Limit Switches

[john_l]

I don't fully understand the use of limit switches. My machine doesn't have them.

Are they used just to stop the machines gantry from plowing into the stop blocks or are they used for setting X and Y zeros?

Any other pros or cons to having them?

Are they difficult to install and setup?

I will most likely buy from Shopbot if I decide to add these to mine but I have seen switches for sale on ebay that are described as limit switches, is there something particular about these switches?

Many Thanks,
john

[Gary Campbell]

John..
Yes... they can stop the machine from plowing into the blocks.

They are used most often to zero the machine to predetermined coordiates.

Depending on your machine, you will need switches that match the inputs on the control board. You might get extremely lucky and find some on ebay, however I doubt it. ShopBot will get you the right ones, inform you how to install them.
Gary

[john_l]

Thanks gary. Is there a difference between Proximity Switches and Limit Switches? I have heard both terms used here.

[Gary Campbell]

John...
Even tho the technical definitions may be slightly different,as far as SB usage goes, the terms are interchangeable
Gary

[butch]

John
The switches are proximity switches. This just means that the switch works without mechanical action. The shoe gets close (in the proximity) of the contact and the switch operates electronically.
On the ShopBot they use the proximity switch to stop the carriage before it hits the end of the rail, thus they are limit switches.
ShopBot uses them to set the X&Y zero point location.
Some equipment uses proximity switches to align print heads. That requires very exact positioning, so you can see how acurate the SB zero can be.

Butch

[richards]

Proximity switches require a target. Usually that is just a bolt head that is positioned so the proximity switch turns on (or off, depending on the switch) when it senses the metal. Be sure that you grind or machine the bolt head so that it is smooth and flat. (Brady Watson gave that tip, but I couldn't find the reference this morning.)

I have a small metal lathe that I use to turn the head of the bolts. With the heads turned smooth, the repeatability of the proximity switch is almost perfect (+/- 0.003") when using the standard Shopbot xyzeroing routine. Before turning down the bolt heads, I had inconsistent results, sometimes as much as +/- 0.2".

Also, verify that the height of the proximity sensor from the target is correct. Different proximity sensors have different distance requirements. Mine are set at 1.5mm which is just a little less than 1/16".