Usability Improvements

[Custom 3D Creations]

There is one main feature that we would like to see, that we believe should be relatively simple to implement, but quite beneficial:
- The ability to define speeds for various features (outline, solid infill, etc.) with absolute speed values, rather than being relative (a percentage) to a default printing speed.

For quick prints and newer users, relative values are easier to understand and don't require as much knowledge for what speeds are appropriate for various features.
However, with advanced users, added functionality of absolute speeds (not replacing the old system, just adding to it) would allow for quicker turnaround from slicing to printing, better profile management, and better print tuning and tweaking.

- The only actual issue we believe we have run into is that of stacking modifiers. It seems that multiple modifiers are able to stack their effects on the print speed, typically causing much slower speeds than intended. This is most noticed on the first layer of a print, where the First Layer Speed modifier stacks with Outline Underspeed, Support Structure Underspeed, Rafts, etc.
------ We have found that there is a lowest speed threshold that our printers can print adequately, and we try to avoid going below that. Also, on the first layer, for best adhesion, we want to have the speed as close to that threshold as we can go, especially for materials that need help with adhesion. The issue is that when modifiers stack their effects, some features such as support print slower than that threshold. Currently there is no good solution to this, as it would require printing far enough above the threshold to account for this or to remove some modifiers.

- The reason we would like the absolute speeds the most however is for easier setup and tweaking. As we said, we like to have a set first layer speed that stays the same whether the rest of the part is being run slow or fast. Currently, anytime we change the default printing speed, we have to do the calculations to find what percentage will give us the first layer speed we want. This takes time in our regular workflow, but becomes a serious issue when we want to tweak a single variable, such as the default print speed, for testing, as we have to make sure to recalculate all the modifiers to be the same absolute speed.

- Even on something such as the speed reductions for layers below a certain time, it makes more sense to have that value as an absolute minimum speed, rather than a percentage. As it is now that value is essentially an absolute speed unless it gets modified by other speed modifiers, which again can cause problems.