[JimmyL]

Ive been looking all over the forums for this answer and i was wondering if someone could help!

Im planning to build a DIY routing machine to cut out about 3x3 ft complex shapes out of 3/4 inch Medium density fiberboard. How do people prevent the router from cutting the work table when the router has to plunge deep enough to cut out the complex shape but not to deep as to keep from cutting up my table? Ive heard of limit switches but how accurate can we get? thanks!

Jimmy

[mkc2]

Put a peice of scrap board under your job, that way you can cut the full thickness of your mdf and not cut through your nice table top.

Michael

[Boots]

yep,,,, that's pretty much what we all do.

[ignisuti]

Really..!?

I'm in the process of building my 1st CNC machine. So, I can't say I speak from experience, but I was planning to program the stepper motor to know when it's at just the right depth.

Not 100% sure how I'd do this yet, but maybe have a calibration mode before I start the CNC job so I could manually tell the CNC where the absolute lowest cut should occur.

[mactec54]

Hi jimmy

You control the Z depth in you program, once you have set your Z offset (set your cutting tool to the top of your work) then if your material is .750 thick, your program depth for your Z will be set Z-.750 it will not go more the this number

If you have to go a litte deeper because the table is not flat,then put something under your work being cut

[ignisuti]

Hi jimmy

You control the Z depth in you program, once you have set your Z offset (set your cutting tool to the top of your work) then if your material is .750 thick, your program depth for your Z will be set Z-.750 it will not go more the this number

Seems like you're relying on the drill bit height to be consistent each time you load in a new bit. Can you really count on this? Or, would you have to re-calibrate with each new bit?

[mactec54]

ignisuti

Yes that is the correct way to do it every tool should always be set to your work 0.0

You can also have stops on your cutters set at the same height as each other, so when you change a tool you don't have to reset each tool

[ignisuti]

Thanks for the advice.

What about this similar procedure?
1.) Install new bit fully in place.
2.) Move unit until is just about 1mm above the base (non cutable material).
3.) Loosen the bit and let gravity force it down approx. 1mm. and then re-tighten the bit.
4.) Push a calibration button on the machine that indicates you're currently located at the lowest point you'd possibly want to cut. (Perhaps, your software would take it just 1 motor step higher to be on the safe side...)

With this procedure, your software doesn't need to know anything about the depth of your work. It just knows the absolute lowest point it can safely cut/drill.

[Jay C]

Even better is to make/use a touch plate. A simple circuit that feeds to your controller to tell it when the bit contacts a metal plate. The thickness of the plate used is used to set the Z height.

[ignisuti]

Even better is to make/use a touch plate. A simple circuit that feeds to your controller to tell it when the bit contacts a metal plate. The thickness of the plate used is used to set the Z height.

Very interesting idea, but I'm not sure I follow you 100%. Could you elaborate a little more on how you envision this being setup? Are you saying the drill bit would connect the circuit on the touch plate?

[Jay C]

[ame="http://www.youtube.com/watch?v=BjHpCuH0Te8"]YouTube - Auto Z Axis Setting with Touch Plate[/ame]

[ame="http://www.youtube.com/watch?v=sCnZs7A59yg"]YouTube - DIY CNC Router Z-axis auto zero with touch plate[/ame]

[ignisuti]

Thanks for the videos!

If I understand correctly, the drill bit completes the circuit. Also, the software knows the thickness of the touchplate and factors that in to determine the exact height of the material under it. Do I have that right?

Pretty clever! Thanks again for the suggestion.

So, let's take this idea one step further and have a touch plate installed permanently on the work table. Then, before each session, it goes over and calibrates it's height by checking the touch plate.

[Jay C]

It's faster to bring the plat to the work depending on your table size IMHO.