NordicCNC's build log

[NordicCnc]

Home & limit switches

Z-axis home switch at the top end of the travel. Soft limit will be used for the lower end of the travel.


X-axis home switch & limit switch on the moving part. Adjustable bolts in the t-slot in the lower right and upper left of the picture. The lower right will be used for home & limit switch and the upper left will be used for limit switch.


Y-axis home and limit switch on the moving part. Adjustable bolts in the t-slot on the left side of the base frame. Upper left one is used for limit switch and lower right one is used for home & limit switch. On the opposite side (right side) is the second home switch. The purpose with 2 home switches is to be auto to auto square the gantry when homing the axis.


Alternatively I could have all the proximity sensors fixed and not on the moving parts. Then I could use soft limits for all axis's in the opposite end of the homing position, same way as with the Z-axis. Would that be a bad idea? It would be less cable routing of the sensors in the cable drag chains,

[AndyUK]

I'd recommend having the homing positions on the dual screw axis finely adjustable - like how your Z position can be adjusted by turning that bolt. At the moment you'll have to loosen that bolt and t-nut and just hope you can push it accurately back and forth. It'll help when trying to square the gantry, where you need (ideally) sub-mm changes to switch triggering position and I wish I'd thought of that earlier. I've had to do quite a bit of back and forth trying to get the gantry squared.

You can work around it in software (I can't remember what controller software combo you're planning to use - but generally speaking its possible), but easier done once in hardware.

[Clive S]

Z-axis home switch at the top end of the travel. Soft limit will be used for the lower end of the travel.

I personally would have the switch fixed and have the target moving

[NordicCnc]

I personally would have the switch fixed and have the target moving

Yes, that is how the Z-axis switch is planned in the picture.

[NordicCnc]

I'd recommend having the homing positions on the dual screw axis finely adjustable - like how your Z position can be adjusted by turning that bolt. At the moment you'll have to loosen that bolt and t-nut and just hope you can push it accurately back and forth. It'll help when trying to square the gantry, where you need (ideally) sub-mm changes to switch triggering position and I wish I'd thought of that earlier. I've had to do quite a bit of back and forth trying to get the gantry squared.

You can work around it in software (I can't remember what controller software combo you're planning to use - but generally speaking its possible), but easier done once in hardware.

Extremely good point, thanks for letting me know. I will make some changes to the design to allow for fine adjustment.

[BobTSkutter]

The proximity sensor at the top of the Z-Axis appears to be very close to the grease nipple on the bearing block. Could the grease nipple cause interference with the sensor?
Adjustable bolts looks like a clever way to adjust the trigger point but are the bolt heads big enough for the gantry limit switches to "see". The sensor is round and I think you're using set screws which appear to be the same size as the sensor with the hex indent in the middle. It looks to me as though the hex indent is exactly where you want the sensor to trigger. Would using a conventional hex head bolt instead of a set screw be better?
Regards
bob

[Clive S]

Yes, that is how the Z-axis switch is planned in the picture.

Yes sorry I was looking at it wrong.

[NordicCnc]

The proximity sensor at the top of the Z-Axis appears to be very close to the grease nipple on the bearing block. Could the grease nipple cause interference with the sensor?
Adjustable bolts looks like a clever way to adjust the trigger point but are the bolt heads big enough for the gantry limit switches to "see". The sensor is round and I think you've set screws which appear to be the same size as the sensor with the hex indent in the middle. It looks to me as though the hex indent is exactly where you want the sensor to trigger. Would using a conventional hex head bolt instead of a set screw be better?
Regards
bob

Good catch, but this is just a 3D error that I didn't correct yet. I plan to have all grease nipples facing inwards and with a common lubricating hose and nipple externally mounted.

As for the screw heads, I am not sure really. This is something that I can easily fix later if it turns out it is not working as planned. I have access to both lathe and mill so manufacturing a better target, e.g. with a flat surface for the sensor will be possible.

[JAZZCNC]

Extremely good point, thanks for letting me know. I will make some changes to the design to allow for fine adjustment.

Don't waste your time, the way you have it now will work fine, that's exactly as I do them. It's simple and works. If I was to make a suggestion it would be to move the switch onto the side, fastened to the ballnut bracket and use the top slot for targets. How you have it now leaves the switch wide open to debris when cutting and if you cut steel or aluminium then could get false triggers when blasted with chips. Also the crap from cutting aluminium with lube can build up on the sensor.

As for the screw heads, I am not sure really. This is something that I can easily fix later if it turns out it is not working as planned. I have access to both lathe and mill so manufacturing a better target, e.g. with a flat surface for the sensor will be possible.

Again exactly as I do them and they work fine, the round head doesn't cause any issues. The only suggestion I'd make is to stiffen up the bracket. The one I use are 3D printed, You can just see it between the mass of pipes and wires in this pic.

[Kitwn]

For users of LiunuxCNC with the option to auto-square the gantry it is essential that the switches cannot overshoot their targets during deceleration and reset themselves before the whole sequence is finished. In this case you may need a larger target, especially with a large and heavy gantry.