Z axis zero changes in middle of job

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Re: Z axis zero changes in middle of job

Postby Kayvon » Sun Feb 12, 2017 12:37 pm

Kayvon wrote:It's also possible for the Z alignment to mismatch as a result of bottoming out against the table/workpiece or topping out against the max height of the gantry.
I found another way for this to occur.

Yesterday, I repeatedly encountered the exact problem you're describing. After some troubleshooting (and mangled spoilboard), I determined the problem was the Do separate last pass option that I was trying out for the first time. (Yes, this probably should have occurred to me right away.)

I had the separate last pass set to 0.001", which was a small enough amount that I didn't think it would cause any problem. Because I was using an upcut bit, the movement of the bit pulls the material towards the router, upwards. Because the material is secured to the spoilboard, this has the effect of pulling the bit/router downwards. Even though the bit was tightly secured in its collet, the half-inch thick material provided enough pull to steadily pull out the bit, even only cutting 0.001".

If anyone else has experience with the Do separate last pass option, I'd love to hear about it. Until then, I'll stay away from using it.
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Re: Z axis zero changes in middle of job

Postby Rando » Sun Feb 12, 2017 5:33 pm

Wow, that is a new one on me. Thanks for identifying it and describing it in detail, Kayvon.

Sounds like maybe it's time to take apart the collet/chuck and clean it out well; might have some wood resins that are not allowing a tight fit? or a slip?

One thing to note is that if the cutting is taking 0.001" horizontally off the sides of vertical walls, if those walls are tall and a lot of the flute length is engaged, that will definitely create a lot of downward force (with your upcut bit) on the spindle/bit, when you contrast that to taking 0.001" off a wall that's also only 0.001" tall.

Hope you resolve it!

Regards,

Thom
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Re: Z axis zero changes in middle of job

Postby Kayvon » Mon Feb 13, 2017 2:34 pm

The collet is fairly new. It's made by Elaire Corporation and they do good collets. The problem is more likely to be in the bit, which was a cheap HSS bit from China. I favor them in several projects because they cost less than a buck each, so I don't feel bad tossing them.

In my tests, I went through a couple different bits with the same result. I suppose I could try a nice whiteside bit with the stock collet, but at this point I think I'll just avoid the feature for now.
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Re: Z axis zero changes in middle of job

Postby Rando » Mon Feb 13, 2017 6:15 pm

Kayvon wrote:The collet is fairly new. It's made by Elaire Corporation and they do good collets. The problem is more likely to be in the bit, which was a cheap HSS bit from China. I favor them in several projects because they cost less than a buck each, so I don't feel bad tossing them.

In my tests, I went through a couple different bits with the same result. I suppose I could try a nice whiteside bit with the stock collet, but at this point I think I'll just avoid the feature for now.


Sounds like it! I'm a strong believer that often the best way to avoid a problem it to just avoid the problem. I also use HSS too, but probably for a different reason: it expects much lower spindle RPMs in aluminum than does carbide. Well, technically surface feet per minute, but same-same :D.

Man...under a buck each. I sure wish that was true for the 3/16" 2.25" extended-reach end mills (3.5" overall, with just 0.312 length of flutes) that I have custom-radiused to 0.020" tip relief...cost me $58 in onesies, and $49 if I have them make 5. OTOH, if you have to cut a 12mm bore perfectly concentric with a 9mm bore that together go all the way through a 2" block of solid aluminum, well those take different tools :D. I get them from SwiftCarb, in Kent, WA. They actually make their own endmills out of carbide, right there on site. Awesome group, they were a big help to me getting started. So nice to have a retail store where I can go look at calipers, or some odd endmill, or get a replacement chip-blower nozzle quick, that kind of thing. They service Boeing and a lot of their suppliers around here in the Seattle area, so quite top-notch stuff. Though, I'll grant you sometimes a job is just fine with a $1 bit, as I do with the 0.004" 30-degree v-style engraving bits.

Cheers!

Thom
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Re: Z axis zero changes in middle of job

Postby Joseph Poirier » Thu Apr 06, 2017 4:16 pm

A high precision collet will make a world of difference when using those bits. They are the only types of collets we use in house to build parts for the CNCs.

The standard collets usually only have 3 or 4 collective points meeting the bits. While the high precision collets will have a minimum of 6 triangles making up the circle around the bit.

The high precision collet can be torqued much tighter to the bit because the extra connecting points leaves less of an air gap around the bit as it tightens, and at the same time provides more points to close in around the bit.

Standard collets are ok for oversized bits, but horrible for any smaller bits or finer work because tightening the collet typically causes the collet sides to meet each other about the same time or before the collet starts to grip the actual bit, making it impossible to get the grip right.

Best Regards, Joseph Poirier Sr. Software Engineer, Next Wave Automation
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Re: Z axis zero changes in middle of job

Postby Rando » Thu Apr 06, 2017 6:15 pm

Joseph:

thoughts on the musclechuck? That's what I've been using to great success. Fewer shank-size options, so drills have 1/8" shanks, that kind of thing. But, one handed, 4mm - wrench tightening and loosening. My tool changer (me) gets a lot of work, and not having to do the two-wrench jig (I have the spindle, not a router with the button) saves a LOT of time.

And, welcome! Haven't see you around the parts so much lately; it's good to hear from you again.

Regards,

Thom
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Re: Z axis zero changes in middle of job

Postby Kayvon » Fri Apr 07, 2017 10:05 am

Thanks, Joseph. If/when I ever upgrade my Bosch Colt router, I'll try a higher-end collet and see how well the feature works for me at that point. The software feature was heavily anticipated by some users and I'm sure it's been great for them, just not for my current setup.
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Re: Z axis zero changes in middle of job

Postby ChubbyRooster » Mon Jun 19, 2017 5:31 pm

Good afternoon Thom, guess who? Ok, new problem similar to the one listed here. Today we were running a tool path (previously run) and something happened where the z-axis plunged as deep as it physically could into the material. Just prior to starting this toolpath, my son was zeroing the location and pressed down and the gantry went down as far as it could. It has done that twice with two different tool paths (although both were cutting a circular piece of material out. The first time it happened the collet stopped it from going deeper. This was on the first of four cutouts, the second time it made it to the four one, but had been gradually cutting deeper across all four. We were watching and stopped the machine.
It seems (at least in the last case) it is going deeper as it moves from left to right on the z-axis. Not sure what the first case was different.
We have a spoil board, with a secondary "cutting spoiler board" on top. Material is 0.5" thick, 5.5" tall by 19" wide. Using a .25 up spiral end mill.
We had been running all day, running about 7 projects (same in nature) over about 5-6 hours.
I have also noticed that as the gantry moves (left to right) across the x-axis I see the y-axis moving "away" (about .25" over 24"), so think it is moving at an angle. Not sure if the two are related.
Any help is appreciated.
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