Machsupport Forum
General CNC Chat => Show"N"Tell ( Your Machines) => Topic started by: piv on September 13, 2011, 10:10:35 AM
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Here is a machine I built for pattern making. It is controlled by Mach 3 and DSPMC. It has AC servo motors, a water cooled spindle and 8 place auto tool changer.
It is used industrially. It is quite fast, 48m/min rapid feed rate. Typical 3D contouring feedrate in wood is about 10m/min with long tools. Generally the tool length is the limiting factor. It uses a lot of long tools to get deep down the sides of patterns. Many of the patterns are built up in layers, some up to 500mm high.
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Here is a link to a couple of YouTube videos showing it in action.
http://www.youtube.com/watch?v=ZJzpPVXfoUg (http://www.youtube.com/watch?v=ZJzpPVXfoUg)
http://www.youtube.com/watch?v=d8wf1fvHtxE&NR=1 (http://www.youtube.com/watch?v=d8wf1fvHtxE&NR=1)
And some shameless self promotion at my website
http://bdgengineering.weebly.com/3-axis-router-0672.html (http://bdgengineering.weebly.com/3-axis-router-0672.html)
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Excellent machine build - more pictures please.
Tweakie.
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Hello piv,
very nice machine. I have just one question. What is causing that sizzling noise from the servos? You can hear it in the first video. I'm asking because that noise is also coming out of my servos and I'm also using dspmc. Is that normal?
Peter
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I like it! :)
Brett
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The servo noise is pretty common on a lot of servo systems. It depends how "hard" they are tuned. If you go for a soft tune, ie lower gains, lots less D, then the noise goes away but the response is nowhere near as good. Its all a compromise. If you can use encoders with more counts per rev, then its less of a problem. These ones are 12 000 counts per rev (3000 lines) or about 1 micron resolution. The new Fanuc machines and some other systems Ive used use million count encoders or sine/cos systems like Hyperface or endat or BISS and they are a fair bit quieter and more responsive. But 10 times the price. Really they should be quiet but its hard to achieve in all cases. I did have an even "harder" tune but it was tripping the drives sometimes, so I pulled it back a bit and its ok now, but like you say a bit noisy. I will look into it a bit more. Ive done lots of tuning with the DSPMC and havent seen much if any effect from the feed forward terms. Ive used feed forward (position control lagless they call it) on a big system with Beckhoff Twincat and its awesome. Hopefully Rufi can help us with the feed forward stuff.
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Hi,
There is a new feature called "low pass filter" on the latest plugin. I have found it to be very helpful in getting rid all the noise from the servo motors. It will still leave you with a very "hard" tune. Please let me know if you have already tried this, for larger motors we we set it to 10-15 and for medium motors set it to 5-10.
Andrew
MachMotion
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No I haven't tried the low pass filter, but I did see it. I will try it to see how it works. Thanks.
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Here are some more pictures
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Rufi says that feed forward works but it might need a really big number to have an effect. I will give that a try except that the machine is at the customers and I wont go there for a while yet.
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Awesome machine! I'll be working on one about the same size starting late this year, but obviously different in design. I do really like how you built the gantry, seems very efficient.
I'm wondering about how you fabricated the dimensionally critical portions, where rails mount, etc. Did you have the steel stress relieved and then machined? I've been thinking of using 3/16" tubing and welding solid 1/2 inch bar stock to them to be machined for the rails and wonder if they will need stress relieving due to the unbalanced heat that will generate. Would it be better to use 1/4" tubing and have it machined directly instead?
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There are a few ways to do it, I have used most. Yes welding on steel bar works but needs stress relieving. Yes direct machining on thicker plate or tube works but can get heavy. I have also done machines where I have bonded on aluminium or steel bar with epoxy and then machined the strip, I made the tapped holes go through both pieces to make sure there is no chance of a debond. I have also done it by casting a bed of epoxy (filled with aluminium powder) and then machining that. That particular machine was done by making a dam on the edges of the tube and then pouring a self leveling epoxy to make a flat surface that we then just drilled and tapped holes in as a large mill wasnt available (well not a realistic price anyway) for when I wanted to do the job. If you can get it machined its easier. A precision machine frame level and square comes in handy too.
I can sell you a full set of drawings and components at a reasonable price (or a complete machine), if you are interested pm me.
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I appreciate your comments and help, it sounds like we are of like minds! I'd also considered using epoxy as a filler in a couple scenarios, but since there is a great deal of aerospace here in Seattle, there is also a great deal of very large machinery at various job shops. It may cost a bit more, but I had narrowed it down to either welding a rail platform or having the tubing machined directly with a large metal planer (has about a 16 foot stroke). I have designed a stationary gantry style machine and should be able to fit the entire frame on the planer to machine both the rails and the flanges for mounting the gantry. I'm still looking for a shop that can stress relieve it in one piece though.
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If you have access to the machines then definitely machine it in one piece or as few as possible. For stress relief try vibratory stress relief like Metalax.
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For stress relief try vibratory stress relief like Metalax.
I love this place! I learn something new every day.:D