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  1. #21
    The most common configuration for a gantry is the L shape. Mostly others use either 80x40, 90x40 extrusion or 100x50 rectangular box section aluminium. There are any number of threads showing this examples such as any of Kingcreaky's 3 builds, Eddy Current's build etc. etc. have a look at these and you'll see the type of thing.
    Neil...

    Build log...here

  2. #22
    Hi, what do you think of this brother?

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  3. #23
    What Z axis height /work piece/ you are trying to achieve? The gantry seems too high, not sure, may be the perspective on the drawing. For this type of machine 100mm is reasonable, 120mm is best compromise, 150mm is on the limit and more than that is just wishful thinking. Without further reinforcing the gantry with say - a steel plate.
    project 1 , 2, Dust Shoe ...

  4. #24
    Hi yeah I think you are right it does look way too high, I have reduced it by 100mm which would look like this now :



    changed to perspective projection that might look more realistic I hope.

    I was really hoping to achieve more than 100mm z-height, but if I can stretch it to 150mm I guess that would be okay.
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  5. #25
    The best and stiffest way to achieve height is to have the L shaped gantry sitting on the carriages and raise the frame up on legs. If you have an adjustable bed then you can cut deep items but for 90% of cutting have the bed as near the cutter as possible to keep cutter flex to a minimum. What will you be mostly cutting?
    Neil...

    Build log...here

  6. #26
    Hi Neil, mostly wood with occasional aluminium

  7. #27
    hey guys I could use your help on designing the Z axis to complete the machine, I have made it 200x240mm but I don't know if that is the best size given my machine overall design.

    and am thinking of mounting the hiwin blocks on the stationary part and the rails on the second plate which will move up and down, should the second plate and the rails be also 240mm ?

    last thing i need help with (for now lol) is what HIWIN rail and block size should I use for my x axis ( gantry left and right ) and z axis? HGR the heavy duty ones or will EGR be good enough?

    thanks !

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  8. #28
    I forgot to mention that I'm planning on using 2.2kw Chinese spindle and won't be changing that in the future for this machine, the bracket for that is 150mm I think, so should I reduce the Z plates width to 150 or stick to 200?

  9. #29
    In terms of width of Y axis plate then 200mm is reasonable to reduce racking of the Y/Z axis assembly as this spreads the Y bearings apart a bit. Some people make the plate have 'ears' where the Y bearings mount which can help with clearance and assembly. Not mandatory as it depends on the other details of the design, but worth a look.

    I went with less than 200mm spacing to get more working space as it is primarily a wood cutting machine. There is no problem with mounting a 150mm wide plate to this to hold the spindle. You can use the real estate at the sides to mount DTIs, laser pointer, dust shoe etc.

    In terms of height of the Y axis plate only needs to be as high as the Z ballscrew, fixed and floating bearing, and stepper connection dictates. You need to draw these to see how tall it has to be to give the required travel on the Z ballscrew nut. In practise this could be close to 240mm but there is no specific requirement to match the moving Z axis plate in height.

    Bearing sizes - I used 15mm on the Z (but wish I'd used 20mm as they are much stiffer), 20mm on the Y (which I'm happy with) and 16mm SUPPORTED rail on the X (wood cutting machine). If I was to use profile Hiwin style rail then I would use 20mm as a minimum.

    The way you have mounted the gantry to the X bearings looks poor, as seen in the front view picture. A very long cantilever plate which is OK for wood, but not ideal for aluminium. You should redesign this, or add a further connection up to the gantry, or raise the X axis to meet the gantry directly.
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  10. #30
    Well with the Y axis rear plate(across gantry) you have room to have it wider than the front plate because it will over hang the bearings which the front plate can't or will crash into bearings. This will make Y axis much stiffer and be easier to access the bearing bolts. Yes put the bearings on the rear plate, rails on front moving plate.

    For the Z axis you want hi-win HGH20CA Z0 which are the slim type and for the other Axis you want HGW20CA Z0 which are the wider bearing and will give a bit more support. Don't use 15mm the bearing blocks are too small and fiddly making building a Z axis more difficult due to clearences etc.

    With the design I feel you are a little low on the height as it won't leave much room for cutters but then again I don't know what your cutting so may not matter.
    Neils suggestion about X bearings looking poor is valid and has it is will need some bracing to help stiffen which is easy enough. But there's another change that I would make which will lessen the cantilever but more importantly allow for easier adjustment of the ballnut and allow some protection for the screws.?

    Make the Gantry sides drop to the inside of the ballscrew not the outside.? This will shorten the gantry width and reduce bearing plate width and cantilever making it stiffer.
    It allows access from the outside to the ballnut for adjustment and greasing etc.
    Another important and often overlooked thing is screw protection, Your way makes it harder to protect the screw with a cover because of the gantry side being on the out side. If it's on the inside if the screw you can make a cover using C channel with a brush strip on top that covers any gap and wipes the gantry. This makes a very easy way to cover and protect which you'll want to do if cutting aluminium or wood even with screws on outside. (see pic)
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