Problem with work zero

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Clockman
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Problem with work zero

Post by Clockman »

I had a mishap the other day when the cutter plunged down to the bottom of the 18mm MDF I was cutting and ran for a while before I could stop it, it would not cut true circles after that, so after calibrating and tightening the set screws, it cuts the circle perfect and the size is spot on, but it jumps to the left when going down to do the cut and after the cut it does not return to work zero, it is slightly off, and goes down deeper, I have added some photos so you can see before and after, in the photos I have dropped the Z down 1 inch from where I have the work zero set at so you can see it clearly, and when I home the machine again and press G28 it goes back to work zero perfectly, what is causing it to jump to the left
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SAM_1216.JPG

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Adrian
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Re: Problem with work zero

Post by Adrian »

Has to be something mechanical on the Z axis. Is it jumping at the same spot in the travel?

Clockman
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Re: Problem with work zero

Post by Clockman »

Thank's Adrian, yes it seems to be the same spot in the travel all the time , I can't seem to see what is causing it, when I had the mishap it must have been under a lot of stress before I stopped it

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Adrian
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Re: Problem with work zero

Post by Adrian »

How is the Z driven? Could be a damaged tooth if it's a pinion or toothed belt.

potzmannwoodshop
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Re: Problem with work zero

Post by potzmannwoodshop »

Adrian wrote:How is the Z driven? Could be a damaged tooth if it's a pinion or toothed belt.
if this is the case you can just re position the belt.

Clockman
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Re: Problem with work zero

Post by Clockman »

Thank you both for your help, I am not at the workshop now but the Z drive is linear similar to this one https://www.ebay.com/itm/Z-axis-X-CARVE ... 2712810756

garylmast
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Re: Problem with work zero

Post by garylmast »

This happens every once in a while with me. The problem is the mill will bind for whatever reason and throw the G-Code out of sequence vs. the correct position of zero. The last time this happened was quite a disaster.
http://forum.vectric.com/viewtopic.php? ... went+wrong

Gary

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martin54
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Re: Problem with work zero

Post by martin54 »

What sort of motor have you fitted to it? if the motor shaft sticks out the top of the motor casing then it is easy enough to wind the axis up & down with no power on the machine. your z axis should move up & down with ease if the shaft is turned so finding any spots that are causing any kind of binding or any damage to the thread can easily be found.

If the end of the motor is closed then you would probably need to remove the motor to turn by hand as it is unlikely you will have sufficient access to turn the lead screw by hand.

garylmast
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Re: Problem with work zero

Post by garylmast »

I think the problem I have with the mill binding is I probably got too big of mill and/or traveling to fast. Whenever this has happens, I will trade off for a smaller mill which stops the problem.

Gary

Clockman
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Re: Problem with work zero

Post by Clockman »

martin54 wrote:What sort of motor have you fitted to it? if the motor shaft sticks out the top of the motor casing then it is easy enough to wind the axis up & down with no power on the machine. your z axis should move up & down with ease if the shaft is turned so finding any spots that are causing any kind of binding or any damage to the thread can easily be found.

If the end of the motor is closed then you would probably need to remove the motor to turn by hand as it is unlikely you will have sufficient access to turn the lead screw by hand.
Martin, I have access to the motor shaft and I have tried turning the axis up and down with the power off and I can't find any binding, everything moves very smoothly, I can't find anything mechanical wrong, when it returns to work zero it is bout 0.2 inch too low and about the same sideways, if I run it again from that position it does not jerk on the way down to do the cut and goes back in the same circle that I cut before perfectly, I have tried Picsender and UGCS to send the G- code,

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martin54
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Re: Problem with work zero

Post by martin54 »

I would still think this is a mechanical problem, have you checked for backlash & that the shaft coupling is tight, anti backlash nuts on these linear slides are often delrin so you will get wear over time & a shock like your machine had could easily have knocked it out a bit :lol: Same goes for the couplings if they were put under a lot of force.
Is the lateral movement always in the same direction ?

Clockman
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Re: Problem with work zero

Post by Clockman »

Thank's Martin, yes I agree it must be a mechanical problem, I have double checked all connections and the coupling and all are tight, I would have to take it all apart to replace the anti backlash nut if I can get one, and the acme threaded rod, but I can't see any damage to the rod, yes it is delrin, and the lateral movement is always the same, I will have to live with it for the moment as it it is working okay, the cutter goes back into the circle that I cut from the work zero position even when its 0.2 inch off, Thank's for your help

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martin54
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Re: Problem with work zero

Post by martin54 »

Wasn't meaning you replaced the nut just that it may need a bit of adjustment, have you checked for backlash ? Don't forget you are only looking for a very small amount of movement :lol: :lol:

Not that I think you need one but a new anti backlash nut shouldn't be to hard to find, guessing it's a standard size lead screw so should be an off the shelf item but that would be easy enough to check anyway :lol: :lol:

Clockman
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Re: Problem with work zero

Post by Clockman »

I am not sure how to check for backlash, I will read up on it and then check to see if that could be the problem

garylmast
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Re: Problem with work zero

Post by garylmast »

This happens every once in a while with me. The problem is the mill will bind for whatever reason and throw the G-Code out of sequence vs. the correct position of zero.


My recent double sided project, the material was 3-5/8" thick. On the rough cut I used 1/2" mill going a total depth of 60 mm. I forgot to edit the tool information because I was going so deep with the material I was using, which turned out to be too fast. Half way through the cutting sequence, I stopped and checked the Z-height. Turned out it dropped 14 mm. On the backside, at a slower speed, I did not have any problems.

However, on the finish past, things didn't look right, so I stopped it again and check the Z-height. Again the mill dropped about 5 mm. It turned out it slipped in the collet. That collet now is on the way to the city dump.

Two more ideas to check of you're having Z-height problems.

Gary
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