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Thread: DIY CNC machine on the cheap!

  1. #49
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    Default Re: DIY CNC machine on the cheap!

    Thanks David for the quick response!

    Quote Originally Posted by davida1234 View Post
    Imbaine, great respect for doing so much with so little!
    Thanks again. I thought I'd cheap out on this one and see how good a machine I can build without sacrificing too much accuracy. Besides this set back, everything else seem to be headed in the right direction.

    Quote Originally Posted by davida1234 View Post
    The occasional binding you see when you tighten the bearings a bit might go away (hopefully) with breaking in. Push and pull the carriages a hundred (! ) times while tightening them down a tiny bit continuously will smoothen out the steel. Just make sure that the bearings are 100% aligned to each other and the raceways. Otherwise you have toe-in/toe-out.
    This is a bit of a relief! Thought I wasn't getting good straight steel! Honestly, when I'm buying it, It seems perfect at the hardware store, only after trying it out do I see slight imperfections and wonder whether my brain was out on vacation when I was at the store! Great Idea, I'll do just that, and if 100 times is what it takes to break it in, then so be it! I tried to align the bearings as best I could, but I'll double check. It's possible that slight misalignments might be the source of the noise anyway.

    Quote Originally Posted by davida1234 View Post
    The noise in the bearings could be either irregularities on the raceways or particles in the bearing or a bad raceway. $3 for 10 bearings, right? Maybe go over the raceways lightly with some fine sand paper and see if there are any dips/high points?
    Yeap! $3! I wasn't expect much but I just hoped they'd get the job done. Had a look at the race ways yesterday but everything seemed okay. Poorly finished and not polished but no irregularities. I also tired running a few bearing individually on a flat steel plate with a significant weight, but they didn't produce the noise. Not really surprised at their poor quality, but isn't it the stuff most DIY'ers use for their machines? The bearings are a little too small to do any sanding, so if the problem persists and it doesn't affect the overall performance of the machine, I'll have no choice but to live with it. I probably won't hear it over the router when chips are flying anyway. If the noise is all there is to it, then I can worry about the next issue.

    Quote Originally Posted by davida1234 View Post
    If you can rotate the bearings by hand when you think there is no play is that you think wrong. There is play, you just can't feel it. Assuming all bearings are on the same level, you should barely be able to rotate the bearings by hand for no play in the system.
    This is what was buggin' me the most. Hopefully, after breaking in the rails, ill be able to tighten the bearings down enough for them to be soildly on!

    Thanks again! Very informative!

    Isaac

    Last edited by imbaine13; 03-12-2019 at 05:47 PM. Reason: typo


  2. #50
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    Default Re: DIY CNC machine on the cheap!

    Quote Originally Posted by imbaine13 View Post
    The bearings are a little too small to do any sanding
    My mistake, I meant steel surfaces where the bearings are running on.



  3. #51
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    Default Re: DIY CNC machine on the cheap!

    Quote Originally Posted by davida1234 View Post
    My mistake, I meant steel surfaces where the bearings are running on.
    Oh Yeah. I bet that would make a difference. I'll try filing the edges down until I think I've got a uniform track. Then with the bearing assembly, I'll squeeze the bearings down on the filed edge to provide a smooth finish. If that ends in vain, my next best option would be to get some 3/4" (1mm thick) aluminum angle to brace along the edges of the steel hollow section where the skate bearings would ride. The aluminium's really smooth and it might resolve the occasional binding.

    If that still fails with the square steel tubing, I'll switch to some 1.25" diameter curtain pipes I found that had an almost perfect mirror finish. The only problem is they are only 1mm thick, and that, combined with the small diameter means there'll be significant deflection if they're used unsupported. Now, to resolve this, I came up with a crazy idea of filling them up with concrete!!! I know, really crazy, but I'm working with what I have around. The inside of the pipe is rough enough for the concrete to stick. I am aware that concrete shrinks slightly when cured, which might not help with tiny deflections, and the set up will weight much more, but as I mentioned earlier, if it gets the job done, no worries (not sure if vibrations would break the concrete up into powder, only time will tell). Before heading down that road, in order to get a baseline of how much deflection is acceptable, I need to find the JGRO CNC plans and calculate how much his X-axis rails deflect, after finding out how heavy his gantry is. This would all be in an effort to get those thin walled tubes more rigidity. Still open to better ideas regarding this.

    I'll start with your idea first though.
    Thanks.

    Isaac.



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    Default Re: DIY CNC machine on the cheap!

    Don't file anything. It's too much, you will get low points. Just sand slightly with FINE sandpaper. The rest should be smoothed out by the bearings.



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    Default Re: DIY CNC machine on the cheap!

    Quote Originally Posted by davida1234 View Post
    Don't file anything. It's too much, you will get low points. Just sand slightly with FINE sandpaper. The rest should be smoothed out by the bearings.
    Tell you what, just seen this post, after I had already done the filing! Your advice worked great! I've been busy with work, but I managed to put a few hours into the machine. The quality of almost everything in the market in this country is appalling! Fact! Sanding alone wouldn't have done much! Here's a shot of what one of the edges looked like before, and after filing. I run a really fine sand paper over where i'd filed and ended up with a smooth straight surface for the bearings to ride on.

    Attached Thumbnails Attached Thumbnails DIY CNC machine on the cheap!-20190315_154749-jpg   DIY CNC machine on the cheap!-20190314_172540-jpg   DIY CNC machine on the cheap!-20190315_155148-jpg  


  6. #54
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    Default Re: DIY CNC machine on the cheap!

    So, after I did the filing and sanding, I was excited to try it out again. There was a huge improvement in the movement. Negligible binding and the bearings were quieter, but, some of them (bearings) weren't really at the edge of the steel tube. The ones that were, did okay, rolled almost dead centre, but it was a different story at the opposite corner. Only the edges of the these bearings was in contact, causing axial loading and friction. The harder I snugged the bolts up, the higher the friction rose, seemingly exponentially. I found, after taking a closer look, that the steel tube wasn't perfectly rectangular (poor quality steel). The 1' square tubing I was using earlier didn't seem uniform either, so I dropped the idea of using steel square tubing as runners for the bearings and switched to something I was sure was run through a die to get precise dimensions; curtain pipes! As an added advantage, they came already coated with some non corroding metal (not sure whether zinc or tin although some people complain about the it flaking and falling apart under the pressure from the bearings) so my rust worries are kind of gone!

    I was sure that the curtain pipes were nice and uniform, but when the skate bearings also had problems running on them, I instantly had the conclusion that the bearing had to be crappy!! You get what you pay for I guess. Aren't these the same cheap bearings from China most people here use? I went out to look for better quality bearings, no matter the price and found the one in the photo. Slightly bigger, but I was surprised at how much of difference there was between these and the skate bearings! The new bearings (black rubber seals) had much tighter tolerances with no radial play between the inside and outside rings, whereas the skate bearings (red rubber seals) had about 0.5mm of wobble between the two rings as well as significant radial play. The skate bearings would simply bind up when I would get them to about the right tightness on the tube, whereas the new ones run with silk motion. Overall, I'm glad to report that my linear motion problems are close to an end.

    Cheears,
    Isaac.

    Attached Thumbnails Attached Thumbnails DIY CNC machine on the cheap!-20190315_155312-jpg   DIY CNC machine on the cheap!-20190315_154916-jpg   DIY CNC machine on the cheap!-20190315_155426-jpg   DIY CNC machine on the cheap!-20190315_155502-jpg  



  7. #55
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    Default Re: DIY CNC machine on the cheap!

    I was thinking of using these tubes unsupported, but they are too thin to hold the gantry without noticeable deflection. Anyone with an idea of how I could provide structure on the inside of the curtain tube to make them more rigid?



  8. #56
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    Default Re: DIY CNC machine on the cheap!

    Roughen up the inside and pour sand concrete into them! Let it cure for at least 30 days. I really mean it.



  9. #57
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    Default Re: DIY CNC machine on the cheap!

    Hi, those tubes will bend like hell. You need some solid support. I have a project I call my junkyard CNC which has some aims in common with what you are doing. I use solid round bar rather than tube, even that needs solid support. If you have access to extruded aluminium sections as used in window and door frames you may find something that acts as a support. Look at the gantry on this video. I got my steel beams and extruded ali from the scrap yard. It took some time to find really heavy walled extrusions but it is a very strong solution. The ground bar and balls screws are new chinese "junk".

    http://solaire-chauffe-eau.info/cnc/DualX.mp4

    I found extrusions with a groove in the top and bottom so I just sat the round, solid bar in there and gantry bearings are nipped up good and tight, so I don't even need to fix the bars in place. The 16mm chrome-plated, ground bar is accurate and has a durable finish. Such plain bar is not too dear.

    BTW I use SBR20 mounted round bar on I-section beams for X axis and drive from both sides to ensure no twisting between X and Y ( ie remains perpendicular ). With one exception this was made using only hand tools ( patient filing and tapping ) and an electric drill on a drill stand seen in the background ( poor man's pillar drill or press drill ).

    Avoid use of any tube if you can. It will not be solid enough, you will not be able tighten bolts tight enough of tubing to hold things solidly. The tube will crush.

    I have modified the bearing blocks to make them stronger and easier to make since this was taken. I can post a pic if you are interested. On the top I use opposing standard bearings, as can bee seen, underside I've used a single U-groove , double row ball bearing. ie two bearing blocks above to support the gantry ( approx 50kg ! ) and the U-groove to nip up in the middle underneath. The U bearings are chinese junk and you need to order at least twice as many as you need. Seems the chinese have trouble getting the holes in the middle and this causes tight spots when the bearings are clamped tightly. I have not found a EU or US equivalent product.

    Here is an earlier photo which shows the overall construction. Some details have changes since to improve rigidity.
    http://piments.com/cnc/ensemble_bench.png

    Here is the z-axis. I thought of something similar to x and y-axis as you have done but could not find anything compact enough, so I went for classic linear bearings.
    http://piments.com/cnc/3axis_closer.JPG

    Hope that is helpful.

    Last edited by reg.miller; 03-15-2019 at 08:07 PM.


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    Default Re: DIY CNC machine on the cheap!

    Its good to see some progress with the machine,have you learned enough yet to generate a toolpath?



  11. #59
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    Default Re: DIY CNC machine on the cheap!

    Quote Originally Posted by routalot View Post
    Its good to see some progress with the machine,have you learned enough yet to generate a toolpath?
    Hi routalot, if that qu was aimed at me, no, I have not bothered with toolpaths yet since that is more a case of using a CADCAM package. I need to concentrate on finishing the h/w , without which the rest is a bit academic .

    For OP, here is the new format guideblocks. This should be easy enough to make and is way more rigid than messing with bolts and pipes. I does require being able to tap an M10 thread in an ali block. The 45 deg face was cut with a hacksaw and a couple of hours of careful work with a file and an set square, once the holes were drilled and tapped. Conforming to OP's do it by hand objectives.

    http://piments.com/cnc/new-guide-block-pair.jpeg

    mounted on machine:
    http://piments.com/cnc/guideblocks-detail.jpeg

    Note scrapyard origin of the ali blocks. They were previously used by someone to mold lead fishing weights, explaining the odd cut-out on the inside faces ! LOL.

    I originally started with 80mm I-beams but as the weight of the gantry and z-axis assy crept up to 50kg, I found they flexed too much ( a couple of thou ). Always worth digging out the formulae from somewhere like engineering toolbox before building a rig ( or at least putting a dial gauge on and leaning on it ).

    Last edited by reg.miller; 03-16-2019 at 06:08 AM.


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    Default Re: DIY CNC machine on the cheap!

    Is black pipe commonly available in your area ? It's used for things like sprinkler systems and natural gas.
    It's much stiffer than curtain rod and has no coating to flake.

    Anyone who says "It only goes together one way" has no imagination.


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