Limit switch error???

[gundog]

I occasionally get a limit switch error when the spindle is no where near a limit switch. This started happening after upgrading the PC and using the latest control software (latest as of about 4 months ago) this is very intermitant and most of the time it does not happen. Any ideas?

[Brady Watson]

Tell me how your dust collection system & the Bot are grounded...Sounds like a static electricity issue. If there is no 'attractive path' to ground, then your proxy wires will do the trick, and energize the circuit for a split second, triggering a 'Hit' condition.

Bare copper wire...THROUGH the 4" dust hose, terminated to DC chassis, which should have verified continuity to system ground. Other end terminated at dust foot - just fold it over the hose junction - do not connect to metal. .025 MIG solid wire works well. No flux core.

-B

[gundog]

Hi Brady,
I machine plastic almost exclusively my duct work is metal with short pieces of plastic flex duct with the inner wire grounded at both ends. To the duct the dust collector is grounded and so is the table. I may be able to add a ground wire through the center of the flex for the SB but my saws make stringy swarf that would tangle with the ground wire run inside. I am also worried the drill swarf from the table may also tangle with a wire ran inside. What do you think?

I will add the problem started after moving from my old shop to my new facility and at that same time we upgraded to the new PC.

Thanks Mike

[Brady Watson]

I wouldn't worry too much about stringy chips clogging things up. If it does, a wiggle should clear it out. The spiral wound wire on those soft hoses are insulated on all sides and really only there for structural support. A bare wire inside and tied off at your metal ducting would be my suggestion. I would not worry about the saw etc. Just do the leg from the SB foot to your metal ducting, and then make sure you are carrying ground from that ducting back to electrical ground (can be chassis of collector or EMT).

See if that clears it up...

-B

[gundog]

Thanks Brady I will give that a try.

[erniek]

I had a similar problem, couldn't figure it out. Then one day the "Y" axis limit switch sensor broke in half. So I'm thinking that the sensor itself was causing the false limit switch alerts.

[coryatjohn]

Sort of off topic...

I was wondering why ShopBot chose such a complicated system for the proximity switch.

It seems like a micro switch would have been a far simpler and much more robust option, and a lot cheaper too. A micro switch would also be able to be aligned a lot easier than using the top of a bolt. The current setup doesn't always sense the bolt exactly in the same place every time. A micro switch would always switch in exactly the same place. Sure, it would have to be a good micro switch but what would that run? $10? What does one of these fancy electronic switchy things run? $100 or more?

Just curious. Brady probably has an answer.

[steve_g]

John

I reliably get .002" type repeatability with my prox sensors... I've had other type machines with micro switches... even very good switches, Contact bounce, pitting, wear and thermal issues always caused less than optimal results over the long term. Many Micro switches can be damaged if they are approached from the wrong direction like what could happen if you temporarily disable sensing. Proximity sensors rapidly go up in cost with sensing distance... A ShopBot is a controlled enough situation that very short sensing distances are usable. Someone comfortable specifying and ordering their own sensors can find them well under $30.00... I've paid well in excess of that for an industrial sealed micro switch.

SG

[coryatjohn]

Steve,

Question answered. Sounds reasonable.