What have I gotten myself into!

Saturday, June 07, 2014

CNC mill conversion - part 17

Computer stand

Running the CNC mill from the laptop had always been a little inconvenient, and I wanted a more permanent solution, so I purchased a used "all in one" touchscreen computer from eBay.

Taking the stand apart

Next, I made a trip to LOWES for some metal, and a few tools to start working on a new stand.

Metal tubing and new grinder being introduced

I wanted the computer to be able to turn as well as tilt.

I started disassembling the mount and removing the plastic cladding, exposing the tilting mechanism. I would later reuse this part after a few small modifications.

As far as being able to turn, I decided to make a mount that would swivel, so I split the main square support tube into two sections, and inserted a round tube inside them. Because the fit was very loose, I made washers out of 4130 steel, and welded them to the top half of the round and square tubes to serve as bearing surfaces, and hinge points.

Welding the washer to the top of the round tube

Welding the washer to the top of the square tube as well

Welding another washer to the bottom of the square tube

Close up of the bottom of the square tube

Back side of the washer

I also started welding an L channel to a 16 gauge steel sheet to hold the keyboard and mouse.

Welding this much started warping the steel sheet a little

I ended up leaving some gaps between the welds, in order to minimize warpage.

Unfortunately I ran out of Argon, so I had to stop for the day. The next morning I went out early to fetch more gas, and resumed the fabrication of the keyboard platform.

Mocking up the keyboard platform structure

Deciding on a comfortable angle (-55˚)

Using the square tube to work out the spacing of the frame

Basic frame thrown together

Additional frame members added to stiffen the structure

I used some of the leftover small square tubing to beef up the structure below the keyboard.

Frame structure supporting the keyboard

Frame top side

The finished keyboard platform is able to rotate.

Keyboard and mouse tray

Tray rotating

Side view

Finally, I concentrated on the mount for the actual computer.

I butt-welded two small plates together, then welded them a few inches above the keyboard.

Two plates welded together being fitted to the riser

Computer holder plate attachment to the riser

Computer plate attached

Lastly, I welded the hinge mechanism to the plate, and mounted the computer for the first time.

Computer connected to the stand

CNC computer ready to go to work

I added two spacers to the mount in order to miss the lip on the top of my wooden table.

Small spacer welded to the mount

I was pretty satisfied up to this point, except for a little side to side wobble. I traced it down to the fact that, with only one washer in the bottom square tube, the round tube was free to tilt inside of it.

The solution would be to insert another washer further down in order to capture the round tube, and prevent unwanted motion. This would require cutting the tube in half, welding the washer, welding the tube back, then smooth it all out... oh well!

I measured how far into the square tube the round one went, then sliced the square tube a few inches above it.

Cutting it down

After making a new washer, I installed it in between the split tube, welded it, and cut the excess off.

Square washer

Same washer after initial welding

Cutting off the washer's excess

Trimmed washer

Next, I lined up the other part of the tube, and welded them both together again.

Welding the other half of the tube to the washer

Root pass

Everything looked good at this point, except that the round tube would not fit into the washer anymore.

Further investigation revealed that some excess weld was constricting the passage for the tube. Regrettably this was now a couple of feet into the outer tube, and there was no way for me to get to it and fix it, except perhaps to cut the square tube in half again below the washer, reestablish the proper passage, re-weld both halves back, and grind it all to perfection.

Damn it!

Tube sliced anew just below the washer

Note how the round tube doesn't fit anymore

"All clear" after some work with a Dremel rotary tool

The tube finally fits though the bottom washer

Welding it all back again. Can you spot the original welds over the washer? (hint: they are 2" to the left of this weld)

Grinding down the high spots

All blended in

This fix worked beautifully, the wobble was gone, the welds blended perfectly, and I couldn't even tell anymore where the two cuts were made. So, I moved on to the final task of mounting my contraption to the actual table.

CNC computer final position

Wiring details

Mach3 ready to run the mill

I am very pleased with the outcome, there are only a few wires showing, and they are out of the way. The stand rotates with a pleasant drag, and Mach3's DROs are in line with the mill's ones, making it easier to keep tool drift in check.

I haven't even used it yet, but I like it already.

Monday, June 02, 2014

Nose and nose gear - part 8

Bulkheads (6.5 hrs)

I am glad I found this "gotcha" before glassing.

The new issue I’ve been dealing with is that the distance between the nose gear pivot and the forward edges of NG-30 (nose main frame) came out 0.100” (2.5 mm) short.

While it doesn’t sound like that big of a deal, the top of the nose gear leg ends up hitting the forward bulkhead by about 0.080” (2 mm).

The way the bulkhead should fit

Interference between bulkhead and top of gear leg

I’m not quite sure how that happened, perhaps too vigorous a sanding, whatever! What I decided to do is to create a slight depression into the bulkhead, in order to make room for the nose leg protrusion.

Depression outline

This time my hands were not as steady as they should have been with the router, and I really butchered the depression, but it doesn’t matter since it’s going to get sanded down, and radioused with micro.

In the end the depression appeared to work well.

interference removed

Creating a smooth transition in the depression

From there, the usual sequence repeated for the rear face of this bulkhead.

Micro-slurry

Pure epoxy

Curing

What followed was a little trimming, and some sanding.

Trimming

Scuffing up the surface

Changing gears for a moment...

It might just be my paranoia rearing up its ugly head, but one only has to google "fiberglass bird strike" to realize that birds hitting composite planes at 200 mph are going to do a lot of nasty damage.

Birds have the bad habit of folding their wings, and dropping like rocks, when they feel threatened by your presence (bow wave), so usually the ones you end up hitting are the ones slightly above you.

In the ‘90s, I once struck a bird at night over Dallas, TX at 170 kts. Luckily the windshield didn’t break, but the sound of the impact was so loud it made me think for a moment that the engine of the Bonanza had blown itself apart. It was a very scary night, especially since we had no idea what had happened until after landing (which we did right away).

I have had many more birds encounters since then, which always ended up badly for the poor creatures, and always caused damage of varying degrees.

One of my colleagues rejected a takeoff in a CRJ (regional jet) in Washington DC, after striking a large bird. The damage was extensive. The bird ripped the airplane slanted metal skin just below the windshield, and actually entered the cockpit, injuring one of the pilots.

Why don’t bird strike ever happen at high altitudes?

Because that's not where birds are! Birds are down low, and birds strikes always happen at relatively low altitudes (let's say 5'000 feet and below), and guess what? That’s where I will spend a lot of my time flying this thing.

But wait a minute! Wasn’t this blog post about nose bulkheads?

Oh yeah! Back to those...

Not everyone is going to share my concern (not that it matters), but I decided to add 1 layer of kevlar to both of my nose bulkheads, in an effort to reduce the chances of coming face to face with a bird (ask Fabio).

Top of bulkheads will be trimmed to fit a door

Kevlar covering most of the bulkhead except for the top

Peel-plied and curing

These brackets will eventually attach the small bulkhead to the big one

Once cured, I drilled two holes in the bulkhead, and used two nails to affix it to both NG-30s.

Drilling holes for nails

Nails holding bulkhead temporarily

I decided to attach the bulkhead permanently while the nose gear was installed, to make sure the proper NG-30 spacing was not disturbed. This meant that only the outer BID tapes could be installed at this time.