What's the best way to draw a straight line?

[bmuir]

Remember, there are not dumb questions. LOL

I'm building a jig and I need to draw a four-foot line five inches up and exactly parellel to the edge of the MDF board I am using.
Can I use the edge of a four-foot level to connect two marks at each end of the board?
Or, is merely making a number of marks (at least 3) five inches up from the edge and connecting them with a factory edge of MDF or plywood good enough?
How would you do it?
Thanks,
Bill

P.S. I do not own a jointer.

[Tequila]

Not knowing exactly what you're doing, I'll give you an idea what I'd do.
First choice: speed square
Second choice: drywall square
Third choice: two marks and a straightedge

That's just to make the mark. Are you planning to cut along the line? If so, then making the mark is much less important than cutting the line straight, and you'll want to use a straightedge like a piece of angle iron to run the saw against.

[LCHIEN]

I fi I had a reliabel straight edge I would mark 5 inches up at both ends and connect them together with a the straigh edge and draw the line.

If I did not have a good reliable straight edge but I believed the MDF edge to be straight ( a good bet) then I would do as you suggest and mark several 5" marks and connect them with a shorter straight edge.

It is important how you mark the 5" marks. I use a combination square and bury the 5" scribed line on the rule in the square's body so I can just not see the line. Place the square against the edge of the MDF and then use a very sharp (e.g. a scratch awl, knife, or a 0.5 mm mechanical pencil) along the end of the rule, angles so the point is against the end of the rule. This will give you the most consistency.

Another way you can do the job is to use a marking gauge (there are several available like the "cadillac" one from Lee valley) and run it down the edge.

http://www.leevalley.com/wood/page.a...40&cat=1,42936

Another poor man's way of doing it is to run the combination square down the edge of the MDF while holding a 0.5mm mechanical pencil tight to the end of the rule. This requires a little more coordination and is less satisfactory esp. for four feet (works better on lengths of a foot or less).

[mleichtle]

I would rip a board, MDF if you have enough lying around, a little longer than you need, to 5". lay it on top, flush the one side. Theres your line, either use it as a jig or draw your line.