Landing brake - part 5

Electric actuator (14.2 hrs)

I mounted the thinner nuts from Aircraft Spruce on the speed-brake hinge, and that took care of the closing gap issue I was having, so I moved on to the next item on my list, the electric actuator.

Hinge center bolts using thinner profile nuts

The unit I purchased comes from ServoCity, the model number is HDA4-50. 

While I had a vague idea of how to mount it, I had no real plans, since this is not what the original design called for. Lucky for me, my good friend Mike came to the rescue with a 21 year old CSA newsletter (April 1992)! 

How could I have missed that!

In times like this, friends like Mike are better than money in the bank. 

I owe you again, BizMan!

1992 CSA article on electric landing brake

You might notice that these plans call for an actuator with 6” of travel, but I had already bought one with 4” of travel, so the measurements for how to position it (13” and 5.8”) were no longer applicable. I recalculated these distances, and came out with 12” and 4”. These would allow for 60˚ maximum opening, as well as full retraction. 

But first, I needed to build brackets on both ends of the actuator, and a plywood hard-point.

I modeled the top bracket after CS73 from the engine compartment, but I made it slightly longer because I wanted to add a way to adjust it up or down, by slotting the mounting holes.

Developing the bracket profile

Left and right brackets

After trimming

Test fit

The bottom mounts were not modified.

Bottom brackets marked and ready to be cut

Both brackets in place

Next, I went to work on the plywood hard-point.

0.25" plywood

I buried the nut-plates into recesses I routed into the back side of the plywood piece, then I floxed them in.

Routing the plywood for nut-plates

Recessed nut-plate detail

Actuator mounted on hard-point

Nut-plates floxed

In the meanwhile, I gently massaged the bracket placement in order to arrive at the prescribed 60˚ maximum opening.

Setting landing brake maximum opening limit

With all the geometry figured out, I drilled the bottom bracket holes into the speed-brake.

Bracket hinge bolt set 4" from landing brake hinge pin

The prescribed screws turned out to be too short, so I put in an order for longer ones with Aircraft Spruce.

Bottom bracket bolts are too short. Longer ones are on the way.

I then shifted my attention to the top bracket.

The top bracket hinge bolt is 12" from the landing brake hinge pin.

I mixed a new batch of flox, a bit on the dry side so that it would not run...

Flox applied to hard-point

... and attached the plywood to the front seat...

Hard-point attached to back side of the front seat. Bolts too long, shorter ones on order.

Actuator propped while curing

... finally, I cleaned the excess, radiused the edges, and let it dry overnight.

Excess flox cleaned up

The next morning I removed the actuator, and found that I had to do quite a bit of sanding to clean up stray flox, and smooth the radius up.

Hardened flox, clean up with sander needed.

Hard-point sanded and ready for fiberglassing

I ended up propping the fuselage in an unconventional way, so that I could work on the front seat while standing up. This was a huge improvement over working hunched over, or upside down.

I know it looks weird, but it worked!

Since I had to fiberglass over the top of the bolt holes, I filled them with Saran Wrap to keep the epoxy out of the holes.

Twisted Saran Wrap inserted in the hole

Excess Saran Wrap cut off to be reused in the other holes

Wrap will prevent epoxy from entering the hole

All holes plugged

I cut 5 staggered layers of BID...

5 layers of BID

... pre-pregged them...

BID getting pre-pregged

... and applied them to the plywood hard-point, finishing it with peel-ply...

Bid applied and peel-plied

With this layup curing overnight, I wanted to take a few minutes to talk about some of the features of this electric actuator...

Landing brake actuator introduction

Importance of adjustability

The next morning I drilled through the 5 layers of BID, exposing the Saran Wrap, and removed it with a scribe.

Saran Wrap being removed with a scribe

Then, I installed the actuator one last time.

Actuator in place, albeit with the wrong bolts

A view of the actuator from the back seat

As I expected, I ended up needing to adjust the length of the actuator ram again. One full turn clockwise did the trick.

Landing brake activation

CNC mill conversion - Part 2

X axis stepper motor mount

Before I start making stuff today you need a little more background information so that things will make more sense.

In a CNC mill (Computer Numerical Control) a computer assumes control of the movements of the XY table, and Z axis (depth of cut) at a minimum. Additional functions might also be taken over such as spindle control, coolant activation, and many more.

To cut features into the metal the computer follows directions encoded into a cutting program written in “G code”, a common machining language. The programs can be created in three ways: 

1. manually typed into the mill’s controller software interface,
2. automatically generated by selecting options on “wizard programs” built into the same controller software, 
3. feeding a CAD drawing (Computer Aided Design) into a CAM program (Computer Aided Machining) able to generate G-code tool paths for the controller software to use.

The G-code on the left represents the tool-paths necessary to mill the text on the right onto a blank.

A controller software such as Mach 3, running on the computer connected to the mill, reads the G-code, and sends commands to drivers for the electric motor, one for each axes. The drivers receive the binary low power computer commands, and turn them into much stronger and more complex electrical signals for the motors. 

Mach 3 controller interface

The motors can be stepper motors, or servo motors. Steppers are cheeper than servos, and while they have a few drawbacks, they will serve well with proper dimensioning and care, so that’s what I will buy a little further down the road.

Stepper motor

Stepper motors do not turn freely like servos do, rather they turn in finite increments, or steps. Sending an X amount of signals to a stepper motor turns the motor shaft an X amounts of steps. Common steppers take 200 steps to make a complete shaft revolution, which means that each step is worth 1.8˚ of shaft revolution. Smaller revolutions can be had through software by using micro-stepping techniques... but let’s not complicate things further right now.

A few of the items required for the CNC conversion

Obviously, the servos need to be physically positioned in such a way that they can turn the ball-screws. My conversion will employ direct drive for the X and Y axes, and belt drive for the Z axis. With a direct drive the shaft of the motor needs to be aligned with the ball-screw, with a belt drive they need to be merely parallel to each other.

Today I will focus on manufacturing the X axis motor mount out of a raw aluminum plate, and an aluminum rod. 

This was the first time I relied 100% on the mill’s DROs (Digital Read Out), so I was a little apprehensive on the final outcome, but as you will see things turned out great.

I started by parting a few big aluminum plates into smaller blanks, representing all the CNC upgrade components.

Raw aluminum before being cut

Raw aluminum pieces used for various brackets

Next, I used my lathe to cut the rough motor mount standoffs out of an aluminum rod.

Cutting the standoff blanks out of a 0.5" (12.7 mm) aluminum rod

Here’s all the rough stock required for the conversion..

All the required material

The standoffs needed some minor drilling and tapping.

So, I drilled both sides...

Drilled standoffs

... and threaded them.

Threading a standoff

Threading completed 

With the standoffs completed, I put the X axis motor mount blank on the mill, squared it, and brought it down to the required size.

Squaring the future X axis motor mount

Since I relied heavily on the DROs for locating all the features to be milled on the plate, I had to create a cartesian coordinate system, and map all the holes on my plans.

Mapped out plan of action

Here’s how it worked. I zeroed out my mill in such a way that the spindle center was EXACTLY over the lower left corner of the aluminum plate. At this point I zeroed out both my X and Y DROs, and cranked the mill table to the coordinates of every feature to be cut.

Let’s take the hole on the bottom left of the drawing, the one with coordinates (0.323, 0.323). All I had to do was to move the table to those coordinates, as read on the DROs, and start drilling. 

Spindle homed in to the first hole

First hole center-drilled

Let’s try another one. How about the hole on the bottom right of the plans? Its coordinates are (2.177, 0.323).

Spindle moved to the second hole coordinates

Second hole center-drilled

Wow, this is so simple!

You get the idea. 

To make a long story short, I drilled every hole in the plans.

All holes center-drilled

All holes drilled to final size

Now, up until this point I was not too concerned with repeatability, or how well the spindle could line up again with the same hole, given the same coordinates. I figured there might be some minor misalignments due to errors in the DROs themselves, or perhaps induced by my way of mounting them. 

I am happy to report that the precision this DROs brought to the mill is nothing less than astounding!

One way I was positively surprised, was when I went to counterbore some of the holes. The counterboring bit is very particular about being properly lined up with the hole. Getting it to slip into a hole, even while holding the bit in your hand, is difficult unless it is perfectly aligned.

Driving the mill to the coordinates used earlier though, the counterbore pilot slipped right in every hole, effortlessly.

Awesome!

Counterbore bit with pilot section partially inserted in hole

So, I counterbored the holes that needed it with much ease, and satisfaction.

Three holes counterbored to hide bolts

Next, I flipped the plate over, reestablished a cartesian coordinate system, and tapered the back side of some of the holes where flush bolts will reside.

Back side of plate with mounting holes tapered

Bolts sitting flush in tapered holes

The final challenge was cutting the huge center hole. This is just a pass through hole for the ball-screw.

Slowly enlarging the pass through hole with a boring bar

Putting all the parts together, you can get a better sense of how it is supposed to work.

Finished X axis bracket

This mount will fit at the end of the table, where the crank for the X axis is.

The crank wheel you see behind the mount will be eliminated

With the crank removed, the mount slipped right in place. The stepper motor will replace the crank wheel.

Bracket in place

I still have to drill and tap three holes to finish mounting it onto the mill. I will wait until all the other components are ready, including motors, drivers, computer, software, and wiring, before mounting it permanently, since there is a lot more manual work to be done on the mill.

Here is where the stepper motor will go...

Ghost motor in position 

CNC mill conversion - Part 1

Machining the ball-screws

A side project I started working on, loosely connected to building the airplane, is converting my mill into a CNC mill.

After much playing around with the idea, I finally decided to do it!

This will eventually allow me to manufacture more complex metal pieces for the airplane, like brackets, adapters, etc. I have no pressing need for it at the moment, but I'd like it to be ready by the time I get to that point.

Working on the CNC conversion is a valuable distraction, as I tend to get fed up with anything fiberglass after a big layup, and find the challenge of precision metal carving somewhat refreshing. Conversely, machining difficult parts like these ball-screws leaves me yearning for the loose tolerances of composite construction once again, and the building cycle repeats over and over many times, keeping my interest level higher, longer.

I have looked at many different conversions for my X2 mill, and the one I settled on is from Daniel Kemp. I was initially leaning toward spending more money for a kit from "CNC Fusion", but I didn’t like the offset Z axis screw and motor, apparently they have caused a few issue for some people.

One drawback of my chosen design is that Daniel no longer manufacture kits for it, so all you have to go by are the plans. On the other hand, this is also a perfect learning opportunity, and it will allow me to modify things where needed to suit my machine.

Sounds like a familiar theme?

For those who are not sure why CNC could be useful, watch the next video and let your imagination take off.

Just imagine the possibilities...

I will not be making aluminum foot-pegs, but you get the idea, almost anything becomes possible with proper use of CNC.

Machining is of course all about precision, and the biggest offenders are the lead-screws that drive 99% of manual mills. These lead-screws introduce backlash due to the small gap between the thread of the screw and the thread of the nut, which allows for movement, but reduces precision. It would be physically impossible to create a lead-screw without backlash, because the friction with the nut would be too high to allow for relative movement. 

Typical lead-screw 

Nut cross section

The solution to this problem is to use ball-screws. With ball-screws the contact between the nut and the screw is made by tiny metal balls running in a race. The friction generated by the steel balls running in the race is much lower the friction generated by the thread of the nut sliding over the thread of the lead-screw, so we can have achieve tighter tolerances, and nearly zero backlash, and still be able to operate the mill by turning the screws.

Typical ball-screw (top one)

Ball-nut cross section

Ball-screw in action

This is why a nearly universal step in CNC conversions is to replace all lead-screws with ball-screws. Any conversion plans that doesn’t address this area, and retains the original lead-screws, will be plagued by the same backlash that existed before the conversion, and it is not worth the trouble in my opinion. This is the main reason why I rejected the "fignoggle" design (although it seems they are now starting to address this major drawback).

So, it seemed fitting to begin talking about my conversion by addressing this critical component, the ball-screw, upon which all machine movements will rely, and where the foundation of precision are laid. 

I purchased my ball-screws and nuts from Roton (#59321), and I had them cut to length for an extra charge, but there is still a lot of work to be done before they are usable.

One of the ball-screws as it arrived from Roton

Here’s the plan of action for the ball-screws...

The main issue I ran into while machining the ball-screws, is the fact that the ball races are hardened steel, and they required specialized cutters. I wore out every type of cutting implement I had (High Speed Steel, Carbide, and Crobalt), getting very poor results, while the lathe almost shook itself apart, spitting flames and swarf so hot it turned electric blue.

Worn out Crobalt cutter trying its best against hardened steel :-(

Thankfully, I did finally receive a suggestion from a machining forum about using a tool post grinder to cut through the tough stuff, so I bought one from littlemachineshop.com and started grinding away.

Initial grinding of the ball-screws

Final grinding to exact dimensions. "Look Ma', no heat!"

Freshly ground surface

Man... what a difference that made! Like night and day! The only problem being the abrasive dust going everywhere, requiring a complete lathe teardown and clean up. No sweat!

The next step was machining the thread onto the shaft.

Single point threading on the lathe

Here’s a before, during, and after shot of the ball-screws being machined...

Ball-screws before, during, and after machining.

... and the mostly finished X and Y axes ball-screws...

Ball-screws with bearings, nuts, and electric motor couplers.

Close up of the X and Y ball-screws and accessories.

I decided to leave the stems a little long where they connect to the electric motors, until I can fit them in place later.

Ch 25 - Finishing

Learning from the Maestro

Recently, I’ve been able to spend a whole day at the Whiteman airport, not too far from Hollywood, home to some of the finest Long EZ people I know. 

My friend Chris has built and restored numerous Long EZs both for himself, as well as for other people, so I was really excited to be able to pick his brain once again, as he worked on another project.

This time, I caught him doing some finishing work on the right landing gear leg of someone else’s Long EZ, and decided to catch as much of his thoughts as I could on tape.

Chris has worked at Scale Composites in the past, and is unbelievably talented so, when someone with such experience talks, I listen!

Chris explaining how to finish the structure