The New Machine

[fragger6662000]

Cheers Ian, Me too, In fact many of the sites I checked started at 12 teeth.



Thanks Jonathan, I did Intend to use a 10 and 25 tooth pulley to give me the ratio I needed, and going for anything smaller as you say may put too much load on the reduced number of meshed teeth. So 10 and 25 then.

So the pulleys will be as above.

For those people that are not aware of why I would like to use pulleys then let me explain.

:confused:Using 1605 ballscrews will give me a pitch of 5mm, that is to say 360 degrees in 1 rotation of spindle will advance the axis 5mm.

If i use a direct coupling stepper to screw,

The stepper will give full steps of 1.8 degrees.

360/1.8 will give me 200 steps per revolution.

5mm / 200 will give a resolution of 0.025mm per full step.

This is an odd measurement to use in my head, i have done it though..

Using a ratio of 2.5 to 1 ( 10 and 25 tooth pulleys) will give me a step resolution of 0.001mm per step.

and if i were to use half steps as the stepper is capable of doing, it would be 0.0005mm per step...

thats a fair bit of resolution/accuracy, there are however disadavantages to using pulleys.

its upto the individual who is designing/building and using the machine.

(a special thank you to i2i who educated me on this subject in the first place)

There you go clear as mud!!!!:confused:

Rick

And hurry up moderator.

But you should be using 8 / 10 mirco stepping for best performance of the motors and why are you worried about the interger as it is a cnc'd machine that will be controlling it.

As before i have done it with this machine, 0.001 res is pie in the sky, £200,000 machine tool struggle to get that with direct drive and servo's. 0.025 per step is what i run and gives me 1500mm/min rapid you would be lucky to get 700mm/min as you would be over spinning the motor and have not torque.

resolution and power work againest each other.

here a like to my Thread on cnc zone.

http://www.cnczone.com/forums/bencht...g_machine.html

[Ricardoco]

And hurry up moderator.

But you should be using 8 / 10 mirco stepping for best performance of the motors and why are you worried about the interger as it is a cnc'd machine that will be controlling it.

As before i have done it with this machine, 0.001 res is pie in the sky, £200,000 machine tool struggle to get that with direct drive and servo's. 0.025 per step is what i run and gives me 1500mm/min rapid you would be lucky to get 700mm/min as you would be over spinning the motor and have not torque.

resolution and power work againest each other.

here a like to my Thread on cnc zone.

http://www.cnczone.com/forums/bencht...g_machine.html

Ok Hi There fragger, the steppers two x 23 & 1 x 34 from motionking, the 'integer' is for me, not the software, I design what would end up on the machine in the first place as i said "This is an odd measurement to use in my head" Now as for accuracy, wouldnt you say, that aiming for the highest accuracy you can in the begining is the correct thing to do.

I would never suggest I would get that resolution at the end of the project but if i allow the push for accuracy to become secondary to simplicity of build i would not be true to myself, and speed/feedrate well this is a hobby for me, im not in a hurry, im still one of those sad individuals that likes to sit there and watch, and i know im not the only one AM I???

Would i not get more torque with a 2.5:1 setup then?

I have read with interest the posts about this machine type on cnczone.

Pulleys are the way i would like to go as i dont like the positioning of the steppers in the other projects I have seen, they may be fine for you and make the conversion simple and speedy but that is not what im after, I have learned a lot from the conversions on cnczone but they just dont fit my requirements.

Stevie Nicks and her famous song told me all i needed to know lol

I do like the way you have mounted your x axis ballnut, that is simple effective and a touch inspired and look much more stable than the other ways i have seen.

I will follow your thread with interest and i may even use some of your ideas (giving credit of course), "if thats ok of course"

Rick
.

[fragger6662000]

No you don't get more torque, stepper motor produce most torque when stalled, as you increase the rpm the torque drops.

I know well know manufactures of encoder scale that produce an 8um pitch and you have all the american stuff.

When i built my first cnc'd x1 i was using a imperial z screw, you never need to know the interger apart from the time you enter it into the control software.

By using pulleys you get
-another source of backlash
-drive flex(belt stretch)
-reduced top speed
-side load on the screw
+ratio change
+allignment flexabilty

i tried belts on a lathe, big disapointment. now directly driven.

if we are quoting "you can lead a horse to water but cannot make it drink" I personally think your logic is flawed, if you want an additonal challenge that is far enough.

As for i am old school i like to watch it, the x1 had a rapid of 400mm/min and it got very old very quickly and that was a smaller machine.

[Jonathan]

I don't see the point of wanting a round number. As soon as you've entered it into mach3/EMC you won't need to know about it at all. I've forgotten what the value is per step on mine...

As fragger said, you will almost certainly be using 1/4 or 1/8 micro-stepping anyway which effectively changes the value but doesn't really gain accuracy.

By using pulleys you get
-another source of backlash
-drive flex(belt stretch)
-reduced top speed
-side load on the screw

1) no, unless your pulleys are awful. Mine have not added backlash.
2) negligible from my experience.
3) What! That's impossible to judge without calculating it properly. You need to get the motor running in the optimal region of the torque/rpm curve and to do that you need to get the ratio right which, unless you're very lucky, requires pulleys.
4) Surely the bearings in the mill are going to cope with that...if not add more? I'd be more worried about the bearing on the stepper motor.

On my router I've found that generally increasing the size of the pulley on the stepper motor has increased the top speed, but of course sacrificed resolution. It's less clear cut on a milling machine as it's heavier and the coefficient of friction is greater.

[Ricardoco]

I don't see the point of wanting a round number. As soon as you've entered it into mach3/EMC you won't need to know about it at all. I've forgotten what the value is per step on mine....

I had decided that for the way i wanted to position the steppers that belts and pulleys was the way to go and at a 2.5:1 ratio i would get that round '1' it was not a requirement i could have even gone 1:1 and still can ill just swap out the pulleys and belts if need be and i will probably forget about it as you have.

The little ratio and ballscrew tutorial I wrote down in the middle of the post was perhaps to make things easier for some people to understand as it was a source of many questions from me when i did the other conversion. Using round numbers just made it easier in my mind to see what was going on thats all..

As fragger said, you will almost certainly be using 1/4 or 1/8 micro-stepping anyway which effectively changes the value but doesn't really gain accuracy..

Shouted! :lol:

on another note what do you think of the idea of a counter balance on the Z... please dont shout your reply its only a question...:heehee:

Rick

[Jonathan]

on another note what do you think of the idea of a counter balance on the Z... please dont shout your reply its only a question...:heehee:

[whisper]I think someone on this forum is considering it / has done it...
As I'm sure you know it should improve your Z-axis feedrate, but when do you actually need a high feed there? Possibly small drills (definitely with PCBs) and maybe with 4th axis in some situations but that's about it?
You can use an 'oversize' (i.e. greater than the mass of the head) counterweight to eliminate backlash in the Z-axis.
[/whisper]

Are you using a rotating ballnut on Z, just out of interest?

[Ricardoco]

Are you using a rotating ballnut on Z, just out of interest?

Hmmm tell me more...

[Rogue]

[whisper]I think someone on this forum is considering it / has done it...[/whisper]

I'm playing with the idea, primarily because I think it looks good, effectiveness be damned! :twisted:

On a related note, I also asked similar questions about the under-table mounting, the consensus seemed to be that it wasn't a problem. The following thread might have useful things for you: http://www.mycncuk.com/forums/showth...or-under-table

[i2i]

on another note what do you think of the idea of a counter balance on the Z...
Rick

Denford used to do this on the early triacs, they stopped it quite quickly.

[Ricardoco]

Denford used to do this on the early triacs, they stopped it quite quickly.

Hmmmm Your not the first to tell me that, i wonder if the bell is tolling for the counter balance idea!!!!