Aluminium on Steel corrosion problem?

[Dengue]

I have a machined cast iron plate I am looking to use as a router table with a 50 x 6mm thick aluminium angle bar as a fence.

If this sits for some time in a humid tropical environment, will corrosion occur?

Is there any way I can avoid this by coating the aluminium bar with a hard wearing compound or something?

regards,
Jill

[Dengue]

Jill, have a look here (http://www.finishing.com/360/71.shtml) at the web site titled "Corrosion build up between Aluminum and Steel plates" . Here is the most relevant post:


This is a very common problem. I ran in to this in 1978 when working on aluminum runnning boards mounting to steel brackets and trailer hitches bolting to aluminum bumpers on cars and trucks. It is a galvanic process. The automotive industry uses stainless steel to mount aluminum trim to prevent the galvanic corrosion. Nickel plating the steel parts and using stainless steel mounting bolts and nuts should help prevent the galvanic action. However, be careful to use different grades of stainless in the bolts and nuts and plenty of lube. Identical Stainless steel grades can seize.


Personally, I would be using a timber fence :wink:

regards,
Dengy

[.RC.]

Can you put plastic between the alum and steel??? that would stop it..

[hughie]

Can you put plastic between the alum and steel??? that would stop it..]


But ideally you would need to isolate the fixing method as well. Liberally coat you bolts with a grease to help prevent corrosion forming at this point. Or use stainless bolts and a plastic washer under the head as well.

You need to mechanically isolate the dissimilar metals to prevent corrosion

[Dengue]

Thanks everyone. I was looking to used a large 80 x 80 mm aluminium angle section as a fence on a cast iron router table surface, but in the light of the above comments, I have decided to use a timber sliding base for my fence instead :)

regards,
Jill

[BobL]

Thanks everyone. I was looking to used a large 80 x 80 mm aluminium angle section as a fence on a cast iron router table surface, but in the light of the above comments, I have decided to use a timber sliding base for my fence instead :)

I use 3 mm thick high density polyethylene strips on my fences/routertables/mitreslides

[Dengue]

Sounds a good idea, BobL. Where do you get these 3mm sheets of high density polyethylene, and how do you cut them to shape?

How do you fix them to the base of the fence and the jigs?

regards,
Jill

[BobL]

Sounds a good idea, BobL. Where do you get these 3mm sheets of high density polyethylene, and how do you cut them to shape?
Some hardware stores, or plastics suppliers have them. Problem with plastic suppliers is having to buy a whole 1.2 x 2.4 m sheet can costs several hundred $.

You can treat HDPE almost like wood. eg It cuts with a very nice finish with a table saw. If you have a triple chip or negative rake Circ Saw blade then that is the way to go, other wise do it slowly with as high a tooth count blade as you have. The other way is using a handsaw and then a hand plane!



How do you fix them to the base of the fence and the jigs?


I use countersunk gold passivated screws if it's into wood, or galvanised or brass countersunk bolts into ally and in both cases make sure the heads are below the level of the surface. If the ally is 3 mm or more thick I tap a suitable thread direct into the ally which is what I did on my chainsaw mill, plus I used loctite for extra security. This HDPE is 6 mm thick which is better if you can get it because the 3mm does tend to warp a bit more.

I also routed a rolled over edge onto the edges of the HDPE to help it slide a little easier.

http://www.woodworkforums.com/attachment.php?attachmentid=122050&stc=1&d=1258256646
http://www.woodworkforums.com/attachment.php?attachmentid=122049&stc=1&d=1258256646

[Dengue]

Very impressive!!

Thanks for the detailed replies to my questions and for the photos. Looks like 6mm is the way to go.

Can anyone please advise where I might get some 3mm or 6mm HDPE? I haven't ever seen it around.

regards,
Jill

[rrobor]

Same stuff as they use for kitchen chopping boards I believe. Ive done in the odd board in my time when her indoor has her back turned.

[joe greiner]

Kitchen chopping boards are sometimes available at garage sales.

I've recycled some HDPE containers into thicker material by laminating and cooking in the oven. Details upon request.

Cheers,
Joe

[Retromilling]

I don't think it would be a huge problem in a covered dry area.