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biplanefan
04-24-2007, 01:59 PM
I'm in the planning stages of building a CNC hotwire machine to cut out Radio Controlled aircraft parts and I have a stepper motor question. I found some stepper motors for a good price and was wondering if they would work. Here's the info off the sticker on the back of the motors...

Astrosyn Miniangle Stepper
p/n HM000310000
AST TYPE 23LM-k055-01
NO. H1524
3.4 V/Phase
2.1 A/Phase
1.8 Deg/Step
Minebea Co., LTD

If these are not what I need, what should I be looking for?

Thank you

Robin Hewitt
04-24-2007, 02:12 PM
I usually look for the diameter rather than the coil rating.

More diameter = more leverage on the rotor :)

biplanefan
04-24-2007, 08:21 PM
What should I be looking for when shopping for stepper motors? I trying to buy the pieces as I go, I can't afford a complete setup like hobbyCNC sells at this time.

What is the difference between Bipolar and uniploar? What is the difference in the number of wires.

Robin Hewitt
04-25-2007, 04:16 AM
The web is full of stuff on steppers, but if I had to pick out one thing to look for it would be a graph of torque against speed.

Max pull in rate is fairly imaterial once you hang heavy lead screws on it.

Detente/holding torque tells you little about dynamic performance.

Inductance/resistance and volts want to be low, but you will end up driving it way over the stated voltage anyway.

OTOH, a diagram showing which wire goes to which coil is very desireable :)

cnccutter
04-25-2007, 02:53 PM
Steppers are easy, everthing else is hard. check out www.probotix.com they have a 4 axis system. Software is your next problem http://gm.cnc.free.fr/index_en.html ....seems to work the best....I just finish a cutter...trying to work out all the bugs.
Mark

flyingwingnut
04-25-2007, 05:35 PM
I'll add to the question.

I'm also planning a CNC foam cutter for wings, mainly. What is the minimum holding torque I should be looking for, for a simple machine like the 8linx (http://www.8linx.com/cnc/cnc.htm) setup.

Is a nema 17 equivalent too small? Should I be shooting for a nema 23? Like most guys I'm all about a good deal. But I won't buy cheap or underpowered gear like the motors and controllers.

Also, it's hard to find a deal (i.e. ebay) on 4 steppers together. Usually they sell in 3's. So I'd like to know that the motor will work when I see it.

BTW, just bought 5 Vexta PX245 6v .8a 1.8deg steppers (nema17) for $18 shipped, so I won't complain if they're too small. :)

Robin Hewitt
04-26-2007, 05:09 AM
Is a nema 17 equivalent too small?


Nothing is too small, but 1.7" is about as small as they get.

Your design may need to compensate for the lack of torque if you want any kind of speed, but is that a problem?

flyingwingnut
05-07-2007, 05:44 PM
Nothing is too small, but 1.7" is about as small as they get.

Your design may need to compensate for the lack of torque if you want any kind of speed, but is that a problem?

No, not a problem. I'm not really worried about speed at this point. I'm cutting for myself. I'll build in the ability to swap out motors at a later time if necessary.

BrianT
05-08-2007, 07:48 AM
Foam cutting works by the hot wire providing enough heat to melt away the foam. There is zero contact between the wire and the foam. Equally there is zero force to be overcome by the stepper motor if the feed is slow enough to 'premelt' the foam before the wire.

NEMA 17 should be plenty for a well controlled hot wire rig.

HTH
BrianT

flyingwingnut
05-08-2007, 08:32 AM
Foam cutting works by the hot wire providing enough heat to melt away the foam. There is zero contact between the wire and the foam. Equally there is zero force to be overcome by the stepper motor if the feed is slow enough to 'premelt' the foam before the wire.

NEMA 17 should be plenty for a well controlled hot wire rig.

HTH
BrianT

It's interesting that HobbyCNC offers 84oz/in and 127oz/in packages. Are the high torque motors faster? Does more torque equal more speed in this case?

Warpspeed
05-30-2007, 05:43 AM
If you want to get a good finish on your foam, run the wire only just hot enough to do the job, and go very slowly. As Brian T says, there is really no mechanical load on the motor at all if the wire is melting through the foam properly.

The motors you have should work fine for small model work, such as you are doing. There is simply no real need for vast speeds or very high power.

kreutz
05-30-2007, 09:12 AM
It's interesting that HobbyCNC offers 84oz/in and 127oz/in packages. Are the high torque motors faster? Does more torque equal more speed in this case?

The torque vs rpm decay does not depend on motor initial torque, generally, higher torque motors have a curve that decays faster vs speed, the effect is more noticeable when you go up in size from Nema23 to Nema 34 (and so it is associated with torque because higher size generally correspond with higher torque for the same technology).

Factors that influence the curve are: Motor Voltage, wiring (unipolar, series, parallel), and mechanical /electrical constants (L/R) of the motor.

vulcom1
05-31-2007, 01:29 PM
I just finished buiding a foamcutter based on what I read on the web. I use 2 ball drawer slides on each base and my uprights are slides on each side. Also on the bottom there is a bearing that runs on the arborite that cuts down on any play in the movement. I use 84 oz. steppers($20.00) and if you can turn the screws with your fingers like mine there are no problems.
My board is the hobbycnc 4 axis pro which also will let me run a mill when finished. It cuts down on software as it does not have the clock on board. The GMFC program mentioned has a 30 day trial then you need to purchase the key to unlock it. The only program that I have found so far is Jedicut that is free but it requires the clock. I am running Foamworks and will have to purchase the key shortly and it costs $46.
I am like most that wanted to build from scratch as to me that is the fun part. When I figured out the cost of parts and the availability I changed my mind and went Hobby CNC. I need to purchase some steppers for my next conversion and will be going back to Dave for them.
If I can answer any questions let me know as I would be happy to help.
John

Gluteal Cleft
08-19-2007, 03:42 AM
OTOH, a diagram showing which wire goes to which coil is very desireable :)

Eh. Two minutes with an ohmmeter, and one minute of testing, and you've got it figgered out. :D

steve

Juancar
03-28-2008, 11:33 AM
As BrianT says, there is no force due to the wire and the foam, the only force is caused by the friction on the axes (slides, nut...) if you can keep them low, a small motor will do the job, but don't expect high speed. If you wan to run faster, you'll need a bigger/stronger motor.

automationtechinc
03-28-2008, 09:47 PM
check the torqure curve here: http://www.kelinginc.net/KL23H276-30-8BT.pdf
http://www.kelinginc.net/SMotorstock.html

1041448
02-13-2009, 03:19 PM
Hi all.
I'm building a CNC wood router machine , but i'm a little stuck with the mechanical things . I am trying to get the acme threaded(or square) lead screw and the stepper motors , but i dont know the specifications, which should i get first?? how to choose it's specification???
what should the speed of motion on each axis Be??
My machine is a 3 axis wood router , i'll be drilling MDF wood.
Y-axis : 4 feet long ,25 lbs horizantal movement
X-axis : 2.3 feet ,14 lbs horizantal
Z-axis : .6 feet ,11 lbs vertical
What stepper motor to use on each axis??????


Help please ,thanks.

budP
02-13-2009, 07:59 PM
biplanefan
your motors are 40 in/oz run in unipolar mode
these will work just fine on a hot wire cutter, as for drivers i would recommend a set of linistepper drivers for about a hundred bucks

budP

Arbiter
03-09-2010, 05:04 PM
Hi Folks,
This is my first post, and I am very new to the CNC environment. I am excited to start planning and building my foam wire cutter. My ultimate goal is to develop a cutter for a full sized aircraft I am designing that will require foam and fiberglass construction. One of the big questions I have is what size motors I need. I am planning initially to have a 6 Ft Long, 3 Ft Wide, 6 Ft tall machine. This is mainly so that all of the wing sections and sections of the fuselage can be cut out in one shot. The fuselage will be cut into "Cakes" and put ontop of one another. The wings will be cut out with the wire cutting the wing skin of ~2-3 ft sections at a time. At least, that is the plan. I think I can accomplish this with a 4-axis machine, possibly 3, and I am trying to figure out the size of the motors.

From the discussion above, it looks like the only forces to consider are the torques required to drive the screws. Since my machine is bigger, and I want to keep the rail deflections down, I will need at minimum a 1/2"-10 ACME thread (At least this is the plan right now) driven on each axis. Also, there are considerations for the vertical axis holding torque keeping the carriage where it is. I guess I am blabbering on about this, but I just want to make sure that I understand that there is virtually no cutting force on the wire, and that the torque is purely to overcome friction. Now, are there also any speed limits, like we don't want to go too slow?

Thank you in advance for the replies, and I appreciate your patience with this noob to CNC : ).

-Chris

cnccutter
03-09-2010, 05:55 PM
Chris,
You don't need much power usually under 200oz will be plenty, the machine only moves at about 3.5mm a second unless you really kick the heat up but then you will burn out any square corners. If your only building a machine to built 1 plane I would look into having someone cut it for you and save hundreds of dollars and many hours. I have a 4' x 4' x 30" machine, it uses air cylinders to tension the 60" wire. (see Pics) If I can be any help let me know.
Mark

Arbiter
03-09-2010, 09:09 PM
Mark,
Thank you very much for the input! So, 200 in-Oz motors would be the max I need? I think that's the size I am seeing in the industrial sized outfits (hotwire direct). I will probably do some calculations based on the screw I have, bracketing the frictions I think I will get based on materials. Then I need to consider the torque I need for self locking on the vertical towers. Maybe I can get away with smaller motors if we go 3.5 mm/sec. I am ok with slow, like I said I'm building 1 airplane, but I also want the experience of building this machine. I am just as interested in the journey as I am the end product : ). In the end I want a useable CNC hotwire with decent accuracy (I will add fiberglass and sand to the finish surface, so perfect .001" accuracy is not needed) that produces smooth surfaces. After I build the plane I could start making cool models with it anyway or help friends with their projects : ). Anywho, thank you for the input, and I am glad to see others that tension their wires with the air cylinder!

-Chris