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Thread: GME's New 80/20 CNC Build - My Design

  1. #337
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    Default Re: GME's New 80/20 CNC Build - My Design

    Quote Originally Posted by peteeng View Post
    Hi All - If someone here has a spectrum analyser could they analyse Gary's video and tell us what his vibration freq is? Ta Peter


    Spek – Free Acoustic Spectrum Analyzer / Spectrogram Viewer

    Gary you could try this one. Or anyone interested out there.... will be a couple of days before I can...



    here's a great video using sand. But as our vib is back and forth you can't stick sand on a vertical surface!! But by sliding your screwdriver along the gantry you may be able to find the nodes. Then once we know the node spacing we can identify the frequency. Next is to figure some damping strategies.

    Hello, Peter. I agree; the video is great. I had been having difficulty understanding the node thing. The video explained it well (and without any dialog).

    I downloaded the analyzer and ran the audio from the left and right stepper videos through it. I don't know how to interpret the results, but here they are:

    GME's New 80/20 CNC Build - My Design-left-side-motor-mov-jpg

    Left side

    GME's New 80/20 CNC Build - My Design-right-side-motor-mov-jpg

    Right side.

    To my untrained eye, they look remarkably similar. I suspect that is to be expected.

    I will finish installing my spoilboard base layer tomorrow and will rerun at 5 ipm to see what difference, if any, the BB plywood makes to the resonance. I am also picking up nylon washers, and bolts for the Z axis plates, in the morning. I will isolate the motors and pivot shafts with the washers to add a layer of isolation, as you suggested. I'm going to testing incrementally. I will run at 5 ipm with the only new change being the spoilboard base layer. Then, I will add the washer isolation and run again. Then I will add the bolts to the Z axis mount and test again. I still have to cut the aluminum gussets to see if adding additional bracing helps, but that's for later. I need to finish the spoilboard, which will require a good deal of cutting and gluing. It will take at least a few days.

    I have to alternate work on outside projects, like revising parts of my sprinkler system, with working on the CNC. I wish I could just get the CNC done in one shot, but it's not to be. I thought when I retired a few years ago, I'd have more time in the shop. It hasn't worked out that way. Outdoor projects in the summer and indoor in the winter. Snow in the winter is not much of an issue here, but we get a lot of rain coming off the Pacific. Not as much rain as you get, but more than I like.

    Gary


    Attached Thumbnails Attached Thumbnails GME's New 80/20 CNC Build - My Design-left-side-motor-mov-jpg   GME's New 80/20 CNC Build - My Design-right-side-motor-mov-jpg  
    The Old Man and the C -----NC


  2. #338
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    Default Re: GME's New 80/20 CNC Build - My Design

    Hi Gary - I interpret these as we have frequencies everywhere. I was hoping to get a spike at 170htz and 340htz but the image covers nearly everything. I'll read the manual for spek and see if I can interpret. But I think it's moot. We know the source is the motor and everything that can be done to isolate the structure from the motor or damp the structural elements is to be done. Peter



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    Default Re: GME's New 80/20 CNC Build - My Design

    Re: The spectrograph. The RHS is the dB of the noise. The colour defines the dB level. dB is air pressure which correlates to volume. The LHS is frequency from 0 at the bottom to 22kHz at the top. The bottom is time so 0-0.4 maybe 0.4min? So to interpret, you have heaps of very load high freq noise. Not sure where that comes from. There is a 10kHz band at 40-50dB (yellow) but down where we want it we don't have much definition. This could be because the microphone can't register <200htz. Look at your mic spec? is it a phone camera? Look at the SPEK and see if you can filter the bandwidth. You maybe able to tell it to only listen to sub 1Khtz??

    I looked up phone mics and they generally are 20htz to 20khz. But some have 2 or 3 mics and run noise cancelling software which maybe would get rid of loud low noises?? I don't think we have to dig into this much unless your interested. We know the motors fundamental vibration is 170htz....Peter

    5.09*2000/60= 170htz rpm*usteps/min/sec = usteps/sec = htz fundamental which agrees with the first vib mode of the gantry section at its clamped spacing
    1st harmonic 2*170=340htz
    2nd harmonic = 510htz



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    Default Re: GME's New 80/20 CNC Build - My Design

    Quote Originally Posted by peteeng View Post
    We know the source is the motor
    Maybe, we don't know for sure.

    I still think that the source could also be the bushing or the needle bearing of the pinion gear.

    BryggaCNC.com


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    Default Re: GME's New 80/20 CNC Build - My Design

    Quote Originally Posted by peteeng View Post
    Re: The spectrograph. The RHS is the dB of the noise. The colour defines the dB level. dB is air pressure which correlates to volume. The LHS is frequency from 0 at the bottom to 22kHz at the top. The bottom is time so 0-0.4 maybe 0.4min? So to interpret, you have heaps of very load high freq noise. Not sure where that comes from. There is a 10kHz band at 40-50dB (yellow) but down where we want it we don't have much definition. This could be because the microphone can't register <200htz. Look at your mic spec? is it a phone camera? Look at the SPEK and see if you can filter the bandwidth. You maybe able to tell it to only listen to sub 1Khtz??

    I looked up phone mics and they generally are 20htz to 20khz. But some have 2 or 3 mics and run noise cancelling software which maybe would get rid of loud low noises?? I don't think we have to dig into this much unless your interested. We know the motors fundamental vibration is 170htz....Peter

    5.09*2000/60= 170htz rpm*usteps/min/sec = usteps/sec = htz fundamental which agrees with the first vib mode of the gantry section at its clamped spacing
    1st harmonic 2*170=340htz
    2nd harmonic = 510htz

    Peter, I used the mic in my Canon PowerShot SX200 IS snapshop+ camera. I looked at the manual and online. Not much on auto specs, except that it's 16 bit mono with a 44.100 kHz sampling rate. I'm not particularly surprised - it's a camera after all. I have no way of filtering out the bandwidth.

    I'm happy to go with your suggestion that we not continuing into this aspect. Today, I'm working on motor isolation, filling threaded holes and finishing my spoilboard. After performing those tasks, we should have a better idea of where things are.

    I just returned from the place where I buy my fasteners. They have a very broad range of fastener type products, which their business name suggests: Tacoma Screw.

    More to follow.

    Thank you for working the issue with me.

    Gary


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    Default Re: GME's New 80/20 CNC Build - My Design

    Here's a quick update.

    I got the base layer bolted down and ran at 5 ipm. The least about of vibration I've observed. I had all sorts of small parts on the spoilboard, 6mm button head cap screws, a variety of washers, some hex wrenches and the like. Nothing moved. Nevertheless, as expected, there was still some vibration.

    Marcus at Gecko asked me to remove, bench test at 5 ipm and video record so he could see/hear the stepper. An interesting exercise, but no surprises. The stepper vibrated. Standing on end (the shaft vertical) I got one level of noise. Laying on it's side, I got a higher level. Here is a link to the video: https://drive.google.com/open?id=1hA...yeruPUGu4YPBKn

    I ran this latest video through Spek. Here is the result:

    GME's New 80/20 CNC Build - My Design-left-motor-bench-test-5-ipm-mov

    You will note that there are 4 distinct area. The first and third reflect the sound produced while the stepper was on end. The second and fourth are when the stepper was on its side. It looks like the lower end of the frequency range moved up quite a bit. The upper end is the same. The sound produced is probably influenced to some degree by my bench top. It's a 36" x 72" x 3" piece of phenolic. I'm thinking it is probably introducing some damping effect.

    Peter, you asked about the pivot shaft. From the best I can tell without disassembling the drive, there is a generic ball bearing something like this:

    GME's New 80/20 CNC Build - My Design-4668k15p1-d03c-digitall-1-png.

    I also removed the shaft (a shoulder bolt) from the pinion gear. It also has the same sort of ball bearing. The bearing is pressed in.

    Peter, I believe you also mentioned that you doubted the folks at Gecko would be able to help. While I agree, I had already engaged with Gecko and felt I owed it to myself to see what, if anything, they might have to offer. I'm not expecting much, but who knows?

    Next up: using the nylon washers I bought this morning to try to isolate some of the vibration.

    Gary


    Attached Thumbnails Attached Thumbnails GME's New 80/20 CNC Build - My Design-left-motor-bench-test-5-ipm-mov   GME's New 80/20 CNC Build - My Design-4668k15p1-d03c-digitall-1-png  
    The Old Man and the C -----NC


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    Default Re: GME's New 80/20 CNC Build - My Design

    Morning Gary - I read the Spek stuff and it can be filtered so have a look at the controls. You maybe able to filter out above 1000htz say. Thanks for the bearing info. These are deep groove ball bearings. If it only uses one per shaft then the arm can wobble sideways? If it uses 2 per shaft then if fitted correctly the arm should not be able to move transverse to its thickness. I've been thinking about the vibration direction. From your test it seems greater in the radial direction not the shaft direction. Not sure what that means yet. You could also record its sound while holding it say tied with a string. This will remove the influence of its contact with things.

    Davida1234 - Gary has disconnected the pinion and when the motor is stationary it still vibrated, this means the bearing is out of the picture. A cranky bearing would complain over all speeds I think? I'm 99% sure the motor is the driving resonator as its fundamental freq at 5ipm (170htz) agrees with the gantries calculated fundamental freq (170htz) . See prior calcs <#336. Peter



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    Default Re: GME's New 80/20 CNC Build - My Design

    Quote Originally Posted by peteeng View Post
    Morning Gary - I read the Spek stuff and it can be filtered so have a look at the controls. You maybe able to filter out above 1000htz say. Thanks for the bearing info. These are deep groove ball bearings. If it only uses one per shaft then the arm can wobble sideways? If it uses 2 per shaft then if fitted correctly the arm should not be able to move transverse to its thickness. I've been thinking about the vibration direction. From your test it seems greater in the radial direction not the shaft direction. Not sure what that means yet. You could also record its sound while holding it say tied with a string. This will remove the influence of its contact with things.

    Good morning (your time), Peter. I looked at the Spek controls in the manual (such as it is). Not much there. You can change the db range, but the frequency scale on the left remains static. So, as far as I can tell, one cannot filter out frequencies.

    There appear to be two bearings. The second one is an eccentric with a cap/set screw arrangement. It looks something like this:

    GME's New 80/20 CNC Build - My Design-eccentric-bearing-jpg

    When the cap is rotated and tightened, I don't feel any wobble. It's not adjusted in the conventional way. According to the Avid instructions, "While pushing in on the Eccentric Collar Bearing, rotate it in the clockwise direction until it starts rotating inside the R&P Plate." Then, "[t]ighten the set screw on the side of the Eccentric Collar Bearing.
    " In the usual case with eccentrics, one rotates the cap until tight, then insert a punch in the indent, tighten further with a hammer, and then tighten the set screw. Still, I don't get a wobble.

    I still have the other Y stepper to work on. I'll see if I can scare up some string and record it.

    Gary



    Attached Thumbnails Attached Thumbnails GME's New 80/20 CNC Build - My Design-eccentric-bearing-jpg  
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    Default Re: GME's New 80/20 CNC Build - My Design

    Peter, maybe this Spek analysis will tell you something, but I don't get a thing from it. I ran the stepper suspended from a string.

    GME's New 80/20 CNC Build - My Design-mvi_0671-mov-jpg

    It looks like everything is pretty quiet. Starting around the 11 sec. mark, there seems to be an increase. The motor was so quiet, I moved in within a few inches to give the mic a better chance of picking up something. Where it returns to about the pre-11 sec range, I moved back out. I put it on the bench and still got the vibration. In retrospect, I suppose I shouldn't have expected more. We are measuring noise in the audio. Hanging from a string, there was nothing to vibrate against to produce noise.

    Gary



    Attached Thumbnails Attached Thumbnails GME's New 80/20 CNC Build - My Design-mvi_0671-mov-jpg  
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    Default Re: GME's New 80/20 CNC Build - My Design

    Well, it looks like the nylon washers under between the motor & R&P drive, and between the R&P drive an interface plate did the trick. The noise coming from the area of the motors changed substantially, and the frame stopped vibrating. Who would have thought something as simple as adding a few nylon washer would have such a dramatic effect? Silly question. Peter knew it would help, even if he didn't know the full extent of the improvement with absolute certainty.

    My hat's off to you Peter. You're the best! Cheers!

    Now I have to remove the left motor once again to move the motor pulley outward. My belt tracking off. One edge is riding just a little off the gear pulley. Not unexpected, given that nylon washers changed the previously established pulley relationship. I thought I give it a tumble without making the change. I don't much like loosening and tightening small set screw. They cam out too easily. I had a 50/50 shot, which paid off on the right. The tracking is fine.

    Gary



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    Default Re: GME's New 80/20 CNC Build - My Design

    Okay, I got the belt on my left stepper tracking properly again. This problem I believe it was something to do with the belt itself. Interestingly, the belt tracked fine put to the point where I removed it. I have never had a belt tracking issue.

    I removed the pinion pulley again, looking for something that might have caused the pulley and pinion gears to install catawampus. Nope, nothing there Maybe something with the washer that bears on the ball bearing pressed into the pulley? No, it was fine. The shaft wasn't bent, as far as I could tell. I didn't drop the shaft.

    Before I took the stepper drive off this last time, and for no particular reason, it popped into my mind that maybe I didn't put the belt on the same way I took it off. There was a 50/50 chance I hadn't. So when I took it down again, I paid attention how I took it off and ensured it went on the other way. Bingo! Problem solved! Go figure. It shouldn't matter which way it goes on. It didn't when I set the drives up the first time. I'm guessing there has been some odd stretch over time. I could replace the belts, but they show no signs of wear. I'm going to leave well enough alone.

    Now, I can get on with the business of finishing my spoilboard.

    Gary


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    Default Re: GME's New 80/20 CNC Build - My Design

    Well done Gentlemen.
    Seems like a great result.
    It was like reading a exciting novel with those posts....lol



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