Thread: Thicknesser cutting unevenly

Reading this and your router thread, an unkind person would say "you get what you pay for"

First thing I'd check is whether there is anything about the table that is causing the timber to ride higher on one side than the other.

I haven't pulled apart a GMC thicknesser, but mine is a similar portable unit. The cutter head is raised and lowered by two threaded rods on opposite sides which turn in bushes in the head. To fix your problem, I would disconnect the winder apparatus so that they can be rotated independently of each other, and I would wind one side up or down a turn or two (depending how course the threads are), then do a test cut. Rinse and repeat until perfect.

I've got a similar problem on an entirely different piece of Chinese junk cast iron planer thicknesser combo. The head is fixed and the table below is raised or lowered on a central threaded post. I think the bed either pivots marginally over the central post or the castings are not finished true to the planer head. The cut on the planer side of things is fine, it is the thicknesser that has a problem.

I'm considering trying an auxillary bed by running a length of whiteboard through the thicknesser then flipping that over and using it as a new base to see if it cancels out the misalignment.

Thanks guys, Silent you're right about what you pay for but I think they both worked better before so I'm hoping they will work or else another upgrade .

Tiger,

You haven't just recently replaced the knives in it?

G'day Steve, well actually not replaced because I couldn't find replacement blades for it so I took them out and tried to sharpen them. I used the supplied jig to put them back and thought that I had put them back properly.

Aha! The plot thickens!

My blades supposedly can't be sharpened because they are located by way of a couple of pins in the cutter head which fit holes in the blade. They can only go in one position and so if you try and sharpen them, you'd have to be spot on with removing equal amounts of material across the width of the blade.

Does the jig reference the cutting edge or the back of the blade?

Had the same problem last time I put new blades into my GMC....cutting a taper. Reset the blades twice before I got them right.

My thicknesser blades were actually reversible so it saved me trying to source replacements or finding someone that will actually try and sharpen them.

Tiger,
I would check all blades are absolutely straight after sharpenning if you can do that without removing them. If they are not absolutely straight, try to guage how far out they are off straight to determine whether they are worth regrinding. I can get them ground in Croydon if that helps. I can also loan you dial guages, magnetic stands etc if need be, so long as there is somewhere to work from.
EDIT My sharpener can handle blades to 600mm+ wide but I have forgotten their minimum depth, and never knew the blade depth for the GMC, so they may or may not be able to regrind them, but I can put you in touch so you can enquire.

If the blades are straight and mounted true, then the issue has to be the height adjustment system. These are normally two or four threaded rods operating in nuts on the head, all linked together and to the drive handle spindle by a chain and sprocket system. Over time the chain can stretch or the tension adjustor can release tension a bit allowing the lifts to get slightly out of sync. I have the grizzly equivalent manual for the big Triton which deals with retensioning it but it is a four post unit. Grizzly do have a few smaller units and the manuals are freely available to download. It might be worthwhile to check their range for a similar unit and download the manual(s).
Failing that try for a manual for a 909 brand unit sold via Masters, as their stuff is mostly derived from ex GMC products.

Come back to me if you need help.

Thanks again guys, I will have another look at the thicknesser as soon as I can but I remember using the jig a couple of times to get it right. All I actually did to the blades was hone them rather than sharpen them, I didn't think I had taken that much off them.

Thanks Malb for your offer, I'd hoped to get new blades but was unsuccessful so I went down the honing route, I have a dial indicator and I'll check it out, will let you know.

Finally had a chance to look at the thicknesser and found that the blades were not sitting properly in their slots ie they were sitting in a tapered position. I'm sure that when I set them in that they were in the correct position as no way would I have had them the way they were sitting on the weekend. I also discovered that they were double-edged and in fact I had not sharpened them but simply turned them around. The side that was cutting had some small nicks in them nothing that wouldn't come out with some slight grinding. I worked on this late at night so haven't had a chance to test it but will tonight, thanks for your help.

Yep! Tiger that was my silent guess as to your problems. For memory the blades have three retaining screws and if you don't tighten each a little at a time you often will end up with one end of the blade higher. I'm glad it worked out OK!

Mulga, mine has 6 or 7 screws but I'm sure I tightened them properly last time, I did hear a noise once when I fed some hard Redgum through, maybe that distorted the blades, don't know.

And if you want replacement blades you can always go to masters and get 909 blades seeing its the same tooling to make them. Go to the masters site and lookup 909 thicknesser and see the gmc logo's on it.