Mounting motor under table?

[Rogue]

All round, I'd guess. If I understood the earlier posts correctly, if I had a system for changing pulleys I could get the higher precision if needed, at the expense of speed? If so, this is one of the things that interest me about pulley systems.

[Jonathan]

RE: Turning. Even thou I have a good lathe and capable of turning my own screws I dont bother and buy them pre-machined from china, It's just not worth me doing it my self for what they charge.

That's precisely what I thought. I would machine a ballscrew if someone asked, but it's just not worth is with linearmotionbearings2008 prices on eBay.

All round, I'd guess. If I understood the earlier posts correctly, if I had a system for changing pulleys I could get the higher precision if needed, at the expense of speed? If so, this is one of the things that interest me about pulley systems.

That is correct. Lets say, for example, you have a standard stepper motor so 200 steps per revolution. The travel per step on a 10mm pitch screw will be 0.05mm with direct drive or 0.1mm or 0.025mm depending on if 2:1 or 1:2. Using microstepping will get finer resolution up to a point.

Though I would normally advise 10mm pitch screws (I probably did earlier!) since this is such a small machine it may not make a lot of difference...having said that the main thing is getting high acceleration, otherwise you'll run out of travel before it hits top speed and has to decelerate. To do that a 2:1 (bigger on stepper) with a 10mm pitch screw would be ideal since the motor has to input only a quarter of the kinetic energy into the screw when accelerating compared to a 5mm pitch screw.

Your 'system' for changing pulleys is just an allen key plus a bit of space.

[JAZZCNC]

Agree with what jonathan says just one thing to point out 2:1 10mm pitch is effectivley 20mm pitch. If you can live with this loss of resolution then it's a good way to go.

What's your main intended use.?

Edit: Jonathans comment about accelleration is even more important if you plan to do lots of 3D and intricate V carving. 3D and intricate carving is very time consuming, esp vcarving, with lots of very small moves required with the Z axis dancing around all over the place. The problem with low accel is the commanded feed rate actually never get's meet and therefore the cutting time increase's. On very large 3D jobs this can run it several extra hours or even days.!!

[Jonathan]

Agree with what jonathan says just one thing to point out 2:1 10mm pitch is effectivley 20mm pitch. If you can live with this loss of resolution then it's a good way to go.

What's your main intended use.?

5mm, 10mm .. . it all depends on what motor is driving the screw. If it's a 3nm motor then clearly a different ratio will be optimal when compared to using a 1nm motor.
If you're using it for PCBs then you'll want good resolution, so probably best to use swappable 1:2 pulleys. Can't really thing of anything else that would require it. Maybe engraving, but generally for engraving it's relative position that matters more than absolute which means microstepping is more valuable.

[JAZZCNC]

Maybe engraving, but generally for engraving it's relative position that matters more than absolute which means microstepping is more valuable.

Ermm. . . Not a good idea IMO realying on micro stepping. Really it's horse's for course's when you get into the finer engraving area and resolution rules. So it's finer pitched screws all the way but at the sacrifice of speed. . . . If I intended main use as engraving then fine pitch's would be used for the resolution not M-Steps.

Micro stepping is good but mainly for smoothing motors.

[Rogue]

Micro stepping is good but mainly for smoothing motors.

This is one of the things which I need to get my head around as well. From what I read, microstepping is good... but it's bad. People report motor problems disappearing when they start to use it, but from what you say it seems to be an inferior way to achieve good resolution. I'm assuming that there is a middle ground somewhere that I need to find (not too fine a pitch, not too many divisions for microstepping).

[JAZZCNC]

This is one of the things which I need to get my head around as well. From what I read, microstepping is good... but it's bad. People report motor problems disappearing when they start to use it, but from what you say it seems to be an inferior way to achieve good resolution. I'm assuming that there is a middle ground somewhere that I need to find (not too fine a pitch, not too many divisions for microstepping).

Depends on a few factors really and the drives being used also play a big part to how micro stepping is implimented.

10x micro stepping is about the max usable and beyond this is just pointless unless you have a very high pulse width which is beyond the capabiltys of the std parallel port. . . It's gets complicated so wont go there.!

Generally micro stepping should be used but mainly for motor smoothing at lower speeds IE: small tiny moves and lower rpm's but after a point micro stepping becomes an inderence more than a help and this where the drive comes into play.
A good drive will use a technique called morphing where it changes from micro stepping to full stepping along the power curve. This also brings resonance into play and why belts can help.
Poor drives without morphing and usually mid band resonance compensation can suffer from resonance issue's caused by the vibration frequency's that interfear with signal performance and affect the motors making them run really badly and sound dreadfull. . . . Belts act as a natural damperner.

Good drives like Gecko's etc use morphing and Mid band resonance damping and this really does make differance.

If you work on the principle that micro stepping works but mainly to help with motor smoothing at lower rpm's but with the side affect of slightly improving resolution ( too a point) then you wont go wrong. Just don't relay on it soley to give you the resolution you need.
Like I say the good drives do make a big difference.

Go to the Gecko site and read the FAQ section it has some good info on how morphing and micro steeping works.

[Jonathan]

Ermm. . . Not a good idea IMO realying on micro stepping.

I'm not saying rely on it, just it might help. Clearly the result will be slightly distorted.

I already mentioned about microstepping accuracy (or rather lack of) in post #15...

One thing I'm going to try and do with my stepper driver design is make it effectively run using microstepping, for smoothness, yet only require the number of pulses for whatever microstep division you choose. Effectively it will move through each of the microsteps for every step pulse.

[JAZZCNC]

I'm not saying rely on it, just it might help. Clearly the result will be slightly distorted.

I already mentioned about microstepping accuracy (or rather lack of) in post #15...

ye I know Jonathan and wasn't really picking up or discrediting your referance about microstepping more pointing out for high resolution operations like engraving etc then it's better to use the correct pitch screw.

[Rogue]

if you plan to do lots of 3D and intricate V carving

Engraving would be flat text for a control panel, nothing fancy. I might need to do something fancy every now and then to try and justify it to my wife, but thankfully she has low standards. Well, when it comes to husbands, anyway :whistling: