Stepper As A Lathe Spindle Drive

[mklb]

First Time Post, Long Time Lurking In The Shadows.

I Have A Diy Cnc Lathe Which Is Used For Turning Pool Cue Shafts.
It Is Essentially A 2 Axis Cnc Mechanism Mounted Next To A Small
Lathe (taig Parts With A 4 Foot Aluminum Bed).

The Machine Works Excellent, But I Want To Make It Even Better.
I Need To Be Able To Control The Speed Of The Lathe Spindle. I Am Currently Using A Blower Fan Motor From A Home Ac Unit. It Is A
Capacitor Start Motor, And I Have Not Been Able To Come Up With
A Method For Controlling It's Speed.

My Thought Is To Use My Xylotex Board To Drive A Stepper To Turn
The Lathe Spindle. I Have Everything I Need, I Just Don't Know How To Command The New Axis To Just Spin At A Specified Rpm.

Is This Possible? I Believe I Have Seen It Done Before, But I Can't Find Where I Saw It.

Any Help Would Be Greatly Appreciated.


Btw
This Site Is Solely Responsible For Inspiring Me To Build My Machine. I Have Been Studying This Stuff Off And On For Years, But Never Got The Nerve To Do It, But This Site Led The Way.
Thanks To Everyone Here.

Mklb

[ger21]

I know you can do it in Mach2, but not sure about TurboCNC. I just looked throught he manual and didn't see anything.

[mklb]

Ger21

I Downloaded The Manual To Mach2 And It Looks Like A Very Good Program. I Will Be Needing To Do Some 2 1/2 Dim Dxf Conversions Anyway And It Looks Like Mach2 Does That.

There Is A Ton Of Information In That Manual, How Long Is The Learning Curve? How Is The Support For Someone Who Is In That Learning Curve?

Mklb

[2muchstuff]

mklb,
My first concern is with your spindle motor, an a.c. blower motor. They are pretty much designed to to run at one speed or two ( heating and cooling). The torque will drop off as your speed is reduced. A step up would be a d.c. servo motor with a drive or a pemanent magnet d.c. motor with a pulse-width modulated speed control. With a d.c. motor, you will have more torque available over a broader speed range. Years ago I had a Taig lathe that I mounted/ used a Dayton 90 volt d.c. motor. The speed was controlled by a lamp dimmer driving a bridge rectifier/ capicitor to convert it to d.c. Very simple set-up.

[ger21]

You won't find better support. I'd recommend joining the Yahoo support group. Art also answers individual emails, although you'll probably get a little faster answer from the Yahoo group at times. Once you do your basic setup, it's not really any more difficult than TurboCNC, once you know where everything is. It's just a lot more powerful. You MUST use Win2K or XP, though.

[mklb]

2muchstuff

I Realize That The Motor I Am Using Will Not Provide Much Torque, Especially If I Try To Slow It Down. However, All My Turning Is Done With A Trim Router Spinning A 6 Flute 2" Diameter Slot Cutter At 30,000 Rpm. There Is Virtually No Load To The Spindle Drive Motor At All. In Fact Many Of My Operations I Don't Even Turn It Off To Change Parts, I Use The Spring Loaded Live Center From Taig, And All My Parts Are Turned On Centers.

Torque Is Not The Problem, Vibration Is. When You Turn Small Diameter Long Wood Items Like A Cue Shaft, Speed Will Make Any Vibration Worse. I Currently Spin The Parts At About 200rpm Using The Slowest Speed On The Motor And Step Down Pulleys, But Would Like To Be Down To Around 120rpm.

The Ability To Change The Spindle Speeds Would Allow Me To Experiment To See Which Speed Gave The Least Chatter In The Work Peice. If I Just Machined A New Pulley To Slow It Down Some, I Wouldn't Know If That Was The Right Speed Until I Tried It. That Could Lead To Machining Quite A Few Pulleys.

Driving The Spindle With A Stepper Motor Controlled By The Cnc Only Makes Sense. I Could Experiment With Speeds Very Easily And Home In On The Right Speed For Each Component.

If I Had Easy Access To A Small Dc Motor And Speed Control That Would Also Work, But The Repeatability Would Be A Judgement Thing. You Know, A "I Think I Set Right There Last Time" Kind Of Thing. The Stepper Would Be Easy Set To An Exact Rpm Each Time.

Mklb

[2muchstuff]

mklb,

I see where you are coming from. I have had this vibration problem in the past when machining long thin items. You end up with tool chatter marks and deaf ears. What I use is known as a "steady rest". They can be mounted on the carriage cross slide to follow the where you are working, or to the lathe bed if you are working on either side. In your case because you are using wood (pool cues), a slight adaptation might be required. Using the steady rest idea, change out the metal followers and replace them with small rubber covered rollers like you would find in a copy machine. With cues being tapered, the rollers would need to have a convex surface and be under spring tension against the cue holding it in place. By using a steady rest you will be able to bring your speeds back up and the surface finish quality. Hope this helps you out some.

[mklb]

2muchstuff

i am familier with steady rests. the problem is that steady push the work piece some even if just a little bit. when you are cutting wood, a little bit can make a big difference.

the other problem is that i am cutting tapers. these are not straight tapers, but very complex tapers. so complex that i you could not use a steady rest unless the rest is also controlled by cnc, and i dont think that is all that feasable.


anyway, i like the looks of mach2. i need to upgrade my computer to xp, but that is not a big problem.

anyway, if there is a better way to speed control an ac powered,capaciter start, motor, then i will just have to experiment with that later.

thanks for all your help


like i said, i would not have even built this machine is it were not for this site.

mklb

[Fred in NC]

For fractional HP I find it easier to use a PWM speed controller and a DC motor. I have a Jet Mini wood lathe that I converted to DC. The motor has an encoder so it is essentially a servo. The controller will keep the set RPM regardless of the torque requirements. The minimum speed is <> 60 RPM.

Surplus Center has several controllers for DC motors in their site at <= $50 right now, and DC motors from $10. A 2 HP - 230 VDC motor run at 90 V will still develop 3/4 HP, which should be enough for a Taig lathe.

I have no idea how to control the speed of an AC motor other than with a VFD, which is kind of expensive.

[mklb]

Just update things a little.

ger21, Thanks for the input on Mach2. I have downloaded the trial version, updated my pc to XP and loaded it. I have the setups done and I am now beginning the play with it. I think I am going to like this program. Eventually, I will upgrade to a 4 axis xylotex board, add the z axis to my machine, and use a stepper for the spindle as well. but for now....

Fred in NC, Thanks for the idea about Surplus Center. I had forgotten, but I had a DC motor with a speed controller that I had bought from them many years ago. I blew the spider webs off of it and mounted it on my machine. Sometimes it hunts for the speed a little, but all in all it works pretty well. Slowing down the spindle has allowed me to cut down to .440" diameter maple, 29.5" long with no chatter. That is machining between centers! The work piece is being driven by friction only. You can stop it with light finger pressure!

All in all, you guys have been alot of help. I knew if I asked my questions here I would be steered in the right direction.

Thanks

mklb

[Hobbiest]

How about some pis of your lathe?

[mklb]

I ould be happy to try, but I haven't a clue as to how to do it. I do have a digital camera (wife's), but I have no idea how to post the pictures.
Maybe you could give me some direction?

mklb