best wedges for joining polycore moulding

[boscawen46]

Hello,
I am making batches of polycore frames but when using my pneumatic underpinner the joints are not tight.

The mitres are being cut on a Morso with very sharp blades and the surfaces are flat and clean. When these are put together on a flat surface by hand they form a perfect joint with no gap. When I place the two lengths in the underpinner the joint is likewise tight but when a wedge is driven in it seems to part the joint so that there is a 0.5 mm gap. I'm putting a small line of high viscosity superglue for extra strength.

My underpinner is a minigraf 4 and I am using UNI-10MM -SW WEDGES from Cassesse.

Can someone advise me please, are there special wedges for polycore that fit a minigraf 4 and should these solve the problem.Thanks

[Not your average framer]

Hi,

This is the principle difficulty with polymer mouldings. Wooden mouldings work better with wedges because wooden moulding have the strength of the wood grain which allow the tightening action of wedges to pull the mitre joints tightly together. All you have in polymer moulding is a core of polymer foam and the foam lacks the ability to resist the tightening action caused by the wedges, so very little meaningful tightening of the mitre joins. Sorry to disappoint you, but looking for better wedges is only going to create marginal improvements.

This does not mean that I am here to slagg off polymer mouldings. I fact they do have their advantages, but the also require a particular way of working. The primary method of getting good joints in poymer mouldings has more to do with the adhestive within the joints that is has to do with the wedges. One particularly popular method of joining polymer moulding is to accurately bond the moulding pieces together securely before insert the wedges. The wedges will supply some strength, but the mouldings have already been bonded together by the adhesive, which is usually of the super glue variety.

Itend to think that hard wood wedges work reasonably well, when the mitre joints have already been secured by bonding together with super glue. If using polymer mouldings already work well as part of your business strategy, I see no reason to stop using them, but instead I would suggest optimising the way which you used to produce nice clean joining of the mitre joints. It you are not already using supper glue, this this may well be something well worth trying! The actual technique is quite important and applying only a small spot of super glue and then holding the joint tightly together while the glue produces a solid bond before proceeding to insert and wedges tend to work best.

I used to use Polcore at one time and in general this was relatively sucessful, but I don't use such mouldings anymore and now prefer to use only wood mouldings. I have inherited some polcore frames I had made some times ago and these will most likely soon be re-made in to a pair of mirrors in the not too distant future, for the friend to sell on eBay and we will split the proceeds, between us. After many years these frame still look like new, so we will give it a go and see what happens.

[boscawen46]

Thanks Mark

[Trinity]

I use UHU all plastics glue which holds well. It says strong cold welding on the tube, I then underpin afterward but am always wary of the shock of the clamp hitting the moulding, its an alfa macchine

[whitbyframer]

I've got a Cassese underpinner with clamps and find that they join fine. I use Gorilla glue, I tried others but also had problems with the joint opening a bit, but the Gorilla glue seems to work well. I only use Polcore and avoid any narrow ones as I'm concerned about joining them, but find that the wide ones offer excellent value for money.