Thread: Advice needed on lengthening sheets of 19mm plywood......

I have done this on a production line, and it could be done in a home shop, but would be more difficult.

The basic technique is called scarfing, and involves shaving matched opposing tapers on the edges to be joined, and then glueing the seams. The taper should occur over a width 6 to 8 times the sheet thickness i.e 114mm to 152mm for a 19mm sheet.

In a production environment, a spindle moulder with an inclinable spindle and a cutter about 200 - 250mm diameter is used to make the taper on one edge of the first sheet in the group, then the second sheet is tapered on the back side, flipped and tapered on the opposite edge. The tapers are normally truncated with this process, leaving a step from the board face to the taper, and a matching step at the end of the taper. The truncation serves two purposes, it sets an alignment reference for the joint and makes it possible to make an effective joint without needing an immense cutter. (200-250mm is just very large). For 19mm, the target would probably be a 3 mm step from the face about 90-100mm from the edge, tapering to 3mm at the edge. With proper gluing, a properly prepared joint would be as strong as the parent panel.

In production, the glue used is a thermosetting urea formaldehyde system. The sheets are glued in a substantial heated press using air pressure to open the press for loading, clamp both sheets to stop them moving, and close the press. The top and bottom plattens of the press are protected with 1mm teflon sheeting, and press cycle times vary from about 2 minutes for 4mm sheet to about 10 minutes for 19mm. Temps are about 90deg C at the heater and pressures are around 100PSI.

If you can get the room to work and support the sheets and glue up, it is possible to do a similar thing using a router and a suitable jig, and glue up using epoxy. However it would be substantially slower. There are businesses in the capital cities who could do the job for you provided that you could organise transport for the finished panels.

Don't know what finish you are looking for on the ply but Some ply sheets are available in 3600mm X 1800mm, Have you considered this ?..
It beats trying to glue sheets together to lengthen them..

Hi fellas, thanks a lot for sharing your valuable knowledge. Malb, that's one heck of a procedure isn't it? I see how that joining process could make the 2 as strong as the parent panel, given the angled surface area and the high bond glue etc., sure makes sense. I think I could probably get away with the router and jig arrangement, if I was to have a bulkhead screwed and glued @ 90deg mid-join, the screws would be passing through the overlapped ends of the joined sheets and into the edge of the b/head panel, locking all three together..... I reckon! These joined "walls" would also be screwed into the floor and have "spars" between them over head. They will be lined inside with a thin veneer and outside with a 1mm ally skin and maybe even completely f/glassed in some cases, depending on the customer, so will be unseen. Strom, I have made a few calls in search of longer sheets locally but no success as yet. I am really stoked they can be found that L and W, and yep...... much easier! I won't need to join any sheets if I can get some. Only killer is freight, I am pretty isolated 600ks west of Adelaide. Do you know where I could find some in S.A? They would have to be pricey wouldn't they? Im guessing "a few hundge", but no joining would make it worth every cent with the labour saved for sure. Thanks again. Oh wow........ LOOK at the TIME!! Jim.

Originally Posted by jimboski

Hi fellas, thanks a lot for sharing your valuable knowledge. Malb, that's one heck of a procedure isn't it? I see how that joining process could make the 2 as strong as the parent panel, given the angled surface area and the high bond glue etc., sure makes sense. I think I could probably get away with the router and jig arrangement, if I was to have a bulkhead screwed and glued @ 90deg mid-join, the screws would be passing through the overlapped ends of the joined sheets and into the edge of the b/head panel, locking all three together..... I reckon! These joined "walls" would also be screwed into the floor and have "spars" between them over head. They will be lined inside with a thin veneer and outside with a 1mm ally skin and maybe even completely f/glassed in some cases, depending on the customer, so will be unseen. Strom, I have made a few calls in search of longer sheets locally but no success as yet. I am really stoked they can be found that L and W, and yep...... much easier! I won't need to join any sheets if I can get some. Only killer is freight, I am pretty isolated 600ks west of Adelaide. Do you know where I could find some in S.A? They would have to be pricey wouldn't they? Im guessing "a few hundge", but no joining would make it worth every cent with the labour saved for sure. Thanks again. Oh wow........ LOOK at the TIME!! Jim.

Hi Jim..
We actually share the same name !!!
1am is not late I'am a kin to scouring through the net much later than that !!!
If you give me an exact location (Pm me if your shy about placing it on the forum) Ill steer you towards a decent supplier.. (I'am guessing your just after construction ply Or marine ply ?? Yes marine ply is alot more expensive)
If you need to get it freighted in (Not available locally) it may also be a good idea to have it cut to size for you as this will also reduce the size of the pallet and freight/handling costs.
I'am guessing you have already asked the trade counter at your local hardware chains if they are able to source it for you ??.. (this may reduce freight costs if it comes with there freight stock)

Just had another thought..
It may also be worth asking around at your local Joinery shops. You may get lucky and they have some laying around or can source it for you. Basically grab the phone and go for broke with your local directory I'am sure you will get lucky somewhere..
Are you in the vicinity of Port Lincolin ??..

Hi Strom, I'm a about 2hrs north of P/L, and heading down today, so I will have a sniff around while in town. There are plenty more places for me to ask down there I hadn't thought of, just tried the hardwares and building supply companies first off, but there are a lot of marine related companys in town as you would know, and I could luck out with them! Sounds like it shouldn't be too difficult anyway mate. I'll keep ya posted. Thanks Jim.