Hello Guest it is March 02, 2021, 07:10:00 PM

Author Topic: Mill going off centre  (Read 3607 times)

0 Members and 1 Guest are viewing this topic.

Mill going off centre
« on: February 11, 2013, 12:17:48 AM »
Hi there.

I'm relatively new to all this cnc and milling stuff but after a lot of research and tips from people here I got things up and running.I'm currently using a desktop milling machine to cut pistol grips.I can cut 1 set out of a single piece of wood,first doing the top side,flipping it over and cutting out the underside and here begins my problem.

Instead of constantly changing drill heads, I cut out about 10 sets for the topside,change the drill and cut out the underside,but somewhere along the line the machine seems to go off by a few mms.I go to home before I start every piece.It's only when I cut out the underside that I see the holes not lining up.Is it possible that home is changing by itself ?.I've tried doing topside and straight away flipping over to do the underside and it turns out perfectly which means the code is good.It just seems that if I do a bit of repetitive work that it goes off.I noticed yesterday that from the 10 sets I made,the first 5 or so were perfect,after that it seemed to be going off a little bit more with each new set.Anybody any idea why this is happening ?

Thanks

Vinny

Offline Hood

*
  •  25,838 25,838
  • Carnoustie, Scotland
    • View Profile
Re: Mill going off centre
« Reply #1 on: February 11, 2013, 03:02:21 AM »
You say you "go to home" by this do you mean you command a move to home position or do you mean you actually home to switches? If the latter are your switches accurate? If the former you could well be losing steps and not noticing.
Hood
Re: Mill going off centre
« Reply #2 on: February 11, 2013, 03:20:46 AM »
Thanks for the reply.Sorry I should of said zero instead of home.Me bad  ;)

Offline Hood

*
  •  25,838 25,838
  • Carnoustie, Scotland
    • View Profile
Re: Mill going off centre
« Reply #3 on: February 11, 2013, 05:06:46 AM »
How do you zero? Are you touching off some point to set it or merely just moving to a spot you think should be zero and seroing the DROs?
Hood
Re: Mill going off centre
« Reply #4 on: February 11, 2013, 05:08:39 AM »
I have a seperate code for zero.I just load that,run it and it sets itself in the middle of the table at zero.

Offline Hood

*
  •  25,838 25,838
  • Carnoustie, Scotland
    • View Profile
Re: Mill going off centre
« Reply #5 on: February 11, 2013, 05:14:21 AM »
So how does that code work? Only way I can see that it could be accurate is if it includes a referencing sequence to accurate home switches or if it uses a probe to accurately reference itself.
If it is simply moving to the middle an setting itself zero then any lost steps in a previous move would be still effective.
Hood
Re: Mill going off centre
« Reply #6 on: February 11, 2013, 05:42:19 AM »
It's the way the guy who made it for me set it up.I manually set my x,y and z.X all the way to the left.Y all the way forward and Z as high as it can go.Then turn on the spindle so it's locked in position.Using mach 3 I load the " home code" .Zero everything.Run the cycle.The drill head then moves to the centre where I again zero x and y.That's how I get my zero.I know it's a bit tedious.Wish there was a simpler way.

Offline Hood

*
  •  25,838 25,838
  • Carnoustie, Scotland
    • View Profile
Re: Mill going off centre
« Reply #7 on: February 11, 2013, 06:04:16 AM »
Ok so that is relying on you starting things at exactly the same position each time and unless you have a means to do that then it could be off if you lose position. Thats what it sounds like, machines that are tuned too close to the edge can often loose position, especially on 3D work as that often includes high accelerations.
You could try reducing the accel for your axes and see if that helps.
The best way to do things is have accurate home switches then Mach will know where it is in relation to them, assuming of course you do not lose position. If you homed to these switches after each part then you could be sure any lost steps during the previous run would not matter on the next.
Obviously you are not wanting to lose steps at all so maybe the acceleration reduction is the best thing to try first.
Hood
Re: Mill going off centre
« Reply #8 on: February 23, 2013, 06:07:40 AM »
Sorry been away for a while.Got going again yesterday.I took your advice and reduced feed speed,spindle speed etc and was able to go the whole day without losing position once.I have to admit I was going hell bent for leather with the machine.The faster the better.Gotta learn to have patience ;)
Re: Mill going off centre
« Reply #9 on: March 08, 2013, 09:15:39 AM »
Is this the kind of situation where having servos instead of steppers is beneficial?