bit diving thru material

Discussion specifically about the Shark's bigger brother, the CNC Shark Pro

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milo30
Posts: 553
Joined: Mon Mar 12, 2012 9:21 pm

bit diving thru material

Post by milo30 »

Anyone have this problem or know what causes it? The cnc cuts properly and then occasionally for unknown reasons, the bit dives deep, getting hung up and flexing the machine until I can hit e stop or the bit breaks the collet and comes out. I have gone through 5 collets and a few bits because of it. I have ran the speeds as low as 50 ipm and making shallow cuts. Happens on mdf, oak and poplar.

Had the board replaced recently for another issue. Happens on different files, same gcode may cut perfect 10 times until it decides to do it. I can't find any logical reason why it does it but is becoming costly and tired of hours cutting to then have it happen and ruin the project
Anyone had the same issue and found the cause?

Eagle55
Posts: 788
Joined: Sun Nov 20, 2011 8:44 pm

Re: bit diving thru material

Post by Eagle55 »

I would run, not walk, to NWA for help on this one. I haven't experience this but it almost sounds like it could be an issue with the SD Card seating properly or something else within the Control box. I don't think it is consistent with something that you have overlooked in the design or the implementation of it. Are you running a large dust collection system that may have grounding problems?

Roger
CNC Shark HD ~ Control Panel 2.0 ~ Windows 7 & XP
Located in West Tennessee near the Tennessee River
http://www.eaglecarver4.com

milo30
Posts: 553
Joined: Mon Mar 12, 2012 9:21 pm

Re: bit diving thru material

Post by milo30 »

No, not running any dust collector at the moment. It's not in the gcode either because it can run the code just fine most of the time, just every once in awhile it will decided to take a plunge. Change the bit and collet, restart the gcode and it will not duplicate it.

milo30
Posts: 553
Joined: Mon Mar 12, 2012 9:21 pm

Re: bit diving thru material

Post by milo30 »

Eagle55 wrote:I would run, not walk, to NWA for help on this one. I haven't experience this but it almost sounds like it could be an issue with the SD Card seating properly or something else within the Control box. I don't think it is consistent with something that you have overlooked in the design or the implementation of it. Are you running a large dust collection system that may have grounding problems?

Roger
You are right, I believe I am still under warranty so I sent an email to NWA. I had the control box replaced not long ago when it stopped working. I hope that I don't have to ship it off again. I haven't even used it since the last occurrence because I am tired of wasting money on the wood,collets and bits not to mention all the hours spent cutting to ruin it at the end. I have projects starting to stack up now but have lost alot of confidence in using the machine. I even started shopping for another machine to just replace this one.

jeb2cav
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Re: bit diving thru material

Post by jeb2cav »

I did experience this twice when I first started out over the course of a few months. After eliminating lubrication, mechanical, SD card seating, etc - and given that many jobs ran 'just fine', it dawned on me that I had power conditioners in front of my home computers and flat screen in the house because the power is sometimes pretty poor where I live. Not unusual to see a +/- 5-10v fluctuation, and momentary on/off conditions.

I have not experienced this since I put the control box, the computer and the router behind a power conditioner/battery backup box (spent !$140 at the time).

While I also replaced the USB cable, the CNC machine's instructions are stored on the SD card in the control box. Once you start the job, the control box is 'in charge'. The only thing the computer can do is pause/continue and e-stop the job. The computer would have no role in driving the gantry off course.

At that point, the only role of the usb cable is to convey where in the job the gantry is.

So you're down to intermittent behavior, and in your case, you've stated that the same job has run successfully more than once before, and every now and then it does this dive thing. So, it seems like there are no issues with the job (for example, an aggressive feed rate results in dragging and tool really not where it thinks it is, and then the next move results in what appears to be a dive, but the tool is not where it is 'supposed to be').

So, SD card could be loose or out of place - resulting in intermittent behavior. SD card may be failing or need reformatted to clear a spot up.

Electrical interference of some kind resulting in the dives/off path moves.

Control box failing.

Depending on shop conditions and how often you use the shark, I've also seen humidity, poor air circulation around control box, and other environmental factors contribute to poor outcome.

All that being said - you could still have a loose coupler in there - that is 'new'.

I of course don't know that a power conditioner will cure this - but this sounds like what I was experiencing at one point, and haven't seen it since.

pjmayer
Posts: 11
Joined: Mon Aug 23, 2010 11:09 am

Re: bit diving thru material

Post by pjmayer »

My Shark Pro has done this, but it hasn't happened in a long time. It happended a few times randomly, but then it happened consistently after I moved the Shark Pro to a different work bench.

To fix it, I had to work on the connector in the wire harness that goes to the z-axis motor. It turned out that pushing the connector halves together wasn't good enough because the pins inside the connector were loose and being pushed back. They were touching but not fully stuck together. Most of the time it worked, but once in a while it would miss steps or "forget" which direction it was supposed to go.

Next Wave told me that one of the wires controls the motor direction. It turns out that if this wire is not connected, the motor gets every move command, but thinks they are all moves down. This could be what is causing the z-axis to drive you bit into the table.

You can poke at the connector with a small screwdriver after it's connected. Use the point of the screwdriver to push on the back of all the metal pins to try and force them together better. It may not be the solution you need, but it's an easy thing to try.

milo30
Posts: 553
Joined: Mon Mar 12, 2012 9:21 pm

Re: bit diving thru material

Post by milo30 »

I will check them. I updated and have been using it a lot the last few days with no problems

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