Month: March 2013

Assembly Starts

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I still have a few design details to work out, but I’ve gotten anxious to see some metal take shape. I started with cutting all of my aluminum extrusions to length. I installed my new blade on my miter saw and checked to see that it was square in both directions. The built-in clamp was too wide to properly hold the 20×20 extrusion so I used some quick clamps instead. This was an 8 ft long piece so I supported the far end with the table from my Woodmaster Multi Tool (the original Shopsmith).
I noticed after a few cuts that the ends weren’t getting cut quite as clean. I took a look at the saw blade and picked off a few aluminum chips that had gotten stuck. Then I used some wax lubricant on each tooth and also put a bit along the cut line of the extrusion. For each subsequent cut I just lubricated the extrusion. Things seemed to go very cleanly after that.

I checked the ends with a square and they seemed fine, but I would later find out that they weren’t quite good enough for one location. The length came out very close; within half a mm.

All the extrusions, ready to go:

 I was getting ready to tap one of the MakerSlide extrusions for the X-Axis when I accidentally pulled my clamp apart too far and pieces went flying so I had to take a quick detour to figure out how to get it back together. This was NOT how it went together:

Finally I think I got it back in order:

I clamped the end of that quick clamp in a vise and then clamped the MakerSlide and a scrap piece of 20×40 extrusion in the quick clamp so I could tap the end. Here I’m using another small piece of extrusion with one hole drilled out for clearance for an M5 to help keep my tap square.

I also decided to put a transfer pin through the other hole to keep my tapping guide in place while I worked.

After the holes were tapped I bolted the carriage plates to the end of the X-Axis and checked them for perpendicularity. This is the only spot where I really needed to be concerned with being square because this will determine how square my X axis is to my Y axis. Unfortunately it wasn’t very square:
It’s cold out and I didn’t really feel like getting my mill ready to clean up the end so I decided to shim the extrusion with some aluminum foil. Six layers did the trick here and brought my extrusion square with the carriage plate.

Next I needed to adjust the length of some spacers I bought. McMaster didn’t happen to have a 13.35mm spacer so I had to make due with a 14mm one. (This is what happens when you mix English and metric parts.) I tried using a bit of sandpaper on my bench and rubbing the spacer on that, but I couldn’t keep it perpendicular. Next I tried resting the spacer in the slot of some scrap extrusion and using my disk sander and a miter gauge. This worked pretty well except on the second spacer when I over-achieved and had to use a shim washer to make up for the extra mm I took off. I used my thumb to press the extrusion to the miter gauge and my forefinger to slide the spacer into the sanding disk.

Using my spacers and lots of other hardware in my fancy parts bin shown in my last post, I started assembling the X-Axis assembly.

The lower wheel axle is quite a pain to get together because it has two eccentric spacers which protrude into the aluminum plate. Therefore you need to leave the top screws loose a bit so you can open up the bottom of the plates. I have a feeling this will be a pain to adjust later too.

Next I started laying out my bottom frame pieces. I used an old mirror I had to act as a flat build surface. I added some extra T-nuts into the extrusion before I tightened the ends. It’s easier to ignore them later than to unbolt everything to add some.

I did the same with the top frame. Here I had to use some vise parallels to keep the V rails of the MakerSlide extrusions off the flat surface.

Before I tightened the left end of the frame down, I made some measurements to make sure my Y-Axis MakerSlide rails were parallel. I noticed that once I locked down three corners, the forth had a bit of spring to it and didn’t want to rest closed. I flexed it into place though and I don’t think it will cause me trouble.

Next it was time to add the legs. The design calls for the lower frame to rest half an inch above the floor so that a wooden milling surface can be placed underneath. I neglected to build my wooden plate first to space the lower frame, so I had to make due with some half inch aluminum jig plate instead. I also added some L-Brackets loosely near the top in preparation for the upper frame.

To rest the upper frame in place before I tightened everything down I used some quick clamps on each leg. Then I measured and tightened each corner down.

Finally I added the X-Axis assembly. I had to remove the lower wheels and then replace them after I rested the assembly on the upper frame’s Y-Axis rails. So far it’s looking just like how I designed it. The Y-Axis movement is very smooth. My goal is to finish the X and Y movement and get my electronics in place before I start fabrication of some of the trickier Z-Axis parts.

Lessons Learned

  1. This assembly will definitely need some adjustment screws for leveling the top frame to the build floor. I should be able to incorporate something without much trouble though.
  2. My miter saw did not cut square enough after a basic setup. It would benefit from a proper zero-clearance fence and floor insert. I knew about these things, but I didn’t have the right material to make one and was lazy.
  3. Surface mounted angle brackets would have been better for the top and bottom frame assemblies. (The ones that would sit on the top or bottom of the frame rather than on the front or side.) This would eliminate the need for an elaborate flat surface with vise parallels in assembly.
  4. A little wax lubricant helps quite a lot for cutting aluminum with a miter saw.
  5. Aluminum foil is a handy shim stock.

Parts!

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I recently received the remaining parts I’ll need to build my desktop fabrication machine: glass for my build plate, a bunch of metric hardware, heat resistant tubing, timing belts, tiny drill bits, spacers, an M5 tap, 20mm T-slot extrusion, and some aluminum angle (architectural):

McMaster was incredibly fast at getting the parts out (as usual). I placed my order at 11pm on a Sunday. At 11:30 that night I realized I forgot to add something so I emailed them. They were able to add it and my whole order was out the door before 7am Monday and at my door on Wednesday.
Harbor Freight had a nice plastic organizer on sale. Things look so much more awesome when neatly organized. (Pay no attention to the mess behind the box.)

I bought some more hangers to store my extrusions in my garage too. That’s my MakerSlide stock in front.

I also picked up a saw blade for cutting the extrusions and some drive pin punches my “reman” activities.

Cartesian Robot Takes Shape

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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:

[youtube https://www.youtube.com/watch?v=vgAIgSvzitE&fs=1&source=uds&w=320&h=266]

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.