Re: [CAD_CAM_EDM_DRO] Dial indicator say machine is accurate in MDI screen. But out when

Peter,

Routers usually are built with universal motors, which have
brushes. Noise from the brushes is an incredibly effective source of
electrical interference.

For a machine I built with a router, I opted to suppress the noise at
the router. To do so, I placed a small capacitor (about 0.003 uf,
600v) across the brushes. The value isn't particularly
critical. This was for a 1/2 hp laminate trimmer. The value might
want to be larger for a higher HP router. I had to open up the
router to get the cap right between the brushes.

I tried a filter at the plug, but it had nearly no effect at all. So
much interference is radiated by the power cord that filtering at the
plug does just about nothing.

It is possible that the capacitor may slightly increase the brush
wear, but I haven't seen any problems yet.

There may be better ways to suppress brush noise, but this was the
easiest and most effective.

-- Carl, KB1NXK



At 07:53 AM 9/11/2006, you wrote:

>Dial indicator say machine is accurate in MDI screen. But out when
>cutting.
>
>Okay. So I have been mucking around with my plasma/router machine. I
>am trying to get some positional accuracy out of it. It is maily just
>a CNC plasma table. I put a router in it so that I could take more
>accurate measurements, as measuring a plasma cut part has other
>factors to deal with.
>
>So I have been cutting MDF. I tell the machine to move 100mm but it
>will be out. I clamped my dial indicatior to the frame set it all up
>at 0 etc. Went into the "Set axis steps", the automatic thing. I
>tell the machine to move 5mm. After a few goes I get it spot on!
>
>I can then go into the MDI screen and tell it to move 5.00mm and it
>will move the 5.00mm. Then I can go forward another 3.54mm and it
>will do that fine. Then tell it to go back to 0, and the dial
>indicator will be spot on the 0 mark.
>
>But. I go to cut a bit of MDF with the router 100mm long and it will
>be the incorrect length.
>
>What bugs me is that it is working in the MDI screen, ie move 10mm it
>will. Even move 300mm and then back to the 0 the dial indicator will
>be on 0. I was impressed with this.
>
>So, after a bit of reading here ther and everywhere, I decide that it
>could possibly loosing steps when the router is cutting. So I slow
>the acceleration down. This has no effect. I'm using two 1200oz/in
>steppers slaved one either side, then they are belted down. I am only
>cutting at about 500mm/min at a depth of 5mm. So there is plently of
>torque from the stepper motors etc etc. So I think that I can rule
>out the missing stepps theory.
>
>But could it possibly be electrical interference causing my troubles?
>
>Have a look at this picture, this is my power supplie, breakout board,
>stepper drivers etc. It is very messy... etc etc.
>
><http://i90.photobucket.com/albums/k259/peterapalais/electronics1.jpg>http://i90.photobucket.com/albums/k259/peterapalais/electronics1.jpg
>
>http://i90.photobucket.com/albums/k259/peterapalais/electronics2.jpg
>
>What are the chances that this birds nest is causing me trouble? ie
>20% 40% 60% chance of electrical noise etc.
>
>If so, what is the solution. Make up a new board and space everything
>right out so that things are further apart? Should I use sheilded
>wire etc? If so for what connections.
>
>Cheers
>Peter
>Australia
>
>

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