Triac limit switches and mach 3

[toby1995]

Hi all

I am in the process of upgrading my Triac PC to mach 3. I have bought a "CNC kit" (https://www.ebay.co.uk/itm/203718263502) and intend to pretty much start again with the electronics and have them in a new electronics enclosure bolted to the back of the machine, similar to what you would see on industrial VMC's. i have most of what i intend to do all planned out and can see a clear(ish) roadmap on how to do it. for controlling the machine i am going to use an RNR mach 3 board with USB connection. This is purely because its inexpensive, functional and there is lots of info online regarding this board.

Once completed i will have a complete control box available if anyone wishes to buy it, if so make me an offer

My questions to all you clever people on this forum are what to do with the limit/home switches on my Triac. what is the purpose of having an inductive proximity sensor with limit switches? (from what i can see on the x axis, not sure about the other ones), can i not use just limit switches on their own for homing and travel limits? or is this not recommended? what is the easiest solution for interfacing them with my new system and mach3?
would it be easier to start fresh with different switches and power them from the 24v power supply i intend to use to control the new spindle VFD via the RNR board?
what voltage are the original switches/sensors and are they readily interfaceable with my board?.
it would be nice if i could use the original switches on my machine to save unnecessary work.

Any and all advice is appreciated, thank you

[moray]

With the original setup, the limit switches were wired as part of the E-stop circuit, so if any were triggered, the entire machine came to halt.
There are arguments both ways as to whether that is appropriate or not, but for a primarily educational machine, it's probably the correct choice.

The homing sensors are NAMUR output, which would require a suitable interface to connect to a more typical switched input (I think there is a post on here somewhere with a circuit diagram of how to achieve it).
I personally replaced the homing sensors with more standard 4 wire inductive sensors, and replaced all the wiring under the table while I had it off, as it had started to go brittle with age.

[toby1995]

Hi Moray,

Thanks for your reply. i think ill do the same and replace the NAMUR system with new cables and 3 wire sensors or micro switches then. what sensors did you go with to home the axes? particularly the X axis as as the original proximity sensor for this is tiny! (may be the same for the other axes i havent looked) image from another post: viewtopic.php?t=1822

can i not just use limit switches for homing and travel limits? as i feel it would be far easier to change those out and do away with the proximity sensor. is this a bad idea?

[moray]

I can remember the sensor came from RS, and there were very few options the same size.

I won't have time to find the details until next week, but the details of my retrofit can be found at https://www.mycncuk.com/threads/10344-Y ... -thread%29 which might contain the details.

[toby1995]

okay ill have a good look through that. thank you very much

[moray]

I've just checked my old orders, and this is the sensor I used - https://uk.rs-online.com/web/p/proximit ... rs/4370735
You may want to be sitting down when you look at the price though!

[toby1995]

holy mackerel!! thats pricey! i assume there are no other options for this as they are such an uncommon size? hence the ludicrous price. i have looked around online and had no luck finding anything like these. if there isnt any other option im not sure what to do now, i have already spent a pretty penny on this machine to upgrade it! would i be able to just use roller limit switches for homing and travel limits? surely the travel limit in X- Y- & Z- is the same as the home position?? is there a reason why proximity switches were used as well as limit switches? maybe im missing something in the way it works?

if i just replace the limit switches with 24v DC ones that will fit were the original ones have, surely i can make this work?

also is one switch on the home position technically all thats required? can travel limits be put into mach 3 so as to not over travel once the home position is established? sorry for asking possibly stupid questions, ive been a machinist for 15 years or so but i am pretty new to this machine building business but very keen to learn!

[toby1995]

Hi Moray,

just a quick update,

In regards to the 24vdc inductive proximity switches required, in which you kindly provided a link for, i believe if im not mistaken that i could, instead of buying 3 of these (at £80+ each!) i could get away with only getting 1, just for the X home. as this is were the space is tightest.
The Y and Z axes home appear to have a bit more room to play with potentially allowing my to get a more common sized sensor for less cost.

[toby1995]

Apologies if thats what you meant anyway!

[moray]

Only just seen this.

I honestly can't remember how much space there was to fit longer sensors. I just took the easy option of replacing both with identical sensors.