Thread: Making a veneer cold press

somehow posted twice.

Today I knocked up the veneer press. As you can see its a pretty rough bit of construction - more of a prototype then the real thing.

Used 8 press screws - bought from McJings at $12 each. The upper and lower plattens are made from old kitchen counter tops salvaged from the council clean up. The rest is scrap lumber. Maximum workpiece size is 1000 x 540mm.

Does it work - well it seems to, but it could be a lot better. Looking at the press screws, it seems they are really designed to be used on a press with a subtantial superstructure above the plattens. The screws would be mounted on the superstructure, and when wound downwards they would press on a loose platten beneath. The way I've done it is not ideal - winding the screws up and down is a bit fiddly as you need to keep them roughly in sync or they will bind. Also, doing up is anticlockwise - a real pain. The final problem is that as the screws are tightened they tend to pull away from their feet, and are only restrained by a single grub screw travelling in a ring milled in the central screw. Obviously that wont last.

I think I should have bought an additional two press screws too.

still, it works for now.

cheers
Arron

After making a substantial number of modifications its more or less pressing evenly edge to edge. The mods included increasing the number of press screws by 4 so that that the cauls are on 120mm centres, increasing the camber on the bottom of the cauls to 2mm, and adding more cross members below the lower platten.

Now I'm finding the press screws popping out of their little steel footings when under pressure. The retaining grub screw sheers off. This is a result of using them in the way not designed for.

Clearly this is one of those jobs which is much harder then it looks. A redesign is called for.

Arron

Aaron, this is an outside-the-square idea where you could modify the bench you have made to use ratchet straps instead of screws. You would have to fit substantial stretchers lower down on the legs. Then you would need to modify the cauls so that the edge that is screwed to the particle board plate is flat or very nearly so (perhaps a 1mm convex) and the opposite edge would be a much greater convex (maybe as much as 40-50mm higher in the centre).

Now rather than using just one strap per position, use two (using one strap is likely to provide more pressure to one side than the other - may not but I'm erring on the side of caution). Cut the straps shorter to leave just enough to attach them securely to the lower stretcher, or the legs in the case of the outside stations. I'll leave you to work out a suitable way of attaching the strap to the wood. So the picture so far, you would have four short straps on each side, each ending with the ratchet mechanism and a bunch of leftover strap that you cut off. Four of these leftover straps are laid across the cauls (it would be good if you could also include a way of keeping them captive but still being able to slide (perhaps even as simple as some wire passed through a hole in the caul and twisted into a loop). Each end of these straps is fed through the ratchets so they can be tightened from both sides. I envisage you would leave the straps threaded through, but slack so the press could be held open with a couple of sticks. The work would be slid between the plates, the sticks removed and each pair of ratchets used to tighten the cauls evenly. Hope that makes sense.

Cheers
Michael

Actually, Michael, thats a dam good bit of lateral thinking. I cant see why it wouldnt work. Those straps can generate an awesome amount of tension. The positives would be that they dont take long to undo - just flip the lever and pull a bit of spare strap through. They dont take long to do up either, and if they sit in place permanently then there isnt much fiddling around. Nothing much to break or go wrong either - good rugged technology.

One of the key pre-requisites that I have here is that the upper platten should be lowered into place gently and with minimal sideways movement. Sliding the plate around can cause the veneer to slip across the surface of the workpiece, which can be disastrous. Your method could accommodate this quite well if the platten were lifted up and down from above - say by a pulley on the exposed ceiling beams. With nothing above the platten and cauls, and with the straps being very easy to slacken off or tighten up, it could be very quickly and easily raised or lowered.

I cant use your idea though because there is so little space in my shed that I wont have access to the sides of the press once its in its final resting place. It will be jammed up against a cabinet on either side with scarcely an inch to spare. Thats why I have to have a design that I can operate from above.

Also, now that I"m the proud owner of 12 veneer press screws I want to put them to a use of some sort.

General comment on progress so far
Since I made this press a few days ago I've been doing a couple of trial presses per day. Todays trials were pretty much perfect. The pressure applied is such that the veneer comes out with a surface that feels like its been sanded with 600 grit - its all squashed flat down to the last fibre. I know you dont need that much pressure in use, but its good to see it applying maximum pressure evenly across the workpiece. Its not robust though, the screws are sometimes popping out of their little boots. Also, the screws no longer turn smoothly because they are damaging the grub screws which retain them against the upward pressure. It looks like I'll have to go the superstructure route.

Good idea anyway.
cheers
Arron

Hi Arron,
I made this press years back, the outer threaded rods are in tension,and the inner six threads on each frame compress , I could do 1.2 x 1.2 with this press ,and the pressed sliced veneer came out flat and perfect. It had 36 screws
Getting a good outcome was all about spreading the glue the right way.

Longer sections could be done in two separate pressings, like in the picture. It worked well but took half an hour to tighten up, the main problem was the huge amount of wood would flex 1.5 mm in the middle, I would have to compensate for that with layers of news paper that graduated up to 1.5 mm , so that the job to be veneered had to sit on a 1.5 mm peak in the middle before pressure was applied .

I ended up cutting it up , and it is now polished shelves in a cupboard at home.I went and bought a vacuum press but don't believe it is any where near as good as a screw press.
I would like another but would do it in steel ,with trusses ,that should take out the flex and then it would be much quicker to tighten up, I have been drawing up designs that would go under a work table . so I could prep a job, slide it in down near the floor, flip the top up and tighten the screws, that's the dream press at the moment,dont know if I will get around to it though

Your table press looks like the timbers need to be 100x 100, held apart by 8 threaded rods. the four upper ones get drilled for the 12 screws.3 in each. It may be even better to make the bottom ones double thickness, so most flex goes to the upper cross timber with the screws.

I got all my info from two books on veneering.this one has the best info on building a press
The complete Manual of wood veneering by William A lincoln
In it he writes about needing a screw every 9 inches across, and down the length, in my one I did it every 8 to be safe.

The other book, is Practical veneering by Charles H Hayward,
not so much on press making that I can see now ,but has many great hot and cold techniques , a good read .
regards Rob

Good info Rob. Thats pretty much the same as I'm working on now - threaded rod on the outside to hold thick crosspieces above the work - and screws mounted in the crosspieces pressing downward. Photos in a day or two.

Taking half an hour to do the screws up !!! thats pretty much what I'm trying to avoid.

One thing does puzzle me though. If you were finding that the timber was flexing, and you were having to compensate for it by packing up the middle with newspaper, why didnt you just chamfor the bottoms of the cauls, so that they were 1.5mm deeper in the middle then at the ends ?

cheers
Arron

I'm sure we must have discussed the option of shaving the bottom bearers, it would be almost eight years back that we made that press. when I built it I was trying to do it as cheap as possible, the timber I bought was a hardwood meant for carpentry and was still wet, I was thinking , build it quick and cheap and see how it works. So I didn't want to put any more time in to it, It worked well but started showing signs that it had a limited life pretty soon. one was the flex, I would tighten the six screws per frame up with a torque wrench to 17 ft lbs ,but had to go over them six times.I broke some of the welded nuts off,
the dovetailed blocks that slid along for different size work started jamming up. and the thing was heavy and took up to much work space. if there is a next time ,steel and under a work table. I did a few nice jobs on that press though. the best thing was a drinks cabinet a lady ordered, quartered figured Cherry with big stars in Walnut and Maple radiating out from the center of each door .
Rob

Rob, I would also use steel if I were making a veneer press. You don't need to tighten the things too much though; the pressure with a vacuum press is atsmopheric pressure which is only 14.7 lbs./sq. in.

I would also consider using pneumatic rams to close and open the platten.

Yes, I was thinking you shouldnt need much pressure. How much pressure should it take to hold a piece of soggy veneer against a piece of plywood till the glue dries ?

I was wondering whether the many accounts I read of people struggling to provide enough pressure is really indicative of design problems with their press. I think some are simply made to massive - too rigid. If you have a very slight fault in the press - such as a slight undulation in the platten, then a very rigid construction is going to require a great deal of pressure to flatten it out. I think a bit of strategic flex in one platten might be better.

Arron

Originally Posted by Woodwould

You don't need to tighten the things too much though; the pressure with a vacuum press is atmospheric pressure which is only 14.7 lbs./sq. in.

It would be interesting to know how much pressure the wood was under at 17 ft lbs going down through 36 screws over 1.2 x 1.2 wouldn’t it Woodwould . That’s almost a tongue twister.

What I do spend a bit of time thinking about is the best size to build one at, if I wanted to do table tops it’s got to be big, a 2440 long press means I could construct tops 2840 long with a mitered top that has 200mm ends. its just that its a huge press.

But if I forget the big tables, and just think cabinets like two part bookcases and smaller then something maybe 1.4 long x 1.2 wide.
Big tables could be done as panel tops possibly

I did a job with the vacuum once, two parquetry panels for a table that was missing its extensions. Three of us spent a day cutting and jointing, it was pressed in a bag one on top the other with a caul on top of each. I couldn't detect any leaks. When it came out the next day it was revealed that it was an average pressing, a few bubbles here and there. We fixed it up but much worse and it would have been an expensive disaster.

Rob

Originally Posted by Woodwould

Rob, I would also use steel if I were making a veneer press. You don't need to tighten the things too much though; the pressure with a vacuum press is atsmopheric pressure which is only 14.7 lbs./sq. in.

Could you not be underestimating the power of a vacuum press, Woodwould?

Realistically, a good result is a 70% vacuum, about 10 psi. Now Arron's thinking about a veneer press of around 1000 x 600 mms, say 39 x 24 inches, or 936 square inches. With pressure of 10 psi then the total pressure is 9,360 lbs on that little veneer press.

Cheers

Graeme

Originally Posted by auscab

What I do spend a bit of time thinking about is the best size to build one at, if I wanted to do table tops it’s got to be big, a 2440 long press means I could construct tops 2840 long with a mitered top that has 200mm ends. its just that its a huge press.

I choose to make mine to fit a maximum 900 x 500 because above that size common sense kicks in and I take the job to a professional veneering outfit. A larger job I can get done professionally (ie veneer supplied and glued up) for less then it costs me just to purchase the veneer.

Below that size, I can usually do it for nothing due to having a good collection of offcuts. Plus theres the convenience factor that always seems more pertinent with small jobs.

cheers
Arron

Originally Posted by auscab

It would be interesting to know how much pressure the wood was under at 17 ft lbs going down through 36 screws over 1.2 x 1.2 wouldn’t it Woodwould .

Depending on the caul positioning, it could be neglgible in places, but with a good criss-cross of cauls (they don't need to be huge in cross section), the weight should be fairly evenly distributed.

Originally Posted by auscab

What I do spend a bit of time thinking about is the best size to build one at, if I wanted to do table tops it’s got to be big, a 2440 long press means I could construct tops 2840 long with a mitered top that has 200mm ends. its just that its a huge press.

If you build a huge press, you'll take on bigger jobs and the press will never be big enough. If you break the jobs down into manageable sizes as you suggest, then the press doesn't need to be too large.

Any press can lay idle for periods of time, taking up valuable space. My last wooden press consisted of three trestles, several sets of sheets of 3/4" ply (the largest set were 5' x 4'), dozens of 2" x 2" cauls (which I built up in three criss-crossed layers) and several 6" x 2" cauls on top. When not in use, I dismantled it and stashed it all away in the back of the shop.