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Surface Rusting in Workshop

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Anthony Salisbury27/12/2010 11:26:23
32 forum posts
11 photos
I've just moved my machines into a new workshop and am getting a lot of surface rusting.  I've just added insulation / plasterboard to the ceiling.  Am I correct to think that its the RH% which affects how much rusting will occur?
I've added a heater in there now but a 3kw heater running most of the time in winter probably isn't the most efficient solution.
Am I correct to think by getting a dehumidifier in the workshop this would sort the rusting issue?  What RH% do I need to get down too?  Its about 83% at the moment.
You can see the rust on my chuck.  It was fine before I put it in the new workshop.

Edited By Anthony Salisbury on 27/12/2010 11:29:58

Andrew Johnston27/12/2010 11:42:58
6664 forum posts
701 photos
The rusting is not directly related to the RH%. It's more to do with temperature changes. What is important is the temperature of the machines relative to the air temperature. The worst case occurs when the machines have had a cold soak at a low temperature. If warm air is then introduced, and the cold machines are below the dew point of said warm air, then condensation, and surface rust will occur. The dew point of a parcel of air will depend upon the RH% and temperature of the air, but the formation of rust will depend upon how cold the machines were to start with. The sort of weather that causes rust in my unheated workshop is a cold, clear spell followed by a warm front.
I expect that a dehumidifier will have some effect, but personally I think that a better way is to stop the machines getting cold in the first place. That's my plan anyway; finish insulating the workshop, and then add a couple of radiators coonected to the central heating system.
keithmart27/12/2010 11:51:11
165 forum posts


I buy caterers size wd40 and spray everything when I quit the workshop.

In four years I have not had a rust problem and my workshop is a 12X8 wooden shed with no insulation



Leeds UK

Ian Sawyer27/12/2010 11:54:12
1 forum posts
I use two three-foot long oil-filled radiator tubes which each have a 150W rating and can safely be left on continuously. They are wall mounted about 18 inches above the floor and I have had no problem with rusting.
They are also available in a number of sizes, each foot length generating about 50W, so a four foot tube will be 200W etc.
I bought mine from an electrical distributor called QVS but I am sure that there will be a suitable supplier near you.
Peter G. Shaw27/12/2010 12:06:44
1454 forum posts
44 photos
Like Keith I have used WD40 in the past and it certainly worked, but it's rather messy and smelly.
A few years ago I bought a couple of 10W small selfregulating heaters for the lathe and this has also worked well plus it has the benefit that the lathe never seems cold. For the miller, I have used one heater, but whilst on the lathe they were bolted to the inside of the bed, on the miller, it relies on a push fit slab of aluminium in the base, possibly not the best idea. I also keep the lathe and milling machine covered by cloth when not in use and this I think also helps retain heat.
The downside of course is expense: the lathe, nominally a total of 20W is actually running at 36W. I haven't measured the miller, but would expect something similar, eg a single 10W heater running at about 18W.
Strangely, the vertical drill does not have a heater, yet doesn't suffer from rust on it's shiny parts - the column and the chuck. Explain that!
Peter G. Shaw 
KWIL27/12/2010 12:52:50
3562 forum posts
70 photos
Like Andrew intends to do, I run two thermostatically controlled wall mounted fan heaters which are integrated with the house CH. Result warm dry workshop and no rusting.
Anthony Salisbury27/12/2010 13:06:43
32 forum posts
11 photos
Thanks for all the replies.  What sort of temperature do you think I need to maintain?  I have a 3kw heater on a thermostat, but wasn't ssure how safe / how much it would cost to leave it on.
Andrew Johnston27/12/2010 13:45:33
6664 forum posts
701 photos
Hi Ant,
It should be possible to make an estimate of the heat needed for the workshop as follows. Select an outside temperature and a preferred inside temperature. You can work out the heat flow per degree K by taking the surface areas of the workshop walls, floor and ceiling and an estimate of the U value of said surfaces. That, multiplied by the temperature differential will give you the total heat flow. Multiply that by the cost per kWh and that's the cost in £ (always assuming that you can make any sense of your electricity bill ).
I'm intending to keep my workshop at about 8-10°C. I don't like hot buildings, my bungalow is normally at about 15-16°C. Experience has shown that a temperature of 8°C upwards is comfortable in the workshop. When it is below 3-4°C, then you only need to touch the machines to numb the hands. Henceforth it's butterfingers all round! I tend to make stupid decisions when I'm cold, so that's another reason to get some heating organised.
Douglas Johnston27/12/2010 13:50:37
773 forum posts
34 photos
I have been using small silica gel units under a double layer polythene cover on both lathe and mill for the past few years with good results. The workshop is an outside wooden shed which is insulated but not heated.
                  The silica gel units run for about two weeks or until the gel changes colour and are then reactivated by connecting to the mains overnight. I tend to abandon the workshop for a few months over the winter and let the machines stay cold. With the workshop insulated I do not get rapid changes in temperature which is the main cause of condensation and rusting.
Frank Dolman27/12/2010 14:57:02
106 forum posts

     I have pointed out in the ''dehumidifier'' thread that it is necessary to prevent
   the tools dropping below the dew point of the air.  You can reduce the dew point
   with an expensive dehumidifier or raise the temperature of the tools with a
   small heater.
      Peter Shaw is talking of a few tens of watts and a cloth.  This is sensible. 3kW
   of room heaters on the other hand is surely only for the rich.
     By the way, heating the air will not affect its dew point.
Ramon Wilson27/12/2010 15:03:47
1379 forum posts
425 photos
Hi Anthony,
You don't say what your workshop fabric is which may have some relevance on your problem eg the ability to retain heat to a reasonably stable level and not fluctuate to extremes causing the situation as admirably described by Andrew above.
For what it's worth however I have a 14 x 14 ft wooden workshop (built 1984) for machining with an extension for a 'cleaner area' added later. It has a wooden floor that lays on paving labs to give an airflow beneath. The walls and ceiling - both pitched roof - are insulated with glass fibre bats between uprights and covered with oil bound hard board as is the floor. The windows were double glazed - I say were as when the extension was added (same length but 8ft wide with a walk through opening) one window was covered in to give wall space and the other lost by the opening. The extension has three windows covering 10 feet of the length again double glazed. This was insulated the same. 
Initially the 14 x 14 side was heated using two 150 watt greenhouse heaters kept on all the time (no thermostat)  throughout the day except the warmest months. On really cold days it would drop to 35-40 overnight sometimes lower and I would need to boost it with a fan heater - all quite expensive. After building the extension I bought two reasonably priced - under 30 quid - thermostatically controlled oil filled radiators. They can be set at 1, 2 or 3 KW. I have never, ever, had the need to use the 3KW and they are virtually always on the 1KW setting but they are on all the time. There is one in each part of the workshop and even throughout this winter the temperature has not gone below 59 overnight. I use it on a daily basis even on the coldest days.
To wit then regarding your question I can honestly say I have never had a rust problem on any of my machine parts - of course these always have an oil covering but nothing special applied as a rust preventative just the normal residue on oiling up. Perhaps a better indicator is the materials in store, some of which are quite oil free but they too show no signs of rusting. The only thing that does is some I" bar cut into various lengths to be used as packing for clamps on the mill. This is some 30 years old and has a very light trace not even enough to warrant removal.
Incidentally I don't know if you have tried to remove the rust from your chuck and other parts yet but something that is very good for this is what are called 'Garryflex' abrasive blocks. If you are not aware of them, they come in four grades and are an absolute boon to finishing most materials particularly when used with parafin as a lubricant. They will also make derusting a surface rust a very easy job without leaving scratch marks like emery does. If you haven't heard of them Google 'Garryflex' and you'll soon find them but shop around the price varies quite a bit.
Finding rust on your prized posession is soul destroying - I remember leaving my newly made rotary table in the model tent overnight at a steam rally - I was mortified the next day to find it orange.
Hope this helps in some way
Regards - Ramon

Edited By Ramon Wilson on 27/12/2010 15:04:44

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