Messages

1

General Mach Discussion / GANTRY RACKING

« on: January 17, 2012, 06:32:58 PM »

I'm running a home made CNC with separate steppers on the 'long' axis: with A slaved to X.
Once or twice, due to my cabling/construction (not MACH3), one of the ballscrews has got out of step with the other and the gantry has racked badly.
I'm thinking of fitting quadrature shaft encoders to the A and X axis to raise an E-STOP if the A and X axis move different distances.

I'll probably use some quadrature decoder chips and a microprocessor to do the job.

Before I start the work, am I re-inventing the wheel or is there a better/simpler solution?

I'm a 'hobby type' CNC user and don't have the means of making a 'rock solid' mechanical solution so an electronic safeguard seems the way to go?

regards Bill Legge
In Australia

2

Mach4 General Discussion / Re: New people welcome !! Come in here and introduce your self!

« on: January 01, 2012, 06:18:36 PM »

Thanks for a great forum.  I've been learning CNC as a hobby for about two years and speedy and useful replies to my post have been invaluable.

Starting CNC with a good electronics knowledge but very little mechanical design and construction experience I would pass on the lessons I've learned after building two machines:

1.  General construction - a combination of MDF and aluminium is quite easy and cheap.  As your skills improve use more aluminium and less wood/MDF.
2.  Splash out and purchase some stainless steel socket head screws - they look smart and make construction easier.
3.  Tools you must have: pillar drill and sliding mitre saw - buy a proper aluminium cutting blade (use cutting wax).
4.  Safety - although the aluminium cutting blade is magic, clamp your metal down before cutting it - I'm lucky to have avoided injury and have learned my lesson.
5.  Go metric or imperial.  Don't mix them, it will cause you difficulties.
6.  Purchasing from the web - all my deals have gone OK, a lengthy delay with a big purchase ($500) from China but it turned up in the end.  The Chinese 'low quality/cheap' seems OK for hobby use.
7.  Ballscrews and shafts - my first machine used homemade linear bearings (bearings and lots of brackets), my second uses Chinese ballscrews and proper shafts - well worth the cost.
8.  Spindle motor - worth the cost ($300) as the noise from a router/laminate trimmer will drive you and your neighbours mad.
9.  Getting started - if, like me an absolute beginner - build a 'test axis' just one set of rails and one sliding platfrom, add limits and home.  Interface to MACH3.  It will hone you skills overall shorten the time it takes to get a useable CNC machine.
Thanks to ARTsoft and this site
Regards Bill Legge in West Australia

3

General Mach Discussion / Re: SLAVE AXIS PROBLEM

« on: January 01, 2012, 05:22:48 PM »

ger21

Thank you.  I had not spotted the 'HOME SLAVE WITH MASTER' check in the General Config.  That must be my problem; I'm very grateful as I was almost giving up and going to spend a long time re-building to use a single stepper.

Any ideas about why the 'GO TO ZERO' causes 'jerky motion' on the pair of slaved axes?  A few notes:

1.  The jerkiness only occurs on the slaved pair of steppers.
2.  I've tried uncoupling the motors from the machine in case it was excessive mechanical stress - but it makes no difference.
3.  The slaved pair run smoothly/easily under manual controll (using the 'HOT KEYS') - so it would not seem to be driver/power supply problems.

What on earth could be the difference between HOT KEY/MANUAL control and GO-TO-ZERO ?

The only slightly unusual thing is that I'm using a lap-top pc - but it's an old one and has a proper printer port.  Could the lap-top be running out of processing power; but then why would the manual mode work OK?

Regards Bill Legge

4

General Mach Discussion / SLAVE AXIS PROBLEM

« on: January 01, 2012, 06:36:42 AM »

I have a machine with two slave steppers on the main axis.
I have slaved X and A and installed home switches on both.
I have set the A axis to linear.
Using manual control the pair of slaved axis move OK and remain in step but:

1.  When I use to 'Go to Zero' command, the axis remain in step but move in 'bursts' of about one second/30mm.
2.  When  using 'REF ALL HOME' the Z and Y axis do the correct thing (touch the home switchs and then back off) but the X and A axis do odd things - one touches/backs-off, the other touches,reverses and keeps going in the wrong direction.

I have very carefully checked:
1. Pulse rate and varied it from 25KHz to 100KHz and it makes no difference.
2. All the ACHIVE_HIGH/LOW, DIRECTIONS, PINS and PORTS.

Any help would be very welcome.

Regards Bill Legge