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  1. #11
    I ordered it from the UK stockist for 8020 down in Portsmouth. Again a pain to do but I was following the plans, the UK profiles didn't seem to have the same T-slot configuration as the 8020 one. Not much in the price though just longer delivery time.

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  2. #12
    Quote Originally Posted by GrahamWhite View Post
    I ordered it from the UK stockist for 8020 down in Portsmouth. Again a pain to do but I was following the plans, the UK profiles didn't seem to have the same T-slot configuration as the 8020 one. Not much in the price though just longer delivery time.
    That's good to know, I have been in contact with them but not had prices yet. They're not far from me so was thinking I could save on delivery charge by collecting but was concerned that the cost of having it shipped from the US would be prohibitive.

  3. #13
    I collected mine anyway and I'm in Lincolnshire lol, didn't trust a pallet delivery and it was gonna be £100 anyway way so I went for a jolly :) I think for 2x3m and 1x2m was about £430,whether that's expensive or not it suited me for the plans and everything else has fitted around that.
    .........
    Just looked at bosch and its actually a fair bit cheaper:( but like I say it suited the plans better

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    Last edited by GrahamWhite; 21-06-2018 at 10:14 AM.

  4. #14
    I've been looking at item, they do a 160 x 80 profile with a slightly higher second moment than 80/20, haven't got any prices from them yet though.

  5. #15
    Neale's Avatar
    Lives in Plymouth, United Kingdom. Last Activity: 6 Hours Ago Has been a member for 5-6 years. Has a total post count of 1,178. Received thanks 215 times, giving thanks to others 5 times.
    Quote Originally Posted by JonnyFive View Post

    Interesting what you say about the R&P. My understanding of the ballscrew / R&P decision was that although ballscrews are more accurate & efficient anything over 1m should use R&P because the ballscrew whipping limits performance - is that correct? There doesn't seem to be much of a cost difference between the two?
    This is where we get into real design decisions! I'm using 2005 ballscrews. There are a few online critical speed calculators available; the general consensus for 1750mm, fixed/floating bearing, screws is around 900-1000 rpm. That gives me 5000mm/min rapids, which is slower than ideal but which works for me using a hobby machine. In retrospect, I could have used 2010 and run faster. However, I am also using 2x3Nm motors to drive these. Pulley drive, but 1-1 gearing. This is because the motors are just about reaching their corner speed (where torque starts dropping rapidly) at about the "whip" speed of the ballscrews. I'm not entirely sure (because I haven't studied other people's designs) if the motors would handle the load of my heavy gantry using 2010 as there is also the acceleration/speed trade-off. I doa fair bit of small fiddly machining where acceleration is more important in overall cutting time than speed.

    All I'm really saying is that you have to balance up all the conflicting requirements for an engineering compromise that is right for you and your intended use. My design/build might not be optimal, even for me, but at least it works! There are plenty of posts one this forum with other designs successfully using ballscrews of this kind of length and I would happily do the same again.
    Last edited by Neale; 21-06-2018 at 11:40 AM.

  6. #16
    That's good to know, I appreciate your input. I'll keep trawling through build logs and see what others have come up with.

    Given what you have said do you think it would be better to have used torquier motors and gear them down to get the speed up, perhaps needing to go up in screw diameter as a consequence? I have no real concept of how fast is too fast / slow or how much torque is needed to cut at reasonable feeds. I have a combination of small fiddly and large uncomplicated projects that I'd like to be able to do on my machine. Initially I'm not that concerned about speed but at some point I would like to make some money out of this and so higher speed would be nice.

  7. #17
    Does this look about the right amount of clearance with the z-axis at its lowest?

    Click image for larger version. 

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    My plan is to have two pieces of wood for the bed, the top one being sacrificial. I've assumed the shortest cutter would stick out about 25mm and allowed this much clearance from the top of the first spoil board. This should allow for the top board to be resurfaced a few times and still give enough travel on the Z. Am I about right with this?

    Cheers

  8. #18
    Quote Originally Posted by JonnyFive View Post
    Does this look about the right amount of clearance with the z-axis at its lowest?

    Click image for larger version. 

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    My plan is to have two pieces of wood for the bed, the top one being sacrificial. I've assumed the shortest cutter would stick out about 25mm and allowed this much clearance from the top of the first spoil board. This should allow for the top board to be resurfaced a few times and still give enough travel on the Z. Am I about right with this?

    Cheers
    Spindle looks ok but spindle plate would be better higher to give clearance for clamps or vice jaws. To still give enough travel the whole gantry then needs to be raised the same amount. But if you move it too high then the Z axis has to extend down further so it is all a balancing act in the design stage.
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  9. #19
    Ok, Iíll move things around a bit to raise the gantry and mounting plate. Cheers


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  10. #20
    Quote Originally Posted by JonnyFive View Post
    Ok, Iíll move things around a bit to raise the gantry and mounting plate. Cheers


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    If you raise the Z plate and lower the spindle in the clamp to stop the Z plate catching clamps etc.
    ..Clive
    The more you know, The better you know, How little you know

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