Disclaimer: This is not a standard Momus build. It is not in my nature to leave well enough alone. Even though this is a well developed plan I have altered or redesigned parts to fit my needs, wants or methods of work. Bob has done an excellent job with these plans and unless you like making extra work for yourself, building to the plans is probably best. But, I can’t, so here we are.
Also, please comment. Positive and negative constructive comments are welcome. I have thick skin, beat me up if you want to. And let me know if I need to resize the pics. I think they are a bit too large and will change them if necessary.
Let’s start with the wooden enclosure. For me, this is MDF. Why? Its dead flat and stable. Moreover, its sitting in the wood rack doing nothing so its free. 3/8” thick sheet goods are not easily come by around here, so we will use either 3/4” or 1/4” material in its place altering plans as we go. Also, we will make the left and right side X-rail locations the same height and get rid of the small height difference in the interest of symmetry. The electronics pockets on the right will be reflected on the left as well. We may put a compact computer motherboard in that side or just use it for tooling storage. Don’t know yet.
Tools: I’m fortunate to have a very nice table saw and a good chop saw, so dimensioning parts is fairly straightforward. Sharp chisels make quick work of inside corners. A good square is essential. Those cheap plastic drafting squares are good for checking alignment and a set of home-made cabinet construction squares help holding things while the glue dries. And you need a whole bunch of clamps. No nails or screws were used in this assembly. Glue is sufficient.
Time to build was two days, but most of that time is waiting for glue to dry. So, I did other tasks around the house in the mean time. Actual build time was probably less than 5 hours excluding paint.
I started by red-lining the plans to suit the material I had on hand. I had half a sheet or more of 3/4” MDF and several cut-offs of 1/4” material. I decided the bottom and top skin would be3/4” and the right, left inner and outer skins would be 1/4”. Most of the other parts as are according to plan. Since it was going to be left/right symmetric, the front and rear plates both have vertical portions that were 2.875” each side instead of the 1.5” dimension on the left side. This, of course changes the overall width for the bottom and top skins and the Y ribs. I eliminated the bottom plates on the left and right as redundant and made the left inner structure the same as the right. Pretty much every part is a somewhat different dimension. I decided I would use T-nuts and bolts as opposed to lag screws for the X rail attachment making the left/right top plate assemblies 1” thick.
On to construction…
Instead of cutting everything out at once, we will cut as needed since we are altering so much. Since my table saw is very repeatable, no issues with accuracy in doing this.
Torsion box: The top and bottom skins were cut and the top notched out on the table saw and finished up with a very sharp chisel. MDF pares easily with a sharp chisel. I do not recommend my method of cutting notches unless you are quite familiar with your table saw.
A little discussion about torsion boxes for a minute. The webs serve to transfer shear from the top to the bottom skin. It matters not how that happens. Within very liberal limits you can use anything you want for this grid including cardboard honeycomb, closed cell foam and the suggested ribs. Rib thickness can be pretty much anything as well. Also, note that the notches add nothing to strength as all the strength is in the glue. Modern glues are stronger than the wood after all. Thus, for this build, I eliminated the notches in the X-ribs and made the Y-ribs in little sections inserted between the x-ribs. This is easier to do since all the pieces are just rectangles. Notches are a pain to make and not necessary. If following the plans, just eliminate the notches in the X-ribs and Y-ribs. Glue in the X-ribs and then cut the Y-ribs to fit each individual location as your dimensions won’t be perfect. Easy.
Note that my ribs are shallower than normal due to the thick top/bottom skins. I guess you could just make the entire assembly taller too, I just didn’t see the need.
And a little glue discussion…Since MDF (and plywood) absorb a lot of moisture on the edges, I like to put a very thin layer of glue on all edges first. Then apply glue to the mating surface. Then go back and add little more glue to the edges. In the end, you still only want just enough glue to make sure when you put the parts together you get glue everywhere. A very minor amount of squeeze out is the goal. Clean up squeeze out as you go with a damp rag.
What flatter surface do you have in your shop than your table saw? Makes a great glue-up surface and will helps your torsion box come out flat. Note the incredibly expensive clamping method. 5 gallons of water in a plastic bucket and a few scraps of MDF to spread the load. This is the part that takes the most time. I glued in the outer Y ribs as one glue-up, then the outer X-ribs. Then worked the inner ribs in sections. 5 total glue-up operations and standard yellow glue needs to be clamped for about an hour to set-up enough to continue. Lots of wait time. Then the top skin was applied. Got to work fast so the glue doesn’t dry before you set the top on. You will also see a couple of strips of plywood in the structure. What can I say, I’m cheap and no one but me and you will ever know.
Is it flat? That straight edge is good to about 0.003”/foot. No light under it. Flat enough.
Since we are eliminating the bottom plates on the left/right we need to provision for transferring the mechanical bending loads from the sides into the bottom. We will do that by dadoing the inner side skins into the top skin. This is more structurally efficient than bonding the inner skins to the bottom plates anyway. I also made sure one of the X-ribs was directly under this location so that the load gets transferred into the rib as well. 1/4 x 1/4 grooves will serve this purpose. Forgot to take a picture of cutting the groove, but you can see the result in this picture. I cut the groove by shoving the entire torsion box through the table saw. You need to do this before anything else is attached to the torsion box, so plan ahead.
Front and rear plates are next. Not much special except to insure that they get glued on square. I used some assembly squares I had previously made. You need to make sure you cleaned up any glue squeeze out in the pockets of the torsion box where they fit or they won’t sit all the way down and leave a gap.
On to the left/right top plates: These are definitely different. I wanted to use machine screws instead of lags. I figured I would assemble/disassemble this multiple times and MDF and lags wouldn’t work well. T-nuts are the traditional choice for embedded threads, but they tend to get pushed out sometimes, so I laminated a ¼” board to the bottom of the plates after installing the t-nuts. I also did not cut out the stepper motor cut-out at this time as it would make the plate too flimsy to glue up. I’ll do that afterwards when I get my motor and make my metal parts.
Lets discuss hole lay-out briefly first. Always layout holes from one end/edge of your part only, not from both ends. Also, layout each hole individually from the end to avoid accumulating errors. For instance, in this part, you have 7 holes spaced 3.75” apart. If you make an error of the width of a 0.5mm pencil lead (0.020”) between each of the 7 holes, you accumulate an error of 0.14” by the 7th hole. That would make parts not mate up. If you instead mark each hole individually from the same end, each hole could only be off 0.020. Measuring from the same end is necessary because you might have mis-cut your 24” length of the top plate and measuring some holes from one end and others from the far end would also introduce error you do not need or want. I chose to use the inside back corner as my measurement reference and will do the same for the metal parts that will attach.
Holes were laid out on one part and the left/right were taped together for drilling. Double stick tape is hard to remove, so I just taped the sides together. I used a brad point bit to drill and its easy to set to long axis offset to the drill press fence by turning on the drill press and sliding the fence fore/aft will viewing the bit from the side. Then, you only need to worry about one dimension when drilling the line of holes. Note the pencil dot indicating the inboard back edge of the part where all the dimensions are referenced.
The parts were separated and the spot faces for the T-nuts were made with a forstner bit. Great accuracy is not needed here, just make sure the spot faces are deep enough.
I pressed in the T-nuts with a large drill bit inverted in the drill press head.
Note that the stepper motor cut-out will be extremely close to some t-nuts. I’ll have to be careful when I make this cut later. I’ll use a well worn router bit so I don’t care if I nick it.
1/4” backers are cut a bit oversized and trimmed later on the router table to exact width using a bearing guided bit.
The end result. I drilled through the T-nuts from the front side and then drilled a relief hole on the back for the screw to poke through the backer.
Sorry for the long diatribe about the X-plates.
Let’s get back to building the basic structure now…
Since we eliminated the bottom plate and most of the guts, we stick build this one piece at a time instead of an assembly. Top plates first. Make sure the inside back corner is properly located since the part looks symmetric.
Inner skins were rabbetted to 1” wide leaving 1/8” in thickness. No need for the taper and I didn’t cut the wrenching relief. I’m going to attempt to not cut those, but if necessary, I can cut them later. Here is the rabbet post-glue up.
Inner skins were marked and notched for the rear plate and then glued-up. They were allowed to be a bit oversized and trimmed with a router and bottom bearing bit to flush. I also glued in the center supports at this time, but not shown in the picture. The center supports were built a little long and trimmed after glue-up to fit.
Outer skins were similar. I roughly cut out the two big holes with a jig saw and trimmed them up to the inner frame with a router and bottom bearing bit post-glue-up. I just left the radii in the corners for now. This panel was cut a bit wider and trimmed to fit after glue-up as well.
A little sanding and some automotive spot putty to fill the defects. I added a round over on the outside edges since they will get damaged if left square. I chose Rustoleum Almond as the color. Kind of industrial but not too dark and its not pure white to show all the dirt. I sprayed with an HVLP gun. I’m not completely happy with the finish and will likely add another coat after everything is built.
We will worry about the front flange and cover once we have a working machine. Doors will be done later as well.
Total cost out of pocket: $12.00 USD for paint. I like cheap.
Last edited by Michael In Cali; 06-08-2011 at 09:46 PM.
Fantastic write-up and photos. Very thoughtful modifications, and the craftsmanship looks top notch. As much as MDF gives me the heeby jeebies, this is going to be a beautiful machine. And for that cost I'd build one out of that in a heartbeat. I'm looking very forward to seeing more progress reports. And I like that blue anodized table saw fence. It perfectly matches your liberal use of blue painters tape.
Well done Michael. Makes me a bit intimidated to post more pix of my build after seeing the excellent workmanship of your build. And all done in a portion of one day - I am at least 3 weeks into the base building process.
All - Thanks for the compliments.
Bob - MDF is a fine material as long as you work within its design constraints just like any material. I really want to make things out of carbon fiber, but thats expensive and slightly difficult. If I had an oven (and a pile of cash), I could do it.
Blue tape? Can't live without it. If I'm doing woodworking, I'll go through a roll a project. Much easier than scraping glue and getting rid of layout lines. Wait until I do the metal work. More blue tape there for sure.
The Table saw fence is a 4 foot Kreg Jig extension. The plywood fence face on my Powermatic 66 was a bit wavy so I ditched it for the extrusion. I wouldn't have cared if it were pink. Its a very nice alternative for a replacement fence.
Dave - Two days to build. 5 hours of clock time. Mostly waiting for glue to dry. Admittedly, I might have some better woodworking tools than many. If you have any question about methods of work, please ask. If I were working on a sawhorse in the backyard with a circular saw and a straight edge, it would go very much slower. And Family issues that many folks have are a non-issue.
I went back and looked at your build thread. You are way ahead of me on the metal work and your woodwork is fine. Nothing to feel bad about there.
Just when I thought you couldn't procrastinate starting your build any longer, you didn't!
I work the opposite of you thought, I build per the plans then modify after. Not the cheapest way to go but it lets me see where I need adjustments to fit my needs. Build the machine, make the changes, build the new machine with changes implemented.
I made one change to mine this weekend and that was the left X-rail. The cold rolled steel bar had rough edges that i filed smooth but still wasnt perfect because I would have had to remove a lot more to get a nice flat surface. I picked up a piece of 6061 bar at 1/4" thick to replace it since aluminum bar is pretty uniform in width and the added thickness let my bearings contact the surface completely. Now I get a nice smooth motion on X and the change only took 30 minutes with drilling and tapping. i am at the point I can start the "all metal" build of the machine. Well all metal except for the ribs of the torsion box which will most likely be delrin.
Lookin forward to see more progress!
Thanks Michael for the compliment. I intended to fix up some rough spots around the hole I cut for the motor cables last night so that I could post a few more photos but got side tracked. Took advantage of my son being available to help with a "dry fit" of the metal machine and found out I need to move the left end out to sit on the left rails. Hopefully that is done and tonight I will get on with what I was planning to do last night.
I actually built the base two weeks ago. I just wanted to write one complete post for the whole frame build and needed the time to write it. I don't like doing little updates. I llike reading them, just don't like writing them.
To a degree, I did "build to print" first. I made a sketchup CAD model of the entire machine and then modified it in the computer to suit my needs and wants. It is not easy to look at flat drawings and make the same assessment.
There are certain things I knew I would change as I built the initial CAD model, but I went and built it that way anyway.
By the way, I have my electronics suit ready and my metal is delivered, but you won't see much about them until I have a big thing to present. I like big.
I still need some things like pulleys, belting, some wire, and to decide on the spindle mount.
Any progress? I'm anxiously waiting to see the rest of your build!
My apologies to all for not staying in touch. Life has been busy. Kids are old enough to take their kid to Disneyland so that is no excuse.
Work and family are more important than hobbies, so they will always come first.
I see we have a few new faces to get to know and a few threads I need to read up on.
What is up with my build? I've had a big long weekend to work on things.
I have all the metal parts assembled excepting the wire booms (haven't figured out what I want there yet.) I'll detail all my trials and troubles about the in one long post like the wood working. Won't be as long as I didn't take nearly the same amount of pictures. I have one or two modifications that are worth pursuing for some folks.
I have tested my electronics on the bench just to make sure the parts were not DOA. Seems to work fine on the bench. I'll start wiring next weekend.
I need to figure out my router mount next. I have no material ordered for that yet.
I don't even have a teaser pic ready to post.
Anyway, progress has been made.