Print Flattening Revisited: Arbitrary Print Sizes

Introduction

Fiber-based print flattening has a lot of suggested solutions, not all of them have been very satisfactory to me. When I first started print fiber-based paper in earnest I researched different suggestions on forums. They varied from very simple to more complex. There are lots of solutions and many people have their favorite method. 

1. Hang the prints back to back (this was never very satisfactory for me).
2. Sandwich the prints between sheets of blotter paper that is weighted with books. (I only got moldy prints from this.) 
3. Vacuum bags. (never tried)
4. Use of watercolor tape (this lead to this solution 

I am not here to challenge other techniques just share what works for me. 

The solution I settled on back in 2014 was based on a method that used water color tape which  has a water based adhesive. The idea was as the print dried the paper shrunk and the taped edges held the paper in tension and resulted in a flat print. One draw back was you cut the paper edges where the tape was applied off so you needed generous margins. I couldn't find the specified tape at the time but I thought about this more and decided to try and clamp the edges of the paper instead. A very simple way to fabricate this was to have Perspex or acrylic sheets cut to spec and use bull dog clips to provide the clamping force.  This method would allow anyone to fabricate the parts without special tools or skills.

I built a version for 8x10 prints and then subsequently made increasingly larger versions. 

• 8x10 Version Blog Post (Original)
• 12x16 Version
• 16x20 Version

My experience with this method has been very positive. The prints come out very flat on a consistent basis. One person used it to flatten commercial prints; I was really happy to hear they liked the results. One person used wood and wingnuts (also mentioned in linked posts) so this is possible as well. The paper will get a slight curl in humid air over time as the paper and emulsion swell differently. I find it offers no problem when mounting with PMA however. The group that adopted it for the business added an extra step of storing the print between two sheets of Perspex using the bulldog clips again. This keeps it absolutely flat until mounted.  

Some drawbacks and lessons are 

• A small risk of paper tearing. I had this initially with some Foma paper but never since. (The user who used wing nuts and wood blocks experienced this with larger paper.) I think the clamp force may be too high. One benefit of bulldog clips is the force is limited and consistent. 
• The clamped edge of the paper becomes slightly glossy. I don't find this an issue as the picture frame or matte will cover this. This is about 4-5mm typically. 
• Because I use Perspex the paper edges take 2-3 times more time to dry as the bulk of the paper. This is because edge is clamped on both sides and it takes a while for the water to wick out. This can result in edge puckering if taken out too soon. (I have some ideas how to remedy this.)
• The clamp blocks don't need to be so wide. I made them about 30mm wide but would be fine at half this width and easier to use. Since they fill the throats of the bulldog clips the positioning of the paper has to be made more carefully. Done again I would change this. 
• Finally the system works well for standard paper sizes. Recently however I have been cutting to different odd dimensions like 8x12", 12x12", 6x6", 9x9" etc. I find myself trying to make due with the parts I have then drilling holes in clamps and backing boards. Generally a hassle with unsatisfactory results.

(I should mention that we are firmly in DIY territory now and the method I outline requires access to woodworking tools and the associated skills. (Update: I have now fashioned simpler version so if the DIY warning here has put you off try looking at this one...)

A Solution for Odd sized Prints

This final point was what became the forcing function for my next iteration. One easy solution I have resorted to is to make my print on a full (uncut) sheet of standard sized paper and then dry it in one of my standard sized fixtures. I then cut the paper to size once dried and flattened. (I did this on a 12x12" print printed on 12x16" paper for instance. This works and is simple. However it wastes paper and fixer having to fix big blank areas of paper. 

I had two ideas in mind. This first would be to use magnets glued into the clamps and using a backing board from perforated steel that has been painted to prevent staining. The perforations would enhance drying and magnets would allow continuous adjustment. Different lengths of clamping blocks would be need to to add up to the different dimension differences. I imagine my prints will probably be in fixed dimension increments of one or two inches so clamps need to be made to different lengths to sum up to these dimensions.

I struggled to find a vendor that would take a small order cut to my specific dimensions so I moved onto my second idea. I may revisit this in the future as it seems quite elegant. 

Update: I finally completed the perforated steel sheet version which can now be found here. So far it seems as good as the solution outlined here but simpler to build and to use. 

My second solution was to use plywood routed with T-slots at intervals with T-bolts used to clamp the blocks down. T-slots are slots in the shape of an inverted T in a sheet of plywood. This allows a T-bolt to locking the slot. A special router bit is available to makes these slots.  

T-Slots

T-bolts have a special head that fits the T-slot in the narrow head dimension. These T-slots are 9mm wide. The bolts are M5 threads (5mm shaft). I had to order there off of eBay from China. I generally avoid buying directly from China but could not find any local stock. 

T-bolts

T-bolts in T-slots

I started with an objective to support up to 12x16 prints. I allowed for an extra inch on all sides so I cut a sheet of 18mm plywood at 18x22". (Sorry for the mixed units! I am an American living in Europe so have become comfortable with both!) 

I then routed T-slots at 50mm intervals. (I recently bought the DeWalt cordless router and highly recommend it. Well made easy to use and no cords.) I left an area about 8x10" unrouted in one corner. This allows prints down to that size. If I want to go smaller the opposite corner can support prints smaller than 8x10.  This saved me some time and effort with the slot routing.

Print Flattening Board with T-slots

Next I fabricated the clamps. I used 40mm wide 12mm thick plywood strips I had left over from a prior project. I routed 4 slots for the T-bolts offset from one edge of the plywood clamps. I made a number of 200mm (8 inch clamps). One of these I cut in half to made two 100mm (4 inch) strips one of which I cut in half again to make two 50mm (2 inch) clamps. This gives the ability to support print sizes to 50mm (2 inches) increments. I may make some 25mm (1 inch) versions as well. 

I made the slots off center to give me some flexibility in using them on the edge of the board. All the wooden parts I painted with polyurethane to waterproof them and keep the wood from staining the wet print. 

I also glued sandpaper along edges on one side of the clamps and left it smooth on the other side. This gives me the option of with and without sandpaper. The idea of sandpaper edges is to perhaps allow better drying of the paper edges by making it easier for moisture to escape. It will also grip the paper better and this may lead to tearing of the paper. (I used 400 grit wet/dry paper. Coarser paper may be better. Wet-dry paper is formulated o be used wet so should not deteriorate with contact to the wet prints. ) Experience will tell. (If sandpaper does not work I may try felt instead.) 

Clamp blocks with offset slots and sandpaper edging on one side. 

I needed something to tighten the clamps. Wing nuts would work but I opted for using threaded inserts in wood handles. I milled a simple pine strip and drilled holes for the inserts then cut them apart. 

Now with tightening blocks.

Finally, I found an odd sized print to try out. I used a recent 10x16" print. On the two fixed edges I used my Perspex clamps and secured two edges using bulldog clips. (One issue is the 18mm plywood is almost too think for the clips and the Perspex clamps. I may route a thinner section on these two edges on the back of the plywood to make it easier to apply them.

 

Next I slid the T-bolts into the T-slots and the put the clamps over the T-bolts and threaded the tighteners on the clamp slots. I used two 8" (200mm) clamps for the long direction and one 8" (200mm) plus a 2" (50mm) clamp for the short edge to make my 10x16" image. I made each clamp slightly shorter than the nominal dimension to allow them to fit between blocks. I adjusted them for the small 3-4mm overlap on each edge of the paper and then tightened them. 

Print in Flattening Fixture

I was pleased so far the clamps are easy to use and adjust. Its is easy to get them very tight and that might be a problem. However since I continue to use the bulldog clips on two edges there should be some ability for the paper to move if needed. 

Results

After few hours to dry the print came out very flat and perfect. No tears. The sandpaper seemed to work but even the edges under the Perspex seemed to dry well. Perhaps the wood surface under was rough enough to encourage drying. It is also possible the had plenty of time to dry as I wasn't in a hurry. There is none of the glossiness on the edges where the sandpaper was in contact though it is present in the areas under the Perspex. 

I am extremely pleased with the results. Next I will try a 12x12" print. 

Flattened print with clamps removed

Video

Here is a short 10 minute video showing its use and the results. (View on YouTube here... )