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  1. #81
    Just a final thought before nurse tucks me in. When i started this project I was going to use mahogany and pitch pine. Now its box, plate and tough stuff. The base I built was a mdf torsion box. That is going to have to change. A steel frame is, I can see, inevitable. Thankfully my ex racing buddy is a great welder so i think that a cream bun in his direction may be required. Thats for the future so good night and thanks.
    Bruce
    The more I know, I know, I know the less. (John Owen)

  2. #82
    If you use the MDF torsion box mounted between a steel frame like I do now you'll have a very rigid machine:

    Click image for larger version. 

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    Mine is 18mm MDF on top, 9mm MDF underneath with 3x1 PAR pine in between ... convenient sizes at the time to fit the leadscrews inside.

    Part of the reason why is you can make it so the height of the bed is adjustible, so you can still machine tall parts without compromising the rigidity (due to large overhang) when machining sheet material. That is also where the Z-axis design you have now drawn with the rails on the spindle plate is significantly stronger - compare the distance from tool to linear bearing blocks.

  3. #83
    While trying to adjust the position of the z motor I realised that it would get in the way of the spindle mounting plate. Solution is obviously to mount the motor on the back of the gantry and use a small belt drive to run the z screw. This probably explains why i see it on many m/c's. Gosh max and jonathan i worked that out all on my own......guess it must be wrong then.

    Bruce
    The more I know, I know, I know the less. (John Owen)

  4. #84
    Using a timing belt is a great idea for a number of other reasons. It enables the ratio between the stepper motor and ballscrew to be changed. This alters the region which the motor operates in within the speed/torque curve, which with careful selection will get better acceleration and or feedrate. For instance I found with my Z-axis by calculating to get an estimate and then trying various pulleys that 42:22 ratio was best, with the larger pulley on the motor. The other big gain is the timing belt 'seperates' the ballscrew and motor so the vibrations do not transmit so easily - in other words it damps the system reducing resonance. Again this improves the feedrate, so it's a good thing to do on the X and Y-axis too. If you put a 2:1 ratio on the X and Y ballscrews it should get better acceleration and less importantly top speed, but you sacrifice resolution slightly (in most cases negligibly) plus you've always got the option of swapping the pulleys round to get better resolution...
    <br>

  5. #85
    got the cable today so i will try and blowup the spindle over the weekend
    The more I know, I know, I know the less. (John Owen)

  6. #86
    Wired up the spindle and did not blow it up. I have a link to youtube to prove it.

    http://www.youtube.com/watch?v=C8bMG...ature=youtu.be

    Bruce
    The more I know, I know, I know the less. (John Owen)

  7. #87
    Nice

    It does always flash. Bear in mind if you run it in reverse without a cutter in but the collet nut on the nut has a tendency to fly off :naughty:

  8. #88
    Quote Originally Posted by Jonathan View Post
    Nice

    It does always flash. Bear in mind if you run it in reverse without a cutter in but the collet nut on the nut has a tendency to fly off :naughty:
    oops

    How can you get the readout to give rpm?

    Just doing a redraw to get some accurate drawings after all the sketching.
    Bruce
    The more I know, I know, I know the less. (John Owen)

  9. #89
    Quote Originally Posted by motoxy View Post
    How can you get the readout to give rpm?
    Assuming you've set PD144 to 3000 you just keep pressing the >> button until you get to RPM.

    I generally leave it set on current - much more interesting as you can see if the cut is drawing too much power.

  10. #90
    Thanks Jonathan. So glad I did not go down the kress route.
    The more I know, I know, I know the less. (John Owen)

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