

Can anyone tell me what the frame size is for this motor?





The shaft appears to be 7/8" and the mounting hole foot print is 5-1/2"? (might actually be 5") across and 5" axially.

Thanks,

Craig

 

[DavidR8]

Can anyone tell me what the frame size is for this motor?

View attachment 11258

View attachment 11259

The shaft appears to be 7/8" and the mounting hole foot print is 5-1/2"? (might actually be 5") across and 5" axially.

Thanks,

Craig

I don't know what frame size that is but I replaced mine with a 145T which has a 5.5" distance across the legs, and 5" center to center on each side.
It was a perfect fit for my mill.

 

[YYCHM]

I don't know what frame size that is but I replaced mine with a 145T which has a 5.5" distance across the legs, and 5" center to center on each side.
It was a perfect fit for my mill.

Sounds about right to me. What was the shaft size?

Thanks,

Craig

 

[DavidR8]

It's a goofy size like 57/64" or 32.4 mm (or something equally odd) so I had to make a bushing to reuse my pulley.

 

[Johnwa]

Or it could be a frame 56, then it would likely have an imperial shaft diameter.

https://www.regalbeloit.com/brands/LEESON/Quick-Reference-Motor-Dimensions

 

[YYCHM]

It's a goofy size like 57/64" or 32.4 mm (or something equally odd) so I had to make a bushing to reuse my pulley.

Interesting (57/64 <> 32.4mm?) What does the original motor shaft measure?

Craig

 

[DavidR8]

Interesting (57/64 <> 32.4mm?) What does the original motor shaft measure?

Craig

Just measured the original shaft at 24mm or 15/16" or .9375.
The new motor has a shaft diameter of .875

 

[YYCHM]

Just measured the original shaft at 24mm or 15/16" or .9375.
The new motor has a shaft diameter of .875

That sounds better. THANKS!!

 

[DavidR8]

That sounds better. THANKS!!

I was kidding about the 57/64
This is the motor I bought:
https://www.emotorsdirect.ca/item/m...&custcol_sca_category_sourced=1&tab=specs-tab

 

[Tom Kitta]

https://esrmotors.com/Literature/References/ESR NEMA Chart 2011.pdf

and all other references mention 56 frame as shaft 5/8 - either they are all wrong (could be) or its 145T - year is 1993 - so post 1964.

I would write frame # on it so you don't forget.

 

[YYCHM]

Still trying to get my head around this stuff.....

What's the useable Hz range on a VFD? I assume Hz translates directly to rated motor RPM in terms of %?

@Dabbler suggested 20-70 Hz of which I assume 60 Hz produces the rated RPM.

Craig

 

[Dabbler]

suggested 20-70 Hz of which I assume 60 Hz produces the rated RPM.

yes.

You can go to 130 Hz on mine, but not recommended. You lose torque at either end of the frequency span. I don't run mine below 25 Hz, which is 25/60*1725 is approx 700 RPM. To get slower speeds, I shift the pulley or go to back gear. I've had it to 10 Hz, which is 287 RPM, but there is too little torque left to be usable.

 

[YYCHM]

What a pleasant surprise......



The motor pulley came off without a fight. Keyed 7/8" with two set screws. Loosened the screws, gave it a gentle pry and she came right off.



The motor shaft is a confirmed 7/8" now.

So something like this

https://www.kijiji.ca/v-other-busin...icient-motor-2hp-3-phase/1528158823?undefined

Would work without much hassle and not break the bank (provided it's in working order).

What do you guys think of that idea? Stick with 2 HP rather than moving to 3 HP.

 

[Tom Kitta]

I would go for the largest motor in the same frame factor.