[Mike F]

I am thinking about limit and home switches and wondered why most, if not not everyone, puts two on each axis. If one switch is mounted on the moving part of each axis and is operated when the switch hits a fixed block on either end of the travel, this would mean only three switches are needed for limits and home, on a three axis machine instead of six.

Can anyone think of reasons why this approach cannot or should not be adopted? It would also make the wiring simpler and allow the existing power chain to be used rather than additional, fixed wiring along the frame.

Any advice would be appreciated.

Mike

[MrBean]

I think the Limit switches will trigger an e-stop condition, meaning that the drives will cut out if used to home the axis, so if you just wanted to "home" all axis then cut a part, you can't, as the drives will cut out, untill you get them off the switch, you have now lost your home position. That's why you have seperate home switches that trigger, usually just before the limit switches.
So you home your axis and if for any reason the motors carry on past "home", the limit switch triggers an e-stop condition, halting all motors.

I have neither limits or home on my machine :nono:
So I may be wrong on this. Best to get another opinion just in case.

Regards Terry.

[ger21]

I think it will work. In Mach3, somewhere you can tell it to use the home switch as a limit, and I think you can assign the switch from the opposite end to the same pins as the home switch. So You actually set up the same switch twice, using the same pins. Try it and see to make sure it works before you wire everything up.

[Mike F]

It's the Terry and Gerry show again Thanks guys for the input. Gerry, on the face of it, I could not see why it would not work, just needed a second opinion and wondered why it wasn't common practice. I will wire one up and try then report back. Terry, I do know that Mach3 can be set up as Gerry suggests, allowing limit switches to double up as homes too on one end of the travel.

I have uploaded a very short (10sec) video of X and Y moving. The camera is a very old one that take floppy discs, do you remember those, it is pretty low res but works.

Mike

[Pat2000]

I am thinking about limit and home switches and wondered why most, if not not everyone, puts two on each axis. If one switch is mounted on the moving part of each axis and is operated when the switch hits a fixed block on either end of the travel, this would mean only three switches are needed for limits and home, on a three axis machine instead of six.

Can anyone think of reasons why this approach cannot or should not be adopted? It would also make the wiring simpler and allow the existing power chain to be used rather than additional, fixed wiring along the frame.

Any advice would be appreciated.

Mike

Have a look at page 36 (or 4-10) of that excellent mach 3 documentation

downloadable from http://www.machsupport.com/documentation/

you want the 'using mach 3 mill' one :idea: but I reckons you should all ready have that one LOL.

light bedtime reading!! - hey pleased for you Mike, keep going now...

pat

[Mike F]

Thanks Pat, I guess it's a case of 'if in doubt, read the manual'. (chair)

I've been doing a little bit of tidying up in the controller box this evening - all those wires!! but it's beginning to look a bit better - just hope everything has gone back the right way.

Mike

[Mike F]

Picture attached of the tidied controller box. Compared to post 242, I think there is a considerable difference and not being an electronics guru, I was rather reluctant to disconnect everything, trim wires and then have to re-assemble everything. I have to report that everything went without any problems and all three axes are still working .

The eagle eyed among you will notice there is a charge pump and relay board in there now although they are not yet connected - got to work out how to do the charge pump

Still not got round to figuring out the Z axis and am undecided as to having a fixed ballscrew/motor or fixed ballnut and moving ballscrew and motor. There seem to be good and bad reasons for both.

Mike

[bp092]

Looks well organized and thought through. Where'd you pick up the e-stop and other components?

[epineh]

Nice work Mike, good to see more progress, keep it going!!! Thats a pretty sweet looking electronics box.

Russell.

[Mike F]

BP092,

As this machine is built in school, I relied on our sparky, in the works department, for supplying the e-stop button so I can't say where it came from. Suffice to say it is a good one, designed for workshop type machinery. As for the other components; drivers are Geckos, toroid transformer, large capacitor and rectifier came from surplus power supplies sourced by my electronics friend, he also provided the plugs, sockets, leds and switches. (A very useful buddy ), CPU coolers came from ? and the parallel interface, mini power supply, relay board and charge pump came from CNC4PC.

Russell,

Yes, I feel a great relief after getting the electronics out of the way. If you have read through the whole thread (as I am sure you have) you will realise that I was not looking forward to the electronics at all but now they are out of the way, there is a huge feeling of satisfaction, especially as I didn't fry any components along the way.

Just the Z to complete now before cutting something - shouldn't be too long now - maybe another twelve months or so judging by progress so far

Mike

[10bulls]

E-Stop switches are very expensive for what they are.
For a cheap and cheerful alternative, I used a push-pull switch from Farnell part #7712600 @ £4.79.
They probably won't pass ISO BS XYZZY standard relating to operating them in a thunderstorm using a bloody stump but hey.

[Mike F]

Andy,

It's a valid point you raise, about standards etc., and it is something I hadn't really thought about but seeing as this machine is in a school workshop and liable to be used by students, albeit always with my supervision, I suppose I should get it checked out by the authorities and get it duly stamped - what a PITBS.

Mike

[10bulls]

...I suppose I should get it checked out by the authorities and get it duly stamped - what a PITBS.

You may have read this one..."Mince pie danger to be assessed" http://news.bbc.co.uk/1/hi/england/n...re/6207970.stm
The world's gone crackers!

...then there was the one about the over zealous building site H&S that insisted they put 'STOP' signs at the end of all their ladders.

BTW: Congratulations on getting things moving! Are you still planning to replace some of the parts with composite ones? (sorry if you've already covered that).

[Normsthename]

I am thinking about limit and home switches and wondered why most, if not not everyone, puts two on each axis. If one switch is mounted on the moving part of each axis and is operated when the switch hits a fixed block on either end of the travel, this would mean only three switches are needed for limits and home, on a three axis machine instead of six.

Hi Mike
Great job on the machine!
Wish I had a teacher like you when I was at school!
About the limit switches.....
When I built my machine I initially built 6 limit switches into the electronics, but when I was finishing the machine, like you I realised that I had 3 extra switches that were surplus, and could cause problems.
So I used one switch on each axis, and then I made up some 'ramps' that I fitted each end of each axis. Using a ramp allows for the machine to slow down and ride up the ramp tripping the limit switch, machines don't stop instantly! I made the ramps so the microswitch will trip when it hits the 'ramp' and then it can continue to ride up the ramp without damaging the switch.
I stole the idea off of my parents stair lift!
I don't have any home switches fitted, because I use the limit switches to act as the home switches. In Mach2 there is a setting to tell it to use the limit switches as homing switches.All you do is tell the machine in which direction you want it to go to search for the limit switch.
When I reference my machine, first the Z Axis goes up, when it hits the limit switch it then reverses off of the limit switch and stops and resets the DRO
It then does the same on the Y Axis, and finally the X Axis.
This works fine for me, and the only problem with this is if you want to machine mulitple parts from the 'home' position everytime you need to put in a high quality optical switch (so I have been told....)
I don't need this because I position the machine everytime to a datum on the workpiece and cut from there.
Hope some of this helps, I look forward to the final photos!

Andy

[Mike F]

Andy (although your username is Normansthename) ,

Many thanks for the input - just what I wanted to hear

Incidentally, I have now read and re-read the Mach3 manual and concluded I could use just three switches, just as you have. However, I am not too sure how these are arranged in terms of connecting them to the interface board. Do you wire then all together and have just one output or do you use three outputs, one for each axis? Reading the manual suggests I can wire all three to one output, treat one end of each axis as the home and limit switch and the other end as the other limit.

This all seems just a little too good to be true - I can get nine operations from three switches wired to one output - is this correct?

I am aware of the sequence of homing as the method you describe is exactly what happens on my small, Isel machine - first the Z homes then the Y and finally the X, each one hitting the switch then backing off slightly.

Andy, do you have a thread here so I can see your machine?

Mike.

[Mike F]

Andy (10Bulls),

Just realised there is an unanswered question in your last post. The answer is yes, I have every intention of replacing the MDF parts with carbon composite parts but that is way in the future and I'm just itching to get this one completed. The idea was to get this one to machine the patterns for making the moulded, carbon parts to replace itself. It's a weird thought of a machine making its own, better replacement - smacks of more than just a little sci-fi - now if I can just get it to think for itself :idea:

Mike

[ger21]

Mike, as long as each axis is homing seperately, you can use one pin. However, I'm not sure if the stadard homing procedure will work, or if you need to individually home each axis seperately. You'll have to try it and see.

[Normsthename]

Andy (although your username is Normsthename)

Mike, its a long story........

Do you wire then all together and have just one output or do you use three outputs, one for each axis?

Not sure if you can just have one switch. My machine has 3 separate outputs, so if one switch is tripped, looking on the diagnostic screen I can that is the Y Axis that is tripped etc.

Andy, do you have a thread here so I can see your machine?

That is something that I must get around to doing!
I have been so busy building the machine and now cutting things out I have not got around to taking a picture!
Here is a 3D CAD Drawing showing the machine.
The main frame is built from 60mm Square Steel Box Section, and the gantry is made from 30mm Square Box Section.
Capacity of the machine is approx. X900mm, Y600, Z140mm
It is fitted with a heavily modified (read butchered!) 2050 watt Router and has a dust extraction system with a homemade Cyclone fitted which really does the business and I would recommend that you look into fitting one to your machine.
I also have a homemade 3D Scanning device that fits to the Router for scanning parts in (my business makes motorcycle parts)
Attached is a couple of test scans of a mini-moto tank and seat unit that I did with it, I will post more information when it is a little bit more refined.....

Andy

[Mike F]

Andy,

Not sure if you can just have one switch.

No, not just one switch, but one on each axis, all in series, on one output pin. So the sequence would be that if any one of the three were tripped as limit switches, the machine and Mach3 would stop. Also, when doing a homing move, the Z axis would move first, in the defined direction, until its limit switch was broken. then it would drive itself off the switch. That sequence would then be repeated for the Y then X axis in their defined direction.

If this is all possible, and I think Mach3 can cope with it, then all I need is three switches, six ramps and one output pin.

Mike

Edit: PS I would be interested to know more about your digitising head.

[Normsthename]

No, not just one switch, but one on each axis, all in series, on one output pin.

Sorry, I meant to say three switches in series on one output!

PS I would be interested to know more about your digitising head.

The above scan took me about 45 minutes to do from start to finish.
I have a couple of tweaks to do to the software and it will be up and running
I will then post some more details......

Mike I forgot to suggest something about your machine.
Would it be possible to have the 'A' Frame gantry removable (or even hinged!) so freeing up even more space when not in use, just a thought.......

Andy