Hi everyone - by popular demand we have made a video explaining how to tune eccentric nuts and V-wheels!
V-wheels are fickle things; too tight and it impedes motion, too loose and it causes inaccurate cuts. They can be the cause of many movement-related issues such as:
See Chris go through the process, with extra diagrams and notes to guide you along the way.
Let us know your thoughts!
Hey Chris how you doing I have a question here in this design why aren’t the the adjustable v wheels at the bottom with the eccentric nuts and the stationary wheels at the top it seems to me with the weight of the x gantry and gravity having a stationary wheels at the top would work better maybe there’s something I’m missing here looking forward to your reply have a great day.
Following…
Maybe I’m missing something too but if the V-wheels are set correctly and you surface your spoil board, wouldn’t any future adjustments to the top wheels affect the spoil board surface accuracy?
I would have thought that for tramming purposes it would be better to have the static wheels on top.
Hey Robert and Terry, so when it came time for Andy and I to approach the design of the LongMill there was the question of whether to place the adjustment wheels on the top or bottom. The benefit to bottom placement obviously being that the static top wheels would take most of the weight of the gantry system and x-rail, but the major downside being much reduced access to make those adjustments - especially on the XZ-gantry where it would be really tricky to get an Allen key in-behind the rial where the reinforcement extrusion is. The resulting decision we came to was to place them on the top for the XZ-gantry and then be consistent for the y-gantries as well.
With that historical nugget, I’ll answer you guy’s questions concerns over loosing accuracy by letting you know that it doesn’t actually matter whether the adjustable wheels are on top or bottom since they will always be clamping against the opposing wheels which will always be stationary and set in place. Obviously this means that keeping good eccentric tensioning is important for accurate machine operation which is why we recommend more, or less, attention to the wheels depending on your application of your LongMill.
With all this being said though, Andy and I are currently working on the next version of the LongMill and for that coming version we will be placing the adjustable wheels on the bottom. The way this new design is made the wheel accessibility should be easier for the bottom wheels than with the current design (we hope) and the adjustment should also be a little easier with them in the bottom location 
Let me know if there are any other questions and I’ll be happy to answer them 
-Chris
Thank you Chris, I am totally thankful I found your design, your company, your endless humble support.
So I tried a few cuttings and ran into a problem. Every time I tried a rapid move on the x-axis from left to right the travel would not go all the way but the UGS coordinates reacted as if it had. Also, when the x-axis travel stalled, the machine gave out a loud whine.
After talking with Chris and Andy, I was advised to check the tension on the backlash screws and the v-wheels. I followed their advice and re-adjusted the v-wheel tension on the x-axis gantry and also, to be safe, on the y-axis gantries. n\Now the machine is working perfectly.
The key to these adjustments is to adjust the wheels using the eccentric nuts to the point where the wheels are not too loose but tight enough that they can just be rotated using your fingers. This is documented in the assembly instructions in the Post-Build/ Machine Maintenance section