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IndustryArena Forum > Mechanical Engineering > Mechanical Calculations/Engineering Design > Moving Gantry column bearing spacing - open discussion
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  1. #21

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    Re: Moving Gantry column bearing spacing - open discussion

    Quote Originally Posted by mactec54 View Post
    No I have tested the IGUS system and it is not suitable for CNC machine use, even at Hobby level, it would be a very bad choice if you where to build a new machine, IGUS can be used for other sliding systems that don't need any kind of accuracy

    The design you have with the round rails would not work with supported round rails as drawn the Bearings would have to be open, round rail bearings also have large clearance between the rail and bearing some have small adjustments that can be made but are ok for hobby level machines, if you want any kind of accuracy then you would use pre-loaded profile linear rails
    I was talking more in general terms of cnc machines, a metal or even a wood router/mill cnc machine should not use IGUS rails, but a low weight 3D printer or a laser, could and can use the IGUS rails with good results.
    I have however, not been able to do any long term tests of this kind of system yet. As I've recently just started testing the IGUS rails out on a custom designed 3d printer made up out of alu, carbon fiber and both IGUS rails and roller wheels in v-slotted extrusions. The design also welcomes the HWIN rails, so if my testing shows that I can't use the IGUS system, I will just move to the HIWIN system.

    The design was just a mockup of a placement idea I had, and was constructed while I had some time of at work. No real design thought beyond the general placement was considered.
    And I agree with you, that pre-loaded profile linear rail system is a better option. It was just to add an option of something someone might think of, and having it in here with both pro's and con's. Which would allow them to decide to choose a similar, or different design. If it would fit most of their requirements, not only in the machine, but also in their pocket.

  2. #22
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    11545

    Re: Moving Gantry column bearing spacing - open discussion

    Quote Originally Posted by --JawZ-- View Post
    I was talking more in general terms of cnc machines, a metal or even a wood router/mill cnc machine should not use IGUS rails, but a low weight 3D printer or a laser, could and can use the IGUS rails with good results.
    I have however, not been able to do any long term tests of this kind of system yet. As I've recently just started testing the IGUS rails out on a custom designed 3d printer made up out of alu, carbon fiber and both IGUS rails and roller wheels in v-slotted extrusions. The design also welcomes the HWIN rails, so if my testing shows that I can't use the IGUS system, I will just move to the HIWIN system.

    The design was just a mockup of a placement idea I had, and was constructed while I had some time of at work. No real design thought beyond the general placement was considered.
    And I agree with you, that pre-loaded profile linear rail system is a better option. It was just to add an option of something someone might think of, and having it in here with both pro's and con's. Which would allow them to decide to choose a similar, or different design. If it would fit most of their requirements, not only in the machine, but also in their pocket.
    Almost anything will work for a 3D printer you are not doing anything serous with hobby level 3D printers, you sound like you are reinventing the wheel as all these types of guiding systems have been well tried out by most hobby builders, which move on quite quickly once they see the results, you don't have to use Hiwin there are may much cheaper that will do the same job, you have to choose carefully though with the cheaper rail sets, the steel round rails work well for 3D printers and don't have to use supported rails because of the low loads, so you have lots of choices, The IGUS bushing system they use is not reliable and not easy to get adjusted correctly
    Mactec54

  3. #23
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    Re: Moving Gantry column bearing spacing - open discussion

    Hi Mactec - So the machines built with twin rails and 4 cars each side did they do better then a single rail and 2 cars each side? regards Peter

  4. #24
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    Re: Moving Gantry column bearing spacing - open discussion

    Good morning CNCers - So Jawz sent me a step file of his gantry & gave permission for showing the images. I stripped it down to the structural parts. Its a combo of extrusions and cnc plates. I imported it into simsolid and used an auto connect command which bonded all the parts together. I then applied a "push" load to the spindle collet of 1000N while the cars were restrained. This is my standard design load. The collet moved 0.123mm. This is a static stiffness of 1000N/123um or 8N/um. Most if this deflection is in the collet as you can see in the image. So I made the collet "rigid" to see what the machine does vs just the nose of the spindle. It then moved 0.090mm so the static stiffness is 1000/90= 11N/um. As the model is bonded ie all connections are 100% efficient I expect the real figure to be around half the calculated one.

    I then deleted one rail to see what the "free" deflection was and its 2.71mm. Then with the rail in its 1.1mm deflection. The columns are two parallel plates and I would suggest that these be addressed as in the exaggerated images you can see these winding. So the gantry is stiff, the columns I feel are the weak link. My other comments are as Jawz has access to commercial CNC to cut his parts why not build a plate gantry vs using extrusions? It will be locally and globally stiffer. The columns have cover plates on them (not shown here) and these could be made to be structural to become better in torsion. Thanks Jawz Peter

  5. #25
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    Re: Moving Gantry column bearing spacing - open discussion

    Modelling Weirdness - Hi All - I decided to put in a 150mm spacing to complete the series and then chart it. But the 150mm deflected less then the 200mm so I played around with the model and couldn't find out why. I decided it may have been the complex sliding contact with the rails and cars as they include the grooves and stuff. So I built a simplified rail and car using only 3 contacts and wow, the same result. So I think its something to do with the deflection of the bearing beam. But its connected to the car and the car to the rail which has an infinitely stiff connection to the "floor" this is weird... So the general rule about spacing may not be correct?? More investigation needed. Hate mysteries... but we are talking about deltas in the 0.01mm band...Peter

  6. #26
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    Re: Moving Gantry column bearing spacing - open discussion

    Hi All - I thought about the issue and decided to make the gantries perfectly rigid. Everyone wants a rigid gantry and this isolates the result to the bearings and rail. And this gives the logical deflection series. 150mm- 0.009mm 200mm - 0.004mm 300mm - 0.002mm and 400mm - 0.001mm. But these are down in the 0.001mm band. So it seems the gantry is complex and requires individual analysis to get the deflections down. Cheers Peter

  7. #27
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    Re: Moving Gantry column bearing spacing - open discussion

    Quote Originally Posted by peteeng View Post
    Hi Mactec - So the machines built with twin rails and 4 cars each side did they do better then a single rail and 2 cars each side? regards Peter
    They are much better when you have a tall Gantry anything over 250mm to 300mm of Z axis travel and they can be a smaller rail size than if using a single one
    Mactec54

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