Z behavior after bit change

I recently cut a pocket that should have been .095 deep and it was .15 deep. I could tell the first pass was too deep but I let it roll anyway. I have had this happen a time or two and figured that I missed a step somewhere but I was pretty careful this time.

I noticed that sometimes the Z position changes before and after the bitsetter and want to understand the way it works. Is the machine supposed to return the same Z height or, does it really move the spindle to the same spot but the difference reported in the Z position on the screen really represents the difference in the bit length. Sometimes I see the difference is only .001 and other times it is more like .45.

When doing a really critical cut it would be nice if there was a way to re-validate Z after the bit change / bitsetter. The only way I have found to do this now is to pause and then stop the job and then jog over and touch off on the surface. Thats OK if it is a single toolpath job but on a multi toolpath there is no way to do that I can find.

I am working on a set of coasters now with 3 colors of epoxy in them and trying to beat the clock for end of year gifts for the kids teachers. I have already had to recut a couple. I am at the flatten the last round of epoxy stage this weekend. If I go too deep I will not have time to recover. I guess I could just sand it down but that would take a while and really gum up some paper.

How are you setting the zero?

If using the BitZero see:

I have the V1, but bought some 1/4 steel dowels to use as pins rather than rely on the bits themselves.

About 90% of the time I zero on the corner with bitzero but sometimes I will adjust Z afterward on the surface. I don’t know if that would be an issue.

I have started to zero on the bottom for through cuts.

I will often do the Z+6mm and then jog down to verify. You just can’t do that mid job. So I was trying to understand if the Z reported in the screen is supposed to be the same after a change or if that has the difference in bit length factored in and the router is at the same spot.

If it is supposed to report the same number then I have something going on I need to address.

What is the exact context you are seeing a discrepancy in the Z height value?

Well, not sure it is a discrepancy, trying to figure that out.

Before change:

After change:

I just happened to notice this and wondered if it was an issue. I notice that whenever it heads to the bitsetter it changes zero to -.93 or something like that every time before it moves. Then it does its thing and comes back and resets Z to something either close to what it was before or kinda close.

The Z-height of the tool change position will change as a tool is changed because it is relative to the top of motion, and is adjusted so as to take into account the tool offset length.

With the machine at the top of its Z-axis motion (less homing switch pull-off I believe), the reported Z-axis position would only be the same if both tools had probed to exactly the same length.

If you click on the “Position” text link you will see this reported in Machine Coordinates/“Machine Position” (see: Machine Motion - Design into 3D ) which will be invariant of tool length.

Ok. So not an issue then.

Gotta pay closer attention and try to identify why I am occasionally going a little deep.

When you pick “Load New Tool” it always asks you to load the first tool for whatever job is currently loaded. Does it really matter there? I sometimes use that to load the 1/4 steel dowel but then then when I start the job I switch to the first bit at that point when it asks.

If I didn’t put the dowel in the. The right bit may be there and I just hit Ok

The way the BitSetter works is first the last time you physically set X Y and Z zero it is persistent over power cycles. Now that persistent X Y and Z zero is dependent on homing. The machines homes first and activates the proximity switches. There can be a few thousands difference every time you home. Although they are pretty accurate the homing sequence can throw you off a few thousands.

When the machine homes it sets up internal coordinates that the machine/Carbide Motion uses. So when you set a new X Y or Z those measurements are offset from the homing sequence. Those are the user coordinates and the internal coordinates are not used by the user.

So when you home the router comes to the front and prompts for a bit. You insert a bit or leave the old bit in and the router moves over to the BitSetter. It plunges once and activates the red light on the BitSetter then the router raises up and plunges again slowly. When the red light is activated Carbide Motion knows how far that is from the internal coordinates and the Z zero from the previous setting is remembered and set as Z zero. Then if you jog over and use the BitZero or manual method to set the X Y and/or Z then a new offset from the internal coordinates is remembered and then those X Y and Z coordinates are persistent over power cycles.

So the BitSetter is not really measuring the bit in the router but simply seeing the delta from the internal coordinates to where the bit triggers the BitSetter.

Another issue for the BitSetter is to make sure your bits are tight. Because when the router comes down it can force the bit up farther up if the bit is not tight. On the Makita/C3d Routers use the stop button to tighten the collet nut so the bit will not fall out. Then use the two wrenches to fully tighten the collet nut. The bit should be pushed up at least to the top of the collet to get the best grasp on the bit. You can push the bit up higher but never all the way up. The reason is the collet is cut in two directions and works like a spring. The inside of the router shaft is an inclined plane. When you tighten the collet nut you are slightly pushing the bit up the router shaft and the collet is squeezing on the bit tighter and tighter. The reason to never push a bit all the way up is the top of the router shaft may be rough and that can cause the bit to be out of round. Plus it might not be tight enough because the collet nut is trying to push the bit up the shaft and if it is at the top it has no where to go and may be loose.

Measuring your material precisely is very important. If you use painters tape and super glue and measure the material before you apply the tape and glue the top of the material will be higher than expected. So after placing your material on the spoilboard use your digital calipers to measure the material in several places and edit CC for the exact height of your material.

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