# VFD conversion - drill press



## precisionworks (Sep 10, 2009)

A 3 hp motor & VFD had been purchased for installation on the mill. After buying the push-pull vise for the drill press, it seemed like that machine would really benefit from a larger motor & variable speed drive. The drill press is a Craftsman, purchased new around 1982, made by the Atlas Press Company - the same company that made the Craftsman metal lathe. I saw one in an Atlas catalog & it had a larger motor & a conventional (wide) belt drive. The first operation is fitting a four step pulley.







The eight step aluminum pulleys gives a speed range from 380-8550 rpm. And the "belt" has barely the ability to transmit 1/2 hp. The front pulley was pulled & the shaft measured:






The shaft is 25mm metric, and a metric bore pulley couldn't be found, so I ordered a 7/8" bore Baldor/Maska four step.







The bore indicated about .0001" total runout using the 3-jaw chuck, so it was ready for boring out. Since the bore needed to be about .109" larger, three passes were made removing .025" each time, followed by .020", followed by .010", then .005". These cuts were made using the dial on the cross slide, which is good enough for roughing work. A dial test indicator was used to get close to the target dimension.






The target dimension was between .9843" and .9845". Any larger than .9845" would give a loose fit, and any smaller than .9843" would make it hard to install the pulley on the shaft. The last pass showed a mic reading of .9842" which was just a bit small, but the pulley was removed from the lathe for trial fitting on the shaft - you can always go back for another cut if needed. Firm blows were able to get the pulley started but it was too tight, even after warming the pulley with a propane torch. Back to the lathe for one more cut, without disturbing the last setting. The 3/4" boring bar will deflect about .0002" when extended 3", so one more pass should remove that amount. The boring bar was run in with power feed, and run back out with power feed. The insert did not touch on the infeed, but just barely made contact as it backed out. The mic showed that the bore was .9844", pretty close to ideal. The pulley was again warmed with the torch & seated nicely. The dial test indicator showed .0002"-.0003" total runout on the bore 






The old motor & mount were removed & distance from top of pulley to top of mounting holes measured at 5.75". To make the new motor fit, a piece of 5" wide, 1/4" thick flat stock was welded to the motor base.






The motor plate is marked & ready to drill. More to follow tomorrow.


----------



## wquiles (Sep 11, 2009)

Very nice. That new vs. old motor picture is very telling of how underpowered the original setup was!

Looking forward to more pictures 

Will


----------



## precisionworks (Sep 11, 2009)

The motor is moved into position using the scissor lift table with a length of 4x4 and 6x6 giving the table added height.






Nuts and flat washers are threaded on both sides of the motor plate. They allow the motor to be adjusted exactly so that the rear pulley & the front pulley are in perfect alignment. Note that the bottom adjusters are threaded out further than the top ones.







The Starret 385-48 straight edge rests on the front & rear pulleys while the rear pulley is moved into alignment.






All the mechanical work is done, time now to start the electrical connections :twothumbs


----------



## wquiles (Sep 11, 2009)

Getting closer and closer 

Will


----------



## precisionworks (Sep 13, 2009)

> All the mechanical work is done,


Well, not quite 

My plan was to wall mount the VFD & use a remote switch & speed pot, but it looked to be more simple to mount the VFD just to the side of the drill press. First step is cutting 2x4 lumber to strap across two studs:






This forms the support base for the VFD mount. The mount is made of 2" angle & 1" square tube, welded together:







The VFD bolts to the mount & is in ideal position to operate when drilling:








> time now to start the electrical connections


The junction box at the motor is the first item to wire:







More to follow


----------



## precisionworks (Sep 20, 2009)

Next step is to bring the four wires from the motor (phase A, phase B, phase C, and ground or PE) to the drive. The first three wires on the left side are the motor phase connections, then the common ground with green wires, and the 240 volt single phase power are the black & white wires on the right.







The black, white & green input wires go to a disconnect (like a very large light switch, rated for 60 amps, that breaks both the hot legs). The drive wires are connected to the bottom disconnect terminals, and the supply line wires are connected to the top.








All hooked up and ready to go :thumbsup:






The disconnect was flipped to the on position which powers up the VFD. Then the VFD start button was pressed to check motor rotation ... and it rotated in reverse. Not a problem with a three phase motor, as swapping any two leads reverse direction. After that, it was just a matter of setting parameters & running the auto calibration. 

The lowest pulley step gives a range from 71-1300 rpm.

The second step gives a range of 115-2100 rpm.

The third and fourth steps may never see any use, as the first two should do everything I need. Power is immense even at 71 rpm, which is just over one revolution per second.


----------



## wquiles (Sep 20, 2009)

precisionworks said:


> Next step is to bring the four wires from the motor (phase A, phase B, phase C, and ground or PE) to the drive. The first three wires on the left side are the motor phase connections, then the common ground with green wires, and the 240 volt single phase power are the black & white wires on the right.
> 
> (snip pic)
> 
> ...



Very nice. Thanks for showing the wiring in detail - since I am using the same drive/controller, mine will be about the same 

Will


----------



## precisionworks (Sep 22, 2009)

After running the drill for a few days, these are the parameters that work well:

Acceleration (or accel) set to 4 seconds. A shorter setting like 3 or 2 seconds would also work well, but a 4 second accel leaves enough time to hit the stop button if something isn't right.

Deceleration (or decel) ended up at 0.4 seconds. I don't yet have the braking resistor, and probably will not buy one, as the motor stops quickly without one. It also reverses very quickly at the lower rpm settings - 70 rpm (like you might use for power tapping) is instant reverse, while 300 rpm takes about one second to stop & reverse.

Setting the decel time is interesting as it's trial & error. I start with 5 seconds & drop down one second each try until the drive faults out. With this drive, 4 - 3 - 2 - 1 - .9 - .8 - .7 - .6 - .5 and .4 seconds all stopped the drive. At 0.3 seconds, the drive faulted - which is a built in protection program to keep regenerated voltage from killing the transistors. Switching back to 0.4 seconds gave the shortest decel setting.

Minimum frequency set to 5 Hz. In America, the standard utility frequency is 60 Hz, so 5 Hz makes the motor run at 5/60 of full speed ... about 8% of full speed. The 1725 rpm motor on the drill turns 144 rpm at this setting, and the pulleys reduce that to 72 rpm.

Maximum frequency set to 90 Hz. This makes the motor run at 90/60 of full speed (150%), so the 1725 rpm motor turns 2588 rpm. This is decreased or increased by the pulleys.

So far, the results have been better than expected


----------



## wquiles (Sep 22, 2009)

Awesome - I am surprised at how quickly you can get it to stop - pretty impressive!

I am finishing some flashlight work, and then I will have to do my own VFD conversion. I am sure I will have plenty of questions for you 

Will


----------



## precisionworks (Sep 22, 2009)

> I am surprised at how quickly you can get it to stop


Without using a braking resistor, there's a lot of variation from machine to machine. The machines that have a low rotating mass - like the drill or the wire wheel machine - will stop on a dime. The belt/disc sander, which turns a 12" cast iron disc plus two large drive drums, will fault out around 3 seconds - it needs a braking resistor.

I'd be willing to bet that your lathe, with its heavy chuck & gear train, will be like the sander. When the stop button is pushed on a VFD, the spinning motor becomes a generator. If you select the "coast to stop" menu option, the generator is unhooked from the VFD & spins down at its own pace. If you select "ramp to stop" the generator is feeding power back to the VFD, and the drive has the ability to absorb a limited amount of energy. To stop a generator plus a gear train plus a heavy chuck (plus any work held in the chuck) is too much for the drive without the braking resistor.

You might as well order that now ... EZXDB2222A1 ... always happy to help spend your money :nana:


----------



## Atlascycle (Sep 22, 2009)

What HP was the Drill Press before the upgrade?

Jason


----------



## precisionworks (Sep 22, 2009)

It was a (weak) 1/2 hp, 380 rpm minimum, with a belt that slipped


----------



## wquiles (Sep 23, 2009)

precisionworks said:


> I'd be willing to bet that your lathe, with its heavy chuck & gear train, will be like the sander. When the stop button is pushed on a VFD, the spinning motor becomes a generator. If you select the "coast to stop" menu option, the generator is unhooked from the VFD & spins down at its own pace. If you select "ramp to stop" the generator is feeding power back to the VFD, and the drive has the ability to absorb a limited amount of energy. To stop a generator plus a gear train plus a heavy chuck (plus any work held in the chuck) is too much for the drive without the braking resistor.
> 
> You might as well order that now ... EZXDB2222A1 ... always happy to help spend your money :nana:



I am not yet sure if I will need it on the knee mill, but I am pretty sure I will have to order this for my lathe. If you watched the video I posted in the multi-use lathe tool, you can see how long it takes the spindle to stop on its own - a long time, in fact, way too long for my taste


----------



## wquiles (Oct 6, 2009)

Barry,

Some email traffic on the yahoo groups talking about VFD's and the breaking resistor mentioned being able to make your own high power resistor. The AC Tech data sheet on the breaking resistors says that for 3-4HP:
R = 42 ohms
Wperm = 145
kWmax = 3.6

and for 5.5HP:
R = 28 ohms
Wperm = 210
kWmax = 5.3

Does Wperm mean the constant/nominal power (as in 145 watts continuous) while the kWmax refers to the peak power the resistor must handle over short durations? Does the R value mean the minimum value, or max. value for that power range?

There are lots of high power, 150-200 watts resistors in Ebay that could be made into a nice external breaking resistor, but I am not sure how to interpret those values above


----------



## precisionworks (Oct 6, 2009)

> There are lots of high power, 150-200 watts resistors in ebay



Braking resistors are made of large coils of resistance wire wound over ceramic forms. Then the resistors are mounted on a heat sink and enclosed so no one gets burned, which also keeps from burning down your shop or house.

By the time you purchase just the components, it's as cheap to buy the unit designed for your drive.

http://news.thomasnet.com/fullstory/500968


----------



## wquiles (Oct 6, 2009)

Barry,

I am not going to make my own, but I do want to understand how they work and how they are rated. Do you have any insight on those numbers and what they mean? Please?

Will


----------



## precisionworks (Oct 6, 2009)

> Do you have any insight on those numbers and what they mean?



For the smaller resistor, kWmax = 3.6 means that the resistor can absorb 3600 watts of energy based on a temperature rise of 375°C above ambient (40°C). As some of the web sites state "If the resistor elements glow red you may need a higher rated braking resistor". 

3600 watts = 36 incan light bulbs at 100 watts each. For a few fractions of a second, that's how much energy the resistor has to absorb & dissipate without exceeding 375°C above ambient. It's a big job, even for large resistors mounted on a heat sink, to stay within the temperature parameters.


----------



## wquiles (Oct 6, 2009)

precisionworks said:


> For the smaller resistor, kWmax = 3.6 means that the resistor can absorb 3600 watts of energy based on a temperature rise of 375°C above ambient (40°C). As some of the web sites state "If the resistor elements glow red you may need a higher rated braking resistor".
> 
> 3600 watts = 36 incan light bulbs at 100 watts each. For a few fractions of a second, that's how much energy the resistor has to absorb & dissipate without exceeding 375°C above ambient. It's a big job, even for large resistors mounted on a heat sink, to stay within the temperature parameters.



Glowing red - that is absolutely insane!. I had no idea it would have been this much above ambient 

So not only we have to select the correct breaking resistor for the VFD, we also have to worry about the duty cycle? So if the 3HP breaking resistor were to get too hot, the "solution" would be to go to the next larger one (5HP)? Would you have to adjust/program the VFD so that it knows that size/rating breaking resistor is using?


----------



## precisionworks (Oct 7, 2009)

> the "solution" would be to go to the next larger one (5HP)



There are different ways to configure the brake resistors to work. One would be to go up in size - on a 3 hp motor with a huge inertial load (like a pump jack) you might need a 10 hp or even a 20 hp brake resistor module. With the SMVector drive, you also have the option of "stacking" modules by connecting multiple modules in parallel.



> Would you have to adjust/program the VFD so that it knows that size/rating breaking resistor is using?


The monitoring software built into the drive is primarily concerned with one thing, which is keeping the DC bus voltage at 114% of max or below. A module that is too small for the inertial load will not keep the DC bus voltage in that range & the over voltage will trip the drive into a high voltage fault. As more or bigger modules are added, the drive dumps all the regenerated energy into whatever is available, so no adjustment is needed.

This tech doc may answer some questions:

http://www.actech.com/documents/techlib/AN0039A.pdf


----------



## wquiles (Oct 7, 2009)

Thanks much Barry for the info and links. It is also good to know that I can connect modules in parallel is the initial one is not "enough" 

As you recall besides the Baldor 3HP that I will use in the Knee Mill's VFD conversion, I also have a brand new Baldor 5HP motor and I would like to use for my 12x lathe. If I recall, I need the 10HP VFD, and use it on a "de-rated" mode? Would I then use the 5HP breaking resistor to match my motor, or would I then need to use the 10HP breaking resistor? 

Of course, if this gets too complicated I might just use the 3HP motor on the lathe as well, but I really like the idea of the larger motor, which is of course what "Toolman Taylor" would do :devil:

Will


----------



## precisionworks (Oct 7, 2009)

> what "Toolman Taylor" would do


:thumbsup:

To run a 5 hp motor with single phase input, you'll need a VFD that's rated for 10 hp with three phase input. Here's why you derate the VFD by 50% for single phase input.

Power in a single phase circuit is V x A x pf (power factor). 

Power in a 3 phase circuit is V x A x pf x *1.732* (sq. root of 3). 

The three phase motor is using the power at that 1.732 value, yet the supply is not, so the power drawn by the VFD from the supply is 1.732 x the power used by the motor. That number is rounded up to 2, because it provides a slight safety factor & gets larger capacitors that help filter out ripple. So 5 hp x 2 = 10 hp VFD needed.



> Would I then use the 5HP breaking resistor to match my motor, or would I then need to use the 10HP breaking resistor?


A lathe is somewhat like a pump jack, because you have a large inertial load (rotor+gear train+chuck) and then add the work held in the chuck or face plate. I'd start with a 10 hp braking module & hope that might be enough, but you may have to add more


----------



## unterhausen (Oct 7, 2009)

The Haas mill at work uses an electric stove element as a braking resistor. 

Before derating by a factor of 2, I would check the manual for the VFD. Some companies don't ask for any derating, a lot of them only ask for 1/3. My guess is that's pretty conservative.


----------



## precisionworks (Oct 7, 2009)

> Some companies don't ask for any derating


For 3 hp and below, drives are readily available for single phase input with no derating.



> a lot of them only ask for 1/3


Unless you can change the laws of physics, 1.333 will not work. For it to work, VFD input current would have to be motor current x 1.333.

The only correct formula is:
VFD Input Current = Motor Current Rating x 1.732

You can size a single phase drive as small as motor current rating x 1.732, so a 5 hp motor will run on a 8.66 hp drive. But no manufacturer makes an 8.66 hp drive :nana:


----------



## unterhausen (Oct 8, 2009)

I'm thinking using a 3hp vfd to drive a 2hp motor is 33% derate, but maybe I'm making up my own definitions again. That's what my Mitsubishi recommends.


----------



## saltytri (Oct 8, 2009)

The bottom line is that guessing is a bad idea. Instead, contact the manufacturer of the particular drive. The last few posts made me nervous about the AC Tech SMVector drive that I have on order. It turns out that AC Tech means what it's specs say - its 1.5 HP drive will drive a 1.5 HP motor from 115V or 230V single phase. Just like Barry said: "For 3 hp and below, drives are readily available for single phase input with no derating." But better safe than sorry. And, make sure you ask someone who really knows: the vendor at first said I'd need a 3 HP drive for single phase input but, to his credit, checked with an AC Tech engineer and set the record straight.

As always, thanks to all for making this a remarkably useful source of information.

David


----------



## precisionworks (Oct 8, 2009)

> make sure you ask someone who really knows


There's one other way to select a drive, based on the 3 phase amp draw of the motor.

For example, if Will is using a Baldor M3615T at 240 volts, Baldor states the full load amp (FLA) draw at 14.2. Multiply 14.2 x 1.732 and you need a drive that will handle 24.6 amps (or greater) at 240 volts. Then look in the instruction manual for the drive you want to buy - the SMVector in this example.

The 7.5 hp drive is a little small, showing 23A in the manual.

The 10.0 hp drive is slightly over size, showing 29A, and is the correct drive.

The instruction manual is the most scientific way to size a drive. For most purposes (above 3 hp) the easiest method is to double the size of the drive for single phase input. An added benefit is that you get larger filter capacitors that help reduce or eliminate ripple.


----------



## alexmin (Dec 5, 2009)

Barry,

I have KBAC-27D driver and on its manufacturer web site it indicates that Brake Resistor is not required for KBAC-27D. I've opened up my VFD and there is nothing there that looks remotely capable of dissipating a lot of heat quickly.
Do they really mean that it needs a separate braking module?


----------



## precisionworks (Dec 5, 2009)

> web site it indicates that Brake Resistor is not required for KBAC-27D



_Jumper J8 is factory set to the "RG" position for Regenerative Braking._ That means your drive uses an internal capacitor for absorbing some of the energy that the motor regenerates under decel. With a very low inertial load, it may do OK.

_For DC Injection Braking, set Jumper J8 to the "INJ" position. When Jumper J8 is set to the "INJ" position, the ACCEL trimpot is used to set both the acceleration and deceleration time and the DECEL trimpot is used to set the DC Injection Brake voltage and time setting._ If you look at the drawing in the manual, the default setting is 70v to produce a 1.2 second decel. The fastest setting is 75v to produce a 1.0 second decel. Again, with a small inertial load, this may work for you.

For a high inertial load you MUST have the Dynamic Braking option (braking resistors and a DB module in most cases), which is not an option that I see on the KBAC-27D drive. Dynamic braking (aka instant stop) will decel the biggest inertial load possible IF you have enough braking resistors to absorb the energy. If you want to have an E-stop that brings the spindle to a dead stop in the blink of an eye, dynamic braking is the least costly way to do that.

Before losing a lot of sleep over this, experiment with the decel settings to see if what you have will do what you need. I don't have dynamic braking on any of my four drives, and all will stop within 1.5 to 2.0 seconds ... because there is not a great deal of inertia to deal with. My drill press is similar (IMO) to a mill as both have the rotor in the motor, the tiny weight of the belt, the sheaves, and the spindle that are rotating - which is small compared to a lathe with a heavy chuck & gear head drive. You may be very satisfied with what you have


----------

