Xcalibur improvement no 2

[9fingers]

I've just completed the next mod to my table saw.

Machines with cast iron tables always run the risk of the dreaded rust. Keeping them waxed is a good precaution but if they have to live in an unheated workshop with changes in humidity rust can still happen.

I have a number of metal working machines and I arrange to heat the machine very slightly. All that is needed to prevent the condensation which leads to rust is to keep the surfaces slightly warmer than the surrounding air.

My engineering lathe is nearly 30 years old and not a rust mark anywhere and the mill is a little newer at 22 years and in similar condition.

The heaters are made from aluminium clad resistors powered from a low voltage power supply. This could be something like a car battery charger or whatever else is around
Typical power per machine is between 20-50 watts ie less than a lightbulb and you don't need to run it in the summer months.

Here are some photos of resistors screwed onto the underside of the Xcalibur table and extension wings. Having a number of heaters helps the power to be changed by altering the series/parallel wiring as well as distributing the heat over the whole table. Cast iron is a poor conductor of heat so heat applied to a single point will not spread readily across the whole table.

I've got 8 x 15 ohm resistors which I will run from around 12 volts which will give a maximum of nearly 80 watts but I doubt if I'll need all this so I can turn down the power by using a lower voltage or changing the connections. This is why I've brought out so many wires.


If anyone want any more info then just ask

Regards

Bob

 

[devonwoody]

If anyone want any more info then just ask


So where do I get resistors ? (I have always had resistance from young ladies) and what resistors do you recommend.

So would an 18 volt or less voltage reducer work, what is the fire risk in dusty conditions like?

 

[9fingers]

CPC, RS Farnell, ebay etc

You need to choose your supply voltage first, best to be under 24v.

Then decide how many resistors you need to distribute the heat as evenly as possible. Then work out the values to give about 20-50watts per machine according to size.

power = volts squared divided by total resistance

PM me some numbers if you need help calculating the values.

hth

Bob

 

[9fingers]

Best/cheapest source of transformers are halogen lighting ones from screwfix or toolstation.

These give 12 volts at 20 to 100 watts according to type chosen.

15 ohm resistor on 12 volts gives 10 watts and place a few of these on a surface to be protected.

To give a long life, each resistor should be rated at 15 watts or more to save them running continuously at the max rating.

Bob

 

[xy mosian]

Bob, that's brilliant . Well thought out! may I just add that a dab of heat sink compound between resitors and cast iron will help conduct the heat.

Your suggested sources of resistors will probably be able to supply. BTW it's the same stuff used between computer CPU's and the heat sink.

xy

 

[devonwoody]

Any other suggestions how to attach the resistors without resorting to drilling, tapping under a tablesaw would make me move receptive and not so resistant to this idea.

 

[9fingers]

If the webs on your table are deep enough then you could drill horizontally (nearly) and use a nut and bolt fixing.

Drilling and tapping CI is not difficult though.

Bob

 

[devonwoody]

Bob is there any way with this system that it can short on to the castiron?

(our freezer in the workshop is on the same ring main.)

 

[9fingers]

It must be run on a transformer which will isolate it from the mains. So whilst is is extremely rare for this type of resistor insulation to break down, there are no safety issues if it does happen. Your machines should be earthed anyway and it is low voltage anyway.

I would not suggest an unsafe method in a public forum!

Bob

 

[jlawrence]

Heat paste between the resistor and the top will help with the heat transfer, clamp the resistor to the top, then a couple of blobs of CA should hold it in place. You might need to experiment with the glue to get one which doesn't melt - they do exist I just can't remember what mine is called, I'm sure it's a version of CA.

 

[Armagh]

Took me ages to find this thread but I knew it was here somewhere! All my machinery is stored in a shed and in damp weather gets a lot of condensation. Is this effective only for tables? I opened my p/t the other day and the blades and barrel were soaked. Any help would be much appreciated. Thanks.

 

[Myfordman]

Took me ages to find this thread but I knew it was here somewhere! All my machinery is stored in a shed and in damp weather gets a lot of condensation. Is this effective only for tables? I opened my p/t the other day and the blades and barrel were soaked. Any help would be much appreciated. Thanks.

I'd say you need to make improvements to your shed in terms of damproofing, insulation and ventilation if the condensation is that severe.

 

[CHJ]

Took me ages to find this thread but I knew it was here somewhere! All my machinery is stored in a shed and in damp weather gets a lot of condensation. Is this effective only for tables? I opened my p/t the other day and the blades and barrel were soaked. Any help would be much appreciated. Thanks.

Getting heat into the machine body will be effective however you achieve it, metal to metal contact will spread the heat around and if you can only do it lower down heat also rises, if you cover the machines with a fabric that provides a thermal barrier to the shop air all the better.


A later update to Myfordmans Resistor Heating method.

 

[Armagh]

Thanks for the link CHJ, and thanks to Myfordman/9fingers(some excellent posts) for the original information. I'm afraid my 'workshop' is an entirely unheated former cattle shed. I've put all hand tools in cupboards which appears to stop condensation, but the machinery is too big to move around. I'll try covering the machines with tarp as well as setting up the resistors. So much air flows through the shed that the contents are protected from rain, but thats about it.