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rmazzullo
12-01-2007, 08:19 AM
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

Photo Engineer
12-01-2007, 08:44 AM
Have You tried ceramic materials or Plastics like Polysufon from BASF. They are chemical resistant and heat resistant.

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.

Photo Engineer
12-01-2007, 08:48 AM
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

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

epatsellis
12-01-2007, 08:58 AM
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.

Photo Engineer
12-01-2007, 09:11 AM
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

epatsellis
12-01-2007, 09:35 AM
From what little I've seen, you make a mold, powdered metal is put in and compacted, then heated to fuse it solid, I'm pretty sure I've seen ad from companies that do all metals, including stainless. I stopped getting alot of the industrial design magazines a year or two ago, as I never had time to read most of them (except for Nasa Tech Briefs) and am going strictly from memory. A quick google search should turn up more hits than imaginable, as many complex parts are made from sintered metal today.

erie

epatsellis
12-01-2007, 09:56 AM
Ron,
I just had an off the wall idea, have you ever seen a printing press ink fountain? it has a flexible stainless blade with what amounts to grub screws with a tapered tip that press against the blade. something similar could be designed simply, and could be adjusted post manufacture, then a drop or two of sealant on each screw would ensure that it stays put. By putting the accuracy part in the final, assembly stage, the tolerance open up, as cost goes down, it shouldn't be terribly hard to get a blade adjusted within .001" by making a jig that uses a dial indicater mounted on a linear stage, the jig cost would be more expensive, up front, but by making it large enough for your largest blade, could be used for all sizes. Depends on how agreeable your machinist is, in an ideal situation a retired tool and die maker with a surface grinder, mill and lathe in the garage would be the ideal machinist.

Alternately a thinner blade could be lapped to within far less than .001" tolerance, as long as you design the holder to allow access to the doctor edge in such a way as to allow lapping. The removable end plates could facilitate that easily.


erie

Photo Engineer
12-01-2007, 10:04 AM
I have blade bodies and end caps in several thicknesses and several designs. The thin ones bend with finger pressure at a length of 8" and longer than that they actually 'quiver' as you draw them across the sheet of film or paper. The present thickness of the end cap was determined by trial and error to be the thinnest that will not bend with finger pressure. However, a blade that thick caused coating defects and so the thicker the end cap, the more taper that must be put on it to keep the edge of the blade sharp. The larger blade end caps are therefore not plates with flat edges, but are plates with a precision chamfer to achieve the optimum width at the contact point with the emulsion.

It comes down to this though, most tool and die works or machine shops don't even want to work on jobs that run much less than $20,000 or so. It takes me about 3 months to get blades done, as they are not high priority because a 20 blade order stretches my budget but is peanuts to them.

I go to the plant and dodge cranes, fork lifts and trucks to just get in the door. They are rushing around like mad to meet orders that tally in the hundreds of thousands of dollars for the big ones. So, I get a few minutes of a guys time and that is it. And, the smaller the shop, the slower they seem to be or the less interested.

PE

PHOTOTONE
12-01-2007, 10:14 AM
You need to find a retired, or semi-retired craftsman machinist that still has his equipment and is willing to work on odd projects, just for the love of quality work, and a reasonable amount of pay.

Photo Engineer
12-01-2007, 10:21 AM
I have a better idea.

As soon as this batch is sold, I'm publishing the plans so that you can get your own made however you want and out of whatever materials you wish.

PE

Tim Gray
12-01-2007, 12:22 PM
Sorry that it has been so frustrating for you PE, but thanks for making the plans available.

I know from personal experience that the quality and cost of shop work varies widely, and they don't necessarily correspond. We needed some 1/2" copper plate with an explosively bonded stainless face bent into a very specific, but odd shape (not circular at all). We had 28 pieces that needed the exact same curvature. One company priced at $3k/piece, for a total of around $90k. We got a second quote from another company for $200/piece. They did a great job and bent it right to spec. This was for a fusion research device, by the way.

The research I participate in requires LOTS of one off designs, and almost everything is custom machined. It really does get expensive.

Not that I have the knowledge to help, but I'm sure a lot of the problems you are running into have already been solved by someone else. If you just knew who to contact...

Kirk Keyes
12-01-2007, 11:38 PM
Ron -

Idea 1 - What do you think about a plate that has a well that is tapered - when looking from the end of the blade? As it you are making them now, you have the well go the entire depth of the blade and at a uniform dimension - what about cutting the well at a 45 degree angle (instead of vertical as they are now) so that the well is say 5 to 10 mm wide right in front of the doctor blade where if meets the paper, but it is wider as you get further away from the paper. Think of a funnel profile but one that is "cut in half" so that one side (the side of the blade) is striaght, and the other side (the side of the body) has the funnel shape. It doesn't need a compound curve like some funnels, a simple triangular well shape would be fine. The body would need to be taller than you currently have in order to hold the same volume, but the triangular shape of the new body would be stiffer than the currently rectangular bodies.

Second idea - only the doctor blade needs to be precisely parallel to the surface of the material being coated - the body of blade does not. So what about a blade body design that has the same U/rectangular shape you currently have, but one that uses a rubber casket/wiper to make contact with the paper along the long dimension of the blade. This way, the long dimension doesn't need to be precise since the flexible wiper contains the emulsion and keeps it from running out of the well as only the ends that the doctor blade that screw into need to be precisely parallel with each other. A slightly larger blade body could be made to reduce flexing and only the ends, which are polished and parallel to each other need precise machining and polishing. It would sure cut down on the machinging expense of these blades.

Kirk

ben-s
12-02-2007, 04:07 AM
... One person has made a plastic blade I understand.
...

That would be me.
It is extremely basic, and entirely hand built. It uses a design broadly similar to PE's blades, but I tweaked the design to make it more stable and resistant to flipping over - a problem I was warned about with lightweight blades.
I haven't had my design snag or flip over as yet, but I haven't exactly used it a lot.

However, it does get the job done after a fashion. It would greatly benefit from a more accurately made doctor blade, but even with the one I have in place, the results are better than brush coating.

I have spoken to PE via PM, and he suggested the lightweight blade might have problems coating particularly on baryta papers - I haven't tried this as yet, so I don't know.
If it did have serious problems, I have thought of several ways to add mass to the blade, but I have not actually tried them yet.

Falkenberg
12-02-2007, 08:08 AM
With the many possibilities of modern 3D printers, it should be possible to print coating blade with high precision and at a price that will allow for changing when the start to corrode if made from metals. A 3D printer will allow for making plastic models, that can be tweeked to optimize performace. Some of the printers will allow for making hollow prints. They could be filled with sand or something heavier. Some printers can print with polysulfon wich is temperature and very chemical resistant. The printers also allow for making moveable parts an integral part of the design if needed. I am not affiliated to any 3D printersupplier, but I have seen some amizing things come out of these printers.

dslater
12-02-2007, 08:18 AM
With the many possibilities of modern 3D printers, it should be possible to print coating blade with high precision and at a price that will allow for changing when the start to corrode if made from metals. A 3D printer will allow for making plastic models, that can be tweeked to optimize performace. Some of the printers will allow for making hollow prints. They could be filled with sand or something heavier. Some printers can print with polysulfon wich is temperature and very chemical resistant. The printers also allow for making moveable parts an integral part of the design if needed. I am not affiliated to any 3D printersupplier, but I have seen some amizing things come out of these printers.

These are fascinating devices that seem to be coming into their own - I think over the next decade or so, we are going to see a revolution in manufacturing based on these 3-D printers.

Photo Engineer
12-02-2007, 09:26 AM
Kirk;

Both ideas sound doable, but in #1 there is more surface to polish and the larger surface area may be more subject to scratching the film or paper. As it is now, the blade can be flipped over if one side becomes scratched. Also, the higher a blade is the more tippy it becomes.

Ben;

I had forgotten your name, sorry. As I wrote that my mind went blank. Good luck.

As for the rest of the suggestions, it seems that there are a lot of ideas that might work. I guess having unhappy customers at Christmas has gotten me down a bit. Those with special orders, please take heart, I am doing the best I can. I just shipped a batch of them back to the shop that were re-done and were very accurate but had minute scratches in the surface finish. This ruined their ability to coat quality material. I have one with scratches but they run perpendicular to the direction of travel. If they run parallel to the direction of travel, they show up.

BTW, Kodak used over 5 different designs including some mentioned above. I have tried all of these before settling on the one now being made. Kodak's versions all worked but probably cost $1 M each to make. ;) If any of you are in Rochester, I would be glad to show you my drawer full of prototypes.

PE