McWire After Build Issues

Some short comings of the McWire design have shown themselves after the build.

The first one concerns the method of attaching the drive screw to the Z sled. I seems the constant pressure on the tape covered coupling nut made the tape move over time. It telescoped out until the holding pressure in the conduit ran out. Then slipped out of the strap.

My solution was to build a bracket that presses the coupling nut against the Z sled, holding it in place. Overall this is a better way to go as you can adjust the height from the Z sled with a shim to get the drive screw parallel to the sled. This was a pain to do with the tape wound design.The X and Y have not been changed out but I will use the same solution if they become a problem.

The bracket material came from an L bracket that is used to hold drapery rods. A piece of 1/8"thick aluminum would do as well. It's held in place by 2 - #10 screws and tapped holes in the sled.

Another failure that has been occurring is breaking swing arms. They are not standing up to the task. I think it is the constant pressure of the spring and the size of the 5/16 hole plus counter sink relative to width of the swing arm. I have reduced the spring pressure as low as I fell comfortable with but failures are still occurring. I had 4 spares made when I ordered the laser cut parts and those are used up and now I am making parts to replace them.

I think the newly designed swing arms are working great and are easy to build. I used 3/16" press board because that’s what I had on hand. 1/4" thickness might be better.  1/8" aluminum would work nicely.

To make one of these :

1. Use a template to mark the outline and hole locations. 
2. Cut it out roughly with the outline markings and the drill 1/16" pilot holes for all 3 holes. (larger for aluminum)
3. Drill the clearance hole (23/64") for the 5/16" bolt holding it to the sled.
4. Mount the bearing with a small washer (M5) under it using a dry wall screw. 
5. Screw in a #2 sheet metal screw to hold the spring.
6. Dremel off the length the the screws protruding from the other side and grind them down just below the surface so the don't scratch the plastic on the sled.
7. File the shape of the swing arm down to the outline marks. 

McWire Laser Cut Files

Well, I have decided to get laser cut parts instead of using that piece of MDF that I had in my shop. I just received an order of laser cut parts for 3 small projects I've been working on. I love that it comes coated in paper that you can scribble notes on while you do the initial fit. I think it was the look of acrylic that did me in. Taking off the paper and revealing the plexi is like uncovering a diamond. It's shinny and mesmerizing.


So, given all that, I down loaded the files for the McWire V1.2 from SourceForge.  In all the files looked pretty good to me but there were some changes I wanted to make. They are the following:

1. The layout file were scaled in millimeters. Since I mostly work in imperial units I scaled it down by 25.4. Note: If your CAD system accepts LISP commands as input this is easily done by entering in (/ 1 25.4) which calculates 1/25.4 instead of typing in a bunch of digits that is prone to error by rounding or having fat fingers. 
2. The LIMITS of the files was change to 11.75 x 23.75 inches. 
3. The parts were rearranged for more efficient laser cutting -  combining edges of the same type of parts to save on cutting time.
4. The text and shapes that were to be etched were removed - again to save on cutting time.
5. Two of the smaller parts were added as spares. Yes, It's adding cost but I think it is value added. I hate to be dead in the water because of breaking one part... or even two.

Anyone is welcome to use these files. They are in AutoCAD 2004 DWG and DXF format. I also scaled a copy back up to millimeters for those who use the saner form of units.

They can be found at: XYZ_Layouts.

If you use these, please let me know if there are any bugs in them.

I placed in a request for quote at Pololu for the XY and the Z layouts. I did not find information about thickness on the McWire page. Searching the forums I found an estimate of 1/4 inch so that’s what I went with.

I can't wait until all my parts arrive! I will be finishing up my 3 small projects. That should keep my build addiction satisfied until then.