Variable Frequency Drive

[erik_f]

Would it be possible to plug a PC Router into a variable frequency drive? I saw one for around $300 that will handle 3hp and 10amps. My goal would be to slow the PC router down enough to be able to play with some types of metal.

[John Paul (Unregistered Guest)]

This is all you need.

http://www.mlcswoodworking.com/shopsite_sc/store/html/smarthtml/pages/speedcon.html

The 3hp VFD that you saw is for 3-phase induction motors or spindles. The PC is a brush-type universal motor. The unit from MLCS is basically a rheostat.

[gerald_d]

Slowing a PC router down takes away its torque and also slows down its cooling fan - it's a very good way of burning it out.

[jay]

Erik & John.
John I think you missed the last line of the Special Features list.

"NOTE: Will not work with soft start or variable speed routers"

Many of the PC Routers have a soft start feature even if they are not a variable speed router.

You don't have to ask me how I know they are right, it does not work!

[normand]

Even without soft start on your router you will burn it. And like Jay you don't have to ask how I know.

[erik_f]

Burning up the router was my fear...so there is no way to do it safely for a router?

Erik

[gerald_d]

An electric with brushes has a very narrow designed speed range. The safe way of moving the speed range is with gearboxes or belts/pulleys.

[gerald_d]

Jeeps! did I forget the word "motor" above? Senility is a b.....

[John Paul (Unregistered Guest)]

Erik,

The PC at 10K RPM will cut aluminum and maybe brass. Go slow.

[erik_f]

Maybe this is just getting silly, but what about running a DC motor with a speed control? I think this could be done pretty cheaply...I don't know what kind of run out you would be talking about with and off the shelf DC motor though.

John Paul,
Thanks for the advice...I will go ahead and give it a shot and see how things work out...just looking to have the most fun possible with the bot.

Erik

[gerald_d]

Erik, why do you think a DC motor will be better than an AC motor?

[erik_f]

I've seen DC speed controls for around 100-200 dollars and dc motors for around the same on some surplus sites. I'm not an expert by any means about this stuff...but my understanding is that a DC motor will not lose torque or will at least have alot more torque than an AC motor...seems though DC motors have a lower top end speed? But are variable from 0 to what ever speed without worry of burnout...I could be wrong...but this is my understanding thus far. But I guess I could just get a 3 phase motor and run a VFD from 220 single phase? The point would be to get the functionality of a spindle. Does anyone know what kind of run out we would be looking at with an off the shelf motor? Also would it be possible to replace stock bearings in a motor with upgraded ABEC 5 or 9 bearings?

Erik

[gerald_d]

"But are variable from 0 to what ever speed without worry of burnout" Think about what will cool the motor at speed 0.....it is the lack of cooling that makes them burn out. AC or DC. A DC motor's speed is very sensitive to the load placed on it.

[gus]

Gerald,
Have you ever thought about hydrostatic. :>)
Air motors? Just buy a small mill, take the head off and hang it on your Z. Things that come into your head when you did not have your morning coffee.

[gerald_d]

This thread started with Erik wanting to slow a PC router down to cut metal. Not a great idea. Now we seem to be at the "clutching at straws" or "re-inventing the wheel" phases of the thread

[erik_f]

If you were able to bypass the soft start in a single speed PC router a speed controler would work..but heat would be an issue...if you are working at little to no load...would the router still heat up to the point of self destruction? I guess I will just stick with what I have now and try some aluminum at 10K.

Erik

[John Paul (Unregistered Guest)]

I think in the end, it comes down to practicality.

Yea, the PC is not designed to cut metal, and it may wear it out prematurely. But it's really not crucial to have a 3K RPM spindle to cut aluminum. 10K will do the trick. Spraying the tooling with some dry lubricant like Dynaglide every few seconds will help. Keep the passes shallow. A shop vac to clear the chips will help reduce heat as well.

Even if one were to buy a MANUAL milling machine, it would cost $1200 to get get the most basic, cylindrical column, belt drive head, Rong-Fu clone. Then add $200 shipping. Even if it somehow got the job done (hard to do with no DROs or CNC), it would probably lose about $300 in value when sold, plus the original shipping cost gone.

The PC router at under $300 is practically a consumable in the world of CNCs.

[gerald_d]

Little or no load means little heat and the PC should survive that. If the router stays cool to the touch, you are probably okay.

Have a look at the Metabo GE900 (http://www.metabousa.com/metabo/us/us/produkte/diegrinders/900wattelectronicstraightgrinderge900plus_06305.ht ml) die-grinder - it is geared down, has good bearings.......

[gus]

$1200? How about 399.99 and I could have picked it up in town yeasterday at the sale. They bring the truck around about 4 times a year.
http://www.cumminstools.com/browse.cfm/4,1485.html (http://www.cumminstools.com/browse.cfm/4%2C1485.html)
Run the head off the slide, mount it to the Z on your Bot, put a tool in it, Zero, FP.......when you are done slip the head back on the little mill and sell it at a garage sale for whatever you can get. After all "The chuck seems to have some play in it but it don't look like it has ever been used." Or throw it away and call it a consumable. It all gets down to how bad/great is your need/want to cut metal and what are you willing to do so you can produce your part with the quality you want.

"re-inventing the wheel" spoken like a true wheelwright.;>)

[erik_f]

I guess I was just looking at if I could get away with spending 300 bucks for the PC be able to drop it in place of my variable speed PC and be able to use it for metal...and if I use shallow passes then all should be ok with the modified/speed controled PC...maybe...

[gus]

Erik,
If you want to invest the time and the money to try something give it a shot. Play with it see what it will and will not do. If you keep a close eye on things you will know if things are getting out of hand. The proof of the pudding is in the eating. If it works for you it works.

[david_moyer]

Hello Gentlemen -

I am new to posting on this forum, but have been an avid reader here for many months. A lot of great ideas are exchanged here!

I've followed this thread and finally have a comment I think is worth posting regarding Erik's VFD question.

When most people think of slowing a router, they think of a VFD, but as John Paul noted earlier, all VFD's, even if they accept a single phase input, all have a three phase output. And, as far as I know, getting a three phase router head isn't an option.

I had a conversation not long ago with a friend from the appliance industry regarding this issue and he stated that slowing a single phase motor is possible. He stated that the device used for this is not a VFD, but is instead referred to as an electronic variable speed drive (VSD).

A search in google for this topic reveals the following company (http://www.anaconsystems.com/)

I am NOT an expert on this piece of equipment, but have been considering the VSD for my own use on a router. One issue - most routers are 3 HP and the largest Anacon unit (their model Optidrive E1) is rated 1.5 HP at 230 V single phase. I have not yet run a test on my router to determine if I am using the full 3 HP, but I suspect that I am not doing so and I think this VSD might work. It is available for $485, which is near the price of a head. I just havent yet convinced myself this will work. Any thoughts from an other members?

[gerald_d]

David, I think that the Optidrive is only efficient with "squirrel cage" motors, like you would typically have on a compressor or bench saw. Squirrel cage motors are brushless and their speed is normally decided by the incoming frequency (60Hz). Typically these motors turn at either close to 3600 rpm or 1800 rpm. To get them to turn at speeds in between you need a variable frequency drive.

However, handheld tools have motors with brushes. Their speeds seem to be more dependent on voltage and load than frequency......
Okay, I am getting out of my depth here, but I think that using a VFD for a brush motor is going to be a mismatch. The cheapie voltage controllers are about as much as you can do to slow down a brush motor, I guess? Which is about where this thread started.....