Shavings fires (intentional!)

[marcus]

I'm building a big traditional veneer press at the moment, and am starting to think about how to heat the aluminium plates (for the hide glue).

I've done quite a bit of this sort of veneering on a smaller scale with plates that fit in the oven, but these plates will need to be a lot bigger (the press is 3' x 6').

I've heard of two methods for heating large plates. Patrick Edwards (http://wpatrickedwards.blogspot.co.uk) suggests laying them over a paraffin heater and boxing them around with scraps of plywood. Seems practical enough.

More intriguingly I've read about how in the past it was done with a 'shavings fire'. Naturally the pyromaniac in me wants to try this! Also it has the advantage of being essentially free. But I can't find any description of the procedure involved. Does anyone have any info about how it was actually done back in the day?

 

[AndyT]

There's a very brief description in volume 4 of Bernard Jones 'The Practical Woodworker' which says

"The caul is heated on both sides, preferably over a blaze of shavings in a fireplace until the hand cannot comfortably be placed on both sides"

Here's a scan of the page:

Charles Hayward says much the same thing in 1949:

Disclaimer - I'm just looking this up - I've never done it - and I've never burnt down a workshop either!

 

[marcus]

Thanks for this Andy, interesting but rather like the stuff I found myself - a few clues but short on the detail about how it's done with really big plates. Perhaps they had massive fireplaces....

I have an area of concrete outside at the back of the workshop, so if i have a go will be there, which should mitigate the risk of expensive mishaps!

 

[Lee J]

PVA has got to be easier

 

[marcus]

Yup, so long as you don't mind it a) creeping [2 or 3mm thick veneer] b) completely devaluing clients antique furniture and c) being completely irrepairable if something goes wrong during glue up or after, having just spent two weeks cutting and fitting marquetry....

 

[xy mosian]

Just as a matter of interest. When the aluminium is too hot to confortably hold. How are you going to move it? At 3' x 6' that will have some weight to it.
xy

 

[marcus]

Don't know yet! Gloves I expect. Though in reality I expect I will end up using the kerosene heater method which can be done at the edge of the press and then you jut slide it on. Also I am planning to use three smaller sheets rather than one big one so not quite as big. I'd love to try it the old way though....

 

[siggy_7]

If I were building something like this, I'd look at bonding some heater mats or some other kind of electrical heating element to the non-press side. You'd have a precise and repeatable process then.

 

[marcus]

If I were building something like this, I'd look at bonding some heater mats or some other kind of electrical heating element to the non-press side. You'd have a precise and repeatable process then.

That's a very good idea, I'll look into it, thanks!

 

[xy mosian]

Your 'heating up' next to the press sounds like a good idea marcus. What sort of thickness of aluminium are you thinking of using?
xy

 

[marcus]

What sort of thickness of aluminium are you thinking of using?

Probably 10mm

 

[Aden30mm]

How about using trace heating cables. But I do not know is they would give you the heat output you require.

Try:
http://www.traceheatinguk.co.uk/product ... at=801&nm=

Kind regards

Aden30mm

 

[adidat]

not really sure of the science behind this, but could heat the plate like a light bulb filament?

adidat

 

[Tinbasher]

A larger version of those things that heat the aluminium hot plates you get in Chinese and Indian restaurants? I think they work on induction? There are also pre heaters used in the welding trade.

I like the idea of fire though!

 

[Eric The Viking]

What temperature does it need to be, and for how long does it need to stay at that temp?

A 3ft square plate of 3/8" aluminium won't be lightweight either, and could prove rather awkward to move. Another issue might be evenness of heating - you couldn't afford cold patches I'd guess.

Would there be any mileage in building a wide flat tank of some sort and then using hot water or steam to heat it? It's a long time ago, but I once operated a plastic moulding machine. I'm morally certain the heating/cooling cycle was achieved by steam and cold water respectively. They certainly did that with vinyl record pressing plants, as it gave a quick cycle time.

Grandpa's sawmill had a bonfire going almost continuously (in the 1960s), and shavings/sawdust were often put on it. You'd expect them to burn pretty fast, but they used to get quite hot and smoulder for ages, rarely with a lot of flame. I'm wondering of the sawdust fire mentioned in the book was rather different, but I can't see what you could do in an open grate.

 

[marcus]

I'm being quoted about £450 for a suitable heat mat (size 900 x 600) with a control unit. Would probably be a good solution, but a bit too much for me right now.

The plates need to be quite toasty. When I've done it before I've put them in the oven at 120 and need to handle them with cloths when they come out. But not too hot to scorch the wood, obviously. They don't need to stay hot for long at all — just until the press screws are tightened, so that the glue (it is already applied to the substrate and is cold when put in the press) is briefly reactivated. The glue gels at 60 degrees, the excess heat is to account for the plates cooling down before it is all clamped up.

I think the heat trace cables wouldn't be powerful enough. I'm starting to see the strengths of the paraffin heater idea — he just pulls the plates out from the press and leans one end on saw horses, then puts the heater underneath so when they are hot they can just be slid back onto the press. Should make handling them easy and quick.

 

[marcros]

you couldnt rig something up using intra red bulbs or heaters could you?

 

[siggy_7]

Aluminium is a very good conductor of heat, so I would be surprised if you had any problems with uneven temperatures.

It's a shame the heat pads are so expensive, that would have worked well I reckon. There are other ways to tackle the problem - bond heater wire onto the aluminium surface driven by a controller, or bond on some high temperature silicone hoses and circulate a fluid with a high boiling point around the loop. I suspect they are both a lot more hassle than just heating it up in a fire or with paraffin though!

 

[Shrubby]

The underfloor heating mat kits aren't expensive. Bond one of theze to each platten and you wouldn;t have to handle lumps of ht metal during a glue up. Ski and snowboard laminating presses are all heated
i'm fairly sure all the big Ott and schubert presses just have electric elements in the platten
Matt

 

[siggy_7]

UFH mats would work but for the low temperatures - I think most are rated to around 40°C. Also even the high power ones are only about 200W/m² - not sure that would be enough to reach the required temps.