How straight can you cut?

[mwahaha]

So I finally broke in the 3m rail have had sitting in my roof space for over a year now, just wondering how straight people are managing to get their cuts? Maybe I need more practice or maybe there is a very slight bend on my rail but I can't seem to get a dead straight cut they are all slightly less than .25mm bowed towards the rail over a 2.4m sheet.

 

[Xoncention]

So I finally broke in the 3m rail have had sitting in my roof space for over a year now, just wondering how straight people are managing to get their cuts? Maybe I need more practice or maybe there is a very slight bend on my rail but I can't seem to get a dead straight cut they are all slightly less than .25mm bowed towards the rail over a 2.4m sheet.

1/64" over 3m is close enough if you are cutting sheet goods IMHO.  Have you ran a dial gauge along your track against your splinter guard and compared the difference.  I am sure that you may even have that much play in your saw guides that may be reflected on the pressure you are exerting on the saw against the track as you walk down the length of the cut.

 

[bobfog]

0.25mm?

So you're worried about a quarter of a millimetre over 2440 mm? That's an error or deviation in the cut of 0.0001%.

Frankly I think you're being silly, but if you want a practical answer I'd say there are two possibilities:

1) Yes the rail is bowed my 0.25mm and that's a perfectly acceptable tolerance.

2) The rail could be absolutely straight (unlikely) but when you cut the sheet, the tension released by the cut is causing it to shift/bow slightly. You might try making a cut thats a few mm shy of the final dimensions then make a second cut to get to final dimensions, but I doubt you'll achieve a better result than 0.25mm of error. 

 

[Holmz]

Does the offcut matche the good side?

... whatever goes on that side will probably bow into whatever shape it is.

 

[AlexThePalex]

Seriously? You're worried about 0.25 mm?

 

[waho6o9]

I use a block to keep the rail from shifting when doing long cuts.

View attachment 1

 

[Cheese]

I think you're at the limits of the normal tolerances for aluminum extrusions.

If your 10' long rail only deviates by .010" or less, then you're straightness is .001" per foot. That's in the realm of a machined part not an extruded part. My guess is a realistic tolerance for an aluminum extrusion would likely be in the .010-.015" per foot range.

So, if you can cut to within .25mm over a 3 meter length, I'd be tickled with that result everyday. And take good care of that rail because you definitely have a keeper.  [smile]

 

[SoonerFan]

So, if you can cut to within .25mm over a 3 meter length, I'd be tickled with that result everyday. And take good care of that rail because you definitely have a keeper.  [smile]

+1, keep that rail because .25MM over 3 meters is an excellence result.  Cannot imagine that tolerance ever not working for me.

 

[Jesse Cloud]

Methinks we may have fallen for the OP's stealth gloat....

 

[Svar]

If your 10' long rail only deviates by .010" or less, then you're straightness is .001" per foot.

It is actually 0.00016" per foot. This is arc (circular) where height to length relationship is non linear.

 

[mwahaha]

Methinks we may have fallen for the OP's stealth gloat....

;D ;D ;D

Seriously? You're worried about 0.25 mm?

That is not a very foglike answer Alex

when you cut the sheet, the tension released by the cut is causing it to shift/bow slightly. You might try making a cut thats a few mm shy of the final dimensions then make a second cut to get to final dimensions, but I doubt you'll achieve a better result than 0.25mm of error. 

I allowed 20mm extra on a 90mm strip to counter the sheet tension on the first strip out of the sheet to gauge sheet tension, there was very little in this sheet. Had a 10mm bow over 2.4m once [blink]

This wee deviation is perfectly acceptable for what I am doing at the moment, was curious to see just how straight others were getting their cuts.

 

[AlexThePalex]

Seriously? You're worried about 0.25 mm?

That is not a very foglike answer Alex

Seriously? I've been here 8 years, you're not going to tell me what is foglike or not.  [tongue]

 

[mwahaha]

Seriously?

See now I swear I had put one of these cheeky little guys in there ---->  [wink]
[wink]

I did manage to confirm today that i cannot scribe, rotate, sight and re-scribe a rail accurately to .25mm using a .1mm pencil.

While dissecting reconstituted tree carcasses today i came to the conclusion that the 3m rail is the best thing since sliced bread, it just makes things so ridiculously simple and lightning quick.

 

[Michael Kellough]

Seriously?

See now I swear I had put one of these cheeky little guys in there ---->  [wink]
[wink]

I did manage to confirm today that i cannot scribe, rotate, sight and re-scribe a rail accurately to .25mm using a .1mm pencil.

While dissecting reconstituted tree carcasses today i came to the conclusion that the 3m rail is the best thing since sliced bread, it just makes things so ridiculously simple and lightning quick.

I'd like see that.

 

[charley1968]

That?

 

[Michael Kellough]

That?

"A pencil is a writing implement or art medium constructed of a narrow, solid pigment core inside a protective casing"

""Rapidograph is a" trademarked name for one type of technical pen. Technical pens use either a refillable ink reservoir (Isograph version) or a replaceable ink cartridge."

 

[mwahaha]

I'd like see that.

Sorry the dial isn't in focus, but its still readable, and a little blurry from camera shake.[attachimg=1]

 

[nickao]

This is a joke right.

 

[promark747]

If your 10' long rail only deviates by .010" or less, then you're straightness is .001" per foot.

It is actually 0.00016" per foot. This is arc (circular) where height to length relationship is non linear.

First, did you mean 0.0016?
Second, I don't agree that it's not linear, at least as far as how Cheese phrased it.  If you are out exactly 0.001 per foot, you would be out exactly 0.010 over 10 feet.  There was no mention of an angle.

 

[Michael Kellough]

An unstraight line is an arc, or a more complex set of curves.