Hatz Biplane Association

I received a quote to make 14 threaded plugs...$251.

I had mine made by a guy who has a CNC lathe. Once we set it up it dropped a part out about every 36 seconds. I'd think he'd make them for a lot less $ than that if he still has the program stored, since it is pretty easy now. Especially if he had an order for more than one plane. I made them with a step or "shoulder" on them so that 1/8" is the full 3/4 inch and does not go into the tube. This eliminates the need to rosette weld them (which I find tricky). I just welded them around the circumference. Since they are in compression the shoulder actually would take up the load even if you didn't weld them at all. Also if it is slightly long you can just grind a bit off the 1/8 inch sticking out and still have be grinding away the weld, so long as you don't grind very much off. I made them like 1/32 long and then just touched the ends to a grinding wheel until they fit nicely. It was easy on the ones that take the threaded insert. Also I later bored into the threaded hole like 1/8" (which still leaves 3/8" of threads remaining - which is more than an AN nut) to allow the shank of the bolt to "seat" into the compression tube slightly to be sure that none of the threaded portion of the bolt was subjected to the shear loads. In other words I wanted to be sure the unthreaded portion of the bolt went ALL the way through the spar plates.

If there was some interest for these I could see if he still has the program stored.

I haven't seen any quote for these so I couldn't offer an opinion other than it doesn't sound all that bad. This will be one of many trade-offs you'll experience on this project... $$$ to have someone else do it vs. doing it yourself... Is the $251 worth it vs. the time it would take you to learn the skill & do it yourself? Only you can make that call.

Do you have anyone in the area who has access to a lathe and can help you out or teach you how to run one? EAA chapter? Machinist friend? Helpful A&P? I imagine you've already run through that checklist, but I thought I'd ask anyway.

Just a couple other things to consider regarding lathe work: In addition to the threaded plugs, you'll also need to machine components for the landing gear spring assemblies. Also, a lathe is very handy for truing up and smoothing the ends of tubing. This helps not only maintain nice square ends for assembling things like compression tubes, but it also help eliminate rough edges that could create friction in your control system like where the rudder pedals attach to the fuselage or the rudder & elevators hinges, etc. So in the larger picture, it is nice to have if you are so inclined.

I'd offer to help you out, but my lathe is not equipped for that work at the moment. Once I clear some of the mess out of the garage I'll finish getting the thing setup. The work I did was at a friend's house which is quite some distance away and not terribly convenient.

Thanks guys. I decided to buy the PEM's from McMaster (reference my 'compression tube' thread') and these are the other pieces that I decided (I think) to have a machine shop make. I have no one to help me here with this sort of work. I researched buying a lathe, and right off that's confusing, especially since I don't even know what to look for or what options I'd need, or not. If these 14 pieces cost $251, how much will I spend on other pieces versus buying a lathe and doing it myself? One thing I think about with every tool is that maybe I can sell it later on to the EAA chapter or someone else at half price, so it doesn't hurt as much. OK, I'm thinking. Have to look at plans to see how much potential lathe work there is.

One consideration on a small lathe is if you can run long tubes through the chuck to turn the ends. The Harbor Freights small lathe, 7 x 10, has a chuck that has a 3/4 bore. This may or may not allow you to feed a 3/4 dia 4130 tube through the chuck. This is not a problem for making inserts but would be a limit if you wanted to turn tube ends. I believe the Harbor Freights lathe is made by the same company in China that makes the Grizzly. Back when I was looking I remember liking the Grizzly more but the shipping cost was to much.

Been reading forums and reviews for hours. One page sums it up:

http://littlemachineshop.com/Info/minilathe_compare.php

Of course, they hype their own model.

Saw this on Amazon:

http://www.amazon.com/12-Mini-Metal-Lathe/dp/B004Q70CP6

Determined that it's a Homier 7X12: http://www.mini-lathe.com/Mini_lathe/Re ... Homier.htm and http://www.mini-lathe.com/Mini_lathe/Re ... update.htm

From reading reviews, I'm not crazy about the HF or Grizzly stuff.

Leaning towards this: http://littlemachineshop.com/4100 or this: http://littlemachineshop.com/products/p ... uctID=4200

My head is spinning. Checked Craigs list...nothing.

Boy....Do I feel lucky. Had a friend of mine do those plugs for the cost of lunch!