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bearing questrion

Discussion in 'CNC Mills/Routers' started by Norm Benjamin, Nov 3, 2014.

  1. Norm Benjamin

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    I have a router kit purchased some time ago and have been running it and accepting it's fault now it's time to address all these and get them fixed might mean replacement of parts.

    The major problem is in the y axis it is about 48" long cut area and uses 1" diameter steel hardened rods with linear bearing attached to the gantry plate which are 1/8 steel. The gantry is quite heavy as it is all steel construction even the z axis is all steel. Now to the problem the bearings on the y axis seem to sort of grumble when moving what I mean is you can feel them move if you touch the table when it is running not loud but some vibration sort of. The axis seems to move smoothly but you if touching the table feel it move. First I guess is this normal? Second what can I do to fix the problem? watching the video on the OX small router those rollers seem to work great I drive my router today with lead screws rather than a belt but the belt might be a better option if the rollers can take the load the base frame is constructed from 20/20 extrusions similar to the OX but much heavier. Would a belt drive system if I can apply it be better than lead screws?

    I know I am asking a lot of difficult questions without all the information but in general the rollers etc. perhaps can be answered. I might be looking at a sell this one and build another perhaps. When I got the kit it was to work a 24"x 48" area but only works a 26" x 28" area. Smaller than I wanted but so far that has been workable. If I were to build another might make it a bit larger perhaps 36" x 48" work area.

    zmpt,
     
  2. Charlie

    Charlie New
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    Hello Norm,
    Can you take the y axis bearings off and turn them?? how do they feel... smooth or rough? second the surface the bearings ride on is it a precision ground surface or what is it?

    Charlie
     
  3. Norm Benjamin

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    Yes the seem to move smoothly. The are riding on a hardened steel rod machined very smooth and hard. they are 1" diameter and are designed for CNC rails.
     
  4. Tweakie

    Tweakie OpenBuilds Team
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    Hi Norm,

    Could you perhaps post a couple of pictures of your machine's construction to give us a better idea of the problem relating to the linear rails movement issue ??

    Tweakie.
     
  5. Norm Benjamin

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    Yes when I get home tonight I will take a few pictures. One thing I did not mention and might be important yesterday I was setting things up to run some projects so flattening the table etc. I watched under the table and was watching the lead screw vibrating up and down. I remember when I got the parts the guy that cut the pieces said he did not have the correct coupling 1/4- 1/2 so he ground the end of the shaft to fit. Well that was done by and not very accurately. That being said the shaft at one end in the drive motor is wobbling a bit and that seems to cause the feed screw to whip. especially at each end of travel. I don't think this will cause a vibration on the table like I feel but I am not sure.
     
  6. GrayUK

    GrayUK Master
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    At a guess I would say the weight is the main problem, being such, that it is bringing out any weakness. From what you say about the screw wobble I think this is how it is finding the weaknesses.

    Likewise, as per your first comments, I think the Belt might struggle with the all steel X and Z axis.
    It might be fine to start with, but the weight might begin to affect the accuracy of the belt.

    Those pictures will help in any advice for you.

    Cheers
    Gray
     
  7. Norm Benjamin

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    Pictures of my dirty router it does work for me just not quite right.

    Info on the design the Z axis is all 1/2" steel
    Gantry sides are 3/16 steel
    the bottom support for the gantry that holds the limit switch etc and drive 1/2"steel
    The base width along the Y axis supporting the bearings is 7 1/2" wide
    The bearings are spaced on 3 1/2 centers

    As you can see this is built like a tank but perhaps some very weak points and in some cases unnecessarily over designed creating some weak points.

    Hope this information helps get some ideas as to what should do to correct my problem
     

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  8. Norm Benjamin

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    A couple of things I forgot to mention. The Y axis shafts are 25 mm and my z axis travel is 4 1/4"
     
  9. Norm Benjamin

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    GrayUK,

    I have been giving some thought about your weight observation and am begining to think you may be correct. I know with the nema 23's I have on the machine if I attempt to run over 70 ipm I begin to loose steps the machine is not able to keep up. Since I have all the electronics I think the more expensive part of the machine the rest is just mechanical and should consider a frame rebuild th make the ubit a bit lighter. I would also be able to increase the size at the same time.

    As I thought about the weight this might be a bit much for the nema 23's to handle well. The only concern then is managing to keep the regidity with a lighter weight material. The plastic gantry sides not sure if that is good for 30" wide gantry supporting a 2 1/4 hp router. I really need to think this through thourly to form a plan here. Watching the assembly here of the OX video and the fact I have assembled one unit, it's just not that difficult.
     
  10. GrayUK

    GrayUK Master
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    You have got to use your existing machine to make your new parts! All the plans are here, and you can modify as you go. Certainly it is the X and Z that need lightening, and yes, you do need to consider flexing when dealing with aluminium. I do believe there is a, sweet point, where weight and strength, balance, and come together.
    Please spend a couple of days, or weeks, reading our forum, the answers are all there, it is just a question of finding them!!

    The X axis has been a topic on many, many, many occasions, with many solutions and decisions reached.
    I myself am still considering modifications with the X. It will stay in the realm of aluminium, it's just a matter of size and weight, once again.

    Anyway, get reading and don't forget ask what ever you want, and someone will get back to you.

    Gray
     
  11. Norm Benjamin

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    I have been all over the site and am having problems getting things together. It seem quite fragmented lots of information but not linked. I am finding drawings that I am not able to read I use AutoCAD and most of these are in sketchup I think. I never heard of the program and can't seem to find it anywhere.

    At this Point it is a bit like wandering around the woods without compass
     
  12. Tweakie

    Tweakie OpenBuilds Team
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  13. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    The .dxf drawings for the plates are here: http://www.openbuilds.com/builds/openbuilds-ox-cnc-machine.341/#openbuilds_files. I'm not sure what ACAD version you are using but they opened fine in ACAD2008. Please note that they are in millimeters.

    Looking at your current machine the deficiencies of the Y-axis are rather apparent. A center pull mechanism on a carriage that wide with a continually unbalanced load is going to result in racking of the carriage. Combine that with the 1" diameter support rails that will not provide much stiffness along the length is creating a system where vibration is unavoidable. That being said however, I question whether the OX is the appropriate replacement for you. The OX is a hobbyist grade machine, a very good hobbyist grade machine but hobbyist grade nonetheless. A 2 1/4 horse router on a 36" beam is going to have deflection issues and belt stretch over a 48" length may be a problem. While these issues can be overcome, you'll need to consult with the forum members who have been battling these issues and can provide insight into what works and what doesn't. You would not be building a stock OX by any means as they just don't stretch that far and this will require a significant amount of planning on your part.

    Ultimately you may be better off replacing the Y-axis of your current machine. A set of properly sized 80/20 side rails with a rack and pinion drive system should have no problems supporting and moving your current X-axis. CNC Routerparts has a pretty good side rail and R&P system and you might reference their drawings for inspiration on how best to proceed.

    Please understand, I'm not trying to talk you out of building an OX as it's a very good system. I'm just hoping to help you avoid a fair amount of frustration and potential unhappiness down the road.
     
  14. Norm Benjamin

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    Rick,

    I thought the same thing perhaps just rebuilding the Y axis gantry is the thing to do. I would i keeping the same length come up with a better rail guide bearing system perhaps adding a drive I do have a control with 4 axis and am only using 3 so I could add a motor to the other side. I was hoping to ind here gantry plates with cross members but not much luck at this point. The low rumbling I eel in the bearings is I think you might be correct two things the weight o the gantry along with the center drive lead screw. Rebuilding the gantry side plates with aluminum would greatly reduce the weight and then the Z axis with aluminum that I am reasonable sure will help.

    Seems there are many different ways to create a bearing surface along the Y axis for the gantry I am just not to sure which is best and then driving it. Belt I am not to sure of seems sort of light to me rack and pinion EXPENSIVE I do appreciate your input this is requiring more thought than I was anticipating but it's interesting.
     
  15. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    You could always start simple by just installing dual screws to see if that solves the problem. McMaster is a good source for screws. You would probably want to get a matched pair of steppers to run them.
     

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