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torker
03-27-2009, 08:43 AM
Hey guys! I put in a late one last nite...machining out a bunch of parts for a big alu transome mount for a motor boat.
It's two plates that act as a sandwich to go over the transome but I made an alu third member for this that snaps into slots in the two outer plates...sorta like a big Lego set.
The plates are 30" long so I had to use my Ohio with the BP M-head to get the travel I needed.
What a cool old machine this thing is now that I have the M-head on it.
This is the first time I've really got to put it to work.
The old M-head is really very handy...thanks Bguns for talkin me into trying it!
I ended up using 7/32 and 3/8" endmills on this project and being alu it needed some pretty good speed.
I had installed the 3/4hp 90V DC motor I got from David Cofer
After using it for a couple hours...I was just tickled with it.
So easy...just a quick turn of the dial and get the speeds I needed.
Nice light motor...lots of power...very smooth!
So...it got me wondering...why don't they put more DC motors on mills and lathes?
Vari speed...good grunt...instant reverse...what's not to like?
If I end up getting to keep my equipment...I'd like to put another DC motor on my lil turret lathe and would sure be into putting one on almost anything else in the future.
So...what am I missing?
Why don't we see more of these?
Russ

wierdscience
03-27-2009, 08:58 AM
Hey Russ,well they work fine,but the motors new are expensive compared to a 3~AC motor.They are availible used and surplus though and the controllers are cheaper than a VFD.

These guys usually have some,then there's always ebay-

http://www.surpluscenter.com/

ptjw7uk
03-27-2009, 09:13 AM
Hi Torker nice to hear from you, best wishes with the probs.

Only reason I can see is that with brushed motors they will not stand up that well under lots of load whereas a properly sized 3 pahse will run all day with no brushes to wear and cause interference to electronic parts (cnc)
I now think the modern brushless DC motors are another thing to think about although I thought the modern thing was a linear motor on the slides.

Peter

Bill Pace
03-27-2009, 09:38 AM
Good to have you back Russ - I hurt for you...

I have loved DC motors for years. Back in the early 90's Surplus Center (that Weird mentioned) had a treadmill motor with controller for sumpthin like $29, got one and put it on a Chinese DP and I loved it! Went and bought 2 more... Since then I've scrounged 4-5 others just picking them up here and there. I've currently got 4 pieces with DC motors. My mill-drill - (like yours, you know, that piece of s**t that nobody loves;))- has one of the larger treadmill motors on it and that thing will get it. Got one of the smaller ones on a DP and another on my little 9x20 Chinese lathe, then another larger one on a 16" wood band saw converted to metal cutting. It really IS nice to just tweak that little knob and change the speed.


Keep an eye out for tread mills, -- theyre thrown away, donated to thrift stores, sold thru local advertising for cheap, etc. The best ones though are from the larger units, like a health club would use, and of course thay are a bit harder to find

Jimno2506
03-27-2009, 10:45 AM
All,

I've added to my list the retrofit of my noisy, bashlashing, 6-speed head on my RF. I have two 220v and one 110v 1.5hp motors and the variable speed Dart controller that I salvaged off the ole Smithy. I have no way to get 3ph (homeshop) and this will cost me very little...Just timing belts and sheeves.

Now with spring here I'm sure I'll have lots of time :rolleyes.

Regards,
Jimno

Forrest Addy
03-27-2009, 10:51 AM
DC motor Dc drive - AC 3 phase motor VFD? It's a toss up for actual running features. The deal breaker for me is the DC motor is a bit more fragile than its AC xounterpart other things being equal. The other big consideration is const of replacement should failure occur and I need the equipment it powers ASAP. Direct replacement AC motors are about 1/2 the cost of DC if you don't have a spare handy.

There'fore I lean toward AC as the more robust and lower in replacement cost compared to DC especially in recent years when even new VFD's are about 1/2 the cost and physical size and double in terms of electrical features than their equivalent VFD's of ten years ago.

But a full featured varaible speed drive with instant reverse whether AC or DC is well worth the cost and time to install. The first thing I would install in a new;y acquired manual machine tool would be a DRO. The second would be a variable speed drive AC or DC, I don't really care so long as it has the oomph.

camdigger
03-27-2009, 11:13 AM
If I can recall the discussions from my school days...

The advantage to DC power is lower stall currents, variable speed (although not as closely controlled without a feed back loop). The DC motor puts out a relatively constant torque through a wide speed range.

The advantage to synchronous AC motors (single or multiphase) is the speed is locked to the input power's frequency (50 or 60 hz line power) unless the power is processed through some kind of VFD which varies the input frequency put to the motor. Synchronous motors put out a wide range of torque over a relatively narrow speed range. Unless some kind of current limiting device is on the input, the current draw increases rapidly with decreased speed and typically, the motors electrics won't withstand the currents at or even near stall (releasing that expensive magic smoke).

The next advantage is maintenance. AC motors usually do not have sliding contact through brushes. Most large DC motors need electricity to the rotor winding to create a rotating magnetic field for the stators' rotating field to work against the current for the rotor winding runs through the brushes. Sychronous motors AKA induction motors, aka squirrel cage motors have no electrical connection to the rotor. All the magnetic field in the rotor is Induced from the staor winding.

Simpler construction = less maintenance and less $ In an nut shell, you get more predictable speed for less $ and maintenance hassle for the same ouput motor which would you pick?

pgp001
03-27-2009, 04:22 PM
When designing new machines we tend to use AC motors with an inverter and filter these days.
We used to use a lot of DC motors with speed control boards, but apparantly these are much harder to get through the EMC tests which are now a requirement.

Phil

Boucher
03-27-2009, 06:52 PM
There are lots of power wheel chairs around that might be a source of heaver duty DC motors. I ran across one left over at a grarage sale. The people were moving and did not want to take it with them. You may not be interested in 12V but just a thought.

S_J_H
03-27-2009, 09:59 PM
I have 3 machines with DC motors and 1 with 3ph AC and vfd.
My SB9A I fitted a new Leeson 3/4hp 90 volt DC motor and a Minarik variable drive. It's dead simple to use with the simple dial and reverse toggles. Has plenty of adjustments for torque/speed etc.
I have the 3ph and vfd now setup on my old Artisan lathe.
Again, dead simple to use but a lot more bells and whistles.

Both motors are very quiet. The dc motor "seems" to have a little better extreme low speed power.
The Leeson DC motor was quite expensive but since I got my SB9A for free I figured I would splurge on a good drive for it.
They are both great systems and a hell of a lot better than a single phase single speed motor.
Steve

macona
03-28-2009, 04:55 AM
The Monarch 10EE, 13EE, 1000EE, and their little chucker all had DC drives. They work nice but the are nowhere near as maintenance free as a AC Motor and a VFD.

Most CNC machines, lathes and mills, until recently have brushed DC motors for spindle drives. Now they uses AC or DC brushless motors instead.

Its only recently that the price of VFDs has dropped to a level where they are cost effective for them to come stock on machines. Regen DC drives and motors are quite a bit more than a VFD setup.

Bguns
03-28-2009, 05:29 AM
Mine has been doing heroic Duty on 3/4 steel. It is machining Its own replacement adapter for a Beat J Head I have...

On the DC Motor Thing, There is a Lot more Copper in the DC Brush Motors which = $$. A 3 Phase AC Motor is just so Simple...

I'm Kind of tough on it tho, Only a Static Phase converter. So only 1/3 hp or so...

Noticed that my Original 3 Phase US Motor is rated 30 Minute Intermittant Duty...

I have exceeded that often... Had to spend a Day picking Grease out of windings from 50 + years of Overgreasing that melted when I ran it a bit too long. I usually give spindle a spin by hand to Give the Poor Static a bit of a break when Starting... Went to Start in the Morning and Spindle would Not Move. That grease really locked up the motor when cooled down...

The adapter is coming along.. When presentable will post Pics... A Round Ram with a J Head AND Nod adjustment/reinforcement..

Hang in There, Been there done that...

John Stevenson
03-28-2009, 06:10 AM
I do a lot of work On DC motors for the simple reason AC is easier to replace Dc is usually special for an application, often max torque at low speed, that makes them worth repairing.

So basically it's down to cost, more copper wound armatures with comms and brush gear to be maintained.

Some medium sized fork truck motors can cost up to $5,000 just for the motor so these are well worth repairing.

However times are changing in that the motor of a fork truck is one of the most expensive / unreliable items on it.

Some of the new truck have standard 440 volt 3~ motors driving the hydraulics, simple off the shelf motor that's easy and cheap to replace.
The truck charges it batteries as normal from a mains supplied 48 volt charger then it takes this 48 volt DC and inverts it to 440 v 3 ~, a bit like a backwards VFD.

Electronics nowadays are cheap and very reliable so the inverter method works well and allows then to tune the system to suit the truck in question.

.

jackary
03-28-2009, 07:12 AM
I would like to make a brushless DC motor for a lathe milling spindle, say about 300 watts. I was planning on using an existing brushed motor armature as the internal stator and remaking the rotor using the original magnets. Is this viable?
My main problem is what electronic operation/control is required. Lack of Knowledge here.
Regards
Alan

macona
03-28-2009, 08:53 PM
I would like to make a brushless DC motor for a lathe milling spindle, say about 300 watts. I was planning on using an existing brushed motor armature as the internal stator and remaking the rotor using the original magnets. Is this viable?
My main problem is what electronic operation/control is required. Lack of Knowledge here.
Regards
Alan

I wouldnt waste your time. There are brushless motors and drives meant for RC Cars, boats, and airplanes that will do this a whole lot easier than trying to make one.

That being said there are several sites on how to make your own brushless motors from scratch.

J Tiers
03-28-2009, 09:04 PM
I would like to make a brushless DC motor for a lathe milling spindle, say about 300 watts. I was planning on using an existing brushed motor armature as the internal stator and remaking the rotor using the original magnets. Is this viable?
My main problem is what electronic operation/control is required. Lack of Knowledge here.
Regards
Alan

Agree with macona, UNLESS you have a special purpose that absolutely requires a specific size and performance. And then I'd contact a maker of the motors, who will be far better able to deal with it.

of course, if I just wanted a challenge, I might....... but then I might just train for a marathon instead. More long-term benefit.

jackary
03-29-2009, 06:43 AM
of course, if I just wanted a challenge, I might....... but then I might just train for a marathon instead. More long-term benefit

Thanks for the reply. I suppose you are right in the long run.
Regards
Alan