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Z axis construction

Now we are going to try something different.  I did not want to use bearings to run the Z axis.  I wanted something cleaner and more compact.  Using the same aluminum angle idea I decided to make some bearing blocks from UHMW ( ultra high molecular weight polyethylene).  Its cheap, easy to machine and provides a stable smooth running surface.


Not knowing exactly what I wanted I did a prototype to test how much pressure I would have to put on the blocks to get a smooth running slide.  I built what would be the final router mount.  The brown stuff is leftover composite decking  It is a lot like MDF. Machines the same and is a bit soft.  The white piece is a piece of PVC molding scrap.  The router mount is about 5.5" wide by 12" long.  I cut the PVC smaller in width to give room for the UHMW blocks and stay within my 6" Z axis width.  You will see below there has been some clearance machined into the decking.  This is for the bearing.  I have not done the PVC at this time.  The aluminum is only 1/2" wide instead of 3/4" like the other slides. 

The PVC was chamfered like all the other slides.  The aluminum angle was then glued (liquid nails) to the PVC.  I then glued the PVC to the decking.  Note the screws again. I like screws. I trust them but not the glue.  :)  The UHMW was screwed (no glue) to a piece of plywood.  I clamped the whole thing together to test the needed pressure.  I was surprised to find very little needed to make things run smooth but keep them in line.  Notice the UHMW blocks don't run the full length of the slide?  There is no need as they will be at the bottom where all the action will be.  Making them longer would be a waste and possibly create binding as the slide is fully retracted.

Here is a pic of the whole assembly.  A simple split clamp for the router mount.  i will use wing nuts to replace the hex nuts for tightening.  There is a 1/4" T nut embedded in the back of the decking (see pic1 right side)  This holds the 1/4" threaded rod in place.  The back portion of the clamp is bolted to the slide and locked in place with nuts.  The front part of the clamp is free to float. 

I have a Porter Cable 690 router.  1.5 hp  It should be plenty of motor for this machine.  It will take up to 1/2" collets.  I also have a Harbor freight trim router for smaller jobs 1/4" collets.  I have not made a clamp for it.  It will sit in a second split ring which fits the main split ring.  This will keep the center of the cutting bit the same for both routers.  Should make it simple for tool changes until I design my own tool changer.  Not yet done is the vacuum assembly that will bolt to the bottom of the router mount. 

One thing I have noticed is people using dremel tools for cutter motors.  They are great for small jobs detail work but will take forever on most jobs.  Larger cutters are often cheaper more stable and produce final product much faster than any dremel size bit.   

Here is the first pic of the final Z axis assembly.  I used some aluminum extrusions I had on hand.  The profile creates a nice tight fit around the UHMW.  I currently do not have any mechanical fasteners holding the UHMW blocks.  They have not moved during testing.  I can always add a screw if needed.  ;)  The aluminum, UHMW and slide were clamped together to get a final measurement for the MDF spacer between the aluminum.

A side profile of the slide.  The top section between the aluminum is empty.  This gives me a lot of room to mount the Y axis drive nut.  It also makes the whole assembly much narrower keeping the weight closer to the Y axis slide. The aluminum is screwed to the MDF spacer on the bottom.  The same at the top.  The top piece of MDF is long to support the motor and mount.  The back is held together with a piece of MDF and my homemade barrel nuts.  No pic yet as I am having a bit of a problem with them.  Its the simple things that get you.  ;)



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