Planer Producing Convex Edges - Any thoughts?

[OPJ]

Hi guys,

I noticed this minor problem with my planer thicknesser (Axminster AW106PT) many months ago but, I've just kind of lived with it. It isn't a huge problem but I can't seem to get a perfectly straight edge from the machine. When I place two edges against each other they're not hollow in the centre but there's a enough of a gap towards the ends for me to see they aren't perfectly straight (I'm not talking snipe here!).

I've been through all the usual checks - my knives are all the same height and I've checked the height of the cutting circle in relation to the outfeed table using the block of wood and 3mm lines method.

Now, I'm wondering if this has something to do with the 1m Straight Edge I've been using from Axminster? - I know these have been frowned upon from forum members in the past. I've checked the length of both tables with a light source from behind and I can't see a gap. Running a scrap of wood over the gap between both tables is smooth - there is no suggestion the timber would ride up over the edge of the outfeed, for example.

Or, perhaps it's my technique! I admit to pressing down too hard (sometimes) when planing a face, though this largely depends on the type of timber I'm using. I try keep my edges fed at a constant speed and maintain pressure on to the outfeed ASAP.

Sorry, I've gone on quite a bit! :roll: Does anyone else have similar problems with their machines? Any advice on buying a 1m straight edge?

As I said, I don't consider this a major problem - it gives you the equivalent of a 'hollow' when edge-jointing boards, I believe. All the same, it would be nice to be able to plane a dead-straight edge some times...

Any thoughts would be appreciated.

Olly.

 

[p111dom]

This was the issue that drove me mad with the my Record to the point where I don't use it as a planer any more. If your boards have a gap in the middle, I guess you would call that concave it's usually because your outfeed table in relation to the infeed side tilts down ever so slightly. For your problem the reverse would be ture so the outfeed table is tilting up slightly. I don't know your machine but usually the only way to check is to set the outfeed table higher than the in feed, preferably above the cutter block. Place the longest, truest straight edge you have and clamp it to the outfeed table. Then with a micrometer or similar measure the vertical distance between this edge and the infeed table at the start of the infeed table and just before the gap for the cutter block. They should be the same. They are probably not. The problem is that on most machines you cannot adjust this alignment. On the record you could which you would have thought would be a plus but the adjustment screws were always vibrating loose so I would have to set this all the time. The easiest solution is to just take a deeper cut. If you're cutting at less than a mm then that could be your problem. Cutting at 1.5mm of 2mm if possible allows more material on the outfeed side of the planer. The initial cut might start out at 2mm but may finish at the end of a long board taking off only 0.5 of a mm. That's fine as it will still give you a stright edge but setting the depth of cut on a machine that has this problem would result in a concave or convex result.

 

[WellsWood]

In my experience this is usually to do with outfeed table height relative to knife edges. Check that they are properly sharp and set.
I find a dial guage indispensable for accurate setting of planer knives, and set mine only about 1 1/2 thou (0.0015") above the outfeed table.
Beware of sharpening knives in-situ on machines without adjustable out feed table height, as you are removing material from the edge (obviously :roll: ), and this can have quite an affect on edge straightness in particular after a couple of honings.

 

[OPJ]

Thanks Dom, interesting point. I do generally take off a maximum cut of 0.5mm, yes. This is because I generally try and work with only English timbers, where the grain can run wild! I'll try taking a deeper cut with some softwood and see if that makes a difference.

What I reckon could be happening is that the table is moving slightly as it is lowered - as you have pretty much suggested. I don't think there's any kind of adjustment for this.

 

[bjm]

As Mark said it is down to the knives being ever so slightly higher than they need to be in relation to the outfeed table. In theory the cutter block should be at the height of the outfeed table but in practise needs to be a fraction higher. If there is too much discrepancy once the front of the timber has passed the cutter block and you transfer pressure onto the outfeed side you will force the timber onto the table rotating the back end up. You probably won't perceive it but the more you plane the length the greater the error will get and you end up with a convex cut. A little trial-and-error adjusting the height of the outfeed table normally rectifies the problem.


Brian

 

[OPJ]

Yes, that does describe what it feels like is happening sometimes... I think I'll try and raise the table so that the block moves by only 2mm next time, thanks.

 

[MooreToolsPlease]

are both tables parallel to one another?
The over hand I have in my shop's tables weren't parellel and had a similar effect to yours, after spending a couple of hours shimming it out I had it to within 0.05mm parallel anywhere on the tables.
Made all the difference