How straight does a straight edge need to be?

[Sir Stinkalot]

Ok so it sounds like a silly question but I was after some comment on how straight a straight edge needs to be in a woodworking situation.

I have decided a straight edge would be quite handy in the garage to help set the knives in a jointer, as well as some other general tasks such as checking the alignment of the table wings on the table saw as well as possibly using it as a guide for the router or circular saw.

So my first stop was the Carbatec website to look at the Veritas offerings. They have steel versions from 12" to 36" and an aluminium version at 38". As expected these are fairly accurate along their lengths (0.025mm over the entire length) which seems good, however the length seems somewhat short for checking along the table length of the jointer or to be effective as a tool guide.

I then started to have a look around at some other tool suppliers and came across this range (SYDNEY TOOLS - Straight Edges (http://www.sydneytools.com.au/categories/9814-straight-edges)) which claim:
"A structural grade alloy section, accurately manufactured to offer the straight, clean lines that are essential where a straight edge is required."

The advantage here is the range of lengths available 1200 - 3600mm. They seem to be a 35x85 aluminium section which would be good for a tool guide and the ability to easily stand on its own edge without any support.

Out of interest I had a look around at Bunnings when I was last there. The tool section seems to have regular spirit levels as well as what appears to be screeding tools which appear similar to the ones above but with a handle (although I am not sure just how straight these would be).

There is also the option of just a section of aluminium rectangular extrusion of a similar size to the straight edges above.

At this stage I am thinking that the aluminium extrusion may be the way to go. The thought of being able to get a 6m length and being able to create a number of smaller straight edges is very appealing. Having to wield around a 2400mm straight edge when setting the blades on a jointer isn't all that appealing.

So after that long winded story I would be interested to hear what others may be doing. I am confident that the Veritas would offer the most accurate out of those mentioned, however is a raw length of aluminium going to be just as effective for the tasks I am looking at undertaking?

Cheers

Stinky.

[BobL]

So after that long winded story I would be interested to hear what others may be doing. I am confident that the Veritas would offer the most accurate out of those mentioned, however is a raw length of aluminium going to be just as effective for the tasks I am looking at undertaking?

I have no idea how absolutely straight it is but use a 3m long length of 50 x 25 mm ally extrusion to mark out sheet goods.
I bought a 6m length from Capral and sold the other half at cost to a WW friend.
Something like 35 x 85 would be better.

[Sir Stinkalot]

Thanks Bob. Do you roughly remember the price of the extrusion?

The local Bunnings have 50x30x2mm hollow rectangular Al in 1m @ $17.10 and 3m @ $51.30. I had intended to check out the local Capral place, they have the sizes listed on their website but I would need to check on the prices.

It would be interesting to know how straight that the Al sections would be given they are directly off the mill with no refinement. I have a feeling they would be perfect for a general straight edge for cutting down sheet goods, but I am not sure if they will be accurate enough for machinery setup.

[BobL]

Thanks Bob. Do you roughly remember the price of the extrusion?
I thing it was ~$60 for 6m

[Cliff Rogers]

...The thought of being able to get a 6m length and being able to create a number of smaller straight edges is very appealing. ....

Capral Aluminium Extrusions, Suppliers - Security Windows & Doors - Capral (http://www.capral.com.au/) will sell some of their 6M lengths in halves.

I bought half a 2" x 1" with a .01" wall thickness for about $30 & the bloke chopped it up into 1200, 900, 600, & 300mm lengths for me.

[elanjacobs]

At work we (well, I) have a Veritas 36" steel straightedge for machine setup, mill finish ally extrusions are fine for everything else.

Just as a side note, we bought one of those 'proper' 2.7m ally straight edges (white with a red label, I think the brand was called Master Finish) ... had a 2mm bow over the length. Got a 2.4m as well, same deal. It's now labelled the 'not straight edge'

[pjt]

I use my Veritas 2' long steel for setting the planer tables at the same hieght for a blade change, all I need is 2" over onto the outfeed to tell me up/down/OK
For other machinery setup I use the above or if I need a bit longer I have a 1000mm steel rule



Pete

[Ashore]

aldi is your friend , or will be when they get to SA

[rsser]

I've got the 38" alloy LV. Effectively it's longer than the nominal length as in some applications I can slide it along the surface to be checked.

For short-piece checking I use an expensive UK-made 150mm rule that I've checked against my LV 12" steel job.

To mark out some sheets for cutting I got a long level from Alltools/TotalTools/whatever for maybe $40 and checked it against the long LV; it's concave by about a thou. Good enough.

Alloy is prone to dings so take care with it if you want not only to check but to mark.

[FenceFurniture]

There is also the local product from Michael Connor Woodwork:
Workbenches and Accessories (http://www.michealconnorwoodwork.com.au/workbenches/workbenches/workbenches.html)

scroll to the bottom of the page.

[starr]

It depends on what you want to do. If you are jointing edges to glue together, it pays to have an accurate straight edge. Blackwoods (which has offices in every state) carries a range of steel straight edges from 600mm to 3m in length. https://www.blackwoods.com.au/search/straight-edges/202004872

I have a 1500mm one and use it often to check for flatness. They aren't cheap, but are accurate. I could use a shorter one at times, but it is nice to have the length when joining boards.

I don't know how good the aluminium ones are, but they would be lighter (but I suspect easier to damage). As you say, being thicker, they could stand up on their own, but they are that shape to give enough strength to keep their straightness.

For accurate work I just don't think that buying a piece of extrusion would be accurate enough, but you might get lucky.

[rsser]

Agree that fitness for purpose is the starting point.

How do you know the Blackwoods are accurate starr?

[starr]

When I plane two edges and the straight edge shows them to be flat, they go together without any light visible at the join, so that's straight enough for me.

I usually put the straight edge on the board and rotate it back and forth a bit. If it rotates at the centre, the centre is too high and similarly for the ends. I then use a thin piece of paper to make sure it doesn't slip under the edge anywhere along the board being checked.

The company should be able to tell you how accurate the straight edges are guaranteed to be (I'm surprised the website doesn't state this.)

[rsser]

Yeah.

OP asked for something reliable at the get-go as the Yanks say.

I was surprised to get my result with a cheap level.

But could only know that with the benefit of quality gear. The maker guarantees 'The reference edge is machined flat to within 0.003" over the entire length.' re V. alloy straight edges.

[rsser]

Re fitness for purpose, my second bandsaw turned out to be somewhat agricultural.

The wheels could not be adjusted to be co-planar (the motive for getting the long LV/V straight edge).

The blade guides were a pox to reset after a blade change.

Well as it turned out it was perfectly possible to cut a straight line without co-planarity.

And blade changes could easily be reduced by using a bimetal blade and sharpening it in situ.

Horses for courses.

[Tung tied]

I used a 3m piece of rectangle ally from bunnies and cut it into 2 x 1.5m pieces for a table saw fence extension. (edge on edge high, not long)

To find a straight piece, I put two of their longer levels together like starr and looked for the gap. Then took this to the aluminium stand and went through the pieces until I found a reasonable straight one.

Cheers

Bryan

[GraemeCook]

Good Morning Sir Stinkalot

Possibly the best value for money Strait Edge is a good quality spirit level with milled faces (not extruded el cheapo). Stabilo is excellent and the 1500mm is not much dearer than the heavy duty strait edge that you quoted. And you get an excellent level, as well! Mine are 200, 600 and 1500 mm, which gives lots of versatility.

For longer lengths a section of heavy duty aluminium can work well. It must have thick walls, at least 3mm, to resist denting. It must also have fairly large dimensions of width and depth - mine is 85 x 35 mm with square corners, not rounded. This is stiff in the 2.5 metre length I use.

For light jobs, steel rulers are the old stand-bye. Mine are 150, 300, 600 and 1000 mm. Again, lots of versatility.

I have been trying to stop buying crap tools for years, and the move from el cheapo to Stabila levels was a good one. I do not feel any need to change my other strait edges.





Fair Winds

Graeme

[Sir Stinkalot]

Thanks for all of the feedback. That is one of the great things about this forum ..... you post what on the surface seems like a simple question and it open up so many other avenues.

I think the problem I have is that I am trying to kill two birds with one straight edge. For machinery set up I think I need something that has been machined to be flat. For the second task that I was hoping to also be able to achieve (as a guide for tools) being machined flat is perhaps not so important.

It sounds as if purchasing Al extrusions or even some of the more generic straight edges may be a bit hit and miss in terms of how accurate it will actually be. It sounds as if some have been lucky, others less so. Having a reliable straight edge to check the quality of the other straight edge seems to be the way to go :U.

So after considering the replies I think I might settle on the 38" Veritas Aluminium version from Carbatec. At $60 its not particularly cheap but it falls within the range of the more generic 2400mm long straight edges which would be good for breaking down large sheets but would be unwieldy for machinery set up. I have quite a few other Veritas products and I am sure it would be a good quality unit.

After I get a reliable straight edge I can then use it to get a reliable Al extrusion to use to break down sheet goods.

Cheers

Stinky

[Glennet]

So after considering the replies I think I might settle on the 38" Veritas Aluminium version from Carbatec. At $60 its not particularly cheap but it falls within the range of the more generic 2400mm long straight edges which would be good for breaking down large sheets but would be unwieldy for machinery set up. I have quite a few other Veritas products and I am sure it would be a good quality unit.

After I get a reliable straight edge I can then use it to get a reliable Al extrusion to use to break down sheet goods.

Cheers

Stinky

Good choice, it's easy to handle and versatile.

To cut sheets with a circular saw I use the factory cut edge of one of the sheets as a guide.

For a long level I use 50 by 25 steel tube and a magnetic spirit level.

[hiroller]

Following Derek's revelation of the Magic Square this week in the Handtools section, I can't help thinking that what you really need is a magic straight edge!
Magic Square - YouTube (http://www.youtube.com/watch?v=dB0MBGiX8TQ)

[GraemeCook]

..... the more generic 2400mm long straight edges which would be good for breaking down large sheets but would be unwieldy ........


True enough, Stinky.

For years I followed Glenn's technique for breaking down sheet material but it does require a large flat cutting surface. Lots of improvisation! Then in a stroke of genius I bought a length of 50 x 25 x 3 mm Al extrusion and cut it to exactly 2400 mm length. I had a real strait edge ! On my first cut I discovered that most sheet material that is labelled 2400 x 1200 is actually 8 x 4 feet. The length is not actually 2400 but a slightly longer 2440 mm. A strait edge that is 40 mm shorter than the material that you are cutting is a right PIA, and introduces lots of subtle errors. Also the 50 x 25 extrusion flexed a little over the 2400 length. I almost cheered when one of my klutzy mate's Landcruiser ran over that strait edge.

The replacement was a half length (3 metres) of 85 x 35 x 3 mm Al extrusion and it worked very well but was a pain to store - my then shed only had 2550 mm height. Then I cut that strait edge to 2500 mm - about 60mm longer than most sheet material - and achieved the best compromise. 25 years later I am still using it.



Fair Winds

Graeme