'Tis the season of rust and mellow fruitfulness

[9fingers]

Apologies to Keats but it just seemed appropriate :lol:

Some years ago I made reference to the anti rust heaters that I had fitted to my table saw.

viewtopic.php?t=14547

The principle is that if an iron surface is kept slightly warmer than the surrounding air, then moisture will not condense onto the surface and rust will not form. Clearly of the roof leaks this method will not work but provided the building is in good condition then applying a modest amount of heat directly to the machine will keep it rust free.
I have been using this on machines for years. My engineering lathe is 32 years old and has not one speck of rust on it.

Every now and then I get a query on this system so as I have been building a new one, I thought I would write it up.

It is important that the heaters are low voltage and isolated from the mains. 12 volts is ideal and in the last few years some very cheap lighting transformers have come on the market. The designs are strictly regulated and have to work continuously whilst being efficient which means they run cool and are fully protected against short circuits.

Currently a 60 watt transformer costs £3.28 inc vat here http://www.toolstation.com/shop/Lightin ... 638/p55497

60watts is more than enough to protect a large table saw, bandsaw etc.
Cast iron is a relatively poor conductor of heat so it is more effective to fit a number of heat sources distributed across the underside of the table.
The heater elements are wirewound resistors encased in aluminium and with two fixing screws.

http://uk.rs-online.com/web/p/high-power/0160720/

The power in a resistor is given by the voltage squared divided by the resistance.

So from a 12 volt supply , a 12 ohm resistor will dissipate 12 watts and four of these will be adequate for most applications and draw 48 watts (4 x 12) from the 60 watt transformer so well within its capabilities.

First job is to extend the mains lead on the transformer using a couple for crimped connectors and providing an earth tag to make sure the machine is earthed ( this is because it cannot be guaranteed that the machine is plugged in and earthed - better safe than sorry!)

[img]http://i115.photobucket.com/albums/n313/9fingersphotos/IMG_1727.jpg[/img]

a length of heatshrink sleeving add further insulation and keeps everything tidy

[img]http://i115.photobucket.com/albums/n313/9fingersphotos/IMG_1729.jpg[/img]

The transformer has a pair of short output leads and to make it easier to connect four heaters, I added a terminal block - sometimes called choc block.

[img]http://i115.photobucket.com/albums/n313/9fingersphotos/IMG_1730.jpg[/img]

The resistors are soldered to cables and more heatshrink sleeving to insulate the connection for belt and braces.

[img]http://i115.photobucket.com/albums/n313/9fingersphotos/IMG_1738.jpg[/img]

It make no difference which way round the heaters are connected but to keep it tidy looking I kept all the brown leads together.

[img]http://i115.photobucket.com/albums/n313/9fingersphotos/IMG_1741.jpg[/img]

Drawing it out as a schematic diagram

[img]http://i115.photobucket.com/albums/n313/9fingersphotos/Heaterwiring.jpg[/img]

Another advantage of using a lighting transformer as above is that the power can be reduced using a dimmer switch such as

http://www.toolstation.com/shop/Electri ... 633/p18884

The way to set the dimmer is to feel the machine table on a cold day. The table does not need to be warm to the touch but just not as cold as another unheated metallic surface. once the dimmer setting has been found - mark the position of the knob for future use. It is not essential to have a dimmer control but it can reduce the electricity consumed.


I hope this might help you have a rust free winter.

Bob

 

[JeremyM]

Bob
Thanks very much for such a helpful post. =D> =D> =D> As it happens I've a spare 12v lighting transormer, will plan out the siting of the resistors tomorrow.

jeremy

 

[AndyT]

Bob

It's people like you who take the time and trouble to present good ideas so clearly that make this forum so valuable.
I know that a while back you were considering leaving; I'm glad you didn't!

=D>

 

[Blister]

Nice one Bob

=D>

Thanks for posting 8)

 

[Richard T]

I expect it beats the two 40w bulbs that my Dad has under the Myford (and under polythene) for economy?

 

[9fingers]

My myford has two resistors bolts on the the flad face at the back of the bed where the taper turning attachment bolts on.
The mill has 4 heaters as does the back panel of a cupboard where I keep my precision tools.
Nothing wrong with light bulbs apart from as you suggest running costs, perhaps being fragile and starting to become unobtainable.

When I use light bulbs I wire two in series, each bulb dissipates 1/4 of its rated power so 2 x100W gives 50watts of heat and near infinite life as the filament is under run significantly.

Bob

Bob

 

[SammyQ]

Bob, I just love it! This is intelligent, elegant and simple; the epitome of design engineering.

Sam

 

[9fingers]

Bob, I just love it! This is intelligent, elegant and simple; the epitome of design engineering.

Sam

Steady on Sam- I'll not fit through the doorway at this rate!!

I guess it must be something to do with working in applied research for 32 years
Most problems have simple solutions!

Bob

 

[jordec66]

I would also like to express my gratitude for such an informative post, and so simple even I could probably rig it up.

Thanks again.

 

[SammyQ]

Bob, I was EXTREMELY fortunate to work with two great imaginative scientific brains when reading for neurophysiology and ecology courses at university. The blokes wot run them could not find the unique apparatuses they needed in any catalogue, could not afford to have the local engineering places run 'em up and did not have the time to set aside for development procedures.

Necessity then, enforced speed, simplicity and gear that fully addressed a need; an approach that mathematicians and scientists alike describe as "elegant" because it so fully does its job, with so little materials. It has been a long time since I saw such a good, clean delivery as yours; it reminded me of my two magic mentors, Tony Cooke and Amyan Macfadyean and I felt I really had to say "Thank you" for such a good idea, but also for reminding me of the fulfilling time I spent in their company.

Sam

 

[Benchwayze]

I expect it beats the two 40w bulbs that my Dad has under the Myford (and under polythene) for economy?

I'm not so sure about the wastefulness of light bulbs Richard. Years ago, I used an old paraffin heater casing and its chimney, with the fuel container and wick removed. That was replaced by a tungsten, 40 watt bulb in a holed biscuit tin. The heat was directed up the chimney and convected in the same way as was the heat from the lighted wick. Using these makeshift heaters, I heated a greenhouse and my old workshop with barely noticeable extra on my bill. That was in the days when a lamp bulb only burned about 2 old pence a day. What has changed to make it 'wasteful' to leave a light on I don't know. Yes the 'juice' is more expensive, but inflation surely cancels this out, and a bulb doesn't burn any more juice than way back then. Anyhow, that was my experience for what it's worth my friend.

I must add, this is not to take away the ingenuity and efficiency of Bob's set-up of course.

Regards
John

 

[Vann]

Brilliant step-by-step write-up. But one query

It is not essential to have a dimmer control but it can reduce the electricity consumed.

Don't these dimmers use a resistor to dim? In other words: won't it use the same amount of electricity, but burn some in the dimmer instead of the other resistors?

Cheers, Vann.

 

[9fingers]

Brilliant step-by-step write-up. But one query

It is not essential to have a dimmer control but it can reduce the electricity consumed.

Don't these dimmers use a resistor to dim? In other words: won't it use the same amount of electricity, but burn some in the dimmer instead of the other resistors?

Cheers, Vann.

Hi Vann,

Dimmers are very efficient and work by only turning the power on for a fraction of the time in each mains cycle. This happen 50 times per second and in combination with the thermal inertia in the bulb, we dont see the light switching on and off it is just less bright.

The dimmers are not perfect switches and so maybe a percent or so is lost but that is all.

Bob

 

[Richard T]

Thanks for that Bob, I'll check to see how they are wired. As they are only 40w my guess would be parallel.

Bulbs in paraffin heaters eh John? Good idea - and how ever expensive, cheaper than &%£$ing paraffin!

 

[Mike.C]

Hi Bob, another very helpful idea.

Cheers

Mike

 

[Benchwayze]

Thanks for that Bob, I'll check to see how they are wired. As they are only 40w my guess would be parallel.

Bulbs in paraffin heaters eh John? Good idea - and how ever expensive, cheaper than &%£$ing paraffin!

Indeed Richard, but some of the modern so-called 'energy saving' bulbs don't run hot. I fixed the bulbs into 'batten-lampholders' but a ceiling rose fixed to something fireproof would work.

Regards
John

 

[Richard T]

As far as I can tell John, not only do they not run hot but they don't run very bright either - I'm beginning to guess how they save the energy ...

I checked my dear old Dad's set up Bob and he did wire them series. He's cleverer than he looks (and considerably cleverer than I look). I should have known as neither have popped for many years.

 

[Fred Page]

Hi Bob,
Keeping your cast iron machines at slightly above ambient temperature is clearly based on sound reasoning and is worthy of attention.
A less theoretically based means of achieving the same is to keep the surrounding air constantly moving. I can offer no theory to this suggestion – I have a mere idea that it works although cannot prove it.
On those nights, or days, where I suspect condensation might occur I leave running in the workshop a 28W domestic 7inch moving fan (the kind you use on hot days). I can be easy with 28W being used even though I’m unsure why this method works (it merely appears to work). Could it be that condensation on cold metal surfaces is taking place but so is evaporation (at the same rate) due to the moving air? Result – no moisture deposited! Perhaps better informed people on this forum would comment?
Fred

 

[9fingers]

I can quite imagine that working for relatively dry atmospheres and not too severe temperature drops.

The worse situation is a damp workshop such as one without a damproof course in the floor and intermittently heated.
The water vapour gets dissolved in the warmed air but the heating is not on for long enough to warm the machines so the warmer water laden air hits a cold surface and drops it water vapour.

Using a fan will also warm the air by a small amount as a result of the stirring the air so this will help too.

Bob

 

[RogerP]

.... all this reminds me I have a roll of greenhouse soil heating cable ... somewhere :|