Which milling machine model?

Back in the day the Reeves Drive method for providing variable spindle speed was the cutting edge. And it still is a good drive system. But, no modern machine incorporates a Reeves system for varying spindle speeds. That's because the VFD offers several advantages once you know how to use them. For instance, soft start and spindle braking are both very nice features to use especially on larger cutters like my 4 inch face mill and my combination boring and facing head. Instant braking smoothly transitioning into reverse is very handy for things like power tapping. Once you learn how to use a VFD to do it, you will never again want to be using a drum switch and cranking a crank to tap. Not when you can have your control pad with speed, stop/start/ and direction mounted on a magnet and placed right at your fingertips.

I have 4 VFD's running in my shop for various machines. I bought one cheapie and will never do so again. The extra time required to decipher its "operation manual" written in some other language and then poorly translated into English was something else. The other three are from US Distributor AutomationDirect. I bought my first one for my mill many years ago and it has been working relentlessly without a hitch since. AD provides live phone support from their well trained techs and do so promptly. The documentation for their VFD's is very complete and comes bound in a spiral notebook with excellent photos and explanation of all possible setup options along with a quick start (adequate for most applications) guide. I happily pay a little more realizing I am getting a first-class product with real support and spare parts and accessories readily available They have been in business a long time and will likely be there in the future if you need something from them.

I am sure there will be many opinions on this. Just my suggestion from a long-time and frequent mill user and happy AutomationDirect VFD customer.

Denis

 

I like to support anybody's decision in and give some input and clarity. I like to help decide whether it is important for them to choose different avenues. I sell Vfd's and this is not a plug. I'm OK with assisting people with a Vfd that I had no interest in. But, there is a lot more to it. Should you go static phase converter SPC, VFD, RPC, RPC with transformer, Phase perfect... I also like to support the proper Avenue people should be taking.

What kind of machine,s is it powering? How many motors are in the machine or machines? What is your price range and what is your future intentions?
1 hp still needs 15 amp single phase 240 V
1.5 hp still needs 20 amp single phase 240 V
2 hp still needs 20 amp single phase 240 V
3 hp still needs 20 amp single phase 240 V
5 hp still needs 30 amp single phase 240 V
7.5 hp still needs 40 amp single phase 240 V
10 hp still needs 50-60 A single phase 240 V

The way to figure out what you need to power a 230 V 3 phase motor is.... take its FLA, full load amps, multiply that by 1.733 and then take the total and multiply it by 1.25%. This is the safe working load for the combined circuit on single phase.

What is the maximum power to your shop? (I sell VFD's up to 25 hp that have 75 amp output. You need 150-165 A input single phase at 240V)

Automation direct is a great place to start out to do window shopping. But, they will not sell you a single phase VFD that is 5 hp or bigger.

Most companies that sell Vfd's that do not specifically say single phase input three phase output, have to be Derated. This means you need to buy a Vfd that is two times bigger. I can explain if you need.

I personally have seven machines now hooked up to a Vfd's and six machines hooked up to an RPC. I also have another 40-60 VFD's just sitting around.

 

Kelly, you would adjust the ramp up speed timing. Almost no machine needs to go from zero to full motor rpm in two seconds. There is also a little button parameter that you can use torque compensation for small periods of time. You can also use sensorless vector which automatically adjusts amperage very quickly to maintain desired RPM.

Air compressor would need an unloader valve. The big problem for any machine is variable torque requirements on start up like a cement mixer. And big lathes that have 12 different gear speeds. These machines are more moving target. It's best to set it for a happy medium.

My air compressor has four different speeds for charging up. It's all dependent on how fast you're unloading it, and then it adjusts.

 

Please explain because I don’t think this is the case. I do think Derating of VFD’s is only needed when used outside their original design parameters. A VFD designed for 1HP with single phase 120 input provides 1 HP 240 3phase output. A VFD designed for 3-phase input will need derating. Every manufacturer site I’ve visited points this out.
Other factors that can indicate derating are higher altitude, humidity, poor input power quality, etc.

Most manufactures (I don’t know of an exception) have a blurb on this. For example:

http://www.vfds.org/vfd-derating-541974.html
“Derating a variable frequency drive means using a larger than normal VFD in the application. Derating is required when a VFD is to be operated outside the normal operating range specified by the manufacturer. Most VFD manufacturers provide derating figures when the VFD is to be operated outside the specified temperature, voltage, & altitude. As an example, derating must be considered when the VFD is installed at high altitude, greater than 1000 meters (3300 ft.). The cooling effect of the VFD is deteriorated because of the reduced density of the air at high altitudes”

But in reality for most of us who are not pushing our machines to the edge of their capacity for long periods of time, the major derating factor would be using a 240 VFD with 120 input which would be rare.

Denis

 

The only reason for derating as I understand it is that rectified three phase needs six diodes in the bridge rectifier and the conduction of those diodes overlap sharing the total current between them whereas a single phase bridge rectifier has much higher peak current flow in the diodes compared to three phase. Now you can feed single phase into a three phase bridge if you derate the unit so the diodes don't overheat as there's only four diodes running at higher peak currents instead of six diodes. Also there's not enough DC filter capacitance in a three phase VFD to adequately filter rectified single phase. Rectified single phase has 100% ripple voltage where rectified three phase has 13.4% ripple voltage so it needs less filtering. I have a 1998 Allen Bradley VFD that will let you bypass the rectifiers and feed 600 Volts DC straight into the filter capacitors to avoid derating the unit.

TLDR: Three phase VFDs have smaller rectifier diodes and filter capacitors compared to single phase VFD's.

 

I would really need to get more information like what size is the feeding circuit? Do you know which line has your starting capacitors on? And how comfortable are you with wiring? And do you know what your line to line voltages are at idle and after the machine has ramped up to idle speed?

For about $30 and a little bit of wire you can add a small modification to heavy load start machines like your sander. The sander you actually have to manually press the start button. You can add 100 microfarad capacitor and a small contactor to the sander. You would have to hold the start button like you did in clothes dryers 30 years ago. But, you can buy from North American rotary phase converter's and American rotary phase converter's special RPCs for hard starting loads.

Sure, there are Vfd's that are specifically designed for single phase input. But majority of VFD's are three phase input. Sure, you can find a lot rated for 3 hp or smaller. Try to find 5 hp or larger single phase VFD's.

 

https://bbs.homeshopmachinist.net/f...awa-vfd-with-a-cheap-import-10hp-single-phase

Not very common to find, but can be useful at times. I have filed this away incase I have a need some time.

 

I think the question at hand is powering a 3-phase 2HP J-head BP. Pretty basic and very common application. Just the ticket for a good single phase VFD.


I’ll be buying yet another AutomationDirect 3 HP single-phase input VFD to power a 2x72 belt grinder I am going to build. I get the steel today. Very excited as this should be an excellent setup. The variable speed will be a huge plus. Just the thing for pattern making etc.


Denis

 

A lot of those Youtube belt grinder designs could benefit from using a properly sized rubber tyred wheel on the motor as they will slip well before the motor horsepower can be used. Also the surface speed of the belt is important with some popular Australian brands running the belt at half the manufacturer's recommended speed by using a four pole motor and then stating their machine extends belt life . I just quickly "borrowed" from this article: https://www.redlabelabrasives.com/blogs/news/optimal-speed-for-a-belt-grinder which says for cast iron you want to be able to reach a maximum surface speed of 8820 surface feet per minute. Looking at the machine in the video Denis linked to, I'm guessing the drive wheel has a diameter of 5 inches, so 3600RPM x 0.262 x 5" = 4716 surface feet per minute unless you run the 2 pole 3600 rpm motor at double speed. Some designs use an 8" rubber contact wheel as the drive wheel on a pulley driven shaft (or directly off the motor) and with a 3600 RPM motor that would give you 7545 surface feet per minute without speed controls.

Material to be Processed, Surface Speed (Feet per Minute):

Cast Iron & Carbon Steel: 4920 - 8820

Lacquers & Varnishes: 1560 - 2940

Hard & Hardened Steel: 1560 - 2940

Plastic & Rubber: 1920 - 3540

Titanium & Titanium Alloys: 1920 - 4920

Wood: 2940 - 4920

Stainless Steel, Tool Steel, & High Speed Steel: 3540 - 5880

Copper & Brass: 4920 - 6840

 

Probably should not take this thread too far afield, but will comment in response to Mark above that this grinder will reach 6000 FPM. It is my understanding that running belts too slow ruins them as the load on each individual grit piece becomes too great and they fail rapidly. It is roughly analogous to running a carbide lathe or mill tool too slow with too much feed—-they also break down but do well with high SFM and lighter loads.

Denis

 

What did the wheels cost?

 

I cast my wheels.

 

I know the market. Two days ago I just set up this machine. 36 inch wheels.

I can get it up to full speed in 15 seconds and it took 90 seconds for it to stop.

 

I’ll be interested to see the build. It seems like a great application for a treadmill motor.

Pete

 

You may well be right about that. I think I have such a motor that has for a long time been looking for a use. I’ll have to see if I can locate it and the controller I salvaged 10 or more years ago.

Denis

 

Is there any utility in buying a 15 hp 3 phase motor from the scrap yard? I see the big ones come through fairly often and they feel like they spin freely so I'm guessing they still work? I usually get them fairly cheap.