Newbie CNC Build

[JAZZCNC]

Hi,

Please don't think I'm picking fault with what I'm about to say it's just my opinions mixed with experience.!

I'm currently building the machines that I think you've seen and based this design from. My frame is using 80x40x3mm and 40x40x3 I can tell you it's more than enough and very heavy so I would recommend you save a bit of money and go with 80x40 it will more than do what you want.

Regards the frame layout I would change several things and add a few.! It's easier to show than explain so I've drawn a quick model to show it. Doing it like this gives more weld area and better stiffer bracing.
One thing I suggest you do is NOT weld the top piece which the rails sit on to the upright legs.? Better if you weld flat plates to the uprights and then bolt the top piece. This gives better control of getting the two sides parallel, basicly you can shim and adjust them into parallel planes.

RE Z axis. See pic with front plate missing (and only1 rail) this use's profiled linear rails but the principle is the same supported round rail.
As you can see the bearings bolt onto the rear plate that travels along the Y axis and the rails bolt onto the Z axis front plate which the spindle attachs too. The reason for doing it this way is to gain from the fact the flex of the front plate become less or more as the extension increases or decreases. Doing it the other way round the extension of the rail from the bearing is always the same distance whether extended fully in or out and with long Z axis this becomes a spring board at any z extension.!!

RE Timing belt. See updated model of current machine. The following will also answer your concern regards steppers falling behind
To be honest if your going to have a piece across the back like the model suggest's then I would urge you to connect the two ballscrews together with one timing belt and use just one motor to drive both. This address's several issue's and saves you some money, my own machine use's this setup so I can tell you 100% it works and works very very good so don't be put off with the use of timing belts. . . .Here's why.!!

First and foremost it completly eliminates any sync problems(falling behind) with the 2 screws and takes away any fear of racking or damage from one motor stalling and the other continuing which belive me when it happens, esp at high speeds, can do lots of damage. This is the main reason why I prefer this method.!
It allows higher rapid feed rates because you don't have to affectively de-tune your motors to be sure your in a safe non stalling tuning range like you have to do with slaved motors.
Because it use's belts it's easy to change ratio's for extra speed or torque/resolution, basicly depending if you gear up or down and the ratio you change one pulley for another and you have either doubled, tripled your speed or resolution/torque.
You only need one drive and motor to drive 2 screws which save a bit of money, thou you dohave the belts and pulleys to buy which lessons it a bit but your still in front and you save some input's and outputs on the parallel port.!!

Like I say don't be put off with belts they work fine and in over 3 years I've only broke 1 belt and that was my fault for not tightening a pulley after messing. The accurecy and repeatabilty of my machine is fantastic and in no way suffers thru using belts and I mainly cut aluminum with it. Just see my Aztec calender too see that and if any issues then no way would it do work to this level of detail.

Hope this helps.!