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Good Straight Edge

I've been looking for a good straight edge for a while now. I want it to serve two purposes:

1.) Straight edge for a cutting guide.

2.) Straight edge to determine if hand planed stuff is flat.

Finding a tool to solve item 2 has been the most trouble. I'm currently working on workbench slabs. I've hand planed the tops and am about to square the edges using a circular saw and cutting guide as discussed in another post.

To check the slab for flatness a large straight edge would be ideal but not required. I can check the top in overlapping sections. I've been using a 48" steel ruler held on edge to check for flatness. The downside to this is that I have to hold the ruler and this makes it difficult to have a strong light source behind the ruler and me far enough away to detect any light. The top is pretty flat so I am looking for minor imperfections at this point.

A straight edge 1" x 48" x .25" would be nice. The quarter inch edge would allow me to stand the edge on the top and step back to check for light coming between the edge and top. A level with a flat edge doesn't suit this purpose because the smallest dimension is too wide to check for minor imperfections. Need something thinner. Goldilocks?

Starret of course makes straight edges that would work great for this purpose but I don't want to spend that kind of money. All I need to do is see light shinning through small peaks and valleys. I do not need to see the individual photons so Starret is too expensive but would be a nice gift to recieve.

Metal stock from the big box stores is incredibly crooked so that is not an alternative either. Clamp n guides are nice but the clamp part would have to be removed to stand them on end (except on the edge of the work)

I've been using Lee Valley winding sticks but they are too short.

Today I went to get a cutting guide to square off the slabs on my workbench. I was going to use the factory edge of a piece of plywood. Lowes is having an amazing sidewalk sale so the place is a zoo. I drive a Saturn so I need the sheet of plywood cut. Looked like a long wait on that so I went to see if I could find a 96" ruler or something.

Long story finally ended. Swanson had a 100" cutting guide that can stand on end. It is two 50" pieces optionally joined in the center. Great tool for 20 bucks that solves both my problems.

Wow. Lots of words to talk about straight lines.

Ken

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Ken
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I use MDF guides that I make myself with HDF sliding bases for the circular saw (7.25" MIlwaukee with Freud finish blade). Look for a straight-line factory edge on the MDF board to rip against. I can usually cut a fair glue-line with this rig. The panel-cutting table is a great tool. Here are the plans for both the table and guides

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Reply to
Andrew Williams

This a little pricey depending on metal suppliers in your area but........a piece of aluminum flat stock 1/8"-1/4" thick and 2" -3" wide makes a nice striaghtedge. I have a 2" x 1/8" x8' piece that has served me well, but at times I wish it was thicker. It deflects in the middle while ripping a sheet of plywood. I clamp a block of wood for a brace as a workaround for this. Good Luck Lyndell

Reply to
Lyndell Thompson

Thanks for the article. Normally I use a clamp n guide but this jig makes it easier to line up your actual cutting edge. I think I'll make one 48" which solves most of my needs. I'm new at this though so my needs are few.

Making one larger than 48" isn't likely during the weekend. Lowes is too crowded and I would need it ripped to fit into my Saturn. Although this looks like a great solution for the cutting guide it doesn't address the straight edge for determining flatness.

Thanks for the great info. I'll be making one of these soon.

Ken

Reply to
Ken

I checked this stuff out at Lowes and Home Depot. It was visibly curved. Even the angle brackets were visibly distorted. I guess I could get a straight piece from a real metal supplier but I don't know of any in my area. Metal stock would be helpful in quite a few jigs so I will have to get around town and see what is available.

Thanks

Ken

Reply to
Ken

That is 'slap my head' / 'of course' kind of good advice.

I'll make two little brackets that come down from the top of a steel ruler to keep it near a 90 degree angle to the surface being checked.

The only potential gotcha is to make sure the brackets holding the ruler up don't also change the way it lies on the surface being checked.

Reply to
Ken

What I would do is make two small blocks. One for each end of the straightedge. Imbed a small magnet in each. No clamping distortion or damage to the scale.

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CW

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pat

Rockler

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Tom

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Woodhead

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Woodhead

to the prices for Starrett. I'm sure these are worth the price for machinists but the surface of wood when magnified to the level of precision of these tools would look like a raging ocean.

I would certainly love to receive one of these or a Starrett as a gift but I can't afford buying one myself. Since wood will never be as flat as the machinist tools I don't think it is necessary to buy them except for the pure joy of having a quality precision tool.

Thanks

Ken

Reply to
Ken

I think I'd go for a section of aluminum channel approx. 1" x 2-1/2 or 3". It should remain fairly straight and would not be subject to flexing easily.

HTH Bill

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Ken wrote: > I've been looking for a good straight edge for a while now. > I want it to serve two purposes: >

You need two(2) different tools.

1.) Straight edge for a cutting guide.

Get an aluminum angle 2"x2"x1/8"x96" and a couple of C-Clamps (I use

3") from Home Depot, etc.

2.) Straight edge to determine if hand planed stuff is flat.

Get an aluminum angle 3/4"x3/4"x1/16"x96" again from Home Depot, etc.

Flip the angle upside down and use the apex as a knife edge.

If you see daylight, it's a low spot.

In the boat building business it's called a fairing batten.

Using it correctly, a 1/32" error stands out like ugly on an ape.

Have fun.

Lew

Reply to
Lew Hodgett

my best long straight edge is a piece of 7074t6 aluminum- your basic aircraft aluminum- that I got at a junkyard. it's about 1/4" x 6" x 7' or so and is as straight as I can measure. it cost me about $11.00

Reply to
bridgerfafc

Grainger and I would guess MSC and McMaster-Carr as well have aluminum straight edges of 4, 6, and 8 ft length. I have a 6 footer that I use for hand jointing among other things. IIRC the cost was under $20 about 5 years ago.

A steel one would be nice but the price of these Al straightedeges is hard to beat. They do require some care to prevent flexing when being used.

I do remember when I purchased it, I had looked up the stock number in the catalog before I went to Grainger. When I went to the counter a young lady waited on me. I gave her the number, she relayed it to one of the warehouse workers, who brought it out to the counter a few minutes later. It was all I could do to keep from laughing out loud when she said, "My, that's a long one, isn't it!"

Reply to
lwasserm

"Ken" wrote

You can tell a great deal by attempting to swivel a straightedge.

If the work is convex or contains local bumps, it will use the humps of these features as a pivot.

If the work is concave, it will just swivel at the end points.

Can save a lot of backache!

Jeff G

Reply to
Jeff Gorman

"CW" wrote

Only providing that the straightedge is not bowed.

If inclined even slightly from right-angles to the surface, it will give a false concave or convex reading.

Jeff G

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Jeff Gorman

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