Occulture: I have friends who talk to the dead on a regular basis, and I've been seeing ghosts since I was four. That being said, I admit I haven't had as much success "summoning" the dead as I would like.
First of all, I have this inconvenient belief that summoning relatives is rude. So the triangle is *out*. Do you use that triangle to summon angels? I actually don't know... I have a limited background in hermetic magic, which is where I understand that the use of the triangle comes from. It's to protect you from what you've summoned, from what I understand.
Here's what i did when I wanted to talk to my father after he passed (we had a falling out just before he died):
I got some things that belonged to my dad. I got a pillow, some candles, some incense, and some music that reminded me of my dad. I was helped along, since I knew my dad pretty well... so you may wish to talk to relatives who knew your grandfather first, to get their impression. and get a picture, so you can recognize him. You might want to get one that's young, or in the prime of life, since I've found that the dead do not always look as old as they died, Tim Burton not withstanding.
Find a nice comfortable place to sit, and cast your circle, with the western direction portal open. Ancestors come from the west, after all. Or you could use a shamanic trip to go into the land of the ancestors to find him, I suppose, too.
After you cast your circle, start making a nice, comfy place that may be familiar to him, inside your head, or in your astral neighborhood. You should also put a gate or something on it, so you can find it again later, as this sort of place is really handy on the astral. Then, try to take the images of the items you have with you in the circle into that realm with you. Or make astral copies.
Then, make a call out into the ancestor's realm, in the western portal, that you'd like to talk to your grandfather. Name his name, and be sure to try nicknames that he may have had. if you don't know any, don't worry about it. Just cover all the bases you can.
And wait. If he doesn't show, he may be busy or somewhere he can't contact you. After you can't wait anymore, then put a call out that you will try again at a certain time at this same place, and leave an astral candle burning on the table that you put stuff on.
Know in your heart that the candle will get near the bottom of the holder when you return, and you can replace the candle then. Then, you clean everything up on the living side of things, and open your circle. The next step is to keep trying until you either meet him or meet a messenger who can tell you what happened, or why he can't meet you. Sometimes you have to go out and find them. But, either way, you will find out something.
I like to leave these things in very general terms because you seem like an experienced person who would know how to craft your own ritual.
If you'd like more details or correspondences, or "handy tips for talking with the dead", I'm your avatar... metaphorically speaking.