I purchased a Lead 1515 yesterday. I want to get started building a table for it so it is ready when it gets here. It looks like people are building tables that are around 70" square - is there a reason for this? I was just going to do 60" square. Any reason why I should make it larger?
60x60 will barely cover the frame and won't cover the drag chain on the right. You'll need at least 60x62 to accommodate drag chain and you'll still have the motors overhanging. If you're not planning on building an enclosure that size will work but I chose 69.5x69.5 to one day fit an enclosure. I also wanted more room to put tools down or what not and service things. You won't have to worry about walking into the overhanging motors as well. I'd also recommend taking most everyone's advice here and building a torsion box for the top. Especially for a machine this large. I didn't do that at first and had to redo the entire thing.
Thanks Rhett E - I was already planning to do a torsion box. What did you use for sheet goods since the dimension is over 4'? I was thinking maybe baltic birch which is 5x5 - but if I need it slightly larger that won't even work. Also - did you solve the issue you and Mark had with the bow in the machine by allowing those lower pieces to overhang slightly?
I used two sheets of 4x8 .75" MDF for my top cut accordingly. For the frame of the table I jointed and planed 2x4's. Open Builds updated the build video addressing the bow. Just follow along and it'll work itself out. The video's are great.
For a torsion box to work properly the top and bottom skins have to be one continuous piece, otherwise it will sag over time. Did you join the 2 pieces together somehow? I wonder if you could limit the sag by alternating where the seam is on top and having the bottom seam rotated 90 degrees so that the seam is not in the same plane top and bottom? Thanks for your quick replies Rhett!
I just butted the MDF pieces together on the top. It's actually not a full torsion box per se because I don't have a complete skin in the bottom but it's braced for a nuclear winter. When it was all said and done you could fit a piece of paper in the sag which could be from the tolerance of the level or just MDF itself. I would imagine alternating skins on the bottom would help but I'm not the person to answer that. I usually learn more by redoing it after I break it the first time. I've taken the LEAD 1515 apart so many times I can give you some 'what not to do's' once you get there. I'll try and get some pictures up soon.
That sounds awesome Rhett! Thanks again for your replies and help. I just ran to the store and picked up some MDF. I have some ideas on how I'm going to construct it. I'm glad you responded about the size because I'll make it a little bigger than the 60x60. I was thinking 64" square because I don't intend to ever build an enclosure for it.
That is a very good suggestion Giarc. Yesterday I bought my MDF and edge glued the panels together with biscuits for my top and bottom panels. I'll also place that seam on a support rib as you suggest, I think the combination of those things should result in a panel that is just as strong as if it had been a whole sheet.
I'm having a terrible time getting mine completely flat. I've got 2x4's and MDF but a few of the 2x4's warped since I bought them. I am removing those today with kiln dried ones to hopefully fix that issue. I have a Shapeoko XXL and one thing a lot of those guys suggest is to put a piece of pink foam under the cnc to help carry the frame and to also help with surfaces that aren't completely flat. I am a 1/16" off where my MDF joins together and it is enough to create a gap under the frame.
Hi Mark, I'm new to the CNC world but I'm a pretty experienced woodworker. You are never going to get a perfectly flat table surface using 2x4's - even if they are "kiln dried". I use quotes around that because what is labeled as kiln dried for construction lumber is not the same as kiln dried hardwood lumber - it still has a much higher moisture content (which means it will still warp and twist as it dries). Still, even if you have old 2x4's that have been truly dried in a climate controlled environment they will sag over time. What was once dead flat will not stay that way. The only way that I know of to get and maintain a dead flat surface using lumber is to create a torsion box. There seem to be a lot of misconceptions on this thread and on other pages as well regarding what a torsion box actually is. A torsion box is made up of an upper AND a lower skin separated by a gridwork of inner webbing. That lower skin is absolutely critical - It's essentially the same principal as what makes an "I" beam so strong. That pink foam idea sounds like it would help to prevent a "lip" where 2 pieces join together, but it isn't going to make the entire thing flat, just so that the hump is less noticeable. At least, that's my assessment - although I obviously haven't done that myself. I'm building a torsion box for mine - I'm building it out of 1/2" MDF. A torsion box doesn't need to be made from thick material to be strong and flat - it just adds weight. I'm going to have roughly 4" webbing, so the total height of my table will be around 5". If you do decide to build a torsion box, make sure you start with a surface that is dead flat or your torsion box won't be flat. You can use a couple of sawhorses with a bunch of jointed 2x4's layed across them and then use a laser level or normal level and a bunch of shims until you get a surface that is level and flat - then lay some plywood or MDF on that as a surface to build your torsion box from.
Thanks for an excellence response Brian. I took my table apart this morning and will be replacing with joined 2x4’s. I’m just out of room and time right now for a true torsion box. I’ve been using CNC machines for a few years now and you can make up some discrepancies in flatness when you surface the wasteboard. Since you’re flattening your work surface parallel to the machine, any small issues will be removed.
You bet Mark! A full torsion box may actually be overkill for this application, but if you're looking for dead flat and no sag - that's the only way I know of. That is a good point about surfacing the spoil board, then at least what your CNC is indexing off of is perfectly flat. I've been wanting a CNC for years so I'm really excited to get this thing up and running!
Brian, good tips about the torsion box and .5" mdf. If you're in the process of building yours please share some pictures. I just finished surfacing my spoilboard and it turned out pretty good, considering the mishaps if you saw my previous posts.
Rhett - I am in the process of building mine. I got my top and bottom skins joined up last night and I'm constructing the leg/apron assemblies today. I will get some pics up when I get to the actual construction of the torsion box top.
Here is my progress from today. Got the leg assembly done and got the lower skin on. It was sagging about 5 thousandths in the middle so I added a leg in the middle primarily to keep it flat while I build the torsion box. I leveled it out with a laser and with the middle leg it is now dead flat and ready to start the torsion box.
Didn't get to work on the table yesterday, but I basically got the torsion box done today. I got all the webbing in place with wood glue and small dots of CA glue to hold the pieces in place while the wood glue dried. I got all the joints completely flush with a block plane. All I have to do now is glue on the top, but I have to get some extended working time glue as I'm all out right now. I'll be gone for a few days, but it is essentially done. I put the top on just to check and it is completely dead flat.
So I've decided I'm going to do something a bit different, but similar. I just ordered some 1" MDF from a building supplier (you could laminate some 1/2" MDF but this is easier). I'm going to cut that down so that it fits in between the frame rails and will essentially raise the table up by 1" in the machine's working area. The I'm going to cut 6 strips of 3/4" MDF that will fit over those, with space in between for T track. The resulting thickness of 1.75" will be almost 1/4" above the 40x20 rails and will leave enough surface for flattening, but will be actually even lower than the .5" MDF mounted to the top as openbuilds suggests which will give me around 1/4" more Z than stock and will allow me to replace the spoil boards from the top as I am going to incorporate some T nuts as well.
Due to some of the "back and forth" about torsion boxes without context or additional information for those unfamiliar with the topic, i spent some time this afternoon scanning, editing, and cleaning up and chapter 15 out of the book "More Woodworkers' Essential Facts, Formulas, and Short-cuts" (Ken Horner, 2006). The publisher has chosen not to keep it in print, which is why I extracted this single chapter (think of a hand out for a classroom) for fair use/educational purposes. This is, by far, the most well formulated corpus of information on the engineering, design, and construction of torsion boxes I've been able to locate. The information that I gathered from purchasing this book leaves me indebted to Ken Horner (the author), Jay Perrine (a technical reviewer on torsion boxes), and Ken's supportive friends from the South Bay Woodworkers Association. We're all the better for the time and effort invested to be so exhaustive on the topic.
That looks like an excellent reference Brian. I opened it up and it is quite detailed! Should be helpful for a lot of people.
Moved the awesome torsion box discussion out of the LEAD1515 Support thread, into its own thread - worthy resource, deserves its own thread. Also helps declutter the LEAD1515 thread (; You may want to consider posting it in Resources | OpenBuilds too for easier reference later
I’m joining this discussion a little late, but… You mentioned rotating the top and bottom skins by 90 degrees relative to each other. You might take that a step further: Instead of one-layer skins, maybe use two-layer skins. So instead of a 3/4 inch skin with a seam down the middle, use two 3/8 inch layers, each with a seam down the middle, with the top layer seam rotated 90 degrees from the bottom layer seam. Do this on both the top and on the bottom…so a two-layer skin for top of the box and another two-layer skin for the bottom of the box. With that construction, maybe you could even go with thinner skins overall. Maybe two 1/4 inch layers for each skin. Might lighten the whole thing while providing the needed strength. Thx, rink.
Hi. My first time here. I realize this is a rather old thread, but perhaps it is still seen. I am designing a cabinet to support/enclose/sound-damp a cnc and plan to make a torsion box table to give it a level surface. My machine will not be too big -- this table will be about 32 x 40 inches. I am thinking 3/4 MDF for the top/bot and ribs. I am a part-time woodworker, have read the above-linked article, and seen torsion box build vids by David Marks and others. My question is about sound: the cavities will be little resonant chambers, working against the sound-deadening goal. I was thinking they should be filled. blocks of sound panel or fiberglass come to mind, or perhaps sand to add mass as well (plus holes to evacuate if needed). Anyone have thoughts on this?
I built one for mine 40"x60" (approximately). It is made from particleboard. It is dimensionally stable and about 20% cheaper than MDF and I hate MDF dust. It works very well. I like the sand idea. Mine does not seem to resonate sound that I can tell, but when I am doing 3D carves with lots of fast short moves, it seems like it wants to jump around but doesn't. It is very heavy. But now you have me thinking about adding sand for more weight. Originally, I had drilled holes in the divider pieces in case I wanted to make a vacuum table, but I have found that unnecessary. Finished product:
Hi Craig: Thanks for the input. Yeah. MDF dust is nasty, but I cut it outside with a P100 respirator (and a blower to clean off the table or track saw before coming back inside). As I am mulling this over, I realize that a main features of a torsion box is to lighten weight, by removing bits that don't add much (like comparing a rectangular beam and I-beam). But then I am looking to add mass (sand) to dampen vibrations, and, sheesh, it might as well be solid. I think for larger tables a torsion box is a great idea, but I am now thinking for my smallish table I may just laminate three 3/4" MDF panels and call it good. I can use my table saw as a reference surface, and I have a good straight edge to verify it ends up flat. I may try an FEM simulation in freecad to compare torsion box vs solid. thanks, Gil
So I have been playing with a simulation. Details on a freecad thread: question on body for FEM sim of torsion box - FreeCAD Forum A couple of teaser pics:
Only thing that caught my eye is the machine isn't going to be applying force as shown. Its two beams front and back and couple runners between them - much more spread out and in itself almost a little single sided torsion box. The table only carries the weight of the machine itself. Downward Cutting forces are opposed by the frame itself, not transferring any force to the table below. Table will only see forces of the 2040s deflection after they can't take it anymore which would be very little: How to calculate V-Slot® deflection Main thing the table has to do, is ensure that XY plane stays flat (from the 4 corners, no twist) Tramming: A generic guideline
Hi Peter: Thanks for your comments -- the table twist is a good point and winding sticks are a great way to visualize that. I applied a force kinda in a center area of my fem models as a means to compare table deflections, not model the actual machine footprint. Actually, I am designing a one-off machine. About ready to start assembly which is why I am now looking into a table/enclosure so I can build it on the table. thx, gil
