I know on my mpcnc anything over .75 causes my 8825 drivers to overheat after about 25 mins of runtime. Cost me 3 drivers and 2 end mills learning that lesson.
I think the internet values that are posted are for a lower duty cycle than a Cnc, or my case needs better ventilation.
@Hiram your an artist so i will try to use an analogy (that may not be completely correct) to explain the situation;
how much paint do you want on your paint brush? enough to get results but no more than needed correct? if you have to little you run into issues, but too much and you have other problems. but how do you explain to someone with no painting experience what is the exact right amount? iām sure many have come up with equations and practices to try to explain it but they very and do not always work out, especially when you consider that the right amount can very with the canvas and painting technique you are using. but generally speaking you can always add more paint but you cant really remove paint from the canvas. so it is better to start low and use more if you find that you are not getting the results you want.
this is the same, start with 0.7V if it is not enough you will know because there will be issues (just like when you donāt have enough paint). in that case you can bump it up by 0.05V until the problems go away (just like you may add a little more paint until you find what is just enough). but it is considered better to have to little than to much (to high and you could damage the drivers or the motors). and do not worry about having to decide by yourself if that is the issue, if your machine has problems you can ask about it here on the forums and someone will help you decide if bumping up your Vref could help 
The specific symptom of ānot enough motor currentā (which is what is being set by adjusting the vRef on the driver) will be skipped steps. The motor will buzz and not move as far as it was commanded to, ending up in the wrong place and probably spoiling the work piece.
There are a few different ways to combat this, and the ārules of thumbā that are being stated are what works for CNC machining, so may not be directly applicable to your situation, depending on the weight of the tool head you end up with and the ādragā of moving it through (or across) the work.
Stepper motors lose steps when they donāt have enough torque to move the machinery to the desired location at the desired speed and acceleration. Stepper torque drops off as speed increases, so eventually you hit the limits of the system. vRef is the primary adjustable parameter for torque, speed and acceleration, which are all interrelated. Machine movement will be influenced by the inertia and momentum of the moving parts of the machine. In my experience, it quickly moves from a mathematical problem that can be solved with a few variables, to a complex tuning process thatās as much art as science.
Starting with a vRef of .7, see if the machine moves fast enough and changes direction reliably enough for your needs. If it does not, then increasing vRef provides more current, and therefore more torque, but at the expense of additional heat in the driver and the motor, as has been explained above. An alternative to increasing vRef may be to tune acceleration down a bit so that changes in movement are more gradual, requiring less torque.
This post has gotten long enough already, and is mostly theoretical until you can get some experience on your moving machine, so I wonāt put down my process for tuning acceleration and speed here, but am happy to share if you would find that helpful.
Hello I just got a voltmeter and I set the Vref to 0.70V I also finished 85% of the mechanics. Thank you ! I am looking for an enclosure for the ramps and the display and I am finishing the table! I will also wire the motors I bought the plug-in socket blocks and I will crimp the wires there ā¦ I am moving forward thanks to all of you
Iām glad you are still moving forwared. Since you stopped posting, I feared you ran into trouble.
I did a bit of research on the authoring side of your project. Iāll share my results once you have your machine up and running.
To clear any language barriers, ābump it up by 0.05Vā means āto change the voltage from 0.7V to 0.75Vā. All languages have local idioms and people who study the language will not learn the local communities type of speaking but only the formal language. There are vast differences. I hope your project turns out well.