4-Blade Darkroom Easel System

Overview

This is my attempt at designing a relatively inexpensive and easy to assemble 4-blade darkroom easel using primarily off-the-shelf parts for the frame and 3d printed components for the blade sliding and locking mechanism. Materials cost is in the ballpark of $50-$100 USD, ultimately depending on what you already have available. As designed, it supports a max paper size of 8x10in, but with longer aluminum extrusion and rulers, you should be able to support larger paper.

Materials

Frame

• 4x - 300mm 2020 aluminum extrusion

  • Left and right frame edges

• 6x - 400mm 2020 aluminum extrusion

  • Top and bottom frame edges and bottom half crossbars

• 12-16x - 2020 corner brackets

  • These hold the frame together and are the primary source of stability

  • Printing these is viable but the frame will have significantly more flex

• 2x - 2020 hinges

  • Printing these might be viable but I never tried. Metal hinges make it much more sturdy

• Varying amounts - 2020 slide-in/drop-in T-nuts + matching bolts

  • Everything can be done with slide-in T-nuts but not everything can be done with drop-ins. An assorted is best

  • You'll probably want various length bolts

Sliding Components

• 2x - 12in thin metal ruler

  • For the vertical blades

  • Look for one that has slightly longer ends. Mine is closer to 12.3in

  • Harbor Freight sells the rulers for ~$2 each but they come with a cork bottom that needs removing.

• 2x - 16in thin metal ruler

  • For the horizontal blades

  • If you can't find a good one you can also cut a longer ruler to size

• 8x - M3 bolts (12-16mm)

  • Used to align/lock rulers/blades in place

• 8x - M3 nuts

  • Same as the bolts

• 4x - M5 bolt (12-15mm)

  • Used to secure the locking knobs to the sliding blade mounts

Paper Base

This has the most flexibility. You can use any material of any size as long as 1) it's no more than 0.75in thick, 2) it fits within the 300x400mm frame area (accounting for the corner brackets as well), and 3) it's stiff enough to keep the photo paper flat.

Here are a few options that I think work well for this, starting with what I used:

• Melamine MDF board - 12x10x0.75in (LxWxH)

• Acrylic sheet

• A perfectly sized, very flat book

Printing

Modifications

You don't have the exact same materials as me, so it's likely you'll need to make slight modifications to some of the models to fit your needs. I'll try to outline most of the possible changes necessary here:

• ruler lead slider

  • If your rulers/blades are too wide, you'll need to widen the opening on the front

  • Depending on the size of the M3 nut you may need to make the 2 front openings more wide/narrow to ensure they can't rotate in place.

  • If you have super thick rulers or a paper base thicker than 0.75in, you'll need to raise/make taller the ruler opening. I suggest you just get a proper sized ruler/paper base instead though.

  • If your 2020 extrusion openings are very different from the model, you may need to shrink the mounting points.

    • This will make the slider looser when not locked, but it should still work properly when locked/tightened.

• Ruler follower slider

  • Width and height should match whatever changes you made to the lead slider.

  • Same for the mounting points

• Ruler shim

  • Change these to match the sliders if you need.

• Paper guide

  • You may want to design your own if you're printing with smaller than 8x10 paper.

• Base offset

  • This will very likely need to be tweaked. Its height is entirely dependent on the height of your paper base. You want these to raise the paper base the match the height of the blades.

• Ruler sliders (extended)

  • If you have short rulers (or if you happen to cut a ruler too short...), these sliders are extended in a little extra to accommodate that.

    • Try to avoid using them if possible because they slide less freely.

What to print

• 4x - ruler lead slider*

• 4x - ruler follower slider*

• Some - ruler shim^

• 4x - lock knob

• 4x - base offset

* you may need to swap some of these with the extended version if you rulers are too short

^ the exact amount varies depending on the thickness of your bottom rulers/blades. These are used to offset the upper level of blades to make sure they glide freely.

How to print

Perimeters/infill/material/etc. don't really matter, just use your best judgement.

Do enable supports.

Orientation is really only important for the sliders. Try to print those on their sides (with the angled edges pointing up) to ensure dimensional accuracy of the mounting points + to avoid unnecessary supports (that are a PITA to remove).

Assembly

1. Assemble the bottom portion of the frame with (4) 400mm bars and (2) 300mm bars. Do not overlap the corners. Secure them using the corner brackets. Add the crossbars to the center before closing the rectangle, otherwise you won't be able to slide in the T-nuts. Secure the crossbars with corner brackets. Assemble this on a flat surface and don't tighten everything fully until you're sure it sits flat.

2. Repeat the process for the top half of the frame. Do not include crossbars in this half.

1. Attach (2) hinges (roughly equal distance from each edge) to a 400mm bar on the top and bottom halves. The two halves should pivot freely around this hinge and should rest flat on the opposite end. If the hinge bolts are too tight the opposite edge may not sit flat.

1. Feed a M3 nut into each rectangular hole on each slider. The goal is to have the nut threads line up with the bolt hole so the bolt can thread through and tighten against the blades properly. These holes may need model adjustment if your nuts don't fit. Thread a M3 bolt through each nut to hold it in place.

2. Secure the M5 bolts to the lock knobs so the bolt feeds through the knob. I used CA glue for this. Attach a T-nut to each bolt but do not tighten it. 

3. Slide each lead slider onto the 2020 extrusion on the top half of the frame, making sure the loosely attached T-nut on the lock knob slides in properly as well. If the slider does not go in easily you may need to adjust the size of the mounting point on the model.

4. Slide all the follower sliders onto the opposite edges of the lead sliders.

5. Feed a ruler though each follower slider and into the lead slider on one edge. Tighten the M3 bolts to hold the ruler in place for now. 

6. Once the first edge is complete, repeat the process for the next edge (i.e., next level of blades), but add ruler shims to the lead and follower sliders to make sure these rulers sit higher than the previous ones.

7. Check that everything slides freely. A little bit of resistance is expected, but a lot of resistance could be indicative of too tight of a mounting point fit, incorrectly shimmed upper blades, and/or a non-square frame. You'll want to fix this before continuing. 

8. With the frame complete you can move onto the paper base. Use the current height of the rulers as a guide for how tall the final base needs to be. Subtract the thickness of whatever base you decided to use. This is roughly how tall the base offsets need to be. Modify these if necessary. 

9. Mount the base offsets to the frame crossbars and position the paper base on top. The bottom rulers should sit very close to (if not directly on top of) the base. The rulers should still slide mostly freely (a slight lift when moving the sliders can help this. If everything looks good you can continue.

1. Secure the base in place using any method you desire. The approach I took was to clamp it together with corner brackets fixed to the crossbars to limit the side-to-side movement and have the up-down movement be limited by friction. 

2. Use a scrap sheet of photo paper to align the paper guides and secure them in place (with tape/glue/whatever). Only one paper guide is really necessary. You can also use a different approach if you'd like, the only purpose of these guides is to help you position the photo paper in the dark.

3. One last time, make sure everything slides freely with the paper and paper guides in place. It should now be fully assembled.

Alignment and usage

With everything assembled, you can move onto the blade aligning phase, then everything is ready to print with. 

Aligning

To align the blades:

1. Loosen the bolts on top of the sliders for the bottom (closest to the paper) set of blades. Also loosen the lock knob if it's tightened.

2. Move the slider so the edge of the (loose) blade is roughly aligned with the edge of the paper/paper guide.

3. Tighten the lock knob until you see the sag removed from the slider. Always make sure you align the blades when the lock knob is tightened like this. The blades may look misaligned when the lock knob is loose, but they should always realign once it's tightened.

4. If the blade edge can be matched to the paper edge while in this state, continue. Otherwise, Loosen the lock knob slightly and nudge the slider until the ruler is positioned properly. Re-tighten the lock knob. 

5. Go back and forth tightening each bolt on top of the slider while holding the ruler so it's aligned with the paper edge. Tightening/loosening the bolt will likely angle the ruler slightly. Keep adjusting until the ruler is aligned when the bolts are adequately tight. Tightening the bolts too much will cause the slider to crack, while leaving the bolts too loose will allow the blades to shift and become misaligned. Try to find a nice balance.

6. Once both bottom blades are aligned, proceed to the top blades. If you're using identical bottom blades, you may be able to use the markings on the bottom blades now to help align the top blades. If you're doing this, make sure the bottom blades are positioned exactly the same, otherwise you'll just be wasting your time.

7. Will all 4 blades aligned, you should be able to loosen the lock knobs, reposition each slider, and re-tighten the lock knobs and still have the rulers aligned with the paper. If this isn't the case, check that the bolts on top are tightened properly.

Using

1. Move the sliders roughly where you want, tighten the lock knobs, then back them off slightly. The blades should now be roughly aligned and you can position them where you want them.

2. Tighten the lock knobs and make sure the blade is exactly where you want it. If it isn't, repeat the lock knob loosening/tightening.

I measure how large I set the borders by using the measurements on the blade perpendicular to whatever blade I'm adjusting. For example, If I'm setting the bottom edge, I'll read where the paper edge sits on the vertical blade, determine how large I want the border to be, add/subtract that measurement to/from the paper edge measurement, then position the bottom edge blade at that measurement. This should work fine as long as everything is aligned properly. 

Quirks

• I've noticed the bottom edge has some slight color bleed.

  • This can be minimized with thinner rulers or (probably) some black tape on the bottom of each ruler.

• It won't stay open on its own.

  • Just jam something in between the halves if you need (or remix with a solution :^))

• Slider movement can be a bit sticky

  • Try lifting the sliders when moving them and/or lifting the top half slightly (this helps the bottom blades mostly).