Multico TH1 thicknesser table not flat enough?

[woodbrains]

Hello,

I've just been thicknessing some timber, nice new set of knives installed and I'm getting a bit of snipe on the infeed end. TBH the machine always has a bit as long as I've had it and I've always just hand planed it out. But today it was bugging me a bit, I should be able to get better on such a solid machine. So I thought I'd check the table for flatness. Now, you might think 'why hasn't he done this before?' as I have adjusted the machine in every way and keep it well maintained. The truth is, I've not had a decent engineers straight edge!

I've been making jigs with some 3/4in tee track and found this is amazingly flat for an extrusion, so much so, it shows how embarrassingly out of flat my Axmonster straight edge is, horrible, horrible tool, that. So I used the track on my thicknesses table and find there is a bump in the middle. I've tested few lengths of the extrusion on the beds of my planer, ( flat as a fluke that machine) all show they are true, so there is definitely a bump in the thicknesses table. Don't have any feeler gauges to hand, but I can rock the straight edge like a see saw. Transversely, the bed is reasonable at any point, but lengthwise, the hump is evident all across. I guess the gap at either end of the straight edge must be about 15 thou or more over 24 inches of bed length.

So, does anyone think I should think about having it surface ground flat? Has anyone had something like this done and is it worth the expense. Does anyone know the cost roughly of this, I haven't a clue what I should expect? Anyone recommend an engineers shop that will do it, would a cylinder head grinding workshop be able to do this? The bed is 12 by 24 inches approx.

Mike.

 

[dickm]

Is it a localised "hump" or a gentle rise and fall? If it's the former and the bed is cast iron (or possible even if its cast ali) then you could try using an engineering scraper? Lots of metalworkers (me included) have successfully scraped Myford lathe beds.

 

[woodbrains]

Is it a localised "hump" or a gentle rise and fall? If it's the former and the bed is cast iron (or possible even if its cast ali) then you could try using an engineering scraper? Lots of metalworkers (me included) have successfully scraped Myford lathe beds.

Hello,

As far as I can tell, it is an apex like a shallow roof. I will have to take the table off to investigate further, the cutter block, feed rollers and steel frame is in the way. And find my feeler gauges. Could be a lot to scrape flat. I'm not sure it is not intentionally machined that way, the high point is directly beneath the cutter block. I can't help thinking the table would be better flat, though. As far as I can tell, the slight up hill incline causes the cutter to take a slightly deeper cut until the outfeed roller engaged and pulls the wood onto the table, on the other side of the apex. The snipe caused Is not terrible, but is more significant on wider boards, perhaps because the infeed roller cannot exert enough pressure to flatten the board to the table.

Mike.

 

[RobinBHM]

The table could have warped, it does happen with cast iron. Sometimes bolting points can introduce warping. I would think you thicknesser bed is supported at tge 4 corners so unlikely to be that.

I have flattened a surface planer bed with a belt sander before, but its a long process.

I used to have an elektra beckum pl-th I think that was aluminium with a stainless plate on top. I suppose if you could self level the surface somehow, you could stick on a stainless steel sheet. Maybe a piece of birch ply, sanded on the underside to the shape of the bed, then the stainless to that. Might be a carp idea, just thinking aloud

 

[woodbrains]

The table could have warped, it does happen with cast iron. Sometimes bolting points can introduce warping. I would think you thicknesser bed is supported at tge 4 corners so unlikely to be that.

I have flattened a surface planer bed with a belt sander before, but its a long process.

I used to have an elektra beckum pl-th I think that was aluminium with a stainless plate on top. I suppose if you could self level the surface somehow, you could stick on a stainless steel sheet. Maybe a piece of birch ply, sanded on the underside to the shape of the bed, then the stainless to that. Might be a carp idea, just thinking aloud

Hello,

In fact the bed is supported by a heavy casting at the centre. The cast bed is full thickness in this area, to receive the mounting bolts, where the rest is webbed. It is possible the cast has sagged towards each end over time.

It is actually not a terrible idea to put on a secondary table, I have done it before on a PT that would not thickness evenly across the width. It is a good way of machining stock that is normally too thin to engage the feed rollers, too. I would like to get the bed corrected if I can, though if it is cost prohibitive, I might end up doing so. It is certainly the best way to establish if a flat bed will fix the snipe problem before I shell out on a permanent fix.

Mike.

 

[custard]

There's been a couple of posts about localised scraping of cast iron recently. I'm no engineer but that seems like a suitable candidate.