I’ve been doing quite a bit of work lately in sorting out the details of my Cartesian robot. One of the big things to do was to make sure I know what all my stock lengths will be and find out how much aluminum extrusion I will need to buy. I was certain SolidWorks custom properties would help me out, but it did end up being a bit more complicated than I thought so I’ll post it here.
First, all of my extrusions have a base SolidWorks part and configurations for each place they are used. In addition to having a column control the extrusion length, I also added the $PRP@StockSize field. This will automatically populate the file property StockSize with the values in the column:
This saves the trouble of having to manually fill in each Configuration Specific file property. Here you can see the same value from the Design Table showing up in the File->Properties window:
Note: Another way to do this without using a design table would be to open that File Properties window and type the following expression under the Configuration Specific Properties (including quotes):
“Length@Boss-Extrude1@@SlideZ@maker_slide.SLDPRT”
Using that above method you could pick different metrics to represent the StockSize in different configurations.
Now onto the Bill of Materials. I created a drawing from my top level assembly with an Isometric view and inserted a BOM. I choose the “bom-stock size” because it already had a column ready to accept StockSize properties. Also, some of my extrusions are within sub-assemblies so I wanted an indented BOM. Finally I said that my part configurations could be grouped only if they had the same name, like “Leg”:
The result was very messy for a real drawing, but it was just the BOM I was after. You can see that many parts don’t have a StockSize, but all the extrusions do (though some are off screen, and off page…):
To get the BOM in a more workable format I right clicked the BOM item in the Feature Manager and clicked Save As to save an external xlsx file. Note: The part names looked funny with weird characters at first, but when I made all the font Calibri everything looked fine again. Now I used some fancy new Excel tricks I learned to sum up all the stocks. In the case of the MakerSlide extrusions I made this formula:
=SUMIFS(F10:F110,B10:B110,”*”&”MakerSlide”&”*”)
Where Column F contains the QTY * StockSize and Column B is the Part Number (or name). The first argument in the function is the range of values that will be summed if the criteria is met. The second argument is the range of values on which to check the criteria. The third argument is the actual criteria, which must be in string form. Here I am building a string with wildcards and some text (“MakerSlide”) that I know will be in the names I’m looking for.
Of course these summaries don’t take into account wasted material from cuts or limited base stock lengths, but it is helpful.
Back to my 3D Printer/Desktop Manufacturing machine:
My build area is going to be about 14.7″ x 12.7″ x 7.6″. This puts my entire machine size at a just-barely-desktop-sized 28″ x 22.15″.
I decided on using belt drives for X and Y. The drive setup will be similar to a Shapeoko desktop mill. I will be using larger Gates HTD 3mm pitch x 9mm wide belts. The image below is a sectioned view from the back of the XZ Shuttle. You can see the belt running under the idler rollers then up over the black pulley in the center.
For the Y-Axis I have two NEMA 23 steppers which will be driven from the same driver board. I would have rather run a shaft across from one to a bearing-mounted pulley, but that proved to be more complicated than it was worth at the moment, seeing as I have plenty of steppers. A shaft in the current setup would interfere with my X axis pulley and my Z axis lead nut. I could flip the Y motor carriage plates upside down and run the shaft underneath the X axis MakerSlide but then the eccentric wheels will be on top. I didn’t like the idea of those eccentric wheels constantly feeling a weight that would act to work them free.
For the Z-axis I have a very similar design to the Shapeoko’s Acme Z-Axis upgrade. I happened to have a leadscrew and nut of about the right size though, so my travel will be 0.3″ per rev vs Shapeoko’s 0.083″. If I find this is too much I can easily buy some acme rod from McMaster.
Another key difference is that my leadscrew passes behind the carriage plate. This allows me to get my Z-axis MakerSlide (and supporting wheels) closer to the carriage plate. I think this will give me a more rigid setup. The bearings are simple 608 skate bearings and are held away from the center of the MakerSlide (in the Z direction) by some aluminum angle mounted underneath. These bearings could be pressed in to the top and bottom caps like I’ve seen in other designs, but I didn’t like the idea of not having a hard stop.
The leadscrew is held in place by the machined shoulders. It will be turned down to fit through the bearing’s bore. Below you can also see a simple model of a 7.2V battery powered Dremel tool that I plan to use as my first cutting spindle. This will help me make some simple parts for my extruder design (TBD).
One final tip: I was looking around trying to find Delrin Acme nuts for cheap. I had no luck at all and (until I realized I already had a leadscrew and nut set) I was going to buy a tap and make my own. If you’ve ever looked for Acme taps you’ll know that they are ridiculously expensive. Well, I was reminded of this simple but effective way to make your own taps. Check out this video on making an Acme tap using only an Acme threaded rod and some simple tools:
Even though this tap won’t be nearly as nice as one you can buy for $60 or more, it will certainly cut Delrin and brass.