Planer/Thicknesser problem

[DaveR]

Hello all

Just signed up to UKWorkshop having found answers to various problems here in the past, so first off thanks for all of that! However I've so far been unable to find a solution to my current quandary so hoped some of you knowledgeable folks might be able to help.
I recently 'upgraded' my little benchtop planer/thicknesser to a Metabo HC260C and am experiencing some unecpected results - after a couple of passes over/through the machine the stock does not come out flat across its width. A central section of the board is flattened but the edges drop away curved, having had more material removed than the centre.
If the board rose to a single point it could be explained by the two knives being set oppositely and unevenly along their length, but the flat centre section seems to throw that theory out.
When this first happened I assumed it was down to bad technique on my part (not having a huge amount of experience with planers) but it happens just the same when using the machine in thicknesser mode, so I think that eliminates that theory.
Finally the effect becomes more pronounced with more passes over/through the machine, scrapping any thoughts of somehow having ended up with peculiarly shaped knives.

Can anyone point me in a direction worth investigating? It's got me beat. As I say I'm fairly new to the P/T world and currently have one that I can't flatten boards with!

Thanks in advance

Dave

 

[williams1185]

it could be one of two problems firstly the knives could have been incorrectly ground leaving them hollow in the centre or they have been fitted incorrectly meaning the bolts have been tightened in the wrong order , i would suggest removing them and place them together cutting edge to cutting edge to check first to see if they were ground wrong if theres a gap in the middle then thats the problem they need regrinding if theres no gap check your manual for correct setting of the knives generally you start in the centre and tighten outwards but dont overtighten

 

[Chrispy]

Can I ask a few questions, is this a new machine or second hand?, does this happen on other pieces of wood or just this piece? How thick is this board? Does this happens when surface planing and when thicknessing? when you say it gets more pronounced do you mean one pass = 0.5mm gap both sides two passes = 1mm gap both sides three passes = 1.5mm gap that kind of thing? if so there is something really wrong going on.

 

[Myfordman]

Is the table made of sheet steel? It could be bending under load.

 

[Mcluma]

it could be one of two problems firstly the knives could have been incorrectly ground leaving them hollow in the centre or they have been fitted incorrectly meaning the bolts have been tightened in the wrong order , i would suggest removing them and place them together cutting edge to cutting edge to check first to see if they were ground wrong if theres a gap in the middle then thats the problem they need regrinding if theres no gap check your manual for correct setting of the knives generally you start in the centre and tighten outwards but dont overtighten

Nail on the head, you have tightened the inner screws to much therefore it makes the knife hollow. it sets it in a curve

 

[Hemsby]

As already mentioned I would remove the blades & check the flatness of the cutting edges, assuming they are ok, when you fit the blades only nip the screws tight in the correct order then progressively tighten them to the required tightness again in the correct order

The sequence is centre screws then the outer ones.

I have the same machine and have no problems producing flat stock.

If you do not have the instruction manual and would like a copy I can email you same

Regards

Keith

 

[DaveR]

Thanks for all of the quick replies. Really appreciate them as I was going round in circles.
It seems the bulk of the problem was that I'd overtightened the knife-retaining screws. (Surprised at how far that had curved the knife/block -I was getting over 1mm deviation at each side of an 8" board!) With the knives reset and screws nipped up less the problem is almost eliminated. A bit embarrassing on my part, but I guess that's a lesson against overkill!
I think what error's left is likely down to the grinding of the knives themselves (tried the edge-to-edge method mentioned and they do look to be slightly hollow). With that in mind does anyone know of a reputable sharpening service / replacement knife supplier -either mail order or in the North East? I bought the machine new and the supplied double-sided knives appear to be hollow on each edge..

Thanks again

 

[Doug B]

Double sided knives are usually disposable ones, I'd take them back to the supplier, show them the deviation & ask for them to be replaced.

 

[SPSlick]

I use Gardner Grinding in Benton use google for his number or pm me