Here is how I set up my machine.
- How square does the machine need to be?
This is important because everything begins on the rails. If one of the rails is crooked the machine will run crooked. Get a machinist square and loosen all the Y rails in the 4 corners and bring them back into square. You may have to actually physically twist left to right on the machine to get it square depending on how out of square it was. Tighten the bolts up slowly in each corner while checking to make sure you stay in square. When you have them all tight check it all again. Then work on the X rail. Make sure it is square in the Y direction and the X direction. Adjust the screws accordingly. You wont have a great deal of movement in the mounting holes but you can move them all a small amount.
- How tight do the belts need to be? If they are too tight, does that degrade accuracy or just wear out stuff sooner?
My belts are tight. When you move the machine to the end of its travel, you should be able to raid the middle of the belt up about 1/2 inch. There are some videos on youtube showing how to calibrate them with a fishing scale by hooking the belt on the scale and pulling it up an inch or so and measuring the weight. I dont think that is necessary but if you want a good measurement you can do that.
- What leads to inconsistent cutting behavior?
Anything that is loose, not calibrated, not square etc. Check every single screw and make sure they are all tight. A pulley that is not tightened down will make for very erratic operations. Make sure the belt pulleys are aligned with the belt. Some have reported the X axis drive pulley has been found backwards. The belts should be straight and aligned with all pulleys. Check the V-wheels for cracks or flat spots. Make sure there is no debris on the rails. Ask yourself if the machine was a car and you were riding on it, what would be the result of that component rolling as the car drives down the road.
- How much do the v-wheels play into any of this (i.e. too tight or too loose)?
Can be huge. If too loose, they wont grip and you will slip steps, If too tight, the motors wont be able to move them on the rail correctly and you will lose steps. How I adjust mine is like this. One v-wheel is fixed on a screw and there is not adjustment. On v-wheel is on an eccentric which allows for adjustment. Usually the eccentric is on the bottom of the rail. With your machine off, the spindle should be able to move on all rails easily. After verifying this, take one of your fingers and stroke the eccentric v-wheel and see if you can move the spindle down the rail. If not, the eccentric is too loose. You want the eccentric v-wheel to barely touch the rail while allowing it to move the spindle down the rail. Too tight and you will bind the v-wheel. Play with this a little bit. You want it to be only as tight as your finger can easily move it.
And the last thing. It is completely likely that your spoil board is not level with your spindle. There are two issues here. First is the support in the middle of the table probably allows the spoilboard to sag. Once you get everything square, calibrated and adjusted you will want to so a spoilboard flattening to make the spindle perfectly aligned with the spoilboard.
After you do this, you may notice little ridges running either left to right or back to front. If so, this indicates you spindle is not square to the spoilboard. You may have to shim your router to correct this and then relevel you spoilboard.
I know this all sounds like a crazy amount of work. But if you will be patient with tuning the machine, and get it close, your accuracy will improve greatly.
Last but not least, dont get frustrated. We have all gone through some subset of this process and are here to help. Apollo frequents the boards also and the Carbide 3D team is awesome in customer service. Just ask and someone will give you some idea of what you need to do.
And make sure you get a machinist square, a dial indicator, a caliper and a set of 3-2-1 blocks. These will help you get it all dialed in.
Hope this helps and good luck. Remember this is no stupid question. If you have it, someone else does too. And we have likely all asked it previously.