The MesoMill™ An Off-The-Shelf Small Milling Machine By Roger Cortesi MIT Precision Engineering Research Group

The Goal of the MesoMill™ is to quickly build a small desktop milling machine

MesoMill™ Design Observations The spindle is likely to be the heaviest single component in the machine, so DON’T fight gravity, make the machine horizontal. Because of the small tool sizes used, the compliance in the tool will be much larger than the compliance in the machine. Because of the two conditions above, the predominate errors will not be from structural deflection. They will be from alignment and accuracy of the linear motion elements. So MINIMIZE the number of interfaces when connecting components.

Components This machine is the extreme of building a machine from off the shelf components Star Linear™ makes modular structural elements that are used for the machine’s structure Star Linear™ makes a wide range of linear motion components which can be used to move the axis of the machine.

MesoMill™ Features 120 mm (5 in) work cube Overall Dimensions of 750 x 400 x 300 mm All Compact Motion Modules are the same for cost savings Minimal custom parts needed

MesoMill™ Concept FPS 2.2 kW Spindle Star Compact Modules Star Super Structure NEMA 23 Motors X Axis Counter Weight Not Shown

ConceptCustom Parts (1) Spindle Mounting Block (4) Compact Module Attachment Fixtures (may not be needed) (1) Work Table (3) Motor Mounts

There are two possible methods for mounting the Compact Modules™ to the Super Structure™ This is an open design issue that still needs to be resolved… Two possibilities are outlined next...

Motion Module Mounting for Concepts 1 and 2 My Method Using Stock Parts From Star Linear™ 2 Custom Plates Needed4 Mounting Bars Needed 2 Mounting Plates Needed 5 Degrees of Freedom Elastically Constrained Interface Errors to do 3 surface interfaces 12 Fasteners Needed Alignment Dependent on Custom Plate 2 Degrees of Freedom Elastically Constrained Interface Errors to do 8 surface interfaces 24 Fasteners Needed Alignment dependant on initial alignment of machine.

MesoMill™ Component List Purple = Star Linear™ Parts, Blue = Still Deciding on Specific Parts, Yellow = Custom Made Parts

Estimation of MesoMill™ Alignment Errors The very rough estimate for the errors due to the roll pitch and yaw of the carriages is about 30 microns. If the L structure is perpendicular to 5 arc seconds this will add about another 10 microns of error at the tool tip Still need data on the super structure straightness… Still need data on the actual roll pitch and yaw of the carriages The big question is are these alignment errors repeatable? If so they can be corrected by the controller. Most of the errors in the MesoMill™ will be due to misalignment of the components

MesoMill™ Market Rapid Prototyping In “Field” Work –Shipboard, Oil Crews, etc. Education –the 5 inch work volume and 75 micron accuracy goal are consistent with most university needs. –Can be sold in “kit” form how about a multi university contest on who can build the most accurate machine using the “kit” –Can be used to teach all sorts of mechanical engineering, electrical engineer and control stuff –Could this be the hardware element that makes the international design contest truly international? By allowing cross national teams to work on concepts and ideas apart and then come together? A standard for CNC controller companies to compare their equipment on.

Motor and Controller The MesoMill™ currently has a NEMA 23 motors with a custom motor mount to save a little space. These could be replaced by the motors out of the Compact Module™ catalog to allow building to go even faster. We still need to select a controler