Touch plate and alternatives

[WillAdams]

Okay, added a section on these to the wiki: http://www.shapeoko.com/wiki/index.php/ ... ouch_Plate

Must admit I’m tempted by the commercial one from Amazon --- at last, something worthwhile to get w/ my Bing reward points.

http://www.amazon.com/Z-Axis-Setting-To ... B00UNXXZAG

Just as a check, my understanding of such a device is:

One homes the machine, then one places the touch plate on either the Wasteboard or the stock (depending on where one wants the reference surface / origin to be), the touch plate lead is then clipped to the endmill, and one enters an appropriate command (or clicks the proper button / engages the correct widget) so as to set the height of the Z-axis — the specific height of the touch plate allows one to do this — that’s why this one is shown as exactly 20mm.

[WillAdams]

Is there a way to set the top Z-axis limit switch’s triggering position to be a positive value? Or is this one of those bad ideas, contrary to good working practices which are unsupportable?

[woodworkerbob]

Is there a way to set the top Z-axis limit switch’s triggering position to be a positive value? Or is this one of those bad ideas, contrary to good working practices which are unsupportable?

I use a similar gizmo as in the Amazon link. With my gizmo a red light lights up when the CNC bit touches the pad. The pad is "exactly" 2.0 inches above the surface. You have to manually set Z to zero, remove the gizmo, move Z to -2.0 inches, then reset Z to zero. Works like a champ, although manual. It's a bit of a pain to clip one lead to the CNC bit, but that's a pretty small price to pay to get a simple and really accurate way to setting Z to zero at the surface.

This would be a really nifty feature in GRBL, "Auto Setting Z Axis to Zero at Surface". If you change bits a lot, this feature becomes critical.

I hope there is some way to automate. Is it possible for me to help add this feature to GRBL?

Bob

[WillAdams]

If I understand things correctly, that's what the probe commands are for.

[cvoinescu]

The one on Amazon is simply a hunk of plastic with a machined piece of metal held by a screw. There is no spring or anything like that to protect your endmill. There are no electronics inside: just the two wires you see. An identical device can be had on eBay for much less, from China (where I'm sure this one originates too).

[lordmundi]

yeah, basically identical thing available on ebay for about $10 shipped from China (don't ask me how that is possible).

[Woodworker]

In China it only costs 10 cents to make then you wrap it in newsprint, put US postage on it and give it to a trained rat. The rat scurries onto a cargo ship and hides in a corner. When the ship docks, he takes the package to the nearest post office. In a few days it is at your door. Simply really.

[WillAdams]

Joking aside, Chinese international postal rates are low ’cause they’re subsidized by the Chinese government, and I believe there’s a favorable cost of living adjustment.

[WillAdams]

Okay, so this is an electronic device simple enough to make that I should be able to make one. AIUI, one would want:

- a metal plate (conductive, for the endmill to contact)
- a wire which plugs into the probe connection on the micro-controller — one end would have a clip for the endmill, the other would connect to the metal plate / housing
- a housing which would feature an adjustment mechanism to allow one to ensure that the metal plate is held level and at a known distance from the base of the housing (which must be level / flat enough to place on a work surface) and a way to ensure electrical connection for the other lead

[cvoinescu]

Why the adjustment? A fixed touch plate is still "at a known distance from the base of the housing". Not predetermined, but known -- measured with your favorite calipers. As for level, that's not usually a problem, especially not if the housing and the metal part are cut or milled from reasonably flat stock, or turned on a lathe. Those are inherently flatter than most people can adjust them.