Stepper Motor As Lathe Spindle

[2_many_hobbies]

I know I know their are alot of these questions but 90% end up as a fight and usualy their is no clear yes/no answer.

I have my Taig lathe and I use it every few days and am quite fond of it but I would like to put it on my current mill and use them together rather than cnc the lathe individually. I will still use it for alot of turning but will mount the cutting tools on the Z in a ganged format.

What I need to know is if I can actually expect to get the same work results out of the lathe if I convert the spindle to run off of a huge nama34 or larger stepper motor. For example if I use a 1200ozin nema34 with a 2 or 3 speed pulley (for torque if needed) and a timing belt for power transmission can I achieve the same results as running the stock 1/4HP AC motor?

I cannot use a PMDC, BLDC, servo or anything else a stepper is my only option here but I can go up to a nema42 if necessary.

Thanks!

[kawazuki]

Its my understanding that a stepper has its most torque when powered & stationary which tails off, slowly at first, the faster it rotates. At max rpm, torque is quite limited so for a spindle drive a slow stepper speed is req to give torque but geared up several times to provide decent turning rpm. All the gear up's will introduce backlash so if used as a indexable drive spindle the stepper might move 100 steps but the spindle could effectively move only 80!
Really servos are suited in this application (note I didn't say BEST suited)

[rowbare]

The nature of a stepper motor doesn't lend itself to use as a spindle motor since it by definition moves forward in discreet steps rather than in a smooth motion. Also the torque output decreases rapidly with speed so that by the time a stepper is turning 600 rpm, the best of its torque curve is behind it. This effect seems worse for bigger motors. Check out the torque-speed charts on keling's site and you will see what I mean. Most of the charts are based on half-stepping the motor so 1000 pps = 150 rpm.

[2_many_hobbies]

Yea I was afraid even a very large stepper wouldn't be able to handle it. I saw a few youtube vids that got my hopes up though.

Im adverse to the servo method as they require a controller and thats expensive for one over 100W. I could use BLDC motor but once again a controller would be expensive for a powerfull enough motor. I tried to use a PMDC motor as I can control them very easily with some SCR's from work but finding a damn motor thats any good is hard and expensive. Just because it says 500W 500RPM doesn't mean its worth anything at delivering power...

Any ideas on how to run the spindle while its on the mill? For indexing a stepper is easy but I want to do some actual turning still and the 1/4HP AC marathon motor is as big as my axis travel.

The goal is to have a setup like Hoss has but as he used the motor from his 7x lathe I still need to find one.

EDIT - Hmmm I wonder if you can buy a replacement motor for the 7x lathes... Their 110V DC and the perfect size for many projects. Anybody know a link?

[phoglite]

Hi, I ran across this guy's site a while back - might help you with ideas.

http://www.lozengy.net/?p=13#more-13

-Keith

[hoss2006]

Originally Posted by 2_many_hobbies EDIT - Hmmm I wonder if you can buy a replacement motor for the 7x lathes... Their 110V DC and the perfect size for many projects. Anybody know a link?

http://www.littlemachineshop.com
They have a cheaper 250W motor too.
Hoss

[2_many_hobbies]

phoglite: Holly crap I almost choked when I opened that link I cant believe the saddle of the Taig mill can handle that much lateral torsion but I would seriously worry about pitting the ways with that setup for long.

I was on the LMS site and didn't see that motor, too bad its ridiculously expensive.. Ill keep an eye on ebay and maybe find something. Sofar this is the closest I have found:

3/4 HP 110V sewing machine motor
1/4 HP Honeywell 90V 1800RPM but its quite long
1.5HP 48V scooter motor

The scooter motor at first glance is the best but I have a 5000RPM, 48V, 250W and I can stall it by hand. Its HP is not the greatest idea of available torque and sadly my $50 motor is useless. That 1.5HP with neodynium magnets could be ALOT better though as mine where very piddily.

Anyone know of a few surplus places in the US that will ship to canada? Up here we got Princess Auto and they suck very badly.

[youngjim]

Originally Posted by 2_many_hobbies Anyone know of a few surplus places in the US that will ship to canada? Up here we got Princess Auto and they suck very badly.

Tell me about it! 900 bucks for a 10x22, when I can get it in the US for about CAD400? Boo.

Jim

[2_many_hobbies]

Originally Posted by youngjim Tell me about it! 900 bucks for a 10x22, when I can get it in the US for about CAD400? Boo. Jim

Uhh do you mean a 7x12 for $900CDN up here and you can get them in the states for $400CDN after the exchange and tax? Even if its a 7x12 I will buy two. If you know where I can buy a 10x22 for $400CDN Ill buy 10!!

[youngjim]

I may have been thinking of the smaller lathes, yes. The point is, we're getting screwed on purchasing these up here. It makes the idea of a road trip entirely worth it.

Jim

[2_many_hobbies]

I live 30min away from Grizzly Tools in Bellingham, Ive been there so many times drooling and dreaming. Im currently working on getting a 10x22 lathe and a RF45 or x3 brought up here this year. You want to see us getting screwed goto amazon.com and realize that things like my nokia internet tablet is $225USD while that same item shipped from the same american warehouse is $318 plus I was going to pay 12% tax as well as $35 duties.

The whole concept of NAFTA doesn't exist anymore because america no longer manufactures the majority of anything and since they don't pay taxes or duties on anything they import from anywhere why would they bother doing it locally.

Anyways I'll ask again, anyone know of a US based surplus that has DC motors that ships to canada??