Experience with PE´s coating blade

[RauschenOderKorn]

I am planning on making a few coating blades following the drawings in PE´s book.

Looking at the drawing and the given specs, there are two "obvious issues" in the plans which are responsible for the high price tag that came with these blades:

1.) The SS308 which is almost impossible to procure in these quantities (ask for 1000 tons - no problem, but 1 kg - huge issue).
2.) The maximum manufacturing tolerance permitted in combination with the steel quality required

So I wanted to ask you guys if from the daily use of the blades, there are any improvements which should be implemented or if you are any improvements you´d put on your wishlist.

As my blade will not be in use every day, I am considering to lower the steel quality requirement to SS304. This quality still has high resistance to corrosion (although not as good as SS308), and is still really expensive, but: available and probably sufficient for occasional use. Furthermore, it is a lot easier to machine, reducing the cost of the high accuracy in manufacturing.

Any comments / ideas??

 

[Nodda Duma]

That's because 308 is used primarily for Welding. 304 is ok (the most common stainless), but I think 316 stainless is better because the molybdenum addition is specifically to resist salt corrosion (we are working with silver halide -- a salt).

Search for 316 stabstahl on www.ebay.de, or 316 stainless bar stock and you'll find what you're looking for. Just be aware of the differences between machining 316 and 304. It's not bad, but you can work harden 316 if you baby it.

-Jason

 

[Photo Engineer]

Yes, 316 is much better, but also more expensive. The steel comes in 20 ft bars here about 1 inch on a side. We cut these to length and then put the "[" cut in. Polish, drill and tap and you are done. Then make the doctor blade itself out of sheet steel and cut the edges and polish. The blades ran over $100 / inch when finished, so you can see the problem with cost.

Why stainless? It is heavy and does not give chatter when coating on a rough surface. It retains heat and thus gives uniform coatings of the emulsion at the proper temperature. Etc.... I have made blades up to 16" long and made coatings with them that were of quite good quality. Those of you that have visited may have seen the 16" blade on a shelf in the office outside of my darkroom.

PE

 

[RauschenOderKorn]

316 should be possible.

I was thinking - just a crazy idea - of uniting the different designs for film / plates / paper in one coating blade. My idea was broadening the short side of the the "[" a little, allowing the doctor blade to be attached from both side and lifting the center of the "[" sufficiently for film & plates. Do you think this makes sense, or would that be a disimprovement?

The maximum tolerance permitted as per plans is 0,001 inches, which equals aprox. 0,00254 cms or 0,0254 mm. That is tough to achieve. Which tolerance would you recommend for amateur use?

 

[Arklatexian]

That's because 308 is used primarily for Welding. 304 is ok (the most common stainless), but I think 316 stainless is better because the molybdenum addition is specifically to resist salt corrosion (we are working with silver halide -- a salt).

Search for 316 stabstahl on www.ebay.de, or 316 stainless bar stock and you'll find what you're looking for. Just be aware of the differences between machining 316 and 304. It's not bad, but you can work harden 316 if you baby it.

-Jason

It has always been my understanding that "photographic" stainless is type 316. Type 304 is what most stainless is that is used in the USA in restaurants and is resistant to most food acids and salt. Don't know if this helps or not......Regards!

 

[Photo Engineer]

316 should be possible.

I was thinking - just a crazy idea - of uniting the different designs for film / plates / paper in one coating blade. My idea was broadening the short side of the the "[" a little, allowing the doctor blade to be attached from both side and lifting the center of the "[" sufficiently for film & plates. Do you think this makes sense, or would that be a disimprovement?

The maximum tolerance permitted as per plans is 0,001 inches, which equals aprox. 0,00254 cms or 0,0254 mm. That is tough to achieve. Which tolerance would you recommend for amateur use?

What you suggest is doable but you have to be careful that the blade does not leak appreciably when loaded with melted emulsion. Also, the best width and height for plates is difficult to achieve and still have it work for paper and film.

As for tolerance, I'm sure that you can work with anything in that range of 0.001 inches +/- .001 inches as long as it is consistent, and that you know what it is, and that it is uniform across the length.

PE

 

[AgX]

316 should be possible.

Type 316 is equivalent to the german type A4, the second most common type.
A further designation is 1.4401