This is a supplemental article to accompany my Youtube video “super slippery planer thicknesser bed hack”
A few years back I bought this old Sedgwick MB 12″ x 9″ planer thicknesser, and although mine is quite an old version, the MB model is still in production even now, with various improvements over the years. They are really well built industrial machines. I like my version because it has depth adjustment on both the top in-feed and out-feed tables, which has some advantages, and the top tables are made from a lovely high carbon cast iron which is really slippery and enables the wood to glide across with ease.
What I am not impressed with though is the thicknessing bed; it is quite worn and no where near as slippery, and two rollers built into the middle of it, presumably some attempt at reducing the friction, but they cause more problems than they solve; introducing snipe if they are set high enough to make any difference, and getting clogged up with chippings all the time.
Removing the rollers causes further troubles, leaving a gap in the bed for the timber to get snagged on, and said gaps being right beneath the feed rollers means the timber is forced down into them, it is a losing battle! so this called for more extreme measures…
Super slippery planer bed Revision A
After doing some research on interwebs, primarily looking for materials with a very low coefficient of friction (at a reasonable price) and being tough enough to have timber run across it, I found a material called Ultra High Molecular Weight Polyethylene or UHMWPE which is a plastic material used in applications where abrasion resistance and low friction are required. I promptly ordered a sheet in 10mm thickness.
Fitting was relatively easy, I lowered the inner bed rollers out of the way, and removed the outer support rollers, which had worn so much that they had sagged below the bed height anyway, and in their place I added some 24mm plywood blocks. These allow for an extended 1m bed for extra support, and an easy material to screw into. Just two wood screws were used at the in-feed end. I also added some double sided tape to the iron bed, believing it might keep the UHMWPE sheet flat. Due to the extra thickness I also needed to move the thickness gauge up by 10mm.
It worked! (kind of)
Things were really promising in the beginning, timber would very rarely get stuck in the thicknesser, and when it did it was usually caused by trying to bite off more than the machine could chew, and sniping was completely eliminated. But as time went by I started to notice a problem; Smaller sections of timber were coming out of the thicknesser out of square. I thought this was a bed levelling issue at first, but when I tried to diagnose this by running a 12″ wide block through the thicknesser it came out perfectly flat! This confused me for quite some time until one day, by chance, I spotted the problem.
I happened to be crouched down and looking down through the apperture while feeding in a small section of timber and noticed as the wood made its way through the machine I could see the UHMWPE being pressed down in the middle, it had apparently developed a hump in the middle! now this made perfect sense, if a small section were to ride down either side of this hump it would kick the wood over and plane it out of square!
Back to the drawing board (Revision B)
After thinking about this for some time I decided on a solution; I planned to make an aluminium/UHMWPE composite sandwich (yummy) and combine the properties of two different materials. I had used some cast aluminium tooling plate on my folding spindle moulder fence and was very impressed with its flatness, it is precision ground on both sides so should be perfect!
I ordered a 6mm plate at 300mm x 1m. in retrospect I think 6mm is probably overkill, it is available down to 5mm and it is very rigid so this would be perfectly fine, infact using cast tooling plate is probably overkill in of itself, and standard 4mm plate would probably do the job, just make sure you get it saw cut, if it is guillotine cut; the edges get rolled over and the plate sometimes slightly bowed by the cutting action.
The UHMWPE has a similar supply problem and is only available (easily) down to 5mm thickness, it would be just as effective even down to one or two millimetres thick, since it is going to be glued to alluminium anyway, and just like the 10mm sheet, the 5mm isn’t anywhere close to being flat! just the nature of the material I guess, it isn’t an accurate engineering type material.
Plastics are often notoriously difficult to glue, especially Polyethylene based plastics, and this UHMWPE even more so, it is contrary to the characteristics to be able to bond it! some research on the net suggests “flame treating” the surface, basically running a hot propane torch flame across the surface for a few seconds and then bonding with epoxy. Not being familiar with this I went with the typical approach for Epoxy which is to simply provide a rough key on both surfaces, since epoxy is designed for just that.
I used brand new 36 grit emery which really scratched deep into the plastic and hopefully will give a long term bond, my rationale is that the surface area of the bond is huge in relation to the load it will see, in fact most of the load is pressing the plastic against the aluminium, and the sheer load caused by the wood feeding across should be absolutely minimal, which is kind of the point of using a low friction material in the first place! Full surface bonding being important here, not just for the bond but also to maintain flatness, I decided to drag out the Vacuum membrane press.
Final surface prep
The yummy composite sandwich came out of the press perfectly flat, at least according to my Rabone chesterman steel rule! Im sure it is flat enough for a planer thicknesser bed at least. This being said I decided to run the assembly through the drum sander to skim it down a little, primarily to negate to need to move the thickness gauge on the machine (again) which would mean drilling another set of rivet holes 1mm or so away from the current holes! but skimming it did have other advantages.
I ran the assembly through the drum sander probably thirty or forty times! well it is abrasion resistant! it took around half an hour to reduce the thickness by 1mm. I ran it through at an angle, alternating end to end and left to right which produced a kind of hash pattern texture on the surface, these very slight ridges reduce surface contact and so should further reduce friction. the sanding also created a kind of fine fluffiness to the surface which made it feel even more slippery still, so while not so necessary I think it is worth running through a drum sander if you have access to one.
The operation seems to have been a perfect success, having planed some very small sections it is now planing perfectly square, and seems even more slippery to boot. Over all I think this is worthwhile upgrade to any planer thicknesser with some small compromises; The most obvious being a 10mm reduction in thicknessing capacity, and the other being cost, the UHMWPE came in a 1m x 0.5m sheet at around £64 and the cast tooling plate was £120 (or around £50 for 4mm 6082T6), not too bad really considering the improvement it makes.