Bearings and bushings are milled to the wrong size

[rwoneill]

I just started building and I am noticing that I spend a ridiculous amount of time effectively re-milling bearings so that they rotate freely.

Why is this the case? With cnc mills, KF should be able to spec hardware to the right tolerance within a few thousandths of a millimeter. My hand sanding is no where near as accurate as a mill and it takes forever. Am I missing something? I would save so much time if the parts were the right size in the first place.

[Shadowrider]

I hear you! What should take 5 min to assemble takes a week. Its a kit, but you will be manufacturing some of the parts. My suggestions is just accept the fact that nothing will fit and everything has to be sanded or reamed. Take your time and get them so they are all fit good. As loose as possible with no play is what your are going for. Put them in a drill and use cut strips of sandpaper. Once they fit make sure to keep track of what ones go in what hinge. Next will be the rudder pedals which take an significant amount of time also. Its all worth it for a great flying plane. My controls have no drag and pedals move perfectly. I am super glad that someone else recommended to me not to rush it and make sure they are perfect.

[rwoneill]

I imagine that it's not that challenging for KF to re-spec parts to the right size. I'm sure there is some added cost but they could dramatically improve their kit if they did that. I hope they do that one day. I also wish that there was a disclaimer before you bought one that said: "WARNING: NOTHING IN THIS KIT IS THE RIGHT SIZE! YOU WILL SPEND MANY FRUSTRATING HOURS OF YOUR DAY SANDING AND REAMING."

At this point I wish I had a mill!

[896tr]

Roger, don't forget that in order to be experimental amateur built 51% has to be built/manufactured by you.
Kitfox could send you a "bolt and glue kit" for five times the price but you building it would change air worthiness
and manufacturing parameters. And what would happen to insurance, business license, manufacturing in your residential garage...….? I'm sure John Debra have had to deal with all of the government headaches to get to
where they are with one of the best "home built aircraft" on the market. Reaming bushings, aligning control
parts etc.. teaches patience and why even the littlest and most mundane task keeps an airplane off the ground.

This post is not meant to belittle anyone or to tell anyone to suck it up and quit whining it is meant to let anyone
that wants to build an airplane yourself it is going to take up a lot of your time and money.
If you don't want the frustration of mundane and repetitive tasks order a "turn key" plane from Kitfox or buy a used certified airplane.
I promise you if you build it will give you the greatest feeling of "I did this" the first time the wheels leave the
ground, and I dare anyone to find builder that will disagree with me.

My $.02, no refunds, no change.

[airlina]

Todays kitfox kits are dramatically improved from when I built my Series 5 that I purchased from the pre Mcbeans , Skystar ownership. I watched the two factory youtube videos that were recently done by John and couldn't believe how much the kits have improved , especially with the prebuilt options. I recall a drill press and dremel tool over a weeks time making the flap and adjustable rudder pedal brackets. I was a bit surprised at the amount of manufacturing that was required from rough stock , but once i realized what was involved , I just worked on one widget at a time not a whole airplane. Before you know it (actually 4 years) , I had an airplane that I have been flying for 17 years and still love it. Enjoy the process it will be worth it. I bow to you scratch builders like John Evens ,with his thorp build ,amazing amount of skill and dedication there , I am not worthy. Bruce N199CL

[rwoneill]

I think the kit would be a lot more enjoyable if it were easier to put together. If it were 1950 and everything was still hand milled I would understand the poor tolerances. But in this day and age with automated milling it's pretty easy to get things right from the start. Unless the factory says "Let's intentionally source out of spec hardware so that our customers spend time sanding bearings so that we can meet the 51% requirements"

I'm just talking about the hardware mostly. I'm going to take the bearings and bushings to a machine shop and have them fit professionally. I understand the lesson in patience but I find that I have better uses for my time than tediously sanding bearings that should have been right from the start. Also I can't possibly replicate a perfect fit with sand paper like one can obtain from a mill.

The other Fab work is great.

[jrevens]

One thing my best friend, gone now, who was a master machinist taught me is that you don't use a mill to do lathe work... sorry, I couldn't help myself. :confused: No insult intended. Lots of good comments. One thing to keep in mind is that when small pieces of tubing are welded to a larger tube it can be very hard to avoid some possible deformation of the tubing or even a little over-penetration. It can happen, not to mention possible paint or powder coat where you don't want it inside the tube. A good tight fit is also desirable between the bearing sleeve and the tube, and when the sleeve is pressed in there is the possibility of the softer material deforming out-of-round a little. Reaming is quick & easy. Granted, adjusting the OD of the steel bushings is harder without a lathe. So, even if the bushing and bearing sleeves are all exactly the same, you probably won't have the kind of fit that is most desirable when everything is assembled, without adjustments. It's the nature of a welded tube structure of this sort to require a bit (sometimes quite a bit) of custom fitting. All that said, I think your comments are reasonable.

Bruce... thank you for the kind words - I'm embarrassed. Building any kind of an airplane is a big job, kit or no kit, but there is a lot of worth in the struggle.

[efwd]

I was reading Dustin's reply and nodding the whole time. These parts are simply right off the shelf of hardware stores. I can pick up those brass bushings any day I want over at McFadden & Dale hardware. In fact I have since I screwed one up doing what your trying to accomplish. You will run into many more situations like this. Wait until you get to the engine cowl. They are reportedly much better now since the factory brought the manufacture of them in house. Keep posting your questions and be sure to review and or research issues you have on the builders tips here on this forum.
Here is what I did to get those bushings done. I run a bolt through them, used a jam nut to secure it, and slipped the bolt into the chuck of my drill press. I ran the drill and used a file to shave the diameter down as the drill turned. It was easy and way quicker than using sand paper from the start. Im one of the luck ones I guess. I really enjoyed the hands on stuff that it took to accomplish this build. Now that I am flying, I miss some of that build stuff, even the fiberglass stuff. In fact I got the most satisfaction out of making my heap of crap fiberglass turn out as good as it did. I just basque in the fact that I had to build the majority of an airplane even though I agree with the previous post. People like John who build from plans have my respect for sure.

[rwoneill]

So after spending about 30 mintues sanding with no visible progress, I took my elevator bearings and bushings to a local machinist to get them professionally fit. $40 and 40 minutes later he had all 7 perfectly fit. 100% worth the money. Let the experts handle the precision machining.

He made an interesting observation...

"The inner steel sleeve diameter was:

OD —-8mm (minus) { ~0.314”}
ID ——4.5mm { ~0.177 inch}

( Bolt is 3/16” or 0.187” )

The Brass Bushing:
OD —— 7/16“
ID ——- 5/16” minus { ~0.311” }

In my opinion, inch & metric parts for this particular assembly got mixed up."

It makes a lot of sense. The hardware wasn't out of spec, it was just in the wrong dimensions. I think there was a famous Mars probe lost because of this.

He did note that he was very unimpressed with the hardware and said, "it looks like it came straight from some factory in Taiwan". His words not mine, but I have to agree that there is a lot of room for improvement with respect to hardware.

For the sake of other builders, I hope KF notes this and makes some hardware adjustments. Fortunately I have an expert machinist in town!

[109JB]

No metric stuff got mixed. The inner sleeve is probably just regular old 4130 tubing. That size would be 5/16" OD with 0.065" wall thickness. The OD has a +-0.005" tolerance and the wall thickness is +/- 15%. So the OD could range from 0.308" to 0.317", which your 0.314" measurement falls right into. The wall thickness tolerance works out to +/- 0.010" or thickness from 0.055 to 0.075. So the ID could range from about 0.160" to 0.200". Again, the original 0.177" measurement is right in that range. In reality it is much much closer than that and that is reflected in the measurements you cited. The nominal measurements would be OD=0.312", ID=0.182". Your starting measurements weren't far off that.

In regard to the hardware, I would think that Kitfox would supply AN hardware. Pretty isn't the main concern with hardware on an airplane. It is function, strength, durability, etc. Pretty comes in last.

[jrevens]

Good post, John. I’m sure you’re right. 4130 tubing is used that way on many airplanes. The bronze sleeve bearings are probably off the shelf parts, again, very commonly used. The fact that some “sizing” has to be done is just one of the tasks that help to meet the spirit and intent of the 51% rule.

[efwd]

Funny that you mention the Mars Probe. Back when I was building my RV4 I called the factory with concerns much like this. Dick Vs reply to me was "remember, you aren't building a Space Shuttle here". Granted, your life depends on your craftmanship but this stuff has been being used for years without problems and as John put it, it needs the 51% rule.

[rwoneill]

John B, very interesting observations. If you're right, we are back to my original conclusion which is that, intentionally or not, the hardware selection is just out of spec.

I'm not talking about bearings and bushings looking pretty. I'm talking about basic functionality. The bearings and bushings from the factory will not function as delivered, full stop! And to get them to function, the builder is expected to perform the task of a lathe with a drill and sand paper. Which is not only incredibly time consuming, but more importantly it is also incredibly inaccurate. I imagine there are a lot of kits out there with some very sticky or very sloppy controls for this reason.

I have a bearing that is a 1/32" smaller than all the others. I can't get it to sit in place without clattering around. Too big can be salvaged, but how am I supposed to deal with too small? Out is spec goes both ways. I guess I have to order another bearing and hope it's too big!

If KF sourced properly spec'd hardware, do we know for a fact that they would not meet the 51% rule, or is that a speculation? There is obviously a price associated with better hardware. I wonder what that would be. Also what do they do in the factory? I'm certain that they don't have a bunch of full time employees milling down bearings in a drill press. They must have a lathe or they have better hardware.