Spartan Router - Head drop issue

[Abstract]

Hello everyone,

New member here with an issue concerning my Spartan PJCM 1325-3. Basically, my boss brought this router about 3-4 months ago to help with our sign production. With one day training, we were able to work the router with no issue.
Unfortunately, a week down the line we started getting a problem where the Z axis would just drop, ploughing through the sacrificial board and sometimes in to the polymer base! The odd thing is that it will go from cutting 0.3mm at the start of the vector to cutting down to 15mm.
http://www.mycncuk.com/attachment.php?attachmentid=13459&stc=1 An example of the Z axis head drop. I was cutting an Acrylic letter B out.

Once this happened we phoned up Radecal Machines, whom we brought it off, and told us to reload the parameters. Once I had done that, I set a test run to cut out a Dibond star - this resulted in the head dropping again and snapping the tool. So I re-installed the parameters a second time and it seemed to work fine.

This started to become a trend where every couple of weeks it would randomly drop the Z axis. After about the 5th time, Radecal sent over a new hand controller, new 6mm collet and locking nut. Once these were installed the machine started working perfectly with no errors.. until today..

After cutting around 90% of a net tray sign, made of 3mm Dibond, the head decided to drop on the final vector whist still displaying '3.3mm' on work piece coordinates . Once I got the machine to return back to it origin and switched it off, I noticed the drill piece had dropped - 10.95mm to be exact!
Now, what I do not understand is how; firstly it got rough 90% of the way through without dropping and secondly I had tightened it up to how I always do.
I have had little experience with CNC machines, but am a quick learner. So, my major question is what is causing this random Z axis drop! Hopefully the pictures should possibly give you an idea on what I'm talking about.

Thanks in advance,
Adam

http://www.mycncuk.com/attachment.php?attachmentid=13460&stc=1http://www.mycncuk.com/attachment.php?attachmentid=13461&stc=1http://www.mycncuk.com/attachment.php?attachmentid=13462&stc=1http://www.mycncuk.com/attachment.php?attachmentid=13463&stc=1http://www.mycncuk.com/attachment.php?attachmentid=13464&stc=1

[EddyCurrent]

So it's the cutter that dropping out of the collet , not the whole spindle or Z axis that is dropping ? also you used the word "drill" so my question is, what type of cutter are you using ?
Also what are your feed rates, depth of cut, spindle speed when cutting, is the spindle one direction only or does it have reverse ?

[phill05]

Are you using imperial size cutters smaller than a metric collet and hoping they close enough to hold? they will for a while but will soon let go.

[JAZZCNC]

You need to do a few test runs cutting air and check if the head is dropping. Do this by setting to a accurate height gauge of some kind that you can move while cutting air. This will eliminnate the tool being pulled from the collet.
Don't home the machine after the test but send it back to Zero work coordinate and check it goes exactly back to same height it started.

Do this several times to be sure if it's dropping or not.!

If it does drop then I suggest you contact the supplier as there are many things that can cause this to happen. Electrical noise on the signal lines could be one cause.? Esp if it's a random happening.!! . . . . Does it happen when something around the machine is turned on IE: compressor etc.?

[Abstract]

Sorry for not describing it clear enough!
@EddyCurrent Basically with the last problem, when I returned the router to the work-piece coordinate (after hearing the horrible noise of the head dropping in to the board) I retested the Z height and it had dropped 10.95mm. I was using a V-groove with a 12mm head and 6mm shank at 3200 mm/min at 24000 rpm. I am cutting 2.6mm in to a 3mm thick material. To my knowledge, the spindle cut only in one direction.
Thanks for the reply

@phill05 I am sure that all components are metric, but thanks for the suggestion!

@JAZZCNC Sounds like a good test, so I'll do that now and reply with the results :D Cheers

[Abstract]

I ran the air cutting test a couple of times to see what was happening. The cutter did not seem to drop depth from the collet.
Once that was done, I thought about having a look to see if the material was ,in a way, pulling the cutter from the collet. So I cut 3 lines in some 19mm foamex with the V-groove tool used on friday. I started at cutting depth; 1.5mm, 2.5mm and finally 3.5mm. The head did not drop after all grooves were done.
With a bit more confidence, I risked putting some work through. I started with the basic route lines (which is where it messed up friday) and it seemed to complete it without a problem. The only thing I noticed was that the corner nearest the mechanical origin seems to cut lower than anywhere else on the board; why could this be?
Also, another question - how often should I clean out the collet and locking nut?

http://www.mycncuk.com/attachment.php?attachmentid=13487&stc=1

[EddyCurrent]

Sorry for not describing it clear enough!
@EddyCurrent Basically with the last problem, when I returned the router to the work-piece coordinate (after hearing the horrible noise of the head dropping in to the board) I retested the Z height and it had dropped 10.95mm. I was using a V-groove with a 12mm head and 6mm shank at 3200 mm/min at 24000 rpm. I am cutting 2.6mm in to a 3mm thick material. To my knowledge, the spindle cut only in one direction.
Thanks for the reply

Still not clear but you seem to be saying later on that it was the cutter dropping out of the collet.


The only thing I noticed was that the corner nearest the mechanical origin seems to cut lower than anywhere else on the board; why could this be?
Maybe the bed is not flat, it's usual to skim the bed using a fly cutter or large end mill to ensure it's flat. Make sure your 'sacrificial' piece of MDF or whatever is securely fastened down to the bed in enough locations that it remains in 100% area contact with the bed, give it a skim.


Also, another question - how often should I clean out the collet and locking nut?
I don't think this is something to worry about as it gets cleaned out each time you change a tool. The collet, collet holder, and collet nut need to be spotlessly clean in order to function correctly, any dirt could let the collet slip and may be where your problem lies.