Straight Edge Question

[Allen Grimes]

Is .003 good enough for checking the flatness of jointers, tablesaws and bandsaw tables and wheel coplanerosity?

[Cecil Arnold]

Allen, when you consider how much even dry, sealed wood moves during climatic changes IMHO that should be close enough.

[Allen Grimes]

Umm, are we talking about the same thing here? I meant the machines themselves, not the wood. Im not sure what you meant though.

[Michael Ballent]

Is .003 across the entire length? Sometimes they give specs that say .003 per inch or over some number of inches... If its .003 over 2 or 3 feet I think that is pretty good or even 6ft would be really good, but I am sure something that is .003 straight over 6ft would be some major bucks :D

[Allen Grimes]

Its the 50" aluminum one. It says .003" over the entire length

http://www.leevalley.com/wood/page.aspx?c=2&cat=1,240,45313&p=50074

[pat warner]

<HR style="COLOR: #d1d1e1" SIZE=1> <!-- / icon and title --><!-- message -->Is .003 good enough for checking the flatness of jointers, tablesaws and bandsaw tables and wheel coplanerosity?
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Good for the bandsaw, probably the tablesaw but not the jointer, a precision machine. Depending (if it exists) on where the jointer fence or table may have an error, you may miss it with a straight edge 3 mils out. Just where is the 3 mill error on the blade?
A jointer requires the utmost in precision set up. A 3 mil booger in a jointer, in the right place, can make your day unpleasant.

Routers & Joinery (http://www.patwarner.com)

[Allen Grimes]

Thanks Pat,

So what would you suggest is the minimum amount of accuracy acceptable for a jointer?

[Mac McAtee]

This is gonna get good.

[Mark Rios]

This is gonna get good.


ROFLMAO:D :D :D



Wait, wait....I have to go get my popcorn.

[John Shuk]

I bought the Lee Valley aluminum straight edge and just got it. Remember that people have been setting up jointers without straight edges for a long time. I think it is just fine for me. It is .003+-

[David Abel]

Is .003 good enough for checking the flatness of jointers, tablesaws and bandsaw tables and wheel coplanerosity?

Allen, while I'm not against using an accurate straightedge (I have a LV steel one), if you are getting good results with each tool, it is irrelevant what measurements you get by scrutinizing the tool. IF you are unable to get adequate results from a piece of equipment, that's the time to investigate what's wrong. ie if it works well, the "proof is in the pudding". NO cast iron surface is going to be accurate to .0001 inch per foot. Some variance is to be expected and will not impact the results.

Jointer tables that are not parallel WILL affect results, depending on the severity.

Summary: got a problem with results--investigate the cause. If not, enjoy the equipment and don't "sweat the small stuff".

[Tom Jones III]

I've got a 6" PM jointer. The results are as flat and as square as I am able to measure. I typically don't joint pieces longer than 5' as the tables just aren't long enough and I don't have a need to joint longer.

To setup the table I use a 3' aluminum level bought at the borg and a plastic jointer pal to setup the knives. I'm pretty anal, so if I had better measuring tools I would enjoy using them, but so far I have had more important things to spend my money on.

[Keith Outten]

If you own an EZSmart guide you can use it as a straight edge, it is probably more accurate than a level.

The diameter of the average human hair is about 0.005"

.

[Bob Noles]

Good point Keith and I have heard you mention that before. I really need to write that down in my tips and tricks diary so I'll stop forgetting.

[Jay T. Marlin]

Dust on the jointer bed can affect your setup. Every little thing plays a role.

I highly doubt that your jointer bed is .003 over its entire length unless you own a Martin or Northfield, so here's how you check for flatness.

Get yourself two 4" x 36" x 4/4 poplar boards. Face joint and edge joint both of them. Place jointed faces down on something flat, e.g. your jointer beds (how convenient), and push the edges against each other. Is there a visible gap? If not, your jointer is fine.

[Jay T. Marlin]

Allen, when you consider how much even dry, sealed wood moves during climatic changes IMHO that should be close enough.

People use this argument frequently but I don't really agree with it. A tabletop can cup 1/4" and still look flat if it's held down by the right fasteners. But if you edge glue two boards with a .005" gap in between and don't have enough clamping pressure, the gap is very noticeable.

[Brian Hale]

Joint 2 pieces of plywood as long as your jointer bed. Put the jointed edges together and look for light between them. If you can see light, try to measure it with feeler gauges. Whatever gauge fits between them, divide it in half and that's your error. If you can't see light, you now have a pair of nice straight edges.

As a direct answer to your question, .003" is more than accurate enough. IMHO, .010" would be good enough. This is wood we're talking about and as soon as the jointed edge absorbs any moisture from the air, it'll change by more than a few thou....

Brian :)

[Allen Grimes]

Thanks everybody, I am going to take the majority's advice and go with the straightedge I posted earlier.

[Barry O'Mahony]

I highly doubt that your jointer bed is .003 over its entire length unless you own a Martin or Northfield, ...My Grizzly 12" parallelagram jointer is. ;)

See the book "the care and repair of shop machines" by White for instructions on how to cheaply check for jointer "co-planeness" over long distances.

Personally, I went with the steel 2" straightedge for short-distance things like knife setting, where 0.001 does indeed make a difference.

[pat warner]

Thanks Pat,

So what would you suggest is the minimum amount of accuracy acceptable for a jointer?
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If I was buying and interrogating the surfaces of a potential new tool I'd use Starrett, (~<.001"/in 48" for the one I use). I'd hate to lug a 400 pounder, yonder the hills and find out the tables tilted fore & aft, listed or were otherwise hollowed here and there. A S. Edge out .003" could miss that error.

I'd want to know about the width of the beds and the fence; I'd use my 8.000" S. Edge (http://www.patwarner.com/straight_edges.html)for that; I grind it to <.0008"/8". A four footer would not be useful across the narrow widths no matter how accurate.

Now the issue of length. A careful bed analysis does require sophisticated metrology tools; that can be done in the lab. The next best thing is a straight edge as long as the jointer, but in most cases, simply not practical. You can step a short straight edge strategically and qualify the tables; but I would use nothing less .001"/3' for that.

Everything starts at the jointer; it should yield flat, straight stock. It has but one moving part; yet it is a monster to bring into parallel and set its blades. If the booger is out of parallel, twisted, hollowed, or otherwise mishappen and you don't know it, you will have setup and use problems. However, technique does play an important part and one can joint quite well on a machine that is "out", given practice & skill!
Routers & Joinery (http://www.patwarner.com)

[Matt Warfield]

I just purchased the same straight edge from Lee Valley. Very good packaging! Also, I had it checked out on the CNC machine with a dial indicator. Over the entire 50" length, it deviated less than .001". Hope that helps a bit.