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How flat is flat enough for a straight edge?

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Forum topic by Sirgreggins posted 354 days ago 1042 views 0 times favorited 15 replies Add to Favorites Watch
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Sirgreggins

292 posts in 839 days


354 days ago

I’m looking to add a jointer to my shop soon. I’m a recent college grad so i dont have much money. I saw an iGaging straight edge at Grizzly for $50 and a Veritas one from Highland woodworking for $65 (both 36-38”). I know that these are relatively inexpensive for the kind of accuracy they claim but like i said i dont have much money. otherwise i’d be going with Starret. I have a decent carpenters level that stays in the case so it doesnt get dinged, but i doubt its flat enough to set up. Of course if you guys think this is accurate enough then i’ll use that. Both of these straight edges claim to be within .003” but ive read mixed reviews on both. What are your thoughts? Thanks as always


15 replies so far

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Dallas

2857 posts in 1091 days


#1 posted 354 days ago

An old guitar string will be more accurate than anything you could by with a straight edge.

Consider this:
Beautiful wood work and furniture was created thousands of years ago with nothing as close as a .003” tolerance. Wood moves. Even if it’s dead, it moves.

-- Improvise.... Adapt...... Overcome!

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HorizontalMike

6915 posts in 1517 days


#2 posted 354 days ago

To be honest, I just use the 3ft, 4ft, and 5ft versions from HD. The 5ftr is just $11, and I have had good luck with them for years. I am about to replace the 3ftr because of wearing it out after making repeated cuts/marks with a razor. Why spend a fortune…

http://www.homedepot.com/p/Johnson-60-in-Aluminum-Straight-Edge-Ruler-J60/100140425

-- HorizontalMike -- "Woodpeckers understand..."

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firefighterontheside

3356 posts in 460 days


#3 posted 354 days ago

I’m happy to hear you guys saying that. I use a straight edge like Mike mentioned. Seems straight enough to me. My joints close up.

-- Bill M. I love my job as a firefighter, but nothing gives me the satisfaction of running my hand over a project that I have built and just finished sanding.

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Loren

7270 posts in 2251 days


#4 posted 353 days ago

I use a level. I have a couple of expensive 24” straight edges
but for jointer setups… meh. Not needed.

-- http://lawoodworking.com

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NiteWalker

2709 posts in 1180 days


#5 posted 353 days ago

I have 24” and 38” veritas aluminum straight edges and they’re great. Plenty accurate for setting up woodworking machines. I though I’d have buyer’s remorse for not buying a steel starrett, but the aluminum veritas are great.

You can get them cheaper direct from Lee Valley.

You always hear about how wood moves, so accuracy to .003 or whatever isn’t needed. The thing is you’re not setting up wood; you’re setting up your machines, where that .003 can make a difference.

-- He who dies with the most tools... dies with the emptiest wallet.

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JoeinGa

3107 posts in 610 days


#6 posted 353 days ago

.003??? REALLY? What are you building? medical equipment? or airplanes to government specs?

Geeze, if anybody thinks wood that is within .003 out-of-flat wont clamp up and the joint be invisible is WAAAY more anal than I am :-)

-- Perform A Random Act Of Kindness Today ... Pay It Forward

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Sirgreggins

292 posts in 839 days


#7 posted 353 days ago

i’m never concerned with wood being within .003”, ive just heard that one might want to set their machines up to be within that tolerance. I will use my level. Thanks for all the great feedback. LJ’s is the best place for WW info around.

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RobsonValley

26 posts in 367 days


#8 posted 353 days ago

There’s a great advantage in being able to align machinery to that sort of tolerance.
You can never blame your golf clubs for your lousy play.

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BJODay

328 posts in 546 days


#9 posted 353 days ago

I was using the “5 cuts to perfect cross-cut sled” to square up my sled fence. I was getting frustrated because I kept adjusting it back and forth and couldn’t get closer than o.003” over the length of the fence. Then I woke up and thought 0.003 ” is a pretty small margin. A sheet of paper is typically 0.004”.

Cut yourself some slack. I would purchase a level. Then you have a tool that can be used for more than one job.

BJ

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Bogeyguy

458 posts in 671 days


#10 posted 353 days ago

Amen!! Not meant to be a religious statement. LOL!

-- Art, Pittsburgh.

View darthford's profile

darthford

532 posts in 527 days


#11 posted 353 days ago

I don’t have the time or patience for frustration, these are my frustration fighters -

Starrett combination square with 12” and 24” satin chrome finish blades. Your average HD square isn’t square.

Mitutoyo coolant proof digital calipers, 6” or 8”. In addition to using them in the shop I almost always takes these to the stores and lumber suppliers.

Dial indicator with magnetic base and T slot jig for setting up tools.

Incra MITER5000 Table Saw Miter Gauge with Sled and Telescoping Fence.

Sharp blades and bits of good quality.

These shop lights with daylight bulbs http://www.homedepot.com/p/Lithonia-Lighting-Industrial-6-Light-High-Bay-Grey-Hanging-Fixture-IB-632-MVH/202193185?N=dnZwv#.Ugfbw8LD-Uk

You can do some fine work even with less expensive power tools if you have the tools to dial them in accurate.

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Sirgreggins

292 posts in 839 days


#12 posted 353 days ago

How do i use a guitar string for determining flatness? I understand that under tension the string straightens out but is there a jig you can point me to? thanks

View Dallas's profile (online now)

Dallas

2857 posts in 1091 days


#13 posted 353 days ago

Clamp guitar string to one far end of piece to be checked, clamp other end of string to other end of piece to be checked under tension.
Anyplace with daylight under it is not flat.

-- Improvise.... Adapt...... Overcome!

View pintodeluxe's profile

pintodeluxe

3279 posts in 1417 days


#14 posted 352 days ago

A Veritas straightedge would be great.

A cheap check for your builders level is to lay it on a jointer bed (a known flat surface). Use feeler gauges to check for gaps at each end, and in the middle of the level. Then flip the level over to the other edge and recheck. If the gap remains consistent, and is less than .002” it is accurate to set up a jointer. If the gap changed, your level is not perfectly straight.

Good luck.

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

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Sirgreggins

292 posts in 839 days


#15 posted 352 days ago

Thanks pinto. Another great tip to stow away

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