Touch Plate sets bits .010" too long.

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FixitMike
Posts: 119
Joined: Sat Mar 26, 2011 1:16 pm
Location: Renton, WA

Touch Plate sets bits .010" too long.

Post by FixitMike »

My touch plate is set in the File>Preferences to .375" thick. That is what it measures. But after running some VCarve toolpaths, I realized that the bit was cutting too deep.

I'm using Control Panel 2.1.

I tested the touch plate by first flattening a board with a 3/4" bit cutting a .06" deep pocket. I then used the touch plate to set the Z for the same bit over the pocket area. I turned on the router and clicked on Move to 0,0,0 to move the bit down to the surface, and then moved the cut around using the jog buttons. The bit cut .010" into the pocket even though it was set at Z=0.000. (This doesn't happen if i set Z0 using a piece of thin paper.) I repeated the test by lowering the bit .001" at a time until it touched the surface. The Z height was displayed as .010".

Another member of our CNC group says that his bit Z is .012" off when he uses the touch plate.

The solution is to tell the Control Panel (under File>Preferences) that the touch plate is .365 thick (.010" less than actual). I would suggest6 that anyone with a touch plate repeat my tests to see if their software is also setting the Z incorrectly.

A .010" error in cutting depth may not seem to be significant. But when I VCarved some .5" high Times New Roman letters, raised, in a .06" deep pocket, with a 60 degree V bit, the reduced thickness of the thin parts of the letters was quite perceptible.

And, if NWA fixes this in a future revision, I would hope they tell us so we can remove the bias in the thickness setting.

tonydude
Posts: 1581
Joined: Tue Aug 17, 2010 9:23 am
Location: Buffalo,NY

Re: Touch Plate sets bits .010" too long.

Post by tonydude »

This is good to know, will have to check mine this week.

Tony
Buffalo,NY

"What will matter is not what you bought but what you built; not what you got, but what you gave”

Aspire 11.015, photo vcarve, cnc mako shark extended bed with the new upgraded HD 5 gantry with Led pendent.

Rando
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Re: Touch Plate sets bits .010" too long.

Post by Rando »

(I'm "that other guy" that Mike mentioned) I'm typically seeing 0.020" total error; the 0.012" was from a particular engraving run :D.

Yes, it's more than a little painful when you're working in metal and really wanting that accuracy. It's especially painful when you needed an 0.010 cut and instead got an 0.030 cut. In metals, this is a problem, not something that can be ignored.

My solution was to stop using the NWA touch plate, but instead using an 0.020" thick piece of sheet aluminum about 1.5" on a side. I use the "no touch plate" option in the Z0 touch-off, and thus don't have to make any changes. I just use that small piece as the touch-off plate. (Added bonus, no nicks from the bit on the part) In my case, I reversed the polarity of the sense circuit so my continuity is between the bed/vise/part and the spindle bit. I cut mostly metal on my Shark, and when I don't, I just connect the metal plate to the bed or vise using an alligator-clip test lead.

Regards,

Thom
=====================================================
ThomR.com Creative tools and photographic art
A proud member of the Pacific Northwest CNC Club (now on Facebook)

Joseph Poirier
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Location: Toledo, Ohio
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Re: Touch Plate sets bits .010" too long.

Post by Joseph Poirier »

There are a Z-offset and touchplate thickness options in the Preferences of the control panel.
and we are on 2.1 build 25 f now.

Best Regards, Joseph Poirier, Next Wave Automation Sr Software Engineer

Rando
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Re: Touch Plate sets bits .010" too long.

Post by Rando »

No, Joseph, this is not that. This is the problem we researched way back when, when you were debugging the virt-z stuff with me. Remember those aluminum plates I cut with the tests? Those, and every other daily cut in aluminum I make proves this to be true, and in our conversations, the resolution was that it was "in there somewhere", but we couldn't find it.

If I touch-off a bit directly to the material, and then hit the HOME button, the bit goes right to the surface. However, a GCODE file that has G0 z0.000 will actually end up about 0.018" inside the material. Honestly, at this point it doesn't matter whether you think it's true. In order to make mil-accurate depth cuts in aluminum, I use an 0.020" thick square of sheet-metal. If I don't do that, the first cut is always 20 thou too deep. If I add that 20 thou plate, the bit is perfectly positioned. Seriously; I used this when I require features to line up across part rotations (as in, a feature that wraps around the corner of the part, and can't be cut in one step), and this gives me EXACT placement, where the cuts line up within that one-thousandths positioning accuracy (actually,it look more like about 1.2 thousandths per step minimum that then gets mathematically rounded every fifth 0.001" step, but whatever...the machine's made out of plastic ;-) ).

My point is, we know about the offsets and the plate thickness setting, and even when there's no plate, it's off.

Regards,

Thom
=====================================================
ThomR.com Creative tools and photographic art
A proud member of the Pacific Northwest CNC Club (now on Facebook)

async4
Posts: 6
Joined: Sun Oct 02, 2011 7:22 pm

Re: Touch Plate sets bits .010" too long.

Post by async4 »

Why is there no solution from Nextwave? It has been over a month, and I don't even see a reply from them stating that they will look into it. I am having the same problem. I bought the touch plate after seeing their demo of accurately v-carving an uneven board and getting precise results. How many projects must be ruined before this is addressed?

Rando
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Re: Touch Plate sets bits .010" too long.

Post by Rando »

Month? It's been YEARS :D. The problem is buried somewhere in the firmware for that old controller, and NWA doesn't have the ability to change it, even if they wanted to: they don't have the source code. :D So, it's a known issue, and I just deal with it. I have my ways ;-).

The reason why they haven't replied they will fix it is that Joseph and I traveled that road a long time ago, trying to find where we could even control it, and the options were the same old: increase the claimed thickness of the touch-plate (I don't use one, since I'm doing aluminum I can touch off the surface of the part), even shift the GCode Z-values by the right amount (cf. "GCodeshim" program I uploaded here somewhere). What I ended up doing was using a thin sheet of 0.020 aluminum as the touch-plate. It keeps any bit dings off my parts, and it compensates for the height issue. The actual value, when I've worked for an accurate value, was between 0.018 and 0.020, at least on my machine.

Regards,

Thom
=====================================================
ThomR.com Creative tools and photographic art
A proud member of the Pacific Northwest CNC Club (now on Facebook)

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