3000mm Guide Rail curve

[phmade]

What is the expected straightness of the 3000mm guide rail?  I have had one for several months and I have been constantly chasing square cuts on my MFT/3.  It turns out that my MFT is perfectly square but the 3000mm guide rail that I rip the material with has a slight bow to it.  When I scribe a line along the length of the rail and then turn it 180 degrees, it varies nearly 1/16" in the middle.  I know this isn't much but it certainly affects the squareness of a cut when I index off the "bowed" edge.  Is this typical or am I expecting too much accuracy? 

I have always stored the rail flat and haven't dropped it or damaged it.  I'm curious to hear if anyone else has had this problem.  If not, is this something that Festool would warranty?  My local dealer didn't seem willing to replace it and told me that I should have always stored it in the box that it came in...

 

[Administrator_JSVN]

Do I understand that you're using a 3000mm rail on your MFT?

Please don't take this as an accusation, but just a general question. Is it possible that you're accidentally introducing deflection of the rail by your technique when moving the saw down the rail?

A straight edge against the rail should be able to determine any issue with the straightness of the rail. But it's possible to "bend" the rail if you are putting lateral pressure on the saw as it goes down the rail.

Honestly, I don't know the "spec" or tolerances for our rails. Let's see if we can confirm the issue is with the rail before moving forward.

Shane

 

[phmade]

Thanks for the quick reply.  I am not using the 3000mm rail on the MFT - I think I explained it poorly.
I am using the 3000mm rail to make rip cuts on 4x8 sheets and then I am moving my ripped pieces to the MFT/3 where I cross cut them (with the standard guide rail).  Because the freshly cut edge of the ripped piece isn't straight, its indexing on the MFT fence incorrectly if that makes sense.  I do not have an accurate straight edge long enough to test the guide rail but marking and line and then flipping the rail 180 degrees should be an adequate test, right?

As far as the technique goes, I don't believe that I'm bending the rail.  And marking a line along the length of the rail with a pencil doesn't exert any force to bend the rail...

 

[Ken Nagrod]

I use the 3000 mm rail frequently with my TS 55 and I had the problem of pushing the saw sideways ever so slightly in the middle section of the rail where it isn't clamped giving me errors in the cut.  You have to make a conscious effort as you walk with the saw down the length of the rail, to keep from introducing lateral forces throwing off the cut.

 

[Administrator_JSVN]

I do not have an accurate straight edge long enough to test the guide rail but marking and line and then flipping the rail 180 degrees should be an adequate test, right?

That seems to be plausible method for testing it. Give that a shot and see what the results are and report back. Thanks.

 

[Ken Nagrod]

If he's marking the pencil line on the strip edge and the strip has been cut off-line, then his pencil mark will follow and be off as well.  The edge with the "hat" might be the better way of marking off of.

 

[bionicus]

Let's trust that OP knows what he's doing and that the rail is in fact out by 1/32" over the 3000mm. What does he do now?

 

[phmade]

I have already marked the back of the rail (along the metal edge rather than the splinterguard) with an accurate .5mm pencil.  When I flip the rail end for end I am getting nearly 1/16" of deviation in the middle.  The rail is definitely bowed.  My question is whether this is typical - would you consider this acceptable?  To me it seems to cause more problems down the line - like when placing that cut edge against the fence on the MFT.

 

[phmade]

Thanks bionicus - I think I'm having more trouble communicating my problem than expected. 

 

[Ken Nagrod]

I don't have the rail out by 1/16".  That seems excessive.  The CNC process of manufacturing the rail should keep a much tighter tolerance than that.  Those long length rails are easily damaged in shipping.  Exchange it if you're dissatisfied.  You paid enough for high quality and accuracy.

 

[Brice Burrell]

Let's trust that OP knows what he's doing and that the rail is in fact out by 1/32" over the 3000mm. What does he do now?

I agree, the op knows what he's talking about and I agree the rail is out a 1/32".  What do you do about it, I don't know, probably nothing.   

 

[phmade]

Can anyone from Festool respond to this?  Just wondering if this would be a warranty issue.

 

[ccarrolladams]

The 3000mm guide rail is such an important tool in my cabinet shop that I own 3 of them, as well as 1 each 2700mm and 5000mm.

All arrived at my shops in their original Festool packaging and in excellent condition. Of course the first thing I did with each of those long rails was check them for straightness and lack of bow. This I do with a laser survey instrument, establishing a parallel line 10mm from the non-cutting edge of the rail. With rail and laser clamped in place I move a target along the rail. Any bow in either direction of as little as 0.05mm is apparent.

As we do with all our guide rails they are handled with care and treated with respect. The long rails have special shelves, one rail per shelf, under our long work tables. We make one of those 18' long especially to protect the 5000mm rail.

Every couple of months when the survey laser is not out on assignment, I go through the same testing protocol with all my rails longer than 1900mm. I test the shorter rails with a 2000mm level which is also a reference straight edge.

 

[harry_]

the rail is 'bent' by 1/32 of an inch in just under 10 feet of rail, aside from the 'point of the matter', this is a problem how? This is wood we are talking about here. Almost any wood that I can think of has more seasonal movement than that.

if my math serves me correctly, 1/32 of an inch == 0.79375mm which may seem like a lot, but when you take 0.79375mm and divide it by 3000mm you get a deflection of 0.000264583333333%. Chasing a problem that many decimal places out in woodworking seems a little over the top to me. Or maybe I am the one who his out of his mind :-X

[2cents]

 

[semenza]

phmade,

Just for the sake of clarity. Is the rail bowed 1/32" or 1/16"  ? 

Seth

 

[mouppe]

the rail is 'bent' by 1/32 of an inch in just under 10 feet of rail, aside from the 'point of the matter', this is a problem how? This is wood we are talking about here. Almost any wood that I can think of has more seasonal movement than that.

if my math serves me correctly, 1/32 of an inch == 0.79375mm which may seem like a lot, but when you take 0.79375mm and divide it by 3000mm you get a deflection of 0.000264583333333%. Chasing a problem that many decimal places out in woodworking seems a little over the top to me. Or maybe I am the one who his out of his mind :-X

[2cents]

The OP said 1/16" in the middle of a 3000mm rail, so you need to quadruple your error! Also, he is cutting plywood which is not affected by seasonal movement and the rail should give him more accuracy than that with which he is getting. If his first cut is off, then all his subsequent cuts will have the error magnified.

[2cents] [2cents]

 

[harry_]

Sorry but no. His 'error' is the one compounded.

When I scribe a line along the length of the rail and then turn it 180 degrees, it varies nearly 1/16" in the middle.

1/16 / 2 = 1/32

But even if that were the case, the %error at 0.000529166666667, is still 4 decimal places out. I realize that plywood has no significant movement, but I am willing to bet you a doughnut there is enough to satisfy that decimal above  ;D

 

[Ken Nagrod]

Whether it's a 1/16" or 1/32", if the rail is out and you're doing fine furniture or cabinetry, you'll definitely see that amount on your finished pieces and have to deal with it somehow.  If a 1/32" isn't important to a joint, why all the fancy tools and techniques to get stuff looking good and fitting tight or snug, however you prefer to look at it.  Can you hide it.  Maybe.  Should you have to?  I say no.  No I say!  Damn thee 1/32"!  [mad]

 

[mouppe]

I was calculating 1/16" halfway along a 3000mm rail, which would be 1/16" over 1500mm, as opposed to 1/32" over 3000mm, or a difference of 4x. If I misunderstood the OP, I hold my hand up.

 

[harry_]

Richard, I think we were both 1/2 right

I came up with 1/32 as it was 1/2 of his measured error. (1/32 error, rotating the rail adds another 1/32).

but at one half the length the error as i understand it, does not double, as the middle would simply be it's maximum error.

Your are correct that my math was wrong as I should have done the % error calculation based on 1500mm which would have been a double.