PDA

View Full Version : Farmhouse Windows



Ian B
11-14-2012, 04:45 AM
I'm in the process of making some windows for my new farmhouse. They're to be copies of originals, which were made of cast iron with a single sheet of glass. Something like this: http://www.goedkopestalramen.nl/images/stalraamrond57rodegrond.jpg

Mine will be double glazed, and have the frames fixed to both sides of the double glazed units with double sided foam sticky tape and sealant. I have the dimensions - about 750mm wide, 520mm high for the oblong ones, and 520mm and 750mm diameter for the round ones.

My plan is to draw them in AutoCAD, have the frames CNC cut from 6mm steel plate, blast & hot dip galvanise, then powder coat in white prior to assembly. So far, so good.
My question; what's my best option for having them cut? I'm thinking of plasma, laser or waterjet. There aren't many places doing waterjet cutting in my area. These don't need to be super high precision; +/- 1mm on all dimensions is fine, and I don't mind doing a bit of cleaning up (I'll need to round the corners anyway).

Which tends to be cheaper - plasma or laser? They need to be pretty flat - are there any distortion issues with either?

Thanks,

Ian

LKeithR
11-14-2012, 04:58 AM
I would say that plasma will be cheapest, followed by laser and then waterjet. This is generally how the prices play out around here and I can't see there being big differences in other locations. for what you're doing a decent hi-def plasma should be fine...

Ian B
11-14-2012, 05:16 AM
Thanks Keith,

That was my gut feeling too. The bars will be about 25mm wide (in 6mm plate) - any issues with distortion?

Ian

winchman
11-14-2012, 07:31 AM
Are you going to have the beveled cuts like in the picture you linked to? It's doable, but I'd think that's really going to up the cost.

We've plasma cut some pretty intricate parts out of 3/16" and 1/4" steel, and there was very little distortion. Getting plate that's really flat in the first place is going to be the problem.

Ian B
11-14-2012, 07:54 AM
Winchman,

The bevels; some of the windows have bevels, some don't. I have access to what looks like a heavy duty hand-held router, with a replacable insert carbide bevel cutting tool and ball bearing follower. It's made for steel, for making weld bevels. I'm thinking of using that. I'll check with the steel supplier to find how flat the sheets are that they use. Good to know that distortion shouldn't be too bad, thanks.

On the finishing. Obviously, one half will be outside in the lovely Dutch weather. I plan to hot dip galvanise, then get them powder coated. Does anyone have experience with this, particularly about how well the powder coating will adhere to fresh galvanising? I've read that asking the galvanisers not to do a post-galvanising quench in sodium dichromate will help the bond.

Ian

Ries
11-14-2012, 01:56 PM
Somewhat irrelevant, but, in my area, laser is almost always more than waterjet. I think pricing is quite regional, depending on who is doing what, but I do know that a similar capacity laser costs twice what a waterjet machine does.

I am quite prejudiced against powdercoat for an exterior metal finish.
I used to do small production runs of furniture, accessories, and various indoor housewares, and have spent tens of thousands of dollars on powdercoating- and its great- for indoors.

Its unsuited for an outdoor application that is expected to last more than ten years, though. Its used on car roof racks, or similar short life span exterior things, where initial price is the most important factor, because its cheap.

But its not a long term finish, and its not site retouchable. When it starts to peel, and its always "when", not "if", the window will have to be removed, and sandblasted at the very least. And powder has a unique ability to peel like a bad sunburn in one location, but inches away on the same piece, require an unbelievable amount of time to sandblast off. Many commercial sandblasting companies just refuse, outright, to sandblast powder, because no one believes how long it takes, and how expensive it is.
Commercial powdercoaters use a 1000 degree farenheit burnoff oven to burn the powder, THEN sandblast.

And it doesnt stick all that well to galvanized.

Instead, etch the galvanized with a commercial prep solution, then paint with a good alkyd enamel or two part epoxy paint. Boat paints are good. Something you can sand and touch up if needed.

Evan
11-14-2012, 02:01 PM
When I read the title I immediately thought that there was some weird new version of MS Windows coming out.

Duffy
11-14-2012, 02:01 PM
Why would you even bother to put double glazing into a METAL window frame? The heat loss through the frame will FAR exceed any saving gained from double glazing.

Evan
11-14-2012, 02:06 PM
That may be true but the heat losses are additive, not exclusive.

ahidley
11-14-2012, 02:17 PM
When I read the title I immediately thought that there was some weird new version of MS Windows coming out.

That version is comming out south of the GREAT WHITE WINDOW version

Ian B
11-14-2012, 03:26 PM
Duffy,

Good point, however. The idea is to have two totally separate metal frames, both made of flat plate. One fixed to the inside, one to the outside, a 25mm thick double glazing pack between. No contact between the inner & outer frames, no cold bridge. Should be fine.

Ries, yes, I was also thinking of epoxy primer / twin pack polyurethane topcoat, thanks.

Ian

Fasttrack
11-14-2012, 03:55 PM
I second what Ries said regarding surface finish. I'm not a fan of powder coating but do NOT use alkyd enamels over galvanized metal! Normally I'm a huge proponent of alkyd enamels, but they won't stick very well to galvanized steel. Definitely make sure you prep the galvanizing correctly. There is an ASTM standard on how to properly finish galvanized steel ... I'll see if I can find it. Sometimes you don't need to do anything other than rough up the surface ... other times it's a full acid wash.


See here:

http://www.galvanizeit.org/about-hot-dip-galvanizing/what-is-hot-dip-galvanizing/the-hdg-coating/enhancements/painting-hot-dip-galvanized-steel/

They even have a list of paints that adhere well. Something that sounds interesting to me is "portland cement in oil" - I'll have to research this. I wonder if it leaves a texture that reproduces the look of cast iron ... ?

kf2qd
11-14-2012, 09:51 PM
Plasma will be the least expensive, for small cross sections you can actually have more distortion problems with waterjet because it is a process with an abrasive added to the waterjet and those abrasive particles act like many little hammers hitting the metal as it is cut.
Plasma, cut under water has minimal distortion due to heat.

elf
11-14-2012, 10:15 PM
Why not have them cast? I would expect it would be more authentic and add value to the house.

sophijo
11-14-2012, 11:45 PM
Have you considered some kind of "color-through" synthetic material; CNC routed?

Ian B
11-15-2012, 01:06 AM
Elf,

The originals are indeed cast, and replicas are on sale. This guy sells them, not far from me: http://www.goedkopestalramen.nl/assets/s2dmain.html?http://www.goedkopestalramen.nl/

Originally, the bars on the windows were either L section (at the edges) or T section (the middle bars) to allow a single layer of glass to be fixed in with putty. I took an original, ground the legs off the L's and T's, but the resulting piece was nowhere near flat enough. Also, I sorted through a dozen frames, they all varied on size. The whole trick is that the inner and outer frames align exactly, and the end result looks like an oroginal - but it insulates. hence me going for cutting from plate.

Sophijo, what kind of colour through material are you thinking of? HDPE sheet? Possible, but I also need sufficient strength to stop someone pushing them in, hence steel frames. I guess aluminium would do too, but would be more expensive than steel.

Fasttrack, thanks for the link!

Ian

Ian B
11-15-2012, 04:50 AM
Sophijo, thanks, you've just given me an idea. The window is fastened to the inside of the outer brick wall by the frame on the inside of the double glazing unit. I can still make this out of 6mm steel, CNC plasma cut. For the outside, I can use 12mm UPVC sheet, routed with a bevel to simulate the putty on the original windows. Easy routing job - just use a steel frame as a template, and a 45 degree ball bearing guided router bit. No corrosion issues, and I can get the UPVC in the same colour as the rest of the windows.

Ian