3m saw guide rail. How straight is straight?

[blackteaonesugar]

Just got a new 3m guide rail for my Makita track saw as I was having slight issues with getting a really straight cut with two 1.4m rails joined together.

I thought it unlikely that this new 3m rail would be absolutely straight but thought it'd probably be fairly good.

I've done a cut through two 12mm boards, then flipped them and put the edges together.

Over a 2.4m board I've got maybe 1-2mm gap at the ends, meaning there is a little bit of 'belly' in the cut.

I tried it again, sort of pushing the central part in a bit then cutting. A little improvement but belly still there.

Is there any way that you can actually straighten or get a rail straightened, or at least improved?

I'm not sure if expecting 100% straightness in an extrusion over that length is just unreasonable or if it can be achieved.

I imagine mostly it would be straight enough, but potentially it might cause issues in some instances.

What to do?
Suck it up, send it back, hit it with a hammer?

 

[marcros]

Is it the rail or is it blade deflection? There have been a couple of posts on this recently, both on table saws and track saws.

Could you put the track on a piece of ply, draw a line, them check the distance from the factory edge to the line in a few places.

 

[DBT85]

get on to them and they'll probably replace it.

As above thouugh, try drawing a line and seeing if the cut matches the line. If not, try running the saw through again.

Though I don't think it's intend for joining two faces as you are, just for cutting long sheets that are then going to be used in a carcass where the amount you're talking about probably won't ever be noticed maybe?

 

[Britman]

Did you clamp the ends?

 

[Rorschach]

0.4mm per meter inaccuracy I would consider very good myself. I would think the natural flex in the extrusion would be more than that.

 

[blackteaonesugar]

I'll try the pencil method.

It's unlikely to be blade deflection imho as the blade is literally brand new this morning.
That's the very first cut, and it's 'only' 24mm of mdf.

I didn't clamp the ends no. I rarely clamp the ends to be fair. Usually stays put very well.

 

[Distinterior]

I have a 3mtr Festool rail and I would always clamp it for a long cut such as you have described. It's as near to being straight as I can ascertain....
If you're planning on using the rail to obtain a glue ready joint butting up to another panel, cut both edges at the same time whilst they are butted together and just run the saw blade down the middle where the 2 sheets meet. That way, any run out/ deflection/ belly will be in both panels and the mirror image of each other and when you push the joint together you will not have any gaps.

If its 12mm MDF, then the deflection could well be due to stress in the panel you're cutting....??

 

[Doug71]

I have a 3m Festool rail which seems to be dead straight, when I first got it I cut down 2 strips of ply to check and they fitted together perfectly, I was amazed!

I always cut large pieces oversize to release the tension then trim to size, it's surprising how much some stuff moves.

I rarely clamp the rail and it doesn't seem to make any difference.

 

[Rorschach]

If you can, just to satisfy my curiosity. Can you clamp the ends and then test the flex in the middle of the rail?

 

[Distinterior]

I have a 3m Festool rail which seems to be dead straight, when I first got it I cut down 2 strips of ply to check and they fitted together perfectly, I was amazed!

I always cut large pieces oversize to release the tension then trim to size, it's surprising how much some stuff moves.

I rarely clamp the rail and it doesn't seem to make any difference.

If I'm breaking down a sheet of material with a load of parallel rips and using the Parallel Guides, there is normally enough friction to hold the rail in place. But, if I need to cut a glue ready joint either with the track saw or a router cut, I always clamp the rail and use the method I described above. I'd hate to have the rail move or deflect by .5mm and end up with a gappy joint.....

Clamping a 3mtr rail on a 2.4mtr sheet?.....I'd be surprised if you could even discern any left or right deflection in the middle of the rail.

 

[HOJ]

Might be worth checking the "friction" guides on the saw it self, and ensure you are cutting plumb, not sure about makita, Festool has 2 thumb screws that take up slack.

Also your test cut method, if I understand it, will exaggerate any discrepancy will it not?

My 3m Festool rail is as Doug71's & bang on for my needs.

 

[blackteaonesugar]

Yes this method exaggerates the issue, but that's kind of the point.
If I wanted to edge join the two boards right off the saw, I'd have problems I think.

 

[Richardhw]

As has been mentioned above, the friction guides. The design isn't great for really straight cuts unless you reset them regularly and always have a few sets spareif you need to be that critical. I like my makita over the Festool for a couple of features but super accurate cuts isn't one of them.

 

[petermillard]

In my experience the Makita rails are a lot less grippy than the Festool, so I’d always clamp over that length, personally. As others have said above there are lots of variables on a long straight cut like this, and you‘ll probably need to work your way through them all before you find the issue - which may, indeed, be the rail; but until you eliminate all the others you’ll never be sure. If it is the rail bowing slightly in the centre, a parallel guide in the middle may be enough to avoid the issue?

Interesting point though; I’m not aware of any manufacturer stating straightness/accuracy statistics for their guiderails; given that these are basically fancy/pricey straightedges, you’d think someone would have made hay with accuracy claims by now??

 

[blackteaonesugar]

Well, I tried a couple of other things.

I strung a line from end to end and to my 47 yr old eye it looks fairly good.

I marked a pencil line along the length and rotated the rail 180 to compare, and it looks fairly good.

I shot my laser level line down one of the ridges on the extrusion, again, looked pretty good.

Then I made another cut through my x2 layers of 13mm veneered mdf, but this time clamped both ends. Flipped them edge to edge and weirdly it's almost like my initial issue is reversed.

This time I have a slight parting of edges (perhaps 1mm) in the middle and fairly well closed (but not perfect) at the ends.

This leads me to the scientific conclusion that.....I dunno

I mean these rails we sort of rely on to be straight, but what is straight?
This isn't straight to me.
I don't want to have to think about my cut every time I do one. It's meant to be quick and accurate.
Maybe it's accurate enough for most instances.

I never really took the time to test the straightness of my 1.4m rails on their own or when joined. It was only when an issue became clear when I was trying to edge joint some long boards that I noticed the issue, but then maybe it's only an issue in a narrow set of circumstances...

If any of you Festoolists have a spare ten minutes to try that same cut test it would be interesting to see what you get.

The Makita saw will run on the Festool track right? Maybe I just need to sell a kidney and get that one...

 

[DBT85]

Did you draw a line along the splinter strip before you cut to see if the blade followed the same path? And are you cutting in the middle of a panel or just trimming 10mm off one end?

 

[blackteaonesugar]

Didn't draw a line no, but I'll try that too.

I'm just trimming about 10mm off the edge each time of two offcuts of veneered mdf, which themselves are about 250mm wide.

 

[Distinterior]

So, you've got a .5mm deflection in each panel edge over a distance of 2400mm...? I would agree that's not perfect but this is woodworking and I would have thought that would be within tolerance by a lot of peoples standards.

If the gap is now in the middle instead of each end like before, with all due respect, it is more than likely to be your technique that is the cause of the issue.

As I said in an earlier post, if you want to join the 2 panels edge to edge, cut both edges at the same time whilst butted together and they will fit without any gap.

 

[DBT85]

Didn't draw a line no, but I'll try that too.

I'm just trimming about 10mm off the edge each time of two offcuts of veneered mdf, which themselves are about 250mm wide.

Unlikely to be built in stress then if you're not trimming much off. Clamp it and try the line with a very fine pencil or ideally a mechanical so its a consistent width line.

Again though, this tool isn't designed for this job. Though it can work if done like the above and others have mentioned rather than individually.

In typical use the issue you are seeing is invisible, assuming it happens at all.

 

[blackteaonesugar]

If the gap is now in the middle instead of each end like before, with all due respect, it is more than likely to be your technique that is the cause of the issue.

No,I realise that. We're taking about a pretty small deflection after all but it happens.

Obviously technique-wise, I try to keep my pressure completely in line with the cut but I guess a small deflection is not out of the question.

Hence my initial question really, how straight is straight....
I suppose with a track saw, straight depending on a variety of factors including operator technique.

These 3m tracks don't seem to be all that abundant actually. I wonder if it's partly due to expectations versus reality.
It's certainly going to be straight enough for most tasks.