New Machine Build- Does size matter ?

[Tempus Fugit]

Hi
Just getting parts together to build my first machine and looking for some advice please.
I have some Astrosyn motors type MY103H702 which on the spec sheet give holding torque 1Nm, detent torque 40mNm, voltage 8.68v 0.7a (8 wire) and have been trying to work out what size table they would drive.
I think they equate to about 140ounce-inch if my maths (or the conversion tables) is correct from the 1Nm figure if this is the correct one to work on.
My initial plan is to use MDF and aluminium angle with roller bearing trucks like buildyourcnc.com with 8mm threaded rod drive.

I have built the HobbyCNC EZ Driver Board Kit and have the RoutoutCNC software ready to hook up.

Would a bed of say 30"x40" be within capabilities of the motors ?, and would the motor windings be better in series or parallel connected mode ?

I anticipate my first attempt will help me make a better version 2 when I have got the hang of things and find what could be done better to my requirements.

[Oldmanandhistoy]

Hi,
I don’t profess to be any kind of expert but I’ll tell you what I think

First ditch the motors or keep for a small engraving/PCB machine of no bigger than 300mm x 300mm work envelope. You could use one for the Z axis if using a small router and don’t mind slow rapids. Why because you’re usable torque will very quickly disappear with speed. I don’t know how much you know about stepper motors but the rated holding torque is given at zero RPM as soon as they start moving the torque decreases. So unless you have high voltage drivers (higher voltage = more torque at higher speeds) at usable cutting speeds you will have too little torque to move the machine and over come cutter forces. Have a search through the build logs; you might get away with it but using threaded m8 I don’t think so.

Any motor using a bipolar drive for a wood routing machine use bipolar parallel gives more torque at higher RPM than series wiring.

IMHO I would say you need at least 1.4Nm (200 oz in) for a small cnc router to give fair cutting speeds in wood.

Hope that gets you started,

John

[Tempus Fugit]

Originally Posted by Oldmanandhistoy Hi, I don’t profess to be any kind of expert but I’ll tell you what I think First ditch the motors or keep for a small engraving/PCB machine of no bigger than 300mm x 300mm work envelope. You could use one for the Z axis if using a small router and don’t mind slow rapids. Why because you’re usable torque will very quickly disappear with speed. I don’t know how much you know about stepper motors but the rated holding torque is given at zero RPM as soon as they start moving the torque decreases. So unless you have high voltage drivers (higher voltage = more torque at higher speeds) at usable cutting speeds you will have too little torque to move the machine and over come cutter forces. Have a search through the build logs; you might get away with it but using threaded m8 I don’t think so. Any motor using a bipolar drive for a wood routing machine use bipolar parallel gives more torque at higher RPM than series wiring. IMHO I would say you need at least 1.4Nm (200 oz in) for a small cnc router to give fair cutting speeds in wood. Hope that gets you started, John

Thanks for that John, that's a good start knowing what torque is needed, I don't have a lot of space for a machine as the garage is also used for some work and storage for work stuff (work from home) and a couple of freezers etc !.
I'll go for a table-top thing to start with and think about something bigger when I find out how the tiddler works, maybe the 300x300 will be big enough for most of the things I need to do, shouldn't suffer from flexing and could user lighter table and gantry materials too.
I thought it would be silly to go too small to start with, it'll give me time to seek out some beefier steppers too, may be able to use the same control gear on two machines with adjustment to the current settings, and clear space in the shed


Cheers
TF