Hall effect endstop switches for Fisher and other printers

I have the impression that the side-on microswitches used on the Fisher are not as reliable and reproducible as might be wished. I took a look at available Hall effect endstop switches on eBay, but all the ones I found were either over-complicated and expensive, or primitive and much larger than necessary. So I am considering making some, not exclusively for the Fisher but for other 3D printers too. They would be about 3mm thick including the sensing element, and the magnet would be about 3mm diameter x 0.5mm thick. What I would like to know is:

1. Is this something that Fisher owners would buy? My target price is GBP15 + shipping + VAT (if applicable) for three.

2. I don't have a Fisher, so I don't know exactly how or where they could be mounted. I envisage a couple of options for mounting them:

(a) Extend the idler bracket towards the centre axis of the printer, and mount them horizontally on the underside of this extension. Attach the magnet to the top of the carriage, between the two bearings, so that it lines up with the sensor.

(b) Extend the idler bracket towards the centre axis of the printer and add a downward-pointing vertical piece on the underside, then mount the sensor on this, facing the carriage. Glue the magnet on the edge of the carriage, between the two bearings.

Are either of these arrangements viable?

3. How long do the cables need to be to get from endstops in these positions to the connectors on the Duet?

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I'm interested, even if I don't understand how it works.
If it's more reliable, I'll take it.

I don't know if it can help you, here is what it looks like with carriage on top



For the wires, they are of 3 different length, I don't have the precise length (they are mounted) but if you extend them with 40-50 mm, this should be fine.
You can "see" (imagine) one cable (with blue tape) on the left side of the first picture. This will give you an idea alf the distance.

Thanks Greg, that photo is very helpful. It tells me that the magnet can be glued to the top of the carriage, and the sensor mounted underneath the top bracket, reprinted to extend it towards the central axis of the machine.

When the carriage is as high as it will go, how large is the gap between the top of the carriage and the bottom of the top bracket?

Edited 1 time(s). Last edit at 08/17/2015 01:35PM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

It's about 6mm and some additional decimals (between 6 and 6.5)
Sorry for the imprecision, but my digital caliper is missing batteries

It's the height of the top part of the longer linear bearing (from the line)




Edited 2 time(s). Last edit at 08/17/2015 01:57PM by Greg_be.

I'd be up for a set as well Dave.

How soon can I have them

Doug

I have already replaced my microswitches with hall effect switches.
Hall Effect Sensor Switch uni SIP-3
RS Stock No.680-7481
£1.666 each EA
£8.33
They work very well and calibration is very consistent maximum change from one calibration to the next 0.01mm
I modified the carrage to take a magnet

I printed a carrier for the sensor IC which simply replaces the microswitch

5v is needed to be supplied from the duet.
Only other change is to the config to change the polarity of the switching

I'd be interested in a set also

John, thanks for sharing your design, that's another way to mount the sensor that I hadn't considered. I am looking at using these sensors [uk.farnell.com] mounted flat on a small PCB with an indicator LED, so you can tell they are working even when the Duet is hidden under the bed. They can work off 3.3V, so they can plug straight into the endstop connectors on the Duet without needing a 5V connection.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

You tend to find that contactless switches work best when the switch is perpendicular to the axis of motion as per Johneto's design, most switch manufacturers advise against inline mounting as it give a less consistent switching position that can suffer from decay over time and environmental issues.

The reason tends to be that the signal rise curve over position (or time at a fixed speed) of an inline mounting is shallower than for a perpendicular mount.