Bow in sheet after ripping on panel saw

[Sean33]

I'm wondering if I extend my outfeed table would it help?

I recently noticed the sliding table was about 1.5mm higher than the cast iron bed of the saw and I adjusted it so it's JUST a fraction of a millimetre higher than the bed, it helped a bit but still not great.

To be honest i am not sure on that, ours runs the full length and i dont have experience with it not being that way, may be worth a try. Also ours is level to a smidge under on the height.
Have you seen DoctorBobs reply, he explains it better than me on pressure and lifting points

 

[sometimewoodworker]

I don't have a panel saw but use my Festool TS 55 with a 3m guide rail and often have to make three cuts. First to split the sheet, second to straighten and third to make it parallel.

maybe @doctor Bob will have some input on this?

With my TS55 and guide rails I haven’t seen anything like the effects that are being reported, being a few thousand miles away the material I have is completely different in sourcing. My feeling is that the saws are almost certainly working perfectly, or nearly so, and it’s the material being used that’s the problem. It’s quite likely that much of the UK material has the same factory as origin.

If buying on price (most reasonable) then the factory will be making economies in production, these can lead to the problems you are having. “shannon's lumber industry update” podcast has just had a few episodes talking about man made sheet material that make the process and pricing really easy to understand.

Basically there are almost no bargains to be had. Cheaper prices means reductions in quality. The only way an individual can get a deal is if they can get a sheet or two from a cabinet shop that’s buying hundreds of sheets at a time.

 

[Jonathan S]

I have not see any problems cutting Finsa board on my Felder saw, the difference could be I'm Spain and I believe my Finsa boards are produced in Portugal.

I generally rip using the parallel rip guide on the slider, it helps with any sag.

 

[petertheeater]

I would never expect a rip down the centre of a board not to ‘open’ up. I would always cut twice even on a narrower rip.

 

[RobinBHM]

I have been having an awful issue this past few months with my panel saw, say I cut an 8x4 sheet of MFC down the middle, I'm being left with a 2-3mm bow on both sides of the cut. I spoke with an engineer about it, he was too busy to take a look at it but he put it down to board tension.

The blade is good, the riving knife is in line with the blade, the fence is parallel with the blade etc. I've checked everything I can think of but I'm still getting it. I have heard that because of the pandemic and the demand for sheet materials is so high that the sheets aren't being properly kiln dried, is there anyone who has heard that also?

At the moment I have to cut everything twice, rough cut to size and then final measurements, which is a pain.

Any ideas what it could be or what I could do to remedy the problem?

if the bow is a mirror image once cut, ie cut edges pushed together leaving a gap in the middle -then it must be the material.

why are you using 8 x 4 sheets -I wouldve thought full 2800 x 2070 size sheets would be a cheaper way to buy MFC.

I used to buy the big sheets then on day of delivery break them down -say cut off 2 x 600mm rips

funnily enough its easier for cutting if the sheet is cut 20mm over size -then when pushing through against the rip fence the board is supported by the sliding bed. If you cut say within 5mm for a trim cut it misses the sliding bed and wants to fall down in front of the saw.

where are you buying from? -big sheet suppliers like Meyers probably have far higher turn over than a local merchant.

 

[doctor Bob]

if the bow is a mirror image once cut, ie cut edges pushed together leaving a gap in the middle -then it must be the material.

why are you using 8 x 4 sheets -I wouldve thought full 2800 x 2070 size sheets would be a cheaper way to buy MFC.

I used to buy the big sheets then on day of delivery break them down -say cut off 2 x 600mm rips

funnily enough its easier for cutting if the sheet is cut 20mm over size -then when pushing through against the rip fence the board is supported by the sliding bed. If you cut say within 5mm for a trim cut it misses the sliding bed and wants to fall down in front of the saw.

where are you buying from? -big sheet suppliers like Meyers probably have far higher turn over than a local merchant.

Exactly what I do, 2 rough cut rips at 620mm and a 830mm. Baselines and wardrobes get cut out of a 620mm, wall units and shelves etc get cut out of 830mm. I get 20 boards and rip them all up in one go, takes 2 of us about 2hrs.

 

[RobinBHM]

Exactly what I do, 2 rough cut rips at 620mm and a 830mm. Baselines and wardrobes get cut out of a 620mm, wall units and shelves etc get cut out of 830mm. I get 20 boards and rip them all up in one go, takes 2 of us about 2hrs.

Yeah, I learnt its so much easier....cut them up on day of delivery, not many smaller shops have the space to fork them around all the time.

fork extensions come in very handy for getting them off the truck

those sheet sizes are designed for beam saws of course....a bit unwieldly on a panel saw.

 

[Misterdog]

No I do mean panel saw, with a scribing blade and 3.2m outrigger crosscut sliding table.

It's the bearings/runners on your sliding table. Assuming you are getting a concave cut on one side of the blade and a convex cut on the other.

I have 2 Altendorf F90's one is accurate to 0.2 mm using the sliding table, the other is older (1973) and the phenolic runner guides are worn and gives around 0.8 mm 'curve' in a 2.4 M rip cut.

If you use the sliding table for lots of short cross cuts in one part of it's travel, that is where the wear will be.

Last time I looked an exchange runner carriage was around £ 1500 so I live with it.