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Dave WM

window defrost grid

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8 hours ago, ensys said:

Just a couple thoughts...

I think perhaps there is a good reason that all the old manuals illustrate repairs being done with an old fashion drafting pen (looks like the long bill of a bird). The advantage is that (theoretically) one doesn't have to mask (the bill or "nib" is adjustable for width, and when used properly, will produce a very clean edge. the other positive is that the bead will have a slightly rounded top that would provide more net cross section.

The other is that isn't such a grid usually coated with a thin, clear protective layer of something?

Or not.

 

the issue is I have lost prob more than 50% of the grid, so its more of a restoration process than a repair. the grid literally appears to have faded away. I don't know about any coating, but I doubt it since that would make even a repair difficult. there are kits that have stick on grids, but I really did not like the idea of that. Maybe they work but seems like that would have its own set of issues. I rarely use the defogger mode, but sometimes with high humidity and my AC on high it does fog up from the outside.

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I bought a defrost fan from OReilly, replaced the cigarette lighter terminal with two spade connectors and connected it to the power circuit for the grid.  It was kind of noisy but it worked.  

The grid is better of course but if you want something to use in the meantime, the fan's only about $20.  The defrost grid is on a 20 amp circuit, so lots of juice there.

https://www.oreillyauto.com/detail/b/custom-accessories-3126/accessories-16449/winter-accessories-16523/defroster-defogger-23801/5aa88c03919b/custom-accessories-defroster/48701/5981244

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Just wanted to ad.. i had 5! rear windows for my 280zx and i installed the one with the lowest ohms.. it was if i remember correctly around 2,2-2,4 ohms.. (incl. 0.2 ohms for leads)  The one i installed worked on every line! so i think the total resistance of your 240z def.grid should be around 2-2.5 ohms..

Long ago i used some bison silverglue on a grid but did'nt like it..  very difficult to put on and not make a mess  haha..

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33 minutes ago, dutchzcarguy said:

Just wanted to ad.. i had 5! rear windows for my 280zx and i installed the one with the lowest ohms.. it was if i remember correctly around 2,2-2,4 ohms.. (incl. 0.2 ohms for leads)  The one i installed worked on every line! so i think the total resistance of your 240z def.grid should be around 2-2.5 ohms..

Long ago i used some bison silverglue on a grid but did'nt like it..  very difficult to put on and not make a mess  haha..

I am hoping the stencil helps, what was the process you used to apply? so far I have tried masking tape and plastic electrical tape applied free hand (masking tape had too much bleed under, electrical tape was better but very hard to get a consistent width). this was on a plain sheet of glass as a test. I also purchased a pin stripe brush hoping it loads better.

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Might I suggest that given a clean surface to start, plastic Scotch tape has a good edge, and is more stable than elect. tape, making a straight line easier to obtain. Plus, it leaves less adhesive residue than moderne masking tape.

 

Just a thought...

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15 minutes ago, ensys said:

Might I suggest that given a clean surface to start, plastic Scotch tape has a good edge, and is more stable than elect. tape, making a straight line easier to obtain. Plus, it leaves less adhesive residue than moderne masking tape.

 

Just a thought...

the plan is to try the purpose made stencil tape, it has provision for a constant 1/16 line once applied then the center is removed. I was not happy with any of the various tape methods as getting the constant width was an issue, esp when considering I have to do the entire grid. The stencil was designed around the idea of quick pin stripe methods not requiring great skill to apply in the automotive industry.

Edited by Dave WM
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19 hours ago, Dave WM said:

what was the process you used to apply?

i used a sort of pinstripe brush.. a small brush with long hairs and just a few hair..  did'nt work well.  the bison silverglue was very liquid..  never tried masking it.

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Do anyone know how the process was originally done? Seems that would help come up with a replacement process

@HS30-H

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Done with a stencil and a liquid-copper spray would be my guess.  Anybody have OEM automotive glass experience?

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11 hours ago, Patcon said:

Do anyone know how the process was originally done? Seems that would help come up with a replacement process

@HS30-H

Roughly as the Captain suggests, I believe it was put onto the glass like a big transfer print.

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So the video addresses my other question. How was it silk screened when the glass curves in dimensions?

Evidently it was screened first and then heated and formed. I was watching somebody using flexible screens to decorate glasses. I wonder if you could order a screen that would flex enough to regrid the glass. In my mind I was thinking you would strip off all the old grid, buff it and then rescreen it. That eliminates the need to line up exactly with the old grid...

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53 minutes ago, Patcon said:

So the video addresses my other question. How was it silk screened when the glass curves in dimensions?

Evidently it was screened first and then heated and formed. I was watching somebody using flexible screens to decorate glasses. I wonder if you could order a screen that would flex enough to regrid the glass. In my mind I was thinking you would strip off all the old grid, buff it and then rescreen it. That eliminates the need to line up exactly with the old grid...

The bend in the hatch glass is subtle enough that I wonder if someone who knew what they were doing could silk screen that after it had been formed. I'm no silk screen expert, but I wouldn't be surprised if they could deal with that gentle bend.

In my distant work past, I was a customer of several membrane keyboards and that technology typically uses a lot of silkscreen processes. I've never done it myself, but my employer bought lots of them and I got closely grazed by much of the technology.

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I have seen the frost fighters, I am not sure I like the idea of a stick on product, but perhaps it will work better than what I am trying. If this stencil product does not work out I may go that way.

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Dave,

Late to this discussion but--- I made readings from a NOS hatch glass with horizontal defroster grid that I was fortunate enough to find and purchase recently.

Using the 200 ohm setting on the VOM 1.6 ohms was the resistance value measured.

I've thought in the past when S30driver and I were discussing this that we might reach out to frost fighter and see if they would consider a purpose built replacement grid for our Z's that would exactly register over the original element lines.

Since almost all defrosters on our cars are non-op and that no source currently offers replacement hatch glass with the lines, there might be enough of a market that they would go for it at some price point.

I'm reluctant to utter that iffy phrase "Group Buy" , but pre-sales might provide leverage as an inducement to them.

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I will see how this works but yes if there was a proper made to fit Z hatch glass replacement I would def try it, if I fail at this attempt. I too assume there are no functional defrost grids left on 40+ year old cars. I tend to try to keep things original as possible hence my reluctance towards going with a generic kit.

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Quote

 There is no plastic backing left on the window to crack or yellow.

That was lifted from frost fighters website.

Apparently there is no residual material after application---only the lines.

A purpose built grid that matches in lengths, spacing and element thickness should be as close to original as one is probably going to get and in my mind would likely be a better performer than a mix of old and repaired segments or a new conductive grid with irregular thickness (hence resistive) properties.

I appreciate your "do it myself" approach and applaud you for it. My only intent here is to see if there is interest in a quality one source solution that virtually anyone can purchase and install with a minimum of hassle and a maximum of performance.

Edited by Zup
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One potential issue that I didn't see discussed in the FrostFighter online materials:  Is the stick-on grid sufficiently thin*-yet-robust that it will tolerate occasional cleaning of the rear glass surface with glass cleaner?  That's one of the strong points of the OEM grids  --  they seem to be ok with paper-towel-and-windex cleaning from time to time. 

(* by 'thin', I mean height above the glass surface)

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I have the frost fighter grid on my 510 rear glass. It’s pretty tough yet thin. No problem cleaning it with a rag and invisible glass cleaner so far. 

 

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well I tried the stencil works well to keep a thin straight line. I have to work on my technique for applying the paint. I purchased a pin stripe brush, but I am not very good at using it. I cant seem to load enough paint for more than a couple inches at a time, and the transitions are not that great. So now I am practicing stencil free just drawing lines on a round glass tube (old light) to try and get better at the application before testing with a stencil again. Clearly what ever the process is, it will be very tedious considering the amount of lines needed to be painted. This is prob what sidelined me last time when I 1st started this thread.

I suspect the biggest issue with this will be even if I am able to apply and it looks good and works well the paint itself maybe too fragile for any kind of cleaning. Its water based and seem to have low adhesion just going on. I will let what I have done dry overnite and then try cleaning with some glass cleaner and paper towels (pretty rough but what is typically used) as a durability test.

Edited by Dave WM

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The only other consideration may be that if the paint itself isn’t resistive (I.e. it’s purely conductive) you will create hot and cold spots that may break the glass on a cold day. I have read about people fixing their modern cars and having this issue.

Well done for the tenacity and effort to make it work - you need to employ an artist with a steady hand!!

I am very much going down the frost fighter route. On my car, the grid has 16 elements with 35mm separations resulting in a grid height of 52.5mm

The frost fighter 16 element jobbie ends up as 50.8 - there HAS to be a way to make their product work for us.

94ea9c6e3dbd5f1efd5a832503478bcb.jpg

It’s definitely worth asking them if they can do a custom size - but even with that, i wonder if the original silk screen has to be rubbed off for good adhesion?

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