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So, you want to make an Observing Chair?
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So, you want to make an Observing Chair?
Ron Boe, March 16, 2017
At some point we all wish we had a chair to plant our bum on while at the scope. I’ve written this little ditty to share what I’ve learned so that perhaps you can make mistakes totally different from the ones I made (and I seem to continue making them). Like any woodworker I have my biases, preferred ways to do things (e.g. mortice and tenon joints) but for the observing chairsI present here there are lots of options open to you; consider your budget, skills and available tools to make your choices.
I’m going to show you how to build an inexpensive chair using your typical school plastic stacking seat shell for the seat (I find the actual seat the hardest to make and if I can cheat so much the better).
|A budget chair for the discerning observer.|
But before we dive into that let’s review some earlier chairs I have built, the mistakes I made and the lessons learned, which led to some design choices for this current iteration. Later you can decide if I was on the right track. With a wee bit of luck you’ll come up with the perfect chair after being inspired here.
Chair Number One:
A basic ladder chassis with a folding leg with brace in back with a sawtooth indexing system that locks the seat at the desired height. It’s the chair in the foreground in the photo to the left.
Pros: comfortable seat, sawtooth indexing worked so well I used it on three other chairs. It’s nice and light and easy to move around the scope and viewing area.
Cons: When the seat was set low (think refractors) it wanted to tip forward. Not good. I also found I had this big dislike for things that fold as they always pinch fingers and are floping about when you least expect it. The rear leg sticks out quite far and the wide foot gets in the way. Very annoying.
Lesson learned: Place the wide foot on the end with the most weight bias. Keep the seat within the foot print of the base. While writing up this article and comparing this chair to the others, I considered rebuilding this chair. I’d move the wide foot up front where the weight bias is and install a much shorter rear leg; maybe attached to the second cross brace. There is still a lot to like about this chair.
Chair Number Two:
Otherwise known as Tom’s chair. I built this one for my buddy Tom in Tucson. Now I had never met Tom nor knew what he looked liked so it was built rather heavy duty. This was not really on purpose, I wanted a chair with a bit more weight (chair number one seemed a bit light so it was not firmly planted on the ground) and I kinda over built the thing using the WAG design method. Oops.
The first version of Tom’s chair did not use the sawtooth index method; expecting the friction of the seat against the frame would be good enough to hold the seat; like the Denver Chair. It did not work. So I added the index system using scrap bits from Chair Number One. Oops number two.
Pros: It’s attractive and Tom has gotten lots of nice comments. Seat is comfortable, the extra weight of the frame makes it less tippy than Chair Number One. It was featured in Star Ware 4th Edition, Philip S. Harrington, Wiley.
Cons: Really over built, folding leg does not fold flat to the frame (cross brace prevents this) so it does not pack as nicely as it could.
Lesson learned: No need to massively over build a chair; I really need a rear leg or brace that won’t fold and pinch fingers.
Chair Number Three:
After building Tom’s chair and now knowing the short comings of Chair Number Two I set about purging the main defect - folding legs. I also gave some thought to keeping the chair from being tippy no matter where the seat was - high or low.
I embedded a strut into a built up cross shaped foot. The seat hung off the strut using the familiar sawtooth indexing system. The foot was long enough front to back to keep the seat within the foot print of the cross. The cross legs to the side were the same width as the other legs which kept the whole affair very stable no matter with height.
Pros: Heavy, stable and very comfortable. Pulling the dowel from the seat allows the seat to be removed from the strut. Pulling the strut off the base allowed the chair to be broken down for easy transport. I did allow the cross to be further disassembled but the friction was too great for easy break down and in any event I found it was unnecessary.
I sold a refined version of this chair so I have Chair Number Three and Three bis (aka #3 2nd version)
Cons: It’s heavy and the cross design does not make this chair easy to shuffle around the scope at night. It needs a smooth surface and does not suffer dips, rocks and other things that make observing at night fun. Not really a problem for the flat desert observing dark sky sites in Arizona, but wheels would be nice. The seat, while comfortable, is labour intensive to make and I always thought a nice factory made seat would make the whole process quicker.
Lesson Learned: While mass in this case can make the chair very stable (desirable feature) it works against you if you change objects a lot and need to move the chair. This chair works very well for public outreach since it is hard to move around. It also works well with an SCT, but less so with a dob, which has much more motion than a SCT. One could redo this chair in a much lighter wood to make it more user friendly.
Which leads us to Chair Number Four:
Design Goals: Something easy to make and much cheaper than the previous three chairs (I used hardwoods like maple, cherry and mahogany. e.g. Chair Number Three took about $300 worth of cherry). Not everyone is a wood nut so something made from SPF (spruce, pine, fir) sourced from your local lumber yard or big box store would be plenty good.
It needs to be a lot lighter than my previous chairs.
Simple to build; a saw, drill and maybe some typical hand tools. I used some exotic tools when I built Chair Number Four, but it was because I had them and wanted to tart up the chair a bit; they are not needed to build it.
So here’s what I noodled up for Chair 4: a 2x4 strut with a foot and braces on the bottom and a 2x4 rear foot (fixed). For the seat, two lengths of 2x4 with a birch dowel front and rear and piece of corrugated roofing trim (to replace the sawtooth indexing strip with a sine wave version - the builder can buy this pre-made and it was just over $4.00 when I bought mine).
The seat was bought online from a school replacement parts business. With shipping it was about $25.00. They have several sizes and colors available so you can knock yourself out. I choose a large purple model, it’s not a bad choice for my skinny bum.
To assemble my chair I used Domino floating tenons and a Festool Domino tool to cut the holes. Makes for a very strong joint but very few folks will have access to one. The joint between main strut and the foot is the most but it’s not under a great deal of stress. Dowels, pocket screws, biscuits, lag bolts etc. The braces need to be strong and glue with screws would be more than good enough.
The first thing you want to consider in a chair is what and how are you going to use it. Typically the chair is a tool to solve a problem. We want to reduce fatigue at the scope and sitting is a great way to do that. So your chair needs to solve your problem, at the sites you intend to use and with the scope you intend to use most of the time.
General Ideas for Chair Design and Construction
You will want to research some chair ideas to see what others have done; especially if you are not skilled in coming up with some ideas on your own (even if you are, you may find that someone else has a novel chair idea that is worth stealing). I like to take some copier paper and do some rough sketches, working through some ideas that may seem good while in my head but perhaps too difficult to build when the bright light of reality is shined upon them. Or maybe I simply don’t have the skills to build the nutty idea I came up with.
At the design phase you start to consider things that will affect the final product; e.g. your budget, wood species, hardware, budget and finally your budget. Great ideas have been nixed by my wallet faster than any other problem.
In the past I have used baltic birch plywood and hardwoods (mahogany, maple and cherry). Hardwoods have excellent strength compared to softwoods, typically look better and in general age better (being harder they don’t dent as easily) and machine very nicely. But they can be expensive. For Chair Number Four I choose your standard 2x4 material as they are pretty darn reasonable when it comes to the pocket book. Just choose a stick with few knots and as tight a grain as possible. Tight grain has a lot more strength than quickly grown farm trees; this can be a critical factor if you are a person of great mass. Remember; the chair is the tool you are designing to hold you, so the mass it will be called upon to support needs to be taken into consideration. Chairs One through Three have already been stress tested by some big friends but they are made with hardwoods with a superior strength. I also choose, (in one case the person chose my chair), the testers carefully; people I did not know well - just in case the chair failed.
I have never worked up blueprints or measured plans for my chairs. I take my rough drawings, make a wild estimate on how much wood I need and start cutting. So I’m not going to create drawing for you either. How high to make the chair depends on the scope YOU intend to use and to a lesser degree; how tall YOU are. Seat size depends upon the size of your bum. I’m a tall lanky Norwegian. You know your requirements better than me.
But I can give you some hints on what to achieve with the basic design to avoid some of the problems I discovered by winging it. For starters, as you look down on the foot print your chair presents to the ground, you will want the seat (or rather the center of gravity of the seat) to be within this foot print. Three of my chairs look, more or less, like triangles on the ground. A broad foot on forming one side with imaginary lines connecting to the other leg forming a triangle. Chair Three uses a cross so it presents a square to the ground. It happens to be the most stable of the four chairs too. It accomplishes this by creating a larger area for the seat's center of gravity to stay in while each of the crosses is in line front to back and side to side, preventing tipping in those directions very well. With chair number four I found that the narrow rear foot, while making a very strong joint where it meets the main strut, does not resist tipping to the side. Widening the foot in the back would help.
In general we think of three points, especially on rough ground as being ideal for a chair as it won’t rock. All of the chairs I’ve built use long flats presented to the ground and in the first two this has not been a problem in use. However; with Chair Number Four I have found that it can be wobbly in front if the ground is a bit uneven. I suspect I feel this more with this chair than the others due to the light weight. Chair 2 and 3 particularly are massive and don’t seem to suffer this problem to the same degree. I’m considering adding feet to the front foot bar and widening the rear leg to help the tipping problem when the seat is very high.
The front foot is twenty four inches wide, the strut angles back at 30 degrees (Chair Number Three is 27 degrees). The width was arrived at by a guess and round number; you will want to increase the width to handle more mass and greater chair height. The angle was found by brute force: I held the strut up then eye balled the angle as I moved the seat up and down. For Chair Number Three the angle turned out to be too steep and I had to go back and tweak the base so the strut would angle back more. It’s a compromise between keeping the seat back enough so when it’s low you don’t tip the chair forward (a problem with Chair Number One) and not so much that you tip over when the seat is high.
This chair has a fixed rear leg (one bad bias that I have; I like to avoid hardware, so if design solutions that will allow a hinged or removable leg present themselves to you - go for it!). In practice this leg has not been the problem I thought would be. It sticks up less than the chair (my other seats are flat so they stow much flatter). This was a pleasant surprise. Now I use a pickup to toss the chair in; if you have a small wagon that also has to haul all your other gear (e.g. Tom’s Forester gets a bit crowded and his chair’s rear leg does not fold flat so it takes up more room than it should) and don’t mind pinched fingers from time to time, then you will want to handle the rear leg a bit differently. Keep in mind, the chair solution has to fit YOUR needs.
Over time I have really been spoiled by the sawtooth indexing system that holds my seats at any given height. The seat moves quickly, locks in quickly and securely; it’s very easy to use. However; it’s not easy to make (I used a router with a V bit and a lot of indexing blocks) and luckily I had enough material left over from Chair Number One that I could use it on Chairs 2 & 3 without making more. It is a pain in the keister to make.
There are other ways to index your seat. For example you can drill half circle holes for a dowel to lock into, but most other methods need a drill press or router or lots of hardware and it would not fit with the design goals of Chair Number Four: Cheap to build and no need for a lot of tools. It turns out corrugated roofing uses wood trim for nailers with a sine wave profile and they are CHEAP! It’s already made, all you have to do is cut to length. Now one reason they are cheap - they finger joint short pieces to make up one eight foot length. You will typically need less than two feet worth, so if you pick through the pile you should be able to find one with a good two foot section that is finger joint free. If you don’t care, just wack off the length you need and use that!
I choose the largest birch dowel at the wood store to index with the corrugated wood but you don’t have to do that. You can use a smaller dowel (to drill the holes in the seat supports for the dowel, a forstner bit and drill press are highly recommended) or even a bit of your 2x4 then shape it with a rasp to fit the groove. One can then screw the 2x4 bits to the supports or use smaller dowels that can be easily drilled with a hand drill or even threaded rod and some nuts. You have choices.
The seat supports are just 2x4 lengths. Make them long enough to hold your dowels and the seat design you will use.
A word about dowel placement. Where you put them will affect the angle the seat makes with the support strut and whether you can tilt the seat back far enough so the rear dowel can clear the teeth in the corrugations. I’ve found that drilling and dry fitting the rear dowel then eye balling it on the strut gives me a darn good idea where to place the second dowel. Keep in mind, the rear dowel need lots of meat under it on the seat strut to counter act the forces of someone sitting down. The forward strut needs more meat on top it in the seat support for the same reason.
I shaped the seat supports on the bandsaw to give them a better look; this is optional. Just don’t make them too thin; there are some good sized forces going on in them.
I’ve been sorely tempted to build a chair with a plastic seat from those stacking seats you see in schools. Google replacement stacking chair shells and several suppliers show up. Of the three sizes available I chose large. I fear those of you with more generous bums than mine will find the large to be too small; you have been warned. It was about $25 (early 2017) with shipping. The most expensive bit in this chair. But hey, it’s professional made and already painted!
If you go with the plastic shell it will need a plywood support base (the seat supports are not wide enough to properly support the seat sides). I happened to have some scrap baltic birch just laying around and I didn’t even cut it to size; I used it as is (it was pretty darn close). Don’t tell anyone but I used screws to fasten it down.
If circumstances dictate that you can not use the plastic shell for a seat then more than likely you will looking at a hunk of plywood for your seat. Round the corners to make them bum friendly. The most comfortable seat I have is from Chair Number Three. Using a rasp and some 1x2’s you could fabricate up something like that. Other choices; old cast iron tractor seats. Replacement tractor seat (or junkyard sourced) riding lawnmower seat; even more 2x4’s! Size it to your bum.
Now the leg, front foot and the braces were attached with floating tenons:
Tape was applied to keep the glue from spilling out on my nice wood and ruining the final finish. 99% of you will not own a Festool Domino so you’ll have to come up with something different than the Domino floating tenons seen in the photos. If you use screws or lag bolts pre-drill and install them so the threads of the screws bite into the cross grain and not into end grain. Pocket screws would not be a bad idea and inexpensive kits to make them are available. Another option; your metal construction helper bits found at your lumberyard; e.g. Simpson, Kant-Sag or USP etc.. Noodle around in the selection for something that would work for your application. It won’t look quite as nice but it will be very strong. Use the matching screws to install them; not the nails.
Once you glue or screw up the foot, braces, leg and strut you can figure out the seat support angle and where to put the dowels. Once the seat support assembly is glued up you can fine tune where to glue the corrugated strip. The lowest seat setting will be just above the rear leg. How high you go is up to you. My strut is about 40” high but I really don’t want the seat going that high - depending on how long of a piece you cut up out of the corrugated trim will determine just how high you can go - that and your fear of heights. If you don’t have clamps to glue the corrugated wood on just tap in some finishing nails. Wipe off any squeeze out and let it dry.
You may notice in the pictures that many edges are chamfered. This was done to break the edges a bit (I had run the wood bits through the planer to clean up the wood so unlike your typical 2x4 mine had sharp edges) and just to give it a look. I used my router table to do this. This is not needed and you may have other ideas to make the chair your own.
I’m a big believer in Benite from Daly’s Wood Finishing products. It hardens the wood and makes a great sealer for your final finish. I used a coat of that plus one coat of Danish Oil. Like the plywood (and 2x4’s) it’s what I have on hand. Paint gives better protection (use latex, it’s more flexible than oils so it won’t crack and peal as fast as your wood expands and contracts with humidity changes). Poly finishes are very tough but harder to rejuvenate so I prefer your tung oils and danish oils. Follow the directions for the finish of your choice prior to applying it.
I used two 2x4-8’ sticks, one dowel, scrap plywood and a commercial plastic seat shell. For hardware; four wood screws to hold the plywood and four carriage bolts, fender washers and unlock nuts (all stainless steel) from the local hardware store to bolt the seat shell to seat support.
I ripped the front foot and braces from 2x4 to 2x2, but full sized 2x4 would be just fine. Or you could buy one 2x4 and one 2x2 or 2x3 for those bits.
This chair met the main design goals: light weight and cheap to build. I’ve found the side braces make good foot rests.
Improvements: adding some feet on front foot so it doesn’t rock on uneven surfaces and to keep it from tipping forward at low seat heights. As the seat is raised up the chair gets a bit tippy and a wider rear foot to correct this (or rebuilding the rear foot and making it go the other way - but that makes its’ attachment at the strut weaker so that would have to rethought). As I carry it around I wish for a handle but have not come up with a good idea for that yet.
I hope this was helpful and have fun with your chair!
PS: Many thanks to Tom Watson for laying on a second pair of eyes, correcting some mistakes and suggesting some changes. Unsung work, but greatly appreciated.
- mwedel, okiestarman56, DreamWeaver and 19 others like this