I mentioned in another thread that I was revisiting an old design of mine that might make use of a linear actuator. 

The design is a ghost from my past that escaped when I was cleaning out my utility/storage room recently.  

I've got a couple sketchbooks that surfaced with drawing of this reclining chair that cover 18 month of repeated contemplation. 

I also had gained access to a Radio Shack 4-pen plotter. I had a copy of MicroCAD or something like it that came with the college's new IBM clone computers. 

I wrote drivers (a plotter program) to take the MicroCAD files and convert them to scaled plotter code to draw out.  That generated precisely drawn elevation views of the mechanical translation between upright and reclined positions.

I could measure carefully the parts and angles of the parts to put into Aspire so I could use its drawing features to draft out the links I'd need to control part angles as the chair reclined.

These drawings are not of the final look of the chair, but just diagrams I used to draft the geometry that tells me where links have to meet and the path they'll slide through.  

    

I'll likely cut parts to make a side mockup to verify that the chair parts move as I expect them to.  The linear actuator will mount between front and rear stretchers between the legs to push/pull the chair from upright to reclined and back.  I'll put wheels on the rear legs so they'll roll on the floor as the chair does the splits.  The chair will have arms connected to the back and ride on the disc. 

Love any comments. I've got a lay back lounge chair.  Comfy but a tiny bit harder to get out of each year I get older.  Might make this recliner to be an action/adventure version of my current lounge chair. 

4D 

Do we get a quarter's credit for taking this class?

This should be an interesting build to watch you muse and experiment with various thoughts, hope you will take us on the full ride 4D

If I still taught I'd sponsor you for the class Cal.  Should be worth 3 credit hours. "Reclining with 4D.  A furniture design journey".

4D

Checked out the travel length of my linear actuator.  From stop to stop it is close to 13".    Doing a little circle geometry on the side view of the recliner diagram I can't find any place between the upright and reclined positions between the legs that moves that length.  Half that, or 6.5" is possible, but it means to use the linear actuator I have I'll have to mechanize it to only move the legs apart half as much as it travels.   I can't use it directly.   In theory I could mount it diagonally rather than directly back to front.  At 45 degrees between stretchers the connection points and travel would be half in the front to back direction (Y axis).  As the legs move apart though the angle from point to point changes.  There is also force in the X direction that will need to be resisted by the chair frame if that is the solution. 

 

What I should do is calculate how much open limit I need/want and look for an actuator with only that much range.  Pick a linear actuator that fits my design rather than adapt/complicate my design for the use of my existing  actuator.   

4D

+1 for what @Cal said. Not sure if my VA benefits will cover the cost of the course, however 

I've told all me nieces and nephews who have college in their future that I'd cover their tuition if they kept a 3.5 grade average or better.  I'd do the same for you Lew, if only I was still teaching.   

I've been using a few geometry tricks (arcs and lines) to figure out where I could line up a linear actuator so a 4" travel would move the legs exactly the right amount.  Took some trail and error guesses, but here it is. Within .03" anyway. 

4D

 

I found a 4" travel linear actuator with power supply and control button at Amazon.  160lb push/pull, and I have no idea if that will be strong enough so I ordered two just in case. I'm sure I can wire them in tandem If I end up needing both for one recliner. If I have a spare I'll find another use for it.  Might put it on my benchtop drill press to move the table up and down.  4" is usually the most I move it for various drilling tasks. 

4D

It took working backward rather than forward to figure out where to mount the upcoming linear actuator.  Going forward I kept creeping/inching down in small steps to try and find an ideal spot that would be 8" from the front stretcher bracket to the rear stretcher bracket when the chair was upright, and also exactly 12" between the brackets when fully reclined. I'd get close but never at 12" with the initial bracket.  Finally drew a 16" circle from the center of the upright bracket position and a 24 inch circle from the center of the reclined bracket position.  Where this circles crossed told me I needed a slighty taller bracket for that front stretcher end.   Brackets in green.  8" and 12" lines in dashed red. Legs 2" wide. stretchers 1", thick and brackets screwed to the stretcher face. Actuators will be her Monday.  I may not post here again until then as I need to verify that they are the dimensions from mounting hole to mounting hole they claim.  The diagram doesn't make that perfectly clear. 

 

4D

I'm contemplating the disk.   It is key to tying the legs, seat, and back together.  I'm thinking of using two 12mm layers of Baltic birch plywood for one side disk.

The front leg doesn't move relative to the disk so I want to mount it on the out side,  It is 1.25" thick  and would be set 1/4" into the disk.  The stretcher piercing the disk to pass across to the other front leg. The center top end would stop before the center as the back leg will actually be pinned to pivot there. 

The back leg does move relative to the disk. I also want it on the outside.  It is also 1.25" thick and would be set into a 1/4" recess that had clearance for the rotation arc it passes through.  The back stretcher would also pierce the disk, and have an arced slot area in the disk edge it can rotate through. The link would be on the outer surface of the disk, with a pin piercing the disk to connect to the link from the back. There would be a slot the bolt would move through as the seat reclined.  

The seat doesn't move relative to the disk. I want it on the inside as the whole seat width is between the two disks.  The outer frame of the seat would notch into the inner face of the disk 1/4" deep.  The back edge of the seat would not extend to the center of the disk. 

The seat back does move relative to the disk.  It has to be on the inside and pivot at the center of the disk. it will be spaced 1/16" away from the disk so it can rotate without rubbing on the disk.  The link from the back on the inside connects to a link from the back leg.  See above. 

The links I'll probably make from 3/16" thick aluminum bar stock. I might get them powder coated or anodized. I have some bar stock on hand, although there are web services that could make the links (4 of them) drilled out, chamfered edges, finished, and send them to me ready to use. 

 

Writing out design intents such as I've done above is a key to not getting lost in a complex build.  An instruction set perhaps. I normally do this on my blog as I'm creating a post for the project, but then delete the boring parts before I publish the blog. 

4D

Edited June 8, 20233 yr by 4DThinker

What the disk would look like after cutting pocket and slot for the legs and link bolt.   Still needs a center hole but I'm considering how to connect the seat back and rear leg through the disk so both can rotate independently.  Bottom image is inside view of the disk.  Top image is the outside view of the disk with recess pockets for both legs. 

 

Other details yet to come.  There will be arms for the chair that ride on the top edge of the disk. I'll probably put and arced slot for a pin from the arm to keep it attached while the seat back rotates it back to recline. 

4D

For the center pin that has to allow the back leg and the seat back to pivot independently I've borrowed an idea I used on a chair design with a push button height adjustment release. 

Essentially a 5/16" diameter metal rod, turned down to 3/16" diameter for about 3/16" of width near both ends.  A 5/8" diameter push button with a conical spring behind it has a keyhole slot in it.  When pushed in the slot opens up to allow the 5/16" rod to slip through.  When released the 3/16" section of the slot slips over the 3/16" section on the rod to lock it in place, but still allows it to spin in place,  Drawing shows the keyhole, but in use that push button would be rotated 90 degrees to the keyhole is in line with the center rod.

 

Conical springs I've already found at McMaster Carr.  They provide cad drawings for all their products which is where I got the image of the spring.  The length and notch position of the rod will need to be very precise.  Drawing is full scale, although I don't know if the image above is.  Cross section of both leg and seat frame is 1.25" thick x 2" wide. 

4D

Edited June 8, 20233 yr by 4DThinker

Modeled up the push button.  I already have some 5/8"d brass and can make this. Keyhole slot for the connecting bolt between the seat back and the rear legs to pivot on. 

 

I very much appreciate that Aspire CNC software has the capability of creating 3D models directly, or exporting the result of toolpaths as 3D models.  If I want a 1/3 scale version of this part I can export it as an .STL, then import it into my 3D printer software and scale it to 33.33% before 3D printing it.

4D 

Edited June 9, 20233 yr by 4DThinker

I've ordered 3D prints in Aluminum before at Shapeways.com. No recollection of them being unreasonably high priced.   Thought I'd see what it would cost to have the make 4 copies of the above push button file for me.  Got the file uploaded.  Picked a Stainless steel option.  For one it listed $43.   I winced a bit and changed the quantity to 4, and was momentarily happy to see the price not change.  I assumed for that moment that up to some number it wouldn't cost more as they could all be printed at the same time on the same machine. 

 

Clicked on my cart to see my grand total for 4 stainless steel copies, plus shipping, was going to be over $400.  Needless to say I backed out and cancelled that order,  Times are changing it seems.   There is something enticing about having custom parts made for me that I'm happy to pay for.  The enticement runs away quickly when value is overwhelmed by excessive costs.  I can make this part 4 times.   Making them precisely and efficiently is the harder part.  Not a big challenge with wood parts on my CNC, but in brass or aluminum on my metal CNC milling machine I'm not that clever yet.   The round part has to be cut from both sides. Flipping a round piece in a vise 180 degrees is the trick I need to figure out.   

4D

Linear actuators showed up today.  A complete kit thankfully with power supply, control pad, and even mounting brackets.  The brackets of course meant that I needed to re-layout where they are mounted.  That led to increasing the stretchers from 1" thick x 3" long to 1" thick by 4" long, and changes in the cuts on the disk. 

 

Lesson learned again is that hardware in hand will save on how many times the drawings need to be redone.   The control pad for the actuator will be a challenge to find a place for.  Not something design to be mounted or inset.  I might see if I can swap it for the one the came with my original linear actuator. Looks different but the plugs look interchangeable. 

4D

Just checked if the control switches could be swapped and the answer is "Yes".  As the disk sides are two layers I was planning on hiding the cabling for the linear actuator in grooves cut before the layers were put together.  Then imbed the control buttons into the inside face of the disk.  Some place easy to reach while sitting in the chair.   Cable feeds from the actuator, so I might split the stretcher that the motor end attaches to and feed cable through the stretcher over to the disk and up to the switch.  The other split of the cable goes to the power supply then to a wall plug.  I could run that cable to the rear of the disk and out on the inside where the power brick might be strapped to the rear stretcher.

 

I found one of a set of wheels that I thought might make good rollers to attach to the bottom inside of the back legs. I know there is one more somewhere, but it has escaped me for now.  I've been salvaging wheels/casters off of everything that I encountered that wasn't needing them any more.  I have a good stash for future projects but only one set among them would be ideal for this recliner. 

4D

Time to fit the arm.  It joins to the back frame, and rests over the disk.  A 1/4" pin in a piece of 3/8"o.d. plastic tube rides in an arced slot to stay hook into the disk. 

 

 

 

In reclined position the arm follows.  I have enough raw material to make one side of the chair full size. Tempted to do just that to verify that the mechanics work as expected. Just a mock up with enough in place to allow it to work.  Short stretcher stubs to provide a place for the linear actuator to mount. A demo frame. I could make one 1/2 or 1/3 size but don't have a 1/3 sized linear actuator.  

 

4D

On a whim I went looking for a linear actuator with 2" travel and 6" total extended length. One like that would allow me to make a half scale test side.   So far I've come close but can't find one as a kit with power supply and control button.   Also seems that cost doesn't appear to scale down with the travel limits. Smaller actuators want to cost more for some reason. 

4D

At first blush, to me, the arm rest looks to be in an uncomfortable position when the recliner is "upright".

9 minutes ago, lew said:

At first blush, to me, the arm rest looks to be in an uncomfortable position when the recliner is "upright".

The first chair I made when in college had the arms running from the center of a pivoting back down to the front corners of the seat.  Similar angle as the upright position of the recliner.   It ended up winning a first place national design award at the IWF Design Emphasis Competition.  While you can't do pushups or rest your beer on the angled arm you can still rest your elbows there and push against it when dismounting the chair.    That chair eventually failed but not because of the angled arm.  Blog post about it: https://4dfurniture.blogspot.com/2022/09/ze-chair-chair-design-that-failed.html.

4D

My mind can't stop, apparently.  It enjoys distracting my conscious moments by dredging up background calculations and solutions for challenges I didn't even know I needed to solve.

The arm can stay linked to the wheel and just follow the chair back around as it reclines. Or I had a vision of an intermediate cam wheel or link that the arm was attached to instead. As the back came up the cam wheel or link would rotate and lift the arm up so it remained closer to horizontal throughout the reclining range. An unnecessary but clever solution that increased the chance of breakdown a tiny bit but might look cool while it worked.  The link would parallel with the seat back relative to the wheel. As the back lays down the link lays down keeping the arm at the same angle relative to the static (almost) wheel. Easier to attach a link.  A challenge to keep the arm attached to the rotating cam wheel.  Might need to make a flat spot on the disk top for the arm to land on as it reclined.  A nice place for fingers to get pinched perhaps?