Update on coating blades

[Photo Engineer]

To those interested parties;

I have had a series of blades made up to 16" coating width. They were either milled or cut by water jet. The cutting method makes little difference in price or quality except: 1. Water jet cuts off center from end to end slightly due to the need to cut while holding one end and this needs some extra milling. 2: Water jet leaves an unmilled rough surface that requires further polishing.

Those are inconsequential. The final problem is this. No matter how the 1" square bars are cut, they bend after cutting due to the stresses placed on them during forging. This bend can be corrected, but leads to a lot of rejects and thus the price. This is a result of using high quality stainless steel to prevent interaction with the emulsions and chemicals. Aluminum would be much easier to work with but would ruin most photographic chemicals, even those of most alternative processes.

The bottom line is this. The largest blade I can currently have made is about 11" coating width. Larger than that, and the defects are just beyond being correctable. I have one 16 x 20 blade that is just marginally acceptable.

So, with the help of a friend, I am looking for other places and methods to have them made. In the mean-time, the prices will have to stay pretty much where they are to cover my expenses.

PE

 

[ben-s]

Thanks for the update. Your prices are already pretty much on a par with the only other coating blades widely available, those used for testing paint.
Still out of my range though

So, with the help of a friend, I am looking for other places and methods to have them made. In the mean-time, the prices will have to stay pretty much where they are to cover my expenses.

PE

Have you considered laser cutting?
It was used quite extensively at my previous place of work.
I think you would probably be looking at a multi-pass operation on high grade Stainless of the thickness you are dealing with, but even so, I think it would be possible.
There is another alternative, as sometimes used by moulding tool makers, which involves bolting flat sections together with precision dowels for alignment.
I think that if done properly, this could also work quite well.

Have you ever considered a "budget option" of a milled plastic body with a stainless doctor blade? - particularly in the smaller sizes.
Delrin would probably work reasonably well, as it machines and finishes well, and is dimentionally stable.
I think if you could produce a cheaper option like this, emulsion coating would come within the range of more people.

 

[Photo Engineer]

Ben;

I've looked at all of the above. I've even priced out welding them in 3 pieces, but the stainless welding and grinding and polishing was very expensive. Drilling for dowels was expensive. Laser cutting of 1" metal required such high power and so many passes that the price was out of sight.

Plastic blades don't weigh enough.

At Kodak, they were either stainless or teflon coated low grade steel or iron.

PE

 

[ben-s]

Ah. You seem to have thought of everything!
Good luck on finding a solution, anyway.
I'll be very interested to see what you come up with.

 

[Ole]

Plastic blades don't weigh enough.

At Kodak, they were either stainless or teflon coated low grade steel or iron.

PE

How about precision cut hollow plastic, filled with approximately-cut steel for weight? Much like what was used at Kodak?

 

[Photo Engineer]

Ole;

Now that is one I didn't think of. I'll have to look into it. It may be that the labor is prohibitive, but you never know.

Thanks.

PE

 

[Donald Miller]

How about machining them from aluminum and coating with ceramic...I know that they do this with journal throws on large engine crankshafts and they have tolerances more precise than what you need.

 

[Photo Engineer]

Donald;

I have not found anywhere to do that around here. I'll have to search further. Again, IDK what the cost would be.

Thanks.

PE

 

[PHOTOTONE]

The logical question, since you worked for Kodak..is..who made them for Kodak? Did they do this in-house? The machinist/vendor for Kodak would be the starting point, wouldn't it?

 

[Photo Engineer]

The logical question, since you worked for Kodak..is..who made them for Kodak? Did they do this in-house? The machinist/vendor for Kodak would be the starting point, wouldn't it?

Actually, they were made in the Research Labs metal shop, in the basement of B-59 at Kodak Park. They cranked them out in batches in about a half dozen different styles for film and paper coating. They also made a coating block with vacuum, heat and chill capability, and special drying cabinets for the hand coated sheets.

They were not adjustable as mine are, but rather were welded or milled at precut values and then engraved with the value. They came in sets at 2, 4, 5, 6, 7, 8 and 10 mil undercut. In the recent cutbacks they destroyed most all of them and were unwilling to loan, give or sell any to anyone. I did contact several friends in current management regarding this, and was turned down. In fact, I was refused any sort of help in any fashion by Kodak in my current emulsion projects.

A number of the people in the shop knew how to make them, but are now all retired. I doubt if a set has been made for over 20 years. Just about every individual who did hand coatings had several sets in different styles. In any case, I see little advantage from this even if I could find one, as they didn't care how much it cost, they just went ahead and made them. So, Kodak's blades probably cost a lot more than mine for all I know.

If I wanted to.... The former head of Facilities and Engineering at Research lives across the street from me. IIRC, he ran the metal shop. I never even bothered to discuss it with him due to the above lack of interest at Kodak and my feeling about their costs.

PE

 

[PHOTOTONE]

I would assume that other emulsion makers, such as Ilford, Fuji, Efke, forte, etc., would also use coating blades for testing, and also it seems the paint industry, and possibly other non-photographic coating manufacturers would use this technology for testing coatings. Who makes this type of coating applicator for the paint industry?

 

[Photo Engineer]

Applicators like this for the paint industry have been described here and elsewhere. They are made of untreated aluminum for the most part, and run about $1200 for a 4" blade.

Have fun.

PE

 

[PHOTOTONE]

Applicators like this for the paint industry have been described here and elsewhere. They are made of untreated aluminum for the most part, and run about $1200 for a 4" blade.

Have fun.

PE

Oh, I won't ever be making a blade. I was just speculating, for general conversation and further knowledge. Sometimes ideas and thoughts put down into sentences and paragraphs can cause new directions in thinking. I was just trying to stimulate discussion about all the options possible.

 

[Photo Engineer]

Try here: Dead Link Removed

This was the first place I called when I started my quest. His prices were out of sight.

PE

 

[ben-s]

How about this:
Use Ole's basic idea, but injection mould the blade body with bars and tapped inserts embedded, then machine down critical surfaces using the threaded inserts as datums?

I know this would incur toolmaking costs, but it might be worth it in the long run.

One material that might work is the epoxy resin used in switchgear mouldings.

 

[Photo Engineer]

Ben;

Great idea.

I'm retired. I can't afford it! Sorry.

So, I have to make it one at a time or in small batches that a small shop can make. And I have to be able to afford making a prototype or two and then a batch of 10 or 20.

PE

 

[Photo Engineer]

Well, after looking into several of the alternatives offered here, I have learned a lot more.

1. Plastic blades with weighted centers: Kodak used teflon on cheaper metals because that was the only plastic (it is really a polymer) that is not photoactive in some way or which does not absorb chemistry from the emulsion.

2. Wood blades with metal inserts and polymer coating: See above, apparently only teflon works.

In the final analysis, the teflon becomes scratched and the contamination or erosion process of the blade material begins.

It looks like titanium and stainless are the only metal options available. Welding or some sort of milling are the only ways of working with these metals.

That is a summary to date and my thanks to all for their comments. I'm still open to suggestions.

PE

 

[wirehead]

Some thoughts.

Either take a rough/bent blade and provide a way for the purchaser to hand-lap it back to true.... or make the blade out of glass.

Remember, the amateur telescope makers are polishing aspheric mirrors by hand with easily available tools.... and a lot of time.

 

[Photo Engineer]

Can you drill and tap glass? IDK.

I have only one bent blade. It was the 16" blade to show how bad the problem is. The shop has never given me any of the other bent failures.

PE

 

[Greg_E]

What about a thick teflon blade bolted to a metal core? Teflon is kind of expensive, but if you could attach a thick sheet and then grind/cut/polish to your needs it might work.

Could you prototype with something cheap like HDPE? Or maybe Delrin?

You can get sheets of each of the above at http://www.usplastic.com/catalog/pr...splastic&category_name=12077&product_id=10533

HDPE and Delrin and a bunch of other materials through the same place. You can get Titanium from http://www.smallparts.com

The idea would be to cover the face of the device with the sheet of teflon and leave say 1/2 inch on the trailing side so that you have less of a chance of getting the solution up on the metal parts. You might still be able to use Stainless for the metal, it just wouldn't need to be as exacting. If you used stainless for the body, you might be able to reduce the amount of teflon needed. That's all going to be dependant on the stiffness that you need.

In theory you could just use a straight bar of metal and let the plastic do all the work. The advantage would be that you could replace the blade if it was damaged.

All the same might go for a stainless body with Titanium scraper. Once again this would off a replacable blade for a lesser price than the whole unit.

I took a quick look around the web to see if I could uderstand the needs a little better, but there are few pictures of what you are making, so I only have a rough idea. Essentially it looks like this device is a scraper that is positioned at an exact level above the paper. A large amount of the solution is applied at the edge of the scraper, and the paper is pulled through to apply the coating evenly over the top of the paper. Speed of pull, thickness of solution, and scraper height above paper determine the thickness of the coat (other factors may apply). The coating needs to be uniform within about 1/1000 inch to make sure that you get even tones when it is exposed to light. A thicker spot will give a higher concentration of silver, which will give a different tone than a thinner spot when the same amount of light hits them.

Is my theory correct? (in it's somewhat simplistic way)

If it is, then you may be able to makes the base metal structure in a modular way so that many different widths can be accomodated simply by switching the length of the plastic scraper (and careful setup of the scraper). Since you are using plastic for the scraper, you could put in adjustment screws in order to fine tune the edge all the way across the device. You could probably provide the same adjustments to the metal blade, but it would take more force to make the corrections.

 

[Greg_E]

You could form the glass around a stainless or Titanium insert. A ceramic might be better if you went this way.

 

[wirehead]

Can you drill and tap glass? IDK.

Drill yes, tap no.

I have only one bent blade. It was the 16" blade to show how bad the problem is. The shop has never given me any of the other bent failures.

Well, you could have them make it the most-economical-yet-not-dimensionally-stable way under the assumption that the purchaser would true it.

 

[ben-s]

Another idea just came to me.
Machine the frame accurately in steel, ali, or low grade stainless, and then e-coat it.
E-coating (aka electrophoretic paint) produces a very uniform paint finish, usually around 20µm thick.
It is good for 1000+ hours salt spray, so you'd be safe on the corrosion front.
IDK what it would do to the emulsion though.

The process is widely used by the automotive industry, so it's easily availlable. Plants are often willing to run small batches of products through between major runs, as the paint stagnates if it is not kept moving.

I guess it's an option worth checking out.
there is a bit more info here: (scroll down to electrophoresis) Dead Link Removed

 

[Photo Engineer]

The shop I use does painting of many items, so I'll have to look into this one. Thanks Ben. They never suggested it to me. Maybe it is because they thought the paint might chip or react chemically.

I'll have to talk to them about it.

PE

 

[avandesande]

How about having a casting done and then milling an edge on it? I have a friend who is a machinist and has the castings done in china and then does the final machining in the US.