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X axis construction

Before we get to the construction some info about tools and materials. 

I will be using MDF (medium density fiber board).  It is a composite material consisting of fine wood dust and resins (glue).  This is not to be confused with particle board.  Also a composite made with saw dust and resin.  Both have their uses and faults.  Both will swell when exposed to water, make a LOT of dust and are heavy.  Both will sag if unsupported.  MDF is more stable, dimensionally more accurate and more $.  MDF is quite soft around the edges so be careful when handling it especially after you have cut a piece to final size.

Tape measures are great for building decks and dog houses.  They are NOT for building precision machines.  The hook on the end is often loose and can give a false reading of 1/8" or more.  Since we are relying on the panels we cut to also be the linear slides 1/8" will create one HUGE problem for final fitting.  We will be using rulers and gauge blocks for construction and setup.  Rulers come in many lengths available in the tool section of Xmart, Lowes, hardware stores.  They are a cheap investment.  Gauge blocks you make from scraps.  This project can be done with a circular saw and known straight edge.  A table saw would be ideal.  If you are relying on some one at the home center to give you precision cuts good luck.  On a good day you might get oversized cuts that are mostly square.  You will not get precision cuts needed for this project.

If you read my design plan you know I want a 24" x 48" cutting area.  MDF is a dimensionally stable and strong material.  It is POOR at support for long spans.  Much over 18" and you will need some kind of structural brace.  So how do we solve this issue?  Its called a torsion box.  This is nothing more than 2 outer skins with spacers in between.  The interior doors of a modern house are a torsion box.  The spacers can be most anything as they aren't the whole reason the box is strong.

I cut a piece of 25" x 49" MDF.  I then cut 4 pieces of 2.75" x 49" MDF for runners.  The rest of the interior structure is made from scraps of particle board I had on hand.  You will notice I am actually building 2 torsion boxes.  The gap in between is where I will run the X axis lead screw and nuts.  In this pic I have completed one side of the bed.  The other side shows the spacers of the torsion box.  All these blocks were glued and nailed together with a nail gun.  They were then glued and screwed to the MDF runners.  The final assembly was then glued and screwed to the top of the bed followed by the bottom boards.  Some say you dont need the screws.  This is a machine with vibration and movement.  I like screws.  :) 

This whole machine is based on the parts also serving as the linear slides.  Keeping sides parallel is imperative.  I plan on running the Y axis on the bottom boards of my bed.  But I have this gap between those boards.  So how do I insure both sides are parallel?  Here we make two of those spacer blocks I mentioned.  I measured the gap between my 2 torsion boxes.  I then cut 2 pieces of scrap pine a little longer.  Clamp these together and cut a notch at each end till I get the exact distance I want to space my bottom boards.  Here you can see one spacer at one end of the machine with a clamp.  There is on at the other end with a clamp.  Measure the outside edges of the boards and you should get exactly the same measurement.  Glue and screw.  :)

We can see the 2 torsion boxes with the gap between them.  The Y axis supports ride on the rails which are mounted to the bottom boards of the torsion boxes.  Why such a wide gap?  I want 24" of Y axis movement.  I figured my Z axis would be around 6" wide.  To allow the center of the router to reach the edge of 24" wide panel I will need 3" on either side of the machine.  So the Y axis support is about 30".  I say about because you will not know until you have assembled your bearing trucks, routed your chamfer on the panel and installed your aluminum angle.  Placement of the bearings, thickness of the aluminum and the depth of the chamfer all effect the dimensions of the final assembly.  There will be end panels that lift the machine off its table and support the X axis screw and motor.







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