Limit switch question - repeatability accuracy


(Luke) #1

Hi guys

I have a question on the limit switches, I will start by saying I’m not using the standard ones similar to this one

http://uk.farnell.com/standexmeder/ksk-1a66-2030/reed-switch-10w/dp/1079469?mckv=aVUnyczZ_dc|pcrid|78108359109|&gross_price=true&CATCI=pla-73752366782&CAAGID=20220692829&CMP=KNC-GUK-GEN-SHOPPING-STANDEXMEDER&CAGPSPN=pla&gclid=CjwKCAiA6qPRBRAkEiwAGw4SdnWimid53lDNPuE-w8-mfng4iM-0T4vkgD9Bl6c3BELPx8M1SsnFXxoCr8kQAvD_BwE&CAWELAID=120173390001312212

However my repeatability is poor, it can be 1mm out quite easily. Would this lie within the switches not accurately homing or something else?

I’d have though repeatability should be within 0.1mm easily…


(William Adams) #2

Ouch.

There’re some links / discussion at: https://www.shapeoko.com/wiki/index.php/Home/Limit_Switches

What’s the mounting for the switches look like? Post a photo?


(Luke) #3

I’ve read up on that a few times, I don’t have a picture to hand but essentially they are mounted in square tubes and mounted to each axis. I’m wondering if that is causing me issues.

I do have some of these I’m considering fitting…

if you had to turn your machine off part way through a job, then return to the same homing point how repeatable is yours?


(William Adams) #4

I’ve had that happen a number of times (I had an early board, and am back to it, pending my getting a new replacement since my 2.4 board died an untimely death) — after re-zeroing, I can re-run a V Carve and not be able to tell which parts were cut only once and which parts were re-cut.


(Luke) #5

Whilst the disconnects have been an issue, with a shiny new board in hand I’m hoping they are gone. There is also the case when I turn on/off the machine there is the possibility I might need to return the the same point again.

I’ve just spent an hour knocking up some new 1mm ali brackets for the above hall switches. I will see how well they handle things, if not joy I might go back to buttons…


(Dan Nelson) #6

Same here, mine are super repeatable. In fact I’ve built a number of jigs that fit onto my waste board for a multipart project and haven’t re-zeroed anything between runs for several days now except for Z axis. I have several different files that all begin at the same origin, and matching jigs with same origin. I home every time I turn the machine on, rapid to current X/Y, do a quick visual verification, set Z zero, and let it run. As Will stated, I’ve also rerun the same VCarve twice on same piece (to try to clean up fuzzies), and the pieces show no double machining.

Dan


(Luke) #7

That’s very interesting. Are you using standard limit switches?

Are you working on wood or metal?

I’ve just fitted my Hall effect sensors along with the brackets. I’m just waiting on a new 10way molex to fit them.


(mikep) #8

Mine have been very closely repeatable, like Will I can’t tell the difference. Be aware that the hall effect sensors are known for being -more- variable than a physical switch. Their big win is that they’re basically impervious to coolant and dirt and extremely durable…the physical ones can be a lot less so.


(Luke) #9

That’s interesting. When I had Normal micro switches with arms I also found them to be off by a fraction. Hence the move away from them. You think Hall effect will be worse?


(Luke) #10

I’ve done some more digging and have put a order in for some proximity sensors - apparently these have the highest degree of accuracy. I’m going to continue with my install on the Hall effect. I might find they are good enough, but just in case…


(Craig) #11

I’ve been using Hall sensors for limit switches since a few months after th SO3 was released. Mine have been extremely accurate, however I had to offset the magnets from the sensor with the sensors I am using.

I used these Hall effect sensors and made adjustable mounting brackets which fit the holes in the plates for limit switches. This was prior to the C3D limit switch kit was available.

We just received another SO3 (Black Friday Sale) with the C3D limit switch kit so I will be able to compare the accuracy between the two styles.


(Luke) #12

I’d be really interested to see how you get on. Have you got a picture of how your hall switched are mounted?


(Stacy Boncheff) #13

This is a write up I did about my limit and homing hall effect sensors. They are still working great and are spot on in accuracy. Not only that but Kevin is a joy to work with.


(Luke) #14

I recall reading your writeup many times back in March. At the time I didn’t fit them, as I didn’t have a 5v pin. However thats since changed, I hope to wire them ups tomorrow when I get some new connectors.