zero to top vs bed

[gene]

What is the benefit of zeroing to the tabletop ( bed) as to zeroing to the top of the material ? How does this work with the safe z height?

[sailfl]

For almost 4 years, I always zeroed to the top of the material but starting at the end of last year, I changed and started zeroing to the top of the spoilboard. I don't think I will be going back. My spoilbard does not get cut up the way it did in the past. I can cut material of different thinckness for the same job with out having to rezero my machine. I don't have to be concerned if the material varies in thinckness.

I can cut 0.5" and 1" Gatorboard with the same file because I cut them in one pass.

I am using Aspire so it takes care of the safe Z.

[rb99]

If you are doing v carved letters you would probably want to use the top of the material.

[sailfl]

Richard,

Why for letters?

[adrianm]

Any job which has critical machining from the top (vcarve, pockets, 3D) AND you can't be 100% certain of the material thickness it's best to zero from the surface of the material IMO.

99% of the time I machine with the zero on the table surface but when I do a VCarve job on a series of boards I'll go for material surface to account for any discrepancies in thickness but I always use the z-zero on the table surface for through cuts.

I machine a wide range of board thicknesses and use all sorts of different length bits so I followed Dana's lead and put a proximity switch on the Z so I don't have to constantly check the Safe Z.

[twelchPTM]

my first experience with cnc was a biesse rover b, big machine - 8 zones, 4 "homes", vacuum pod hold down system, Auto tool change ect. EVERYTHING referenced Z-zero from the bed, getting used to referencing the top of my board as the z-zero was alot easier to get used to then I thought.The other day I started o project that requires many sheets of foam to be machined to an exact thickness, at first I was using my mic and checkin the thickness all over the shee and could not get the consitency i needed then it hit me duh! reference z-zero to the table, now all the sheets come out perfect and the software addapted the same cut from one to the other flawlessly. In conclusion (as stated above) the only time one is "better" then the other is pocketing or v-carving in material where the thickness is inconsitant.

[feinddj]

I zero to the table. It negates the need to mic every sheet to find out what the sander did to the ply that day. When I v carve, I plane the surface and then run the vcarve all from the bed.

[bill.young]

If the thickness of the material that's left is important...I want a tab that's exactly .25" thick... I zero from the table surface.

If the depth of cut is important...I was a slot that exactly .25" deep...I zero from the top of the material.

[Hoytbasses]

another rookie question answered just by lurking about on this forum! thanks
kfh

[Michaelodunk]

This is great info for the new and not so new user.

sys op.

How about starting a thread that specializes in containing this kind of information.
I know this could mean more work for you, reading and deciding what to move. Maybe we the users could request it be move to the new thread like I am doing here.

thanks
mike

[adrianm]

I suppose that's what the Wiki (http://shopbotwiki.com) was originally intended for but didn't get going for some reason.