Messages

2051

General Mach Discussion / Re: CV mode tuning

« on: June 25, 2007, 11:13:50 AM »

sorry - maybe should have said - I'm milling not turning.

2052

General Mach Discussion / Re: Help needed finding stepper driver

« on: June 25, 2007, 11:00:49 AM »

well I've never used these so I wouldn't like to comment on them specifically.

These are unipolar drivers, i.e. only half of each phase of your motors will be powered at any given time. Given that your motors are not the most powerful anyway - you'll get more power out of them driving them as bipolars with a bipolar driver.

Idle current reduction is a moot point. A lot of drivers offer this facility. Upside - you pay less to the electricimy man. Downside - your motors could be forced to "freewheel" (dependent on your screw pitch). i.e. not as much power holding them steady - chances are this would really only be of use when the machine is idle or for the Z axis when cutting 2.5D but you could find your Z axis wandering - ouch nasty.

An ATX power supply in my view would be no use at all - particularly with your 4.5V 1.8A motors. you'll need to give them much more than 12V for any sort of real power at speed. Taking your 2.5V motors into account I'd be looking to experiment somewhere around 50 to 60V. Unregulated supplies are the mutt’s nuts for stepper motors.

1 Farad - wow...

2053

General Mach Discussion / Re: CV mode tuning

« on: June 25, 2007, 08:01:08 AM »

bump - anyone?

2054

General Mach Discussion / CV mode tuning

« on: June 22, 2007, 08:07:42 AM »

Hi all

I'd be grateful for any comments re: the fine tuning of CV mode. I've had a few issues of CV rounding too much and would like to understand setting it up better. I understand what CV is, I'm just not sure how to take full advantage of it's settings.

As I understand it CV will more accurately follow the required curves if feed rate is slower and acceleration capability is greater. Is that right?

Also am I right in thinking that the UG is a little behind the latest lockdown of Mach3? e.g. Chapter 10 - "No Angular Discrimination" - I can't find this on Mach3 but am assuming it's been replaced by "Stop CV on angles >". I understand generally what the idea of stopping CV over some angle is about but some advice with how I configure this with relation to G02 and 3 would be useful. Finally there's two buttons and DROs on the Settings screen labelled CV Distance and CV Feedrate which don't appear to be documented.
If all these questions are answered somwhere I havn't looked then apologies. I know there are lots of threads about CV but trying to wade through them all to see if my questions are answered is making me cross-eyed. - is that lazy? sorry.

Many thanks

2055

General Mach Discussion / Re: Z Drive Ratio

« on: June 21, 2007, 07:54:06 AM »

I use Rhino3d, RhinoCAM and RhinoART cos they were doing a reasonable deal last year. Havn't used VCarve but as you say it looks pretty good. I must get into this sign carving and such cos I need to make some money from this lark. It's getting V expensive!

2056

General Mach Discussion / Re: Help needed finding stepper driver

« on: June 20, 2007, 04:29:50 AM »

Apologies if I'm teaching granny to suck eggs but note also that your six wire unipolars can be wired as 4 wire bipolars if that helps your search. I use Geckos.

cheers

Stirling

2057

General Mach Discussion / Re: cutters

« on: June 20, 2007, 04:06:14 AM »

Many thanks Brett - sorry, hadn't spotted links before.

2058

General Mach Discussion / Re: Z Drive Ratio

« on: June 20, 2007, 03:27:47 AM »

No problem - hope all goes well - like you say - swapping info is how we all get by. I got my motors from homeshopcnc too and would recommend them, Rick LaLonde was the guy, great to deal with, friendly, helpfull and fast. In fact I'm over here in the UK and without wanting to knock Old Blighty too much, I'm very jealous of you guys in the US when it comes to sourcing all the kit needed to build these things - you've got so much more choice. I got the motors from homeshop because even after import duty, UK taxes and shipping they were cheaper than buying over here. In fact Rick apologised once when he took 24 hours to reply to an email - Ha! over here I can wait three weeks for somone to respond - if they bother at all. I also import the Geckos, either from homeshop or from Gecko direct depending on whether I'm getting motors as well. I wanted to get the screws from homeshop but of course over here we work in metric so I got them locally - and that was like pulling teeth! Anyway - whinge over - sorry.

Speaking of spindles, what do you use? - again, you seem to have way more coice.

cheers Stirling.

2059

General Mach Discussion / cutters

« on: June 19, 2007, 04:15:07 PM »

Hi - anyone know of a decent supplier of cutters in the UK for hardwood. I'm looking for 6mm - 8mm shaft. (for a Kress spindle) straight, ballnose etc. any advice on what to look for and where would be appreciated. Thanks

2060

General Mach Discussion / Re: Z Drive Ratio

« on: June 19, 2007, 09:34:56 AM »

(with respect of course) I’d either disagree with the max 80V bit or suggest that maybe you’ve misunderstood. The 80V limit is recommended by Gecko as the max for their drives. They and Bob Campbell along with many others recommend that your motor voltage should be somewhere between 4 and 20 to 25 times the motors rated voltage. Your motors (at least your X and Y) you say are 2.7V so your power supply of 72V is 72/2.7 or 26.7 times, i.e. in excess of their recommendations. Maybe not by much but certainly on the high side. Also if I’m right in thinking your Z axis is a 2V motor then you’re at 36 times, well outside their recommendations.

Regarding "the higher the voltage, the faster the motors will go" - well... yes... in a way. What I think they meant is that the faster stepper motors go the less torque they produce. In order to keep the torque at a usable level at the highest speed you need, you usually need to up the voltage.

Sure, they're going to get slightly warm and I use that as my key to setting my voltages. My rule of thumb would be firstly set the current limiting resistors as advised by Gecko, then up the voltage until the motors run just warm over 15 minutes or so under load. If there's enough torque for the job at the max speed needed and V is below the 20 to 25 times the rated voltage then pay dirt. Otherwise the motors aren’t up to the job. I've read several times where it's said that they should be run hot, as in really hot. This I don't understand. To me, a hot motor is an inefficient and underpowered motor and wont last very long.

Oh yeah, my spindles (I have two rigs) are little Kress electronic 850s. Small I'm sure compared to some of the beasts out there but have proved big enough (just) for what I do at the moment.

Cheers

Stirling