Coating blade update

Discussion in 'Silver Gelatin Based Emulsion Making & Coating' started by Photo Engineer, Nov 29, 2007.

  1. Photo Engineer

    Photo Engineer Subscriber

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    My recent experience has been very discouraging.

    The blades must be made within 1 mil (0.001") tolerance to be usable.

    At present, I have more than a 50% reject rate due to the machine shops < yes shops>, that I have been using. No one can make them. The temper on a 1" square bar of stainless steel causes stress that translates into a twist and bend when milled (or any other operation including water cutting) which makes for a 50% reject rate.

    Therefore, my costs have gone up 2X. The next batch of blades will cost 2x the old price. And, I'm not making a profit. I am sorry, but this has delayed delivery dates and will increase prices. I'm sorry about this.

    In fact, I wanna quit. Waaaaaaaaaaaaaa.

    This is costing me more than I can afford. I will be exiting this phase of emulsion coating ASAP.

    Sorry.

    PE
     
  2. Captain_joe6

    Captain_joe6 Member

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    Ron,

    Do you know if grinding will bring about these flaws? I'm not totally familiar with the design of a coating blade, but I know that there are precision grinders to be found that, when used skillfully, properly, and thoughtfully, will produce very fine work down to .001

    On the other hand, .001 is a very tight tolerance. It makes one wonder exactly what was used before the widespread availability of precision metalworking equipment was available. Any ideas from the depths and ages of Kodak?

    Another thing to consider is that if you've got shops doing the work, then they obviously have a set of schematics to work from, which probably have tolerances listed. Why would it be costing you any more money, except maybe in materials, if the machinists are the ones getting it wrong 50% of the time?

    I worked a while for a spring coiling company and we dealt with tolerance similar to your at times, but usually we had more dimensions to consider as well (things like that usually came up for customers from the medical device field). It was slow work, obviously, but it got done, and if it got done wrong, we had to go back and redo sometimes 10K parts at a material and time loss to ourselves.

    Just a few thoughts...
    -Patrick
     
  3. Photo Engineer

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    Patrick;

    The blades must have 1/2" of material cut from the center by some method. They cannot be welded or assembled otherwise. The cutting relieves some internal stresses on the metal, and this causes a twist and bend which makes grinding and polishing very difficult, especially with the required tolerance of 0.001". To do this, they use a lot of 1" bar stock of 316 or 308 stainless and a lot of labor. It isn't cheap. They had to make 20 blades to get 10 good ones and of the 10, 5 were just out of tolerance. They had 0.001", but the tiny twist made it an uneven 0.001".

    Seeing it would explain the problems.

    So, 5 normal blades and 2 custom blades are out for refinishing. And, I only got 10 blades total when I expected 20. And, I had to pay for bar stock for 20.

    PE
     
  4. ben-s

    ben-s Member

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    Really sorry to hear about this setback Ron.
    I can well imagine the problems you're having. I've seen how badly high grade SS warps when you hack half of a bar's thickness off.

    Just a thought; Have you tried having the blades annealed after the heavy machining?
    It would probably put the unit cost up a bit, but may well bring the reject rate down too.
     
  5. Photo Engineer

    Photo Engineer Subscriber

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    To answer the question about Kodak, every emulsion coating lab had blades of the type needed for the job. Some labs had racks of them of different undercuts which were fixed in place and not adjustable as mine are.

    If the blades cost Kodak a million dollars each, I guess they would have paid that just to get the job done, so the relative priorities and budgets cannot be compared. Kodak's were made in their own prcision machine shops.

    I have seen paint doctor blades for sale made of aluminum. This is unsatisfactory for emulsion making due to the need for an appropriate anodized surface and due to the light weight. In any event, I've seen paint blades for sale for about $1200 for a 4" blade.

    PE
     
  6. Photo Engineer

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    After the bar is bent and twisted, annealing does not undo the damage. The twist and bend is still there. Some sort of retemper during or before the cut might work, but I've found no shop prepared to temper before or during a cut.

    PE
     
  7. ben-s

    ben-s Member

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    I've seen the Aluminium blades listed in various places, and I was amazed at the prices.
    It looks like they might have the same trouble :/
     
  8. JLP

    JLP Subscriber

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    Stainless steel is a bitch to work in. Any others metals that could be used? Brass or bronce would i think be a lot less prone to the problems you have with stainless.
    Just a thought.

    jan
     
  9. Photo Engineer

    Photo Engineer Subscriber

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    Jan;

    Emulsions used with brass, bronze or aluminum are a big NO-NO. Metals that can be used are Stainless (any non-magnetic grade, but the higher the better), Nickel and Titanium. Of course, Silver, Gold, Platinum, Osmium and metals like that would be nice as well. :D

    Well, I take that back. The Osmium blade would probably weigh in at about 10 - 20 kg. IDK for sure, I would have to look up the density, but it is one of the heaviest of metals IIRC :D

    PE
     
  10. richard ide

    richard ide Member

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    Ron,
    Would it be possible to use a low distortion steel like A1 and use hard chrome plating for chemical resistance?
     
  11. Photo Engineer

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    I'm not familiar enough with A1, but chrome plating could be used. The problems arise from the expense of the plating operation and wear and tear exposing the underlying metal. Some plated blades at Kodak began corroding, so they stopped that 'experiment'.

    In fact, ones set of blades was made of cheap iron with a teflon coating. It eventually began to wear and then corrode.

    You see, the surface of paper is quite surprisingly abrasive and does a job on the surface of a blade.

    PE
     
  12. PHOTOTONE

    PHOTOTONE Member

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    But the use of a coating blade by an individual that will only coat enough paper for their personal use would be very light use, as compared to a set of blades that would be used in a photo research lab. An individual may only use their blade 10 times a year. Materials that would not hold up in industrial use, may be just fine for an artist, who coats infrequently.
     
  13. Photo Engineer

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    I'm not entirely sure and in my position cannot take the chance of supplying an inferior product in any way. I would rather supply none.

    What you say is only a guesstimate. Baryta and the clays in papers are quite abrasive. Besides, any slight nick in the darkroom from other equipment could do in a coated blade.

    PE
     
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  15. Steve Smith

    Steve Smith Subscriber

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    Do you think it is the cutting process which is causing the distortion or is it more likely to be an inherent torsion within the material which is held in balance with the removed part - until it is removed?

    If it is the cutting process itself, perhaps spark erosion would work.


    Steve.
     
  16. Photo Engineer

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    I have been assured, after using 3 methods, that the cutting is not the problem, it is tension within the material after forging into bar stock. It cannot be eliminated and it does not appear until the cut bar is removed or released from the jig. Then it immediately bends and twists at random. If it can be fixed, then the blade is rough and smooth polished, then drilled and tapped.

    PE
     
  17. cahayapemburu

    cahayapemburu Member

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    Have you considered any other materials?
     
  18. Photo Engineer

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    Please look at previous threads on this. Yes, I have looked at many many materials. They are too light, too fragile, to hard, too heavy, too expensive and this is getting to be just too much for me.

    I have customers waiting for custom blades and I can't fill the orders due to defects.

    If I had an answer, I would not have this post here! I would be churning out blades and supplying the market.

    Sorry for the rant, but this whole thing has me down. One customer wanted his as a Christmas present and I just cannot deliver for him. How do you think I feel?

    PE
     
  19. cahayapemburu

    cahayapemburu Member

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    Frustrated, undercompensated and underappreciated? No good deed goes unpunished. Wishing you a merry Christmas.
     
  20. Kirk Keyes

    Kirk Keyes Member

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    So if blades out not going to be workable, what technique would be second best?
     
  21. Falkenberg

    Falkenberg Member

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    Have You tried ceramic materials or Plastics like Polysufon from BASF. They are chemical resistant and heat resistant.
     
  22. rmazzullo

    rmazzullo Member

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    possible alternative?

    PE,

    Instead of the coating blade being made from a single piece of stainless steel, can the blade be assembled from pieces of stainless steel bolted together to create the desired configuration? It might make cleaning a pain if the joints aren't tight enough to prevent seepage between components (disassembly, cleaning, reassembly and realignment), but perhaps some sort of sealant that is compatible with the emulsion can be used.

    Another thought that comes to mind is (I haven't tested this, it's just a thought) how does SS respond to grinding / polishing techniques like those that are used for telescope mirror grinding?

    Thanks,

    Bob
     
  23. Photo Engineer

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    Ceramics and glasses cannot be drilled and tapped for addition of the adjustable end cap. If pegs or braces are used, you cannot attain the 0.001" precision.
     
  24. Photo Engineer

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    They tell me that the blade must be one piece. Assembling it is actually as costly or more so due to the jig needed, the drilling and tapping and / or the welding involved. And, they can't guarantee the accuracy any more than what I get now, just no twists and bends.

    The grinding and polishing goes well. All blades are mirror bright! It is the milling out of a 1/2" piece from the center to make a well for the emulsion that causes the problem, and no method will work yet as the temper on the SS bar causes it to warp and twist when the 1/2" piece is removed.

    BTW, this only happens on bars from 8" up. The 4x5 and 5x7 blades are just fine. The problems worsen as the length goes up.

    PE
     
  25. epatsellis

    epatsellis Member

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    A few thoughts come to mind:

    Sintered powdered metal, though probably not cost effective on small runs, though I'd imagine there's somebody doing short runs.

    Are any high density plastics a possibility? not having seen a coating blade, so I'm guessing blindly, but Delrin and the like can be machined like crazy, when properly annealed.

    Is the concept of a holder with a removable or attached blade totally undoable? it shoule be quite easy, for example, to get some .1" x 1" precision ground stainless bar, and with countersunk holes, fastened to a larger piece. If the area that it is attached to is ground true, then the bar should hold it's straightness.
     
  26. Photo Engineer

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    I've tried plastic and wood and found them to be too light. A piece of paper often has a set, or begins to curl when being coated. It also resists the movement of the blade, so I have seen paper lift the light materials up, and the blade sometimes tips over during coating due to drag. These materials are usable, but you may have more defects. I did not pursued wood or plastic due to these types of problems. One person has made a plastic blade I understand.

    There are pictures posted in this forum and on the slide show showing the blades. They are basically a bar of stainless steel cut to yield a [ form. The [ < gap there is the well of the blade and with an 8x10 blade holds up to 50 ml to allow coatings of silver emulsion and even carbon pigment. The gap is capped by an adjustable end cap or doctor blade making a 2 part assembly [ | < where the cap is bolted to the body with 4 bolts while adjusting the opening to about 5 - 20 mils depending on what you wish to coat. In the above, the left carat < is used as a pointer and is not part of the device. All blades are overwidth to allow for edge defects.

    Sintering sounds interesting. No one here has mentioned it to me. Can you do it with Stainless??

    PE