The MesoMill

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The MesoMill

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

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

• The spindle is likely to be the heaviest single
  component in the machine, so DONT 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.

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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 machines structure
• Star Linear makes a wide range of linear motion
  components which can be used to move the axis of
  the machine.

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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

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MesoMill Concept
Star Super Structure
NEMA 23 Motors
X Axis Counter Weight Not Shown
Star Compact Modules
FPS 2.2 kW Spindle
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ConceptCustom Parts
(4) Compact Module Attachment Fixtures (may not
be needed)
(3) Motor Mounts
(1) Spindle Mounting Block
(1) Work Table
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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...
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Motion Module Mounting for Concepts 1 and 2
My Method

• 5 Degrees of Freedom Elastically Constrained
• Interface Errors to do 3 surface interfaces
• 12 Fasteners Needed
• Alignment Dependent on Custom Plate

Using Stock Parts From Star Linear

• 2 Degrees of Freedom Elastically Constrained
• Interface Errors to do 8 surface interfaces
• 24 Fasteners Needed
• Alignment dependant on initial alignment of
  machine.

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MesoMill Component List
Purple Star Linear Parts, Blue Still
Deciding on Specific Parts, Yellow Custom Made
Parts
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Estimation of MesoMill Alignment Errors
Most of the errors in the MesoMill will be due
to misalignment of the components

• 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.

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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.

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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