CNC mill conversion - part 27

Limit switch covers 

One thing I put off for a long time since I installed the limit switches on the mini-mill, was fabricating covers for them. While the switches have been working reliably for a long time, I do get the occasional chip and coolant spray hitting them, and I’m sure this might end up creating a problem eventually.

Since I now own a 3D printer, I thought it might be a perfect opportunity to make something useful with it, and knock one more item off my to-do list.

I developed a “neutral” design, basically a box around the switch, then modified it as needed for each individual axis.

Generic switch cover

The Z axis needed to have the wires coming out of the side, so I changed the hole location in the design.

Modified cover fitted to the Z axis limit switch

Wires coming out of the back side

The Y axis needed to have the wires come out of the back, but a couple of mounting bolts were in the way, so I removed the rear and bottom faces completely, so that swarf and coolant could not accumulate within the switch case.

Y axis limit switch cover

Rear and bottom sides removed

A few minutes of testing of these two covers proved the concept a complete success, but now it would be on to the “difficult child”... the X axis.

I have to admit, I have been plagued with some issues stemming from my choice of X axis limit switch position. I still think the concept is sound, but the implementation had some unintended complication, the biggest one being the tendency of the roller to occasionally snag one of the GIB’s adjustment nuts (seen below underneath the switch's red case) bending the switch's arm into a pretzel. I was never able to engineer out this issue satisfactorily.

Old X axis limit switch mounting

Another problem with my X axis envelope extension scheme was the lack of mechanical stop on such axis, which meant I could actually drive the XY table off the mill. 😱 

The reason I removed the left stop plate was to gain more X axis travel, so important on such a small machine, but that made the limit switch even more critical, since an over-travel condition would entail the ball-nut separating from the ball-screw and spilling the ball bearings all over the shop floor, a mistake that has cost me quite a few tear downs, and a full day of reassembling with each occurrence.

I decided to start from scratch with fresh ideas. Here’s the best one I came up with for a new and improved switch limit cover/end stop...

Hard to believe I have talented painters and sculptors on both sides of my family.

This addition to the XY table is supposed to function as the mount for the limit switch, as well as the occasional mechanical stop (hopefully never to be needed). The switch would fit in a recess carved under the 3D printed body, and would cut power to the X stepper motor at the end of the table's travel. The addition to the table should also protect the switch from debris. 

  

Here are some CAD renderings of it...

XY table extension

Switch limit recess

Switch limit mounting

Wiring hole

The high-def part should take 30 hours to print, so I started out by printing a rough, low infill unit that only took 4.5 hours to print. While it does not have some of the later refinements, it is dimensionally identical to the final design. 

The biggest challenge after taking it out of the 3D printer was clearing the support material from inside the over 2" deep mounting holes. I was able to rip most of the counterbore support material with long tweezers, but finally resorted to ream them to 0.499". This worked very well, and was super quick. 

The ways turned out very tight, so much so in fact that I had to use a rubber mallet to tap them on to see if they'd fit, and could then barely move them by hand. After running the table along the X axis a bit, they wore in nicely. 

Testing for drag in the ways (without limit switch)

It turned out that the low density infill rough ABS print was no match for the stepper motor, because the first time I tried to gently run the table into the new mechanical stop, it cracked the print along the deposition lines (YZ plane). I easily fixed it with acetone (acetone melts ABS and it can be used as a glue of sorts) and I was back up and running in no time, perhaps the denser final print will be stronger. Unfortunately, the easiest way to print this part also makes it the weakest under an overrun condition. 

I will look into replacing the two M6x1.0 mounting screws in favor of long bolts, and machining a steel plate to be fitted on the far left side of the extended bed. This should add a lot more strength to the assembly.

Anyway… the next step was to mount and test the X axis limit switch...

Limit switch mounted and wired up

Some of the plastic behind the roller had to be trimmed back to allow full range of motion of the switch arm, then I amended the final design to account for this.

This is one tight fit!

The wires were well supported by the plastic, and no changes were necessary there...

Wires exiting the 3D printed cover

Here are a couple of shots of the mini-mill referencing the X axis...

Referencing the X axis

Same thing but at a slightly different angle

I am super happy about these results so far. I've been struggling with broken limit switches for some time, and this new design avoids that issue completely, and affords me over 2 extra inches of safe X travel, all the way up to just prior to the ball-nut coming apart. In addition, it protects the switch from chips and spray, and keeps the wires tucked out of the way as well. 👍🏻👍🏻

While I was still testing this initial print in everyday use, I started implementing a few of the changes in my CAD model, including a way to drain chips and coolant from the XY table. 

Added a drain channel

All inner hard corners removed to facilitate drainage of coolant, and cleanup of chips.

Counterbore of screw holes removed, long bolts added, steel plate fitted in a face-wide recess in the plastic.

About the same time I gave the Zortrax M200 the command to print the final high-def part, FedEx delivered the steel plate, and I got on it right away.

Milling the steel face plate

Two days later the print was done.

This printer is a truly awesome tool to have

Here's the new limit switch holder / bed extension

There were a couple of spots where I did get some light warpage, but since it didn't affect the usability of the part, I  installed it anyway.

The corners pulled back a little

This has never happened before, I wonder if the garage got too cold at night.

The steel plate fit perfectly in the recess, and the long bolts were spot on.

The plate didn't require any modifications

The long bolts stick out just enough

I love the look of the new bed extension, it seems more expressive compared to the previous version.

Out with the old, in with the new.

Looking right at home

I filled up the space between the rails to make the print sturdier.

The new print (on the right) is much stronger

Testing the new bed extension

Time will tell how this part holds up, but I feel confident it should give many hours of trouble free service.

Ch 10 - Canard - Part 5

Bottom spar-cap (14.0 hrs)

The process of filling the spar-cap trough for the Roncz canard is identical to the one used on the Center Section spar with one exception, the number of plies and their length is left up to the builder.

“Say what!?”

I kid you not, the directions tell you to use the 3” UNI tape, and to lay enough staggered pieces (with 60º cut ends) to fill in the trough until flush… no more, no less… it is up to you how much fiberglass gets in your spar-cap.

Since it has been done this way for over 30 years, and no canard failures have happened (that I know of), it must be a safe enough method. However, telling whether the trough is full or not while in the midst of fiberglassing, did not seem like a great idea to me. I wanted to know how many plies, and how long, way before that stage, and have them precut and ready to go.

This required mapping the trough depths, and determining how many layers would fit where. Using the bottom contour template and a gauge block set, I measured the trough every few inches, and came up with a surprisingly uneven and slight asymmetrical trough floor.

Mapping the trough geometry 

After measuring the thickness of the UNI tape, I divided the trough measurements by the UNI thickness and determined an approximate layup schedule, then I forced it to be symmetrical. 

A more accurate method would have been to glass 7 test plies, then measure the final thickness and divide by 7. 

Figuring out how many plies are needed

With the final UNI count on hand, I rounded the actual layup schedule this to be 2 full length UNI plies, and 5 smaller staggered plies, each of which would be 16” shorter than the previous (8” each per side). 

As close as this was to my measurements, it still turned out to be slightly proud of the foam, but just barely. I will take care of this minor issue during finishing.

Sanding the shear-web before glassing

UNI plies staggering schedule

Cutting the full length plies

All shorter plies were terminated at 60º 

I used flox to fill the corners because I worried about micro ending up between my structural layers

Laying the thick UNI tape

Hard to see, but I was cutting the red string that holds the cross threads together.

I pulled the cut red strings halves out of both ends

With the red string gone, I removed the cross threads.

Cross threads removed

Layar #1 (full length 108")

Layer #2 (full length 108")

Layer #3 (92")

Layer #4 (76")

Layer #5 (60")

Layer #6 (44")

Layer #7 (28")

Bottom spar cap layup completed

While always an option, I elected not to continue with the glassing of the bottom skin of the canard at this stage. This was not mandatory even on the CS spar, so I decided to save my back to “fight another day”, and peel ply the spar-cap instead.

Clean up was a definite pain and took many hours, mostly because a lot of tape edges had gotten caught under the glass.

Ch 10 - Canard - Part 4

Canard extensions (11.0 hrs)

The first order of that day was to extricate the canard from the 2x4s and nails that suspended it in midair. With the part free of the jig, one could finally recognize the shape of the canard.

"Now, that's starting to look like a real canard!"

I removed the tape and inspected both sides.

Top of canard, after some cleanup.

Canard bottom looking good. I'll work on this side first.

After a little cleanup I moved on to the next challenge… building a straight jig on which to mount my canard. 

However, measuring over 11' in length (roughly 3.5m), getting this jig straight starts to become difficult, and since the canard can only be as straight as the jig was, it is imperative one spends whatever time necessary on this important item. 

Once firmly attached, the extensions would be added, the bottom spar cap built up, and the bottom skin laid.

But let’s not get ahead of ourselves here.

When I purchased the precut foam from Eureka, I also bought all the templates. In this case the nine “K” templates would be called into action.

After checking them to make sure they were all identical, I marked front and back at an arbitrary height of 1.5” (3.8 cm), so that I could use this line to level them on the table. I should mention that being leveled is not a requirement, rather a convenience, and that as long as all the templates are at the same angle, all is well.

Marking the front of the"K" jigs 1.5" from the bottom

I later used a pen to highlight the scribed lines (front and back) 

This is one of those situations where help from technology can really speed things up, especially when working solo. So, after a few futile attempts at juggling multiple variables (9 jigs, 3 dozen shims, a couple of levels, multiple straight edges, a 100 foot roll of string, tape measures, etc.), I decided money might be the perfect "force multiplier" in order to reduce the complex problem into a manageable one.

Enter the Bosch self leveling 360º laser.

Best $230 I spent in a long time 💸💸💸😀

In one word, this thing is awesome! Just turn it on and use it, absolutely no dicking around required!

Luckily for me, I already had a suitable tripod, so me and lady Bosch went straight to work.

I bought this tripod on Amazon for$20 a while back for shooting videos

Using hotel cards as shims 

Leveling the front of the templates (laser light on black lines)

Leveling the back of the templates, then using the glue gun to hold everything together.

I used a string to mark the forward limit for the templates.

The string highlights the forward limit of the templates

A closer view

Even though I had everything leveled, I was still surprised and impressed when I sat the canard in the jig upside down, and the back of the canard lined up perfectly with the laser without any "help".

"I can't argue with that!"

This is when one laser sighting is worth 1000 hand measurements

With the extensions sitting on the jigs beside the canard, it was obvious that the canard was slightly shorter (front to back) than the extensions.

Extension (made out of 1 piece) bigger than canard (made out of two pieces)

Right side has the same issue

Using gauge blocks and the bottom template “E”, I determined that the canard was shorter by about 0.1” (2.5mm). I am still not sure what that could have caused this, certainly all the weights I had placed on the leading edges during curing didn't help. Perhaps, the canard cores had some slop that was supposed to be taken up by the micro joint. I suppose I might never know, but since the authorized mismatch is 1/8” (3.2mm) I decided to press on and later contour the extensions with the sanding block.

Bottom template fits the extension perfectly

Canard main core checking in 0.1" short

Right extension checks good

Right canard also 0.1" short

I then taped the edges of the foam pieces, used wet micro to glue them together, put weights over the assembly, rechecked alignment, and went to bed.

Taping the left extension before attaching them to the canard

Right extension ready to go

Right extension attached to the canard

Making sure nothing moved

Curing overnight

The next day I removed the tape, and marked both sides of the divide. This foam is so light, correcting the shape mismatch took only a few light strokes of the sanding block. I paid particular attention to the sanding block alignment, and stopped as soon as the black lines on the main side of the canard started to fade.

Marking the foam to be removed

The marks on the main part of the canard (left) are for telling when to stop sanding

Foam removed on the extension only. Note the marks are barely touched on the canard.

Another view of the sanding

Left extension and canard marked before sanding

Extension (only) sanded

I'll have to sand the top of the extensions (bottom in the photo) once the canard gets out of the jig