Upper Frame Assembly

Well, the box from MTW arrived a few weeks ago, and last weekend we had the time to sit down and check the components.  One of the two sets of 8mm rods appears to have just enough of a bow in them to be unusable.  This morning I've filed a ticket with MTW to see what can be done about this, but, meanwhile, I have put the Misumi extrusion corners to work.

It struck me as odd how, in the Build Guides, a complicated blind-drilling and special Torx fasteners are used to fasten to cross-members to the upper frames.  This, and the use of printed braces across the corners seemed to me, at least, to be a strange approach to which an inexpensive solution is already available - extrusion corners.

The order of assembly I followed is definitely not standard, as the constraint problems to be solved are different for this assembly technique.  The steps below achieved the best results without too much fiddling.

Start with four extrusion corners.  Check they are square, and smooth off any molding flash with a good file so they are clean and completely square.

Next, take the cross-members.  Install an extrusion corner onto each end of the cross-members loosely enough to slide into position using 5mm X 10mm SHCS with a flat washer.  

Since I installed my corners on the inside of the frame,  my next step was to measure from the end near where the corner was attached a distance of 80mm.  Tighten the corner gently (not fully, just enough to hold them still) such that its vertex is at this distance from the end.  Repeat with the other end of this cross-member and another corner.  (If using corners on the outside, measure 60mm.)

Build the other cross-member exactly as this one.  Once this is completed, check your corners are on squarely, and all are at the same distance from each end of each member.  Adjust as necessary.

Now it's time to assemble the uprights.  Attach one upright to each end of a cross-member with 5mm X 10 SHCS with a flat washer on each.  Tighten these screws gently.

Once both uprights are in place, use your square and check they are square by placing it in the vertex opposite the extrusion corners.  If adjustments are needed, be sure to check both squareness and distance.  Once adjustments are complete, tighten and recheck.

If the corners are placed correctly, the outer edges of the uprights will be at 60mm distance from the outer ends of the cross-member, and the inner edges of the two uprights will be 260mm distance from each other.

Repeat these steps for the other cross-member and uprights, then, when all is checked and squared, place the two assemblies side by side resting on the top surfaces of the cross-members, with the uprights sticking up. Compare these assemblies to each other - they should be identical in all respects.  If not, check, tighten, recheck, and adjust as needed.  The 260mm dimension is the crucial one as this is the width of the frame to which the uprights must attach.

Once both upper frame assemblies are built, check the printed parts for the lower vertices.  The inner and mating bottom surfaces should be true, straight, and free of any plastic flash which might interfere.  Trim as needed, then proceed.

Now trap a T-slot nut in the forward facing and outboard sides of each upright and attach the lower vertices onto the ends of each upright, trapping the T-slot nuts, using 5mm X 10mm SHCS.  (On the parts I had, a flat washer would not fit in the recess, so I tightened snugly, but not overly tight.  This should not be a big deal.) 

When installing the vertices, it is important they face the same direction on both uprights.  (Yeah, I started one backward... caught it before I was done threading up, though.)  I used 5mm X 10mm BHCS (button heads) with flat washers to fasten the  sides of the vertices to the sides of the extrusion using the already trapped T-slot nuts.

The resulting assemblies may now be mated to the lower frame using the T-slot nuts already trapped there for the purpose during assembly of the lower frame.  I used 5mm X 10mm BHCS with flat washers here, and found them to be of positive benefit - my 3mm hex key had a lower profile and better clearance on the inner side of the vertices than did the 4mm used for SHCS. This allowed for faster assembly with less re-positioning between wrench turns.  At this point, tighten the screws gently.

Once both upper frames are in place, check for square with respect to the lower frame and with each other.  If it is not possible to square them in both respects, something is wrong - check your upper frame assemblies and the lower frame, and adjust as needed to bring both into true squareness before proceeding.

Finally, integrate the two upper frames by installing the end supports to couple the cross-members.  Remember to trap the T-slot nuts needed before installing the end pieces.  After both ends are in place and loosely fastened, check again for squareness and that the cross-members are running parallel to each other.  

Tighten and re-check. Adjust as needed.

Once everything is assembled, it should look something like this:

Here's a side view:

 As can be seen, the Y-Axis slide is not yet mounted on the support rail.  This is because we do not yet have the parts in hand.  Once these parts are ordered and arrive, the real fun will begin - installation of the motion components!

At least now it's starting to look like a MendelMax!  Resolution of our trouble ticket and getting the Y-axis gear in hand will get us to the point we can start installing the rest of the mechanicals.

From there, it looks like motors, leadscrew development work on the Z-axis, (yeah, we're experimenting here as I may have already mentioned), and then electrical and electronic controls will complete the assembly.

Tony has diverged, and is working his hybrid Max/Max 2.0 design, so I will be following his work as he progresses.  I am intrigued by what he has put together so far - it has the potential to be a very solid design, and one that existing MendelMax users could easily convert to if desired with just a few printed parts, some  extrusion corners and a bit of re-assembly.

That's it for now.  Next time, look for info on the installation and setup of motion components.

Upper Frame Mounts Ready and Emergency Stop Feature

First things first:  many thanks to my build buddy, Tony, for providing me with parts printed on his Prusa at no cost (he wouldn't even let me pay for filament).  Without his kind assistance, I'd be buying printed parts, and that would drive up the cost of my build tremendously.  I suppose this means that the next round of printed parts will be on me after I get the Max up and running.  Believe me, I'll be more than happy to print for Tony or for the next friend of ours who wants to join us in the adventure that 3D printing has become.

The latest addition to my inventory are the four vertices for the upper frame members to attach to the lower frame.  With these in hand, at least the frame can take shape, and my experiment on the upper cross members can commence.

That will come later (probably this weekend).  I just wanted to take the opportunity to say, "Thank you, Tony" for all the parts!

While I'm here, we had the chance to chat briefly at work about the Emergency Stop feature I want to implement on our printers.  Tony tells me the Sanguinololu controller can issue the appropriate commands to control an ATX style power supply unit.  This means we could also implement a system stop feature in software, too.  As of now, our plans still include a hard-wired "hot loop" to stop the motors and extruder when the E-stop is depressed.

I'm thrilled to be moving forward on the build again.  It looks like our next move will be the acquisition of the Y-axis slides, then the rest of the motion components (GT2 belts and pulleys, stepper motors, etc.)

Gotta run for now, or I'll be late for work (there's that four-letter word again!)

 

Y-Axis Bed Support & Other Stories

It all started after the package from MTW arrived...  

(See last post)

This was a relatively small box, but it contained, in addition to most of our X and Z motion components, the Misumi extrusion corners I've been so interested in trying out.

I brought the box to work with me, and Tony and I wasted no time in divvying up the stuff - rods, linear bushings, etc.  When Tony first saw the Misumi corners, it was apparent he'd figured out why I ordered four extras.  It started him on a path of experimentation which I might pursue a bit later on, myself, after this project is up and running.

The way he tells it, he got to comparing dimensions on the upright frame members between MendelMax 1.5 and 2.0, and, finding them to be similar, decided to experiement with some printed parts from the MendelMax 2.0 to create something of a hybrid.  It might be better, though, if I just show you, though, since Tony was good enough to take a couple of pictures:

Here's the side view:

and a view from the front:

An observant reader will note the use of Misumi corners at the rear of the frame.  Tony was impressed with how much more rigidity the frame displayed just from using the corners to join the pieces together.

As I said, this line of experimentation has promise, but I will be pursuing a path to a more conventional MendelMax 1.5 with only a couple of minor tweaks.  As this experiment continues, though, we will cover it here.  Who knows?  A resounding success might convince me to change my mind, but it's too early for that yet.

So... I mentioned the Y-Axis Bed Support?  I dug out my lower frame assembly (which I had left sitting on a flat surface under some boxes during the long wait) and put it on the glass top of the kitchen table, fully expecting it to still have that slight twist I mentioned.  Nope... all nicely flattened out.  This being the case, I went ahead with installing the bed support extrusion.

It's been a while since I worked with extrusion corners, and the ones we got from MTW were cast.  They're accurate enough (they checked square), but had some sprues left from casting that I took a file to and smoothed down, just for appearance's sake.  (My prior experience with extrusion was with Bosch stuff - very high quality/very pricey.)

After knocking off the rough spots, I mounted the corners onto the inside of the frame, using the already trapped T-slot nuts staged for this purpose during the Lower Frame assembly, and 5 mm X 10 mm socket head cap screws.  

With the corners loosely in place on the frame, I first lined up one set of corners  loosely to the left side of the bed support extrusion.  (It's worth noting that having the extrusion pre-cut to length accurately by Misumi was a real time saver, as it avoided any misalignment.)  After this was done, I started the other set of corners on the right side, running them up loosely, also.

Now began the process of measuring and aligning the support extrusion to be square and centered in the frame.  I started at the back of the frame, measuring 150mm from the centerline of the extrusion to the outer edges of the frame on each side using a good steel rule.  

When I got this end in position, I began running up the screws, gently at first, and re-checking alignment as I got gradually tighter.  To assure repeatability of the measurements, I checked along the entire length with the rule now clamped in a combination square attachment.  

So far, so good, but as I got closer to the front end, I found I had to apply a bit of pressure to get the front end to line up with it.  (There was about 1 mm worth of deflection needed to square it up.)

Rinse; repeat.  Running the screws up at the front end gently, re-checking as I tightened a bit more.  Now the square and rule showed good parallel measurements on both sides for the entire length.

Finally, tighten all screws and re-check.  All is nice and square, true, and parallel.

Except... an almost imperceptible twist in the frame...  Oh, well, back under the boxes until the slide and my upper frame mounts are ready.