What have I gotten myself into!: “Tooling up”

The decision to make my own metal parts has cast a whole new light on the composite aircraft construction method. Lately, I've found myself elbows deep studying machine shop manuals, and steel milling techniques. I feel like I have fallen into a parallel universe, where the words epoxy and fiberglass are devoid of any meaning.

In keeping with the FAA experimental certification motto though, I have been putting the capital “L” in Learning, but unfortunately only the small “r” in recreation so far. So it is, that after a lot of metal working self-education, I decided to finally purchase my very first metal lathe.

The lathe, for those unfamiliar with it, is a machining device used to make cylindrical parts with cylindrical features. A vertical mill on the other hand, is used to work on parts with flat surfaces, like rectangles, bars, plates, etc.

Months of looking on eBay and CraigsList, left me feeling like every good deal had already been had by someone else, and I was literally about to head over to Harbor Freight to purchase their 7”x10” lathe (7” swing over a 10” long bed), one of the smallest, when my wife suggested I take another look at eBay. Unbelievably, I found not only a bigger lathe (7”x14”), but a mill too, plus a lot of the tooling I would need, at a price that I couldn’t ignore, and all in the same place. The items had just been posted, and the only catch was that they had to be picked up in person, ASAP.

12 hour drive there, 30 minutes getting the loot, and 12 hour drive back, 1100 mile round trip. No problem! Honey... how would you like to go for a drive?

Well, that was pretty rough! However, I was too excited to care, until we got back that is. That night I slept like a log.

A complete table top machine shop

These two awesome machines belonged to Craig, a brilliant MIT trained mechanical engineer, who had used them for prototyping automobile parts for Audi. He unfortunately passed away in his 50’s after a 2 year battle with brain cancer, and they sat unused for 2 more years. Both machines were working fine the last time he had used them, but by now they displayed surface rust and other signs of disuse. I knew going into this that I would need to bring them back up to speed, and I was willing to give them all the TLC they needed in order to start making parts for my Long EZ. Craig’s wife Kat, was very gracious under the circumstances, and loved the fact that I would be making airplane parts with them. I’m positive Craig must be smiling as well, wherever he is.

Later that week, I spent a whole day sorting out and cleaning all the things I had acquired, and equally important, cataloging everything I was still missing to make the machines operational again. Buying tools sight unseen is risky, and I really went out on a limb on this one, but I had strong indicators that a good deal was in the making.

Today, after a complete tear down and rebuild of the lathe, I am still happy about this purchase, even after sinking more money into it to replace missing or worn parts.

I have not yet touched the mill, except to verify that the spindle turns under power. Cleaning it will be a project for a later date, since I have no immediate need for it.

So, why was I looking so hard for a lathe in the first place?

Well, I am reaching a stage in the construction where I will soon have to either purchase or fabricate the landing gear assembly (LMGA).

This cylindrical part fits between the landing gear mounts, and will attach to the landing gear bow (aka: gear legs).

LMGA mounted on the inboard side of the rear fuselage

It also features two steel bushings (LMGAB) on either end of it, that will support the BIG landing gear bolts.

So, I needed a lathe to transform raw steel rod stock into bushings, and raw steel tubing into LMGA.

If you are still reading this long boring post, I'm very impressed. So, if you stick around a little longer, I will show you the actual making of LMGAB, the 4130 steel bushing.

Bear in mind that these are my very first cuts with a lathe, and the first opportunity to put into practice everything I have been learning on my own so far. The bushing I am making in these clips is just a test piece, and will not be used on the actual plane, but it will serve to highlight some of the challenges that I am facing, both with the machine and with my technique, and an opportunity to start honing the skills necessary to approximate CozyGirl perfection.

Yes I know, that is never going to happen, sigh! At least not until I get a TIG welder, and a laser cutter, and a ...

Why don't we just take a look at the raw materials as they came from Aircraft Spruce?

Solid core 4130 steel rod

Hollow 4130 steel tube

Although they look round and straight, you have no idea how lob-sided these things are until you chuck them up to your lathe and start making some gentle passes on them with a cutter. Wow, these things are so far off even Wal-Mart would think they are junk! I suppose that’s the whole point behind being “raw” stock. Being a machining newbie, I was just a little shocked.

I shoved a foot of tubing right through the chuck until only about an inch was sticking out of the front end (for rigidity purposes), and faced the end of it to make it square with the longitudinal axis, then I cut a starter hole with a super stiff center-drill.

At this point I loosened the chuck’s grip on the rod, and pulled it out about 6 more inches, and secured the chuck once again. I replaced the drill on the opposite hand with a “live center” that has ball bearings inside, and is able to spin with the piece being worked on. I placed a cutter on the tool post, and started reducing the diameter of the rod.

As you might imagine, this reduction of size is done in multiple passes, starting with some roughing passes of maybe 10 to 50 thousands of an inch, depending on the hardness of the material, and ending in 1 to 5 thousands finishing passes to produce a better surface, and sneak up on the required final size.

After using a “parting tool” (not partying) to separate the bearing-to-be from the rest of the stock, I flipped it around in the chuck, and faced it multiple times, reducing its size to the one specified in the plans.

Switching back to a drill chuck, I center-drilled the flat side, then used a drill bit to cut a hole straight through.

As with the turning, producing a big hole is done in stages, utilizing drill bits of increasing size, until the proper dimension is reached.

At the end of this long process, I was rewarded with the long sought after bearing, that while not a looker, it was at least the correct size.

Test bushing behind its plan

Unfortunately, I later underestimated the power of sandpaper, and using it I further reduced the OD (outside diameter) of the part, in an effort to produce a smoother surface. Not by that much, but the required “light press fit” is definitely gone.