High Precision Homing Switch

[Chaz]

I used an opto slot sensor on my old lathe, and there was never any measurable variation. I used RS part number 480-5231 however I see that part has now been discontinued. The only problem was I had to make sure a bit swarf hadn't landed in the slot prior to homing, as I never bothered enclosing it.

The new lathe uses proximity combined with servo index homing.

You could combine a proximity or microswitch with a slot sensor on the stepper, provided you can add a suitable slot to the stepper/ballscrew, to essentially give you a poor mans index homing.

Does this need a 'receiving part' or anything that it can pick up in the slot?

[m_c]

Does this need a 'receiving part' or anything that it can pick up in the slot?

You need something that goes through the slot. It doesn't have to be anything fancy, I just used a bit bent bar suitably mounted on the cross slide -

[Gary]

we use these on our machines and linear stages we build.
https://www.zappautomation.co.uk/bes...on-sensor.html
The repeatable accuracy is 1% of the distance of the metallic material used to sense.
other things also need to be taken into account as well to see the accuracy though.
Also very low profile, but not the cheapest.

[JohnHaine]

Chaz, I have made something based on the "touch plate" concept used for mill Z homing.

(I hope that works!)
Repeatability seems to be better than 10 microns, and in conjunction with my tool setter on my first trial of homing/applying set tool offset/turning I achieved indicated microm accuracy on diameter. This cost nothing to make, it's essentially a bit of PCB laminated on to 6mm of tufnol superglued to the apron front. Obviously there are issues of wear and tarnishing so I intend to upgrade it with one where the contact surface is beryllium copper.

[Chaz]

Chaz, I have made something based on the "touch plate" concept used for mill Z homing.

(I hope that works!)
Repeatability seems to be better than 10 microns, and in conjunction with my tool setter on my first trial of homing/applying set tool offset/turning I achieved indicated microm accuracy on diameter. This cost nothing to make, it's essentially a bit of PCB laminated on to 6mm of tufnol superglued to the apron front. Obviously there are issues of wear and tarnishing so I intend to upgrade it with one where the contact surface is beryllium copper.

Thanks, I had though of similar - this is the way that we deal with milling offsets, so no reason why it wont work on a Lathe. Ill try the switch from audioandy (Thank you) first and go from there.

Thanks for the other suggestion Gary.

[audioandy]

Hi Chaz

Switch posted today first class so should be with you tomorrow.

Regards
Andy

[Chaz]

Hi Chaz

Switch posted today first class so should be with you tomorrow.

Regards
Andy

Thanks, appreciated.

I retested my cheap proximity switch with a 'semi decent' analog DTI and it was surprisingly accurate. My el cheapo electronic DTI seems not to be repeatable. Go figure ...

I also managed to get my spindle speed / encoder setup to work and tweaked my steps for X and Z, explains why I was getting inaccurate cuts, not out my much, but it was out.

Ill still try the mechanical switch - just need to figure how to mount it with my setup.

[Chaz]

Hi Chaz

Switch posted today first class so should be with you tomorrow.

Regards
Andy

Received, with thanks.