No, this isn't the usual question about Mach3 settings for slaved twin X-axis homing.
I'm upgrading my cnc machine to twin X-axis ballscrews on the gantry. My new home switches have arrived, and reading the Mach3 manual and around the web shows me that I can independantly home each ballscrew to straighten the gantry. All fine.
But what I had been expecting was that you could tell Mach3 how much to back off the switch on the slave side, to tune the final position and make it perfectly square. Otherwise it would seem that you need to design some kind of micro-adjustment on the slave microswitch to fine tune the position.
Can anyone tell me which of these options is required - I was expecting to get the switch pretty close mechanically and then fine tune the amount of back-off in software to get it dead on.
Proximity switches are great for this has you have adjustment via the threads on the switch and altering the sensing distance if needed has well as any lateral adjustment you build into the switch.
I can't get my head round the fact that accuracy of the machine is down to the position and sensitivity of proximity sensors or switches.
I'm talking about repeatability I suppose, it's not so bad when there is one switch per axis but when there is a separate one for slaved motors it makes even less sense.
This is one area where absolute encoders are far superior and there are programmable limit switches based upon encoders but quite expensive.Spelling mistakes are not intentional, I only seem to see them some time after I've posted
Edit: Daft as this may sound then if you want better accuracy from slaved motors than using switches just use Hard stops and slowly drive upto them before setting Zero.!
Last edited by JAZZCNC; 22-02-2014 at 12:02 PM.
If you are fitting home switches, then in general terms what's the best kind? I'm looking for repeatability here, I think, and the choice seems to be some kind of mechanical switch or a proximity switch. I'm happy that I could interface either kind with whatever electronics/breakout board I eventually select. I have some slight concerns because my 3D printer uses simple little microswitches. In principle these should work OK but I've had repeatability problems with the Z axis switch as you are looking for better than 0.05mm or so and the original switch was not capable of achieving that. In the end I swapped switches around until I found one that gave better repeatability but as a result, I'd like to make sure that the new router, when it gets built, doesn't suffer this way. Could be a critical issue if you are using dual X motors when it comes to squaring/resetting, of course.
Mechanical MS are ok for limits, thou I tend to use proximity for both has they are cheap enough and I just use the same 24V supply.
Repeatability tests on YouTube, there's plenty more too.
G0704 Home/limit proximity switch repeatability test - YouTube
Homemade DIY CNC Series - Home Switch Repeatability - Neo7CNC.com - YouTube
Mechanical switch repeat ability - YouTube
These seem to be a favourite and I think it's the ones in that first video.
I got some of these for my limit switches, but will probably use proximity type for home switches. (postage a bit steep if you just want one but if buying more it's a good deal, or get from China if you want better)
Last edited by EddyCurrent; 22-02-2014 at 03:49 PM.Spelling mistakes are not intentional, I only seem to see them some time after I've posted
There are 2 things I don't like about these switches. Magnetic pick up and 5V.
Magnetic is Ok for wood machine etc but not milling machines or near metal for obvious reasons.
Don't like 5v has it's susceptible to picking up electrical noise.
Inductive proximity switches are cheap these days and work just has good I've found and can be run thru the same 24V control system used for Limits etc.
You also have to consider switch hysteresis because that determines how much Mach3 backs off once activated.
These switches for example have to be backed off 5mm before they reset.
TZ-8104 Rotary Roller Lever Arm Enclosed Limit Switch | eBaySpelling mistakes are not intentional, I only seem to see them some time after I've posted
By Wal in forum Gantry/Router Machines & BuildingReplies: 12Last Post: 08-01-2014, 11:04 PM
By daverowland in forum Items For SaleReplies: 7Last Post: 28-06-2013, 05:18 PM
FOR SALE: 4th axis setupBy johngoodrich in forum Items For SaleReplies: 4Last Post: 13-06-2012, 05:17 PM
By HiltonSteve in forum Gantry/Router Machines & BuildingReplies: 13Last Post: 20-05-2009, 10:13 PM
By Hobbit in forum Gantry/Router Machines & BuildingReplies: 4Last Post: 20-02-2009, 07:22 AM