Machining a large workpiece in one setup
Designing machines you have, or certainly will, encounter that you need to machine a large stock of material on the mill. Large workpiece is typical for machine structure. Any large piece of stock for you will want to machine in the minimal number of setups. Ideally in just one setup but this is more often than not not possible. Machining large workpieces can be made very expensive by poor design. Here are some things to consider whend designing with large parts.
There are some things to consider when designing a large pieces of the machine so that it can be easily setup and machined
First thing, and the most obvious is to check the maximum workpiece size that machine that you plan to use has. This is a spec that is easily found for every machine. For example the maximal travel of the axes for this HAAS VF-4 is 1270 x 508 x 635 mm. But these are not the maximal dimensions of the workpiece, they are smaller.
Clamping the workpiece
First you have to take into the consideration that the piece has to be clamped to the table. Most usual clamping system is with clamps.
The table is usually larger than the axis travel so this is not a problem and If the workpiece has holes cut out that are distributed well enough that the hold-downs can be set up so that they do not eat into the space of the machine travel. There are workarounds but this is something to take into the consideration.
Large workpiece -Tool path
Second thing and the one not so obvious is that these numbers are the maximal travel of the axes and not the maximal parameter the tool can make. You see, every tool has a diameter and therefore in order to machine a side the tool needs to be offset from the workpiece and this eats up into the space.
The compensation for the tool needs to be factored in. When machining a large workpiece, or lets say a plate, it is usually of a larger thickness, so more rigid end mills need to be used. Let’s say that the plate is ~50mm thick. To easily machine the sides with a good surface finish you would need an end mill of at least 20mm diameter. Also this tool needs to lead into the part too. Depending on the setup and the machine this also needs to be factored in. All of this means that the maximal workpiece is shorter per axis at least for the diameter of the tool.
So when designing you need to consider following things:
- The maximal travel of the axes on the machine that will be used for machining.
- How will the workpiece be held-down. Does this eat into the workpiece size
- Considering the thickness of the plate, what is a minimal endmill diameter that can easily be used and what is the tools ramp in. For the maximal workpiece dimension that is close to the maximal machine travel subtract the diameter of the endmill (2x radius for both sides)
Last thing what if the part needs to be bigger than the machine’s workable size?
Then you can combine a few more manageable plates and connect them together. There are many ways to connect the plates (workpieces) but this is something that will be mentioned in the future blog posts.