Zeroing: to Bed or Material?

[jTr]

I'm pondering the advantages of zeroing to the bed, though as a new user, I've been using default method of zeroing to top of material.

I've read a number of threads in the past that I thought refered to this method, in many cases incorporating a shop made or aftermarket aluminum zeroing block, though I've been unable to retrieve in a search of this forum.

I'm specifically targeting the infinitley variable plywood thickness issue. For instance, I'd rather zero to the bed, define a dado groove that has a .5" thickness in 3/4 sheet stock, thereby shifting the fluctuation to the inside, resulting in target exterior cabinet dimension. My theory is I'll reduce or eliminate fussing over toolpath adjustments in order to continually cope.

- Any adjustments/ alterations to the machine needed?

- Does PartWorks adjust accordingly when defining this zero point in material setup, or do I need to be setting cut depths to positive numbers above bed of machine?

There appears to be no shift in toolpath diagram when toggling between the two options. PartWorks simply indicates: "... machine must be setup in the same way, ensuring the toolpaths cut to the correct depth"


Any advice would be appreciated.

jeff

[zeykr]

I zero to the bed when cutting cabinets or other 'cut through' parts. I zero to top of material for vcarving and occasionally when 3d carving.

You do not have to have a dedicated table level zero block, but it helps to have someplace beyond your material that is machined to same ht as table top so you can zero to bed even with material on the machine.

Partworks handles the cut depths whether zeroing to bed or material top. You do not need to set to positive number above the bed.

[Greencarvings]

I always zero to the material surface except when cutting out. Then I zero to the table surface. This allows me not to cut up my spoil board. Yes there is an extra step or two when doing it this way, but it is worth it to leave a very thing onion skin, not have to sand tabs, and not have to continually surface the spoil board.

[bobmoore]

Remember to dress your zero spot if it is seperate from your spoil board when you dress the board.
Bob

[adrianm]

I zero to the bed pretty much all the time now. I use an off the table adjustable zzero point with automated routines so setting the Z is not something I have to think about.

PartWorks takes care of everything when you switch between material and surface Z. All you have to do is to recalculate the toolpaths.

[jTr]

Adrian - love the simplicity and adjustability of that device.
You stated:"I use an off the table adjustable zzero point with automated routines so setting the Z is not something I have to think about"

How complex is it to write up a routine? Have you simply set the Zzero routine to a designated spot each time, as it prompts, or is it a little trickier as you're driving past the limit switches to do so?

jeff

[adrianm]

I have a variable set in the PostProcessor that feeds into the Manual Tool Change routines which then knows which ZZero routine to call depending on whether the bit is zeroed to the surface or the bed.

The one that zeroes to the jig is pretty much the standard one with the offsets always used.

Makes for efficient working as the bit automatically zeroes itself once changed.

[bobmoore]

That looks real efficient Adrian. Are you saying you zero to that spot each time and mathematically calculate the spoil board dressings or do you adjust the zero plate each time you dress the spoil board?
Bob

[shilala]

I've been told to zero to the top of my material any time I have artwork or anything that relies on depth of cut. That makes perfectly good sense to me, and that's pretty much all the time with what I do. I surface all my project lumber on the planer to very close tolerances, I have a Wixey guage on it that does a great job.
If I were simply cutting parts where I go all the way through, I'd zero to the table. That also makes very good sense because I can onion skin parts and not destroy my bed. The tool will ignore inconsistencies so far as thickness of material goes.
As is, I generally run a couple profile passes that are incrementally deeper to stay off my bed when I zero to the top. That way I can get real close, save messing around, and not wreck my bed.

[adrianm]

That looks real efficient Adrian. Are you saying you zero to that spot each time and mathematically calculate the spoil board dressings or do you adjust the zero plate each time you dress the spoil board?
Bob

I just use a long straight edge on the resurfaced spoilboard and adjust the zzero jig and lock it off (the black bit is a hand locknut) when it's touching.

I used to use a piece of ali stock that I machined off at the same time as the board but this way is much easier and every bit as accurate.

I find that it's more than accurate enough when machining from the surface of the material as well provided the material thickness is accurately measured.

[jTr]

I have a variable set in the PostProcessor that feeds into the Manual Tool Change routines which then knows which ZZero routine to call depending on whether the bit is zeroed to the surface or the bed.

Is this an easy mod? Not having much luck finding a pathway to such a variable in SB3, which as I understand is the post processor (unless I'm mistaken?).
jeff

[adrianm]

The Post Processor is the instruction file that Partworks/ VCarve etc uses to write the SBP file that you load into SB3.

There are numerous variables that can be added into the file to pass information over from Partworks to SB3. In the case of the zzero location the variable is Z_ORIGIN.

With VCarve/Aspire there is a instruction manual on the Help menu about the Post Processor. Not 100% sure if it's on the PartWorks menu though.

[jTr]

Thanks for clarification - indeed, the documentation is under the help topic in PartWorks. I gather this modification to the post processor is triggered by any tool paths that require a tool change and once set up, all files respond accordingly, rather than a mod that is necessary for each new toolpath created(?)

Not sure if I'm ready to delve this far into tweaking my processor, but eventually intend to utilize this - Looks like I've got some studying to do.

Thanks for the enlightenment!

Jeff