The Shop > CNC
The basics
sparky961:
--- Quote from: John Stevenson on August 27, 2016, 12:26:46 PM ---If you keep belting the end of the table, pay more attention.
Don't be lulled into a false sense of security, seen it happen all to often. Fit a 4th axis at one end of the table and that limit switch is now null and void because it's behind it. now if that switch is also the homing switch and you aren't paying attention........................................ :palm:
--- End quote ---
I'm not convinced you got the point. To summarize: the significant effort required to select, mount, configure and test all of my limit switches was well worth it.
It's easy to be lulled into the trap of omission to save time and money, but if you want to move to the next step, they're essential.
Kinda like ballscrews...... for which I'm sure I'll eventually give into the purchase thereof.
John Stevenson:
No seriously do a rotab or dividing head.
It learns you do do the mechanical of connecting a stepper to the axis of the table and making sure it all revolves free.
Then you move on to the electrics with a simple breakout board like this.
http://www.ebay.co.uk/itm/361459921691
A power supply robbed from a computer, either laptop or desktop and a driver like this.
http://www.ebay.co.uk/itm/TB6560-3A-/301199977453
A simple stepper motor size depending on table but 180 oz/in for a 4" table is fine.
UK based one here.
http://www.ebay.co.uk/itm/Nema-23-Stepper-Motor-1-26Nm-2-8A-4-wires-6-35mm-Shaft-DIY-CNC-Robot-3D-Printer-/121651189123
then it's just a simple thing to wire up and that has taught you how to build a single CNC axis.
And instead of wasting time building a crap wooden router that will only suffice as part for the MKll this will last you all your life.
Every aspect is a learning curve and a keeper, nothing will be wasted.
Plenty of people on here to help you
John Stevenson:
--- Quote from: sparky961 on August 27, 2016, 02:02:08 PM ---
I'm not convinced you got the point. To summarize: the significant effort required to select, mount, configure and test all of my limit switches was well worth it.
It's easy to be lulled into the trap of omission to save time and money, but if you want to move to the next step, they're essential.
Kinda like ballscrews...... for which I'm sure I'll eventually give into the purchase thereof.
--- End quote ---
.
You put limit switches before ball screws ???????????????
philf:
My CNC has limit switches on all three axes and a dedicated home switch only in z. (Limit switches can be just that or can be a home switch.)
When I switch on I always do a "home all axes". This first moves the z axis down to my home position (to get to the bottom limit would take a lot of time - but would be the safest option) before homing x & y to the limit switches. It takes less than half a minute.
Mach3 is configured to home in the same z, y & z directions every time. I mount my 4th axis on the LH end of the table. The x-axis always homes to the left away from the spindle.
In Mach3 you can configure soft limits. When you home all axes it sets the limits accordingly and doesn't forget them even if you zero on the corner of a job. In theory you will never hit the limit switches whilst machining.
If you are machining a job which is towards the limit of the capacity of your machine Mach3 checks the GCode for the job and gives a soft limits warning if executing the GCode will exceed these limits. Better than machining an item and only discovering you have a problem when everything stops as you hit a limit switch (or even worse - if you haven't got a limit switch the control won't know and will try to continue machining - wrecking the job.)
Just my 2p's worth.
Phil.
sparky961:
--- Quote from: John Stevenson on August 27, 2016, 02:11:42 PM ---You put limit switches before ball screws ???????????????
--- End quote ---
Indeed.
On my vehicle, I'd fix a brake problem before I became concerned over a small amount of play in a ball joint or tie rod end. Priorities.
Backlash can be dealt with to an extent in your machining strategy, though it does severely limit the type of cut that can be made based on the direction of travel and where those direction changes occur. Want to drill an accurate hole pattern? Just come in from the same direction (in all axes) after every move. The fundamentals of machining still apply here.
While bordering on being moderately insulting, you're also demonstrating excessive faith in the human operator and control software (written by humans). Do you omit the E-stop switches as well? If you do include at least one E-stop in your retrofits, I bet it would get a lot less use if you included limit switches as well.
Nothing is a panacea but limit switches will remain on my list of CNC essentials.
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