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pap0007
04-25-2006, 05:23 AM
hello all: I quick question from an extreme beginner:

i have a goldberg electra. i am currently building it, finding it a little tough, but doable. a question: i am construsting the main wing spar (inboard), and the instructions tell me to "crosspin" it in place onto the plan.

in the first steps constructing the tail, i put the pins through the balsa on top of the plan. but now this is basswood. in the pics i see the pins going around the wood, this makes me think they want to bend the pin around the wood? the problem with this: the instructions tell me to be "exact" here, im not sure how easy that is having to bend the pin around the wood.

what is cross pinning?

am i way off?

thanks for any help

BillM
04-25-2006, 05:47 AM
pap0007
Cross pining simply means keeping the parts in place by putting the pins at an angle across the part in the shape of an X. One pin on each side of the part at each location.

My solution has been to build my models on ceiling tiles. I buy the 3 x 4 tiles. Dont buy the fiberglass type. They wont work. I usually stack about 5 on my work bench. When they get beat up from cutting and glue globs that fall on the table I just remove the top layer and I'm good to go again. With this method I can use T-pins. I simply push the pins in until the top holds the part in place.

About a $10 investment usually lasts about 4 or 5 years and I build a lot of airplanes.

BM

wyatt
04-25-2006, 07:50 AM
Hi pap0007,
Bill M. is exactly right. All Goldberg is trying to tell you is that since you obviously can't drive the pins through the basswood, you must hold the spars down by crossing the pins over the wood in an X fashion. I have found that it is best to put the pins as close together as possible when doing this, as that will keep the spar from wanting to drift away from where you want it on the plans. There is no bending of the pins required. Goldberg's comment about being precise has to do with making sure that the spar is positioned on the plan correctly when you pin it down. This is important for two reasons: 1) It assures that you will be building a straight and true (warp-free) wing, and; 2) All of the ribs, stringers, LE and TE will later be keyed on where that spar is positioned. If it is wrong, you will find no end of problems getting other parts to fit as you progress. I assume you have gotten yourself a flat building board. If not, do so. There are several good ones on the market, but I use a piece of 3/4 inch birch plywood about 2' X 4' as a base. You can usually find one about that size at Home Depot or other big-box stores that sell plywood. Eyeball it to make SURE it is straight and get the birch because it is sanded smooth. Bill M's suggestion of using ceiling tiles as a pinning surface is great. It's lots easier to push pins into those than into the plywood and, as he says, it's cheap and renewable. I also assume you know that there are two different sizes of T-pins available. Use the big ones for cross pinning. I have found that those pins are available cheaper at a fabric store than as a speciality modeling item. Buy a bunch...you'll need them as you progress in building. Best of luck and don't hesitate to ask if you have more concerns. There ain't no such thing as dumb questions.

Sky Sharkster
04-25-2006, 11:44 AM
To Pap0007, good advice so far! You might also want to check
http://www.wattflyer.com/forums/showthread.php?t=4647
This is under Builders Tips, the thread is titled "What about T Pins" By Ribcracker. More info on building, boards, pinning, etc.
Good Luck!
Ron

mudduck
04-25-2006, 05:47 PM
Cross pin does not mean that you bend the pin around the basswood spar; what you do is use two pins, one on either side of the spar and push them into the building board at 45 degress to each other. This forms an "X" and the spar is therefore trapped inside the bottom portion of the "X" and kept from moving. Hope this helps.






hello all: I quick question from an extreme beginner:

i have a goldberg electra. i am currently building it, finding it a little tough, but doable. a question: i am construsting the main wing spar (inboard), and the instructions tell me to "crosspin" it in place onto the plan.

in the first steps constructing the tail, i put the pins through the balsa on top of the plan. but now this is basswood. in the pics i see the pins going around the wood, this makes me think they want to bend the pin around the wood? the problem with this: the instructions tell me to be "exact" here, im not sure how easy that is having to bend the pin around the wood.

what is cross pinning?

am i way off?

thanks for any help

DickCorby
04-25-2006, 09:38 PM
My Favorite building board is a Cheap (20-30 dollars) Luan mahogany interior door. It has all the attributes listed by the other guys. and lasts a long time. When one edge gets screwed with knife cuts, holes from overdrilling, and glue spots etc, I just turn it around and use the other edge till it gets screwed up. Then turn it over and you have 2 new edges to work with. It usually lasts me 2 to 3 years. Not a bad investment.

BillM
04-26-2006, 12:25 AM
I was lucky. I worked as a designer ror a commercial furniture manufacturer many years ago so I just designed (and built)my workbench. It's still going strong after nearly 40 years. The most important part --the top--is a special drafting table that the company built for the aviation industry. It has a metal frame filled with a honeycomb material and has metal top and bottm. The top then has a layer of limoleum glued on it. It weighs a lot but is as true as can be. This one was a reject and I got it before the grinder. It measures 36 x 60.

BM

pap0007
04-28-2006, 12:45 AM
thanks for all the great responses guy. very good recommendations here.

KP

thunder 21
04-29-2006, 11:15 AM
i used a peice of 4 ft/8ft /.750 phenolic 4 my bench