Messages

751

General Mach Discussion / Re: Questions on driver rating and PSU rating - newbie questions

« on: March 06, 2012, 12:19:26 PM »

I believe also that modern stepper drivers use switched-mode technology, so that though they might be driving the steppers at 4.2A, the average current from the power supply is less than this (theoretically by the ratio of the actual voltage across the stepper to the supply voltage).  Also you seldom drive all the steppers at full current all the time.  In any case for "light work" you don't need to drive them at full current anyway, and modern drivers reduce the current to 50% when they are not actually stepping.  I use a 36V 11A supply for the 3 motors on my Novamill, two of which are type23s which I run at just over 1.5 A for X and Y and the third is a type 34 (what you have I think) which I run at 2.5A for Z.  There's plenty of torque on all the axes and the power supply (and the drivers) don't even get warm.  My drivers are essentially the same as yours as well.  I think you'd be fine with your current drivers and the 10A supply.

752

General Mach Discussion / Re: Mach 2 Fan Running All The Time

« on: March 06, 2012, 12:09:01 PM »

Most fans for years have had brushless motors that go on for ever (or the bearings wear out).  And fans are cheap.  Don't worry.

753

General Mach Discussion / Re: Lathe feed errors due to timing pulley runout

« on: March 02, 2012, 05:00:52 AM »

Hi Hood: yes, quite repeatable in the manner you describe.  Always moving the slide the same way to the measurement point to eliminate backlash.

Rich, I'm not sure who the original pulley supplier was, they were ordered through RS Components.  I mounted then in a 4-jaw by the hub, centred on the existing small centre hole (DTI), and drilled and reamed out to 0.25 inch for the motor or 8mm for the L/S shaft.  However the holes were too small to easily bore so some inaccuracy may have crept in.  Surely backlash shouldn't affect CNC turning to a diameter any more than it does manual as the feed direction is always one way?  And my measurement was ~.02 on a radius which is .04mm on a diameter = .0016".

OK, I realise I may be trying too hard here, but if for example I want to turn down a shaft to be a running fit in a bored hole of a given diameter using CNC, should I expect to be able to do this in one program or to stop a few thou short and use semi-manual techniques for the final fit? 

Thanks, John.

754

General Mach Discussion / Re: Lathe feed errors due to timing pulley runout

« on: March 01, 2012, 04:10:08 PM »

Hi Hood - yes, it uses steppers.  Gearing was just via the timing pulleys.  8x microstep.  Leadscrew, not ballscrew, 0.05 inch pitch.

755

General Mach Discussion / Re: Lathe feed errors due to timing pulley runout

« on: March 01, 2012, 11:28:39 AM »

Maybe I didn't express myself clearly.  Actually the error I measured was 18 microns peak on feed, so that would be .036 mm on diameter or 1.4 thou of an inch.  Manually turning I would expect to be able to significantly better that by careful finishing.  With CNC you don't get a chance.  I decided that it was runout on the basis that the error was periodic and a bit of spreadsheetery showed that it had components at the rotational speeds of the screw and motor pulleys, and the amount estimated correlated with a direct DTI measurement.

756

General Mach Discussion / Lathe feed errors due to timing pulley runout

« on: March 01, 2012, 10:14:36 AM »

Hi all,

After adventures getting my Denford mill up and running I went back to try and see why I just couldn't get my Super 7 conversion working to the accuracy I would like, particularly on the cross slide.  I was getting inconsistent results on final diameter, with errors getting close to 0.02 mm which didn't seem right.  Eventually I decided that the problem was due to slight runout of the timing pulleys through which the feedcrew was driven - since both of these had to be bored out to fit the shafts of the stepper and the screw there was scope for error.  And doing careful measurement of feed with a digital micrometer (Mitutoyo) that can resolve a micron, and separately measuring runout with a DTI, I finally decided that both measurements were consistent. 

I'm now resigned to going to direct drive from the motor to the feedscrew, since I think there is plenty of torque available, but has anyone else had any experience of this problem; and any recommendations on how to accurately bore timing pulleys for future reference please?

John.

757

General Mach Discussion / Re: Denford Micromill convert to Mach

« on: February 27, 2012, 11:19:50 AM »

First - do you have the Denford electronics box with the machine?  If so then you could visit http://www.denfordata.com/bb/viewforum.php?f=36 which is the Denford support forum where someone may be able to help you get the original Denford software.  Even if not they are very helpful with information on the older Denford machines.

If not then others here have given good advice - I acquired a Novamill which is rather bigger without electronics and bought all the drivers and a breakout board on ebay for only about £100.  PSU was about £30 from another UK supplier, everything all in certainly less than £200 (but used some stuff from the spares box).  Got the machine up and running quite quickly using Mach3 with a bit of help on this forum.

Also I think the micromill is based on the Sherline mechanics.

Good luck, John.

758

General Mach Discussion / Re: 3D Printer: Extruder

« on: February 15, 2012, 04:54:48 PM »

Have a look at http://www.denford.ltd.uk/index.php?option=com_content&task=view&id=167&Itemid=97 and scroll down to the Up! 3D printer.  Denford of course well known for educational CNC - I have one of their Novamills and it's excellent.  Click to see the video - printing a salt shaker, two parts, base and top, at the end they screw the top onto the base, the threads are printed.  Impressive I thought.

759

General Mach Discussion / Re: Inserting comment in G-code

« on: February 13, 2012, 05:18:43 PM »

Have now used code generated by G-Simple (an excellent program I find so far) which includes (comments) and they work fine so I'll stick with that form.

760

General Mach Discussion / Re: Inserting comment in G-code

« on: February 12, 2012, 05:48:14 AM »

OK thanks, I'll give that a try.

John.