Thread: The New Machine
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"
.Always bear in mind that your own resolution to succeed is more important than any other - Abe Lincoln
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
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.
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.
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.
I actually felt like you were telling me off then....
Well i will consider myself told shall I....:cry:
Usually people dont have to be so blunt to get the point across, Im not so stuck in my ways that im not open to suggestion, On a recent project I took a lot of advice from the members of this forum and put it into practice, that is why i participate in forums.
I dont really want to just copy you or hoss, but neither do i want to re-invent the wheel.
thats why i dont just guess at this, I've looked at several sources of information and am still looking, here is just one source.
I dont disagree with all you say, and there are sacrifices to be made using pulleys however my 260 is not direct drive, it is very accurate, as much as i need anyhow, and i really dont want the steppers hanging of the end of the axis (not sure what you would call a group of axis lol), so do you have any other suggestions?
Thanks in advance for your input.Always bear in mind that your own resolution to succeed is more important than any other - Abe Lincoln
I forgot to mention the other big advantage of belts which is that they greatly reduce resonance problems.
The site you linked to has mentioned what I did:
'Even though the output speed is reduced by the reduction ratio, some systems will actually have their overall speed performance increased due to better use of the motor's torque curve.'
I wouldn't hesitate to use belts again - I will when I convert my lathe, though admittedly that's partly because it'll have a rotating ballnut.
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..
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:
RickAlways bear in mind that your own resolution to succeed is more important than any other - Abe Lincoln
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.
Are you using a rotating ballnut on Z, just out of interest?
If you are thinking of under slinging the motors on x you will loose lots of travel.
Hope you have fun doing the machine as it is certainly a rewarding thing to do. especially when it works!
By therouterlady in forum Manufacturer NewsReplies: 0Last Post: 18-09-2013, 04:28 AM