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  1. #21
    Member George484's Avatar
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    Default Re: New Machine Build - Massive CNC router for timber components

    Hello Peteeng: Interesting dust collection product, I will be saving this link for when I complete this build/retrofit

    Hello Wizard: So the 16'' Z height was a bit of a random number... honestly 9'' clearance would be ok about 95% of the time for the work we do. I was trying to choose dimensions that would allow me to take on all sorts of unique work with other customers. There are a number of high end furniture makers near me as well as quite a few mold making shops, I had thought it would be nice to work with them making large unique components, hence the 16''Z, it would be an attractive feature I know without a doubt. If I can figure out a solution for a long Z movement that would be incredible but if for whatever reason I am stuck with a max Z height of something in the 10 inch range that will not stop me from following through on this build. I should also mention we have a crane in our shop and a beefy forklift so I am not worried about fabrication, we regularly fabricate welded assemblies larger than this machine might be, although not nearly as complex...

    I am honestly surprised to hear about the morbidelli, it seems to be a very robust machine.

    So I am slightly confused if there is a difference between a moving column and cantilever gantry design? Would the cantilever gantry have the Z carriage built onto it while a moving column create the Z movement in a similar way that a conventional Vertical machining centre does where the whole spindle slides up and down?

    I have to say that at this point an open sided design (On the long side) is almost a must, the loading is just so appealing that I am not sure if I could consider going back to thinking about a gantry design. Right now we have a small gantry router and loading from the end is quite annoying, there have been a few times loading with a forklift and the machine gets bumped and then we have to re-level the feet.

    Hey mactec54, I am surprised to hear you think a moving column would be a bad idea for a large Z movement, I had thought this approach would be the best for Z height. Like Peteeng says, I have seen massive machines plowing through extremely hard materials with a moving column design.



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    Default Re: New Machine Build - Massive CNC router for timber components

    Given enough time and money you can get any sort of machine orientation to work. A cantilevered gantry can work but it depends upon what one means by “work”. There are examples from metal working machines but those machines are of massive construction often requiring a significant foundation that they are often grouted to.

    Unless one is very well equipped to build such a machine it is far better to consider the simple solutions. By this I mean the machine shop facilities but also the engineering chops to model a machine with a cantilevered gantry. This especially if you are tight on time.

    Quote Originally Posted by George484 View Post
    Hello Peteeng: Interesting dust collection product, I will be saving this link for when I complete this build/retrofit

    Hello Wizard: So the 16'' Z height was a bit of a random number... honestly 9'' clearance would be ok about 95% of the time for the work we do. I was trying to choose dimensions that would allow me to take on all sorts of unique work with other customers.
    This is understandable, thAt is the ability to take on other tasks. What you run into is a far bigger engineering challenge. Depending upon the end results you need to achieve that might mean a much larger machine. Larger as in bulky not snigger working area.
    There are a number of high end furniture makers near me as well as quite a few mold making shops, I had thought it would be nice to work with them making large unique components, hence the 16''Z, it would be an attractive feature I know without a doubt. If I can figure out a solution for a long Z movement that would be incredible but if for whatever reason I am stuck with a max Z height of something in the 10 inch range that will not stop me from following through on this build. I should also mention we have a crane in our shop and a beefy forklift so I am not worried about fabrication, we regularly fabricate welded assemblies larger than this machine might be, although not nearly as complex...
    That is good.

    I built a steel frame for a bench in my cellar, for some reason it got heavier every time I welded something to it. At times people underestimate material handling efforts required in a build.
    .

    I am honestly surprised to hear about the morbidelli, it seems to be a very robust machine.

    So I am slightly confused if there is a difference between a moving column and cantilever gantry design? Would the cantilever gantry have the Z carriage built onto it while a moving column create the Z movement in a similar way that a conventional Vertical machining centre does where the whole spindle slides up and down?
    A moving column machine could easily be a horizontal mill or even a boring mill.
    I have to say that at this point an open sided design (On the long side) is almost a must, the loading is just so appealing that I am not sure if I could consider going back to thinking about a gantry design. Right now we have a small gantry router and loading from the end is quite annoying, there have been a few times loading with a forklift and the machine gets bumped and then we have to re-level the feet.
    Sounds like you need to invest in cranes. In any event yes thinking about how to load the machine and the human factors involved is important if the primary job of the machine is to handle large heavy timbers.

    Note I have no experience with a Moribidellie (sp) but don’t assume one persons problem will also be yours.
    Hey mactec54, I am surprised to hear you think a moving column would be a bad idea for a large Z movement, I had thought this approach would be the best for Z height. Like Peteeng says, I have seen massive machines plowing through extremely hard materials with a moving column design.
    Nothing you buy will be perfect!! It doesn’t sound like you need incredible precision here, so consider your options carefully.



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    Default Re: New Machine Build - Massive CNC router for timber components

    I would definitely like to second many of wizard's bits of advice and perhaps expand on a couple of them.

    A very effective machine, no matter what type of construction or purpose, begins with a great deal of design and engineering expertise and even then, there is usually a few iterations of trial and error before it reaches an acceptable solution. It doesn't come from cherry picking things from very different applications and hoping they all fit together. If you were just building this as a hobby, that is a different story. However, with the constraints of only a couple of months, and needing to work right out of the gate, even the big machine building companies would likely lose a bit of sleep on that sort of thing.

    It seems to me that the material handling component needs as much attention as the machine itself and yes, cranes may be an important part of the solution.

    Although it is possible to build a moving column machine it is astounding how much beefier it needs to be than a fixed gantry/ moving table machine. As an example, the 2 machines I converted, as I mentioned in a previous post, were both built with similarly heavy beams for the shorter 5 foot axis (approx 10" by 12" with 1/2" wall) yet the fixed gantry machine ( with 3 feet of Z) was probably 10 times as rigid as the moving column machine (with only 12" of Z).

    There is a whole lot more I would like to add but have run out of time for today. Will check in tomorrow.
    Rick



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    Community Moderator ger21's Avatar
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    Default Re: New Machine Build - Massive CNC router for timber components

    Hi Gerry - Is this condition within the recommendations of Morbidelli? I'm sure they would like to know if their machine vibrates within normal service parameters? Peter

    Let me clarify a bit. You can't feel a physical vibration. But you don't often hear a 5/8" diameter tool screaming when making a cut. I think a big part of it is the long tool length, which is what the OP needs. It actually might be entirely an issue with the long tools, and not really a machine issue. The machine probably weighs 6000-8000 lbs.
    But they no longer build machines with these cantilevered gantries. As cutting speeds get faster and faster, I think the design reached it's limits.

    The machine is intended to cut sheet goods, and it's very good at it. I'd by another in a minute. But I wouldn't buy one for the OP's intended purpose.

    Gerry

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    Default Re: New Machine Build - Massive CNC router for timber components

    A gantry design may still be feasible for easy loading.

    1. Design so the work table is the highest surface (other than the gantry) - all linear rails, screws, wires etc are out of the way.
    2. System of rollers built in. You can have a series of conveyer type rollers built into the worktable. You could lower these after positioning material. This would make it easy to slide the material on and reposition.

    7xCNC.com - CNC info for the minilathe (7x10, 7x12, 7x14, 7x16)


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    Default Re: New Machine Build - Massive CNC router for timber components

    Quote Originally Posted by peteeng View Post
    Hi Mactec - There are many moving column designs in aerospace that plow through aluminium and titanium. Its not the configuration at fault if it does not work. Its 1) either the machine is being used outside of its intended service 2) it was not designed correctly for its intended service 3) it needs service to bring it into its intended specification 4) it was poorly executed in general. In this machines case loading and unloading is important so should be included in the design requirement. There are many ways to skin the cat and in the initial design phase all options should be explored. Can get all the discussed configs to work some need need more footprint then others. Looked up GDL looks like a large outfit....Cheers Peter
    I would like to see one that has a 16"/ 20" Z axes travel and the Z axes is working at the end of it's travel 5" and doing aerospace work, I have worked in this manufacturing industry and have never seen a machine like that being used for aluminum

    The Morbidelli Machine that was quoted only uses round rails it would be a total waste of time to even look at it for the work the OP has to do, that whole concept type of machine design would be no good as a machine for the work he wants to do

    Here is another style that will work for the OP it is a moving platform ( sliding pods ) which may suit his work better this is just like a moving Table just a different concept can have any type of Head he wants to build with his 16" to 20" of Z axes travel

    Not a hard machine to build seeing he has a fab and machine shop

    Attached Thumbnails Attached Thumbnails New Machine Build - Massive CNC router for timber components-platform-moving-png  
    Mactec54


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    Default Re: New Machine Build - Massive CNC router for timber components

    Hey guys,

    I do not have too much time today to process all the information from the last few posts but I just wanted to give a small update and will reply to the previous posts later on tonight.

    I am going to look into using a VMC as a starting point. First of all I need to see if any good used ones are near me, ill keep you updated.

    In the meantime I spent a few minutes this morning and whipped up a VERY low detail CAD model. This is a design I am thinking of. Making the whole thing from 10x10 and 4x6 tubing as well as a couple welded plate assemblies to create the larger columns. I would use rack and pinion on the long axis and ball screws on the shorter axis and Z movement. I should mention we have most of this material left over from other jobs, and can get the critical surfaces which the linear rails mount to ground/machined for free by a friend of mine (Other than the very long tubing which the whole Z carriage slides on, not sure how we'd get those flat yet). So in the model I have made the linear rails RED so its easy to understand my approach and which way components will be moving. Basically the whole column slides in the X direction, the tables moves in the Y direction and the Z movement is quite obvious, the spindle would be bolted onto the end of the horizontal column while the column moves up and down.

    Please keep in mind I have not included ANY important details, I just wanted some input on the basic idea.

    Attached Thumbnails Attached Thumbnails New Machine Build - Massive CNC router for timber components-cnc2-jpg   New Machine Build - Massive CNC router for timber components-cnc1-jpg  


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    Default Re: New Machine Build - Massive CNC router for timber components

    Hi George - Keep your rails near an edge where its locally stiffer. (commercial machines rarely have "air" behind a rail) It will be less stiff and vibration prone if rails are in the centre of large sections. Otherwise looks workable. The Y dirn rails need to be spaced carefully to be away from the table vibration nodes otherwise it may ring as well. Also get heavy preloaded cars for the rails, will make a difference and keep them lubricated. Does your CAD have FE capabilities? Look for "modal analysis" for vibration modes...The table will need to be stiff (or more rails depends on vib modes) some thought needed with that. Peter

    for instance if the table was 50mm thick steel (2") 3000mm long (120") and 1200mm wide (48") at 81 htz it would wobble around the rails see attached. So if there is an operational vibration (motor, cutter) at 81 htz then the table will want to do this... unevenly spaced pairs of rails could get around this but needs more detail. eg small stringer beams under table between bearings. Do you have thoughts on what the table will look like? Solid metal? Frame with plates? Granite maybe good? I've been driving by a stonemason nearby for a couple of years and finally dropped in and had a chat the other day. Cost of slabs seem good and he has large wet CNC stuff to cut slabs and polish etc. Maybe you have someone similar nearby...He's at the local cemetery Peter

    Attached Thumbnails Attached Thumbnails New Machine Build - Massive CNC router for timber components-table-jpg  
    Last edited by peteeng; 12-02-2019 at 05:26 PM. Reason: added info


  9. #29
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    Default Re: New Machine Build - Massive CNC router for timber components

    Pippin88 - You make good points about a gantry design. Given the amount of knowledge out there on gantry designs I would be foolish not to look into it a bit more seriously. The roller idea is nice, I will take note of that. As you mentioned, if I end up going the gantry route I will no doubt design a machine that has all its components safety under the table, or something of that nature.

    Scooby - Your points are fair about utilizing old methods, we had made the first few sets of trusses/gables this way but we have just had such better results on the CNC. The joinery is incredible and our customers have been exceptionally pleased with our products. I am always interested in gaining a competitive advantage for my company, a machine of this nature will accomplish that. I have found it exponentially easier to program a CNC and deal with all the issues that come with the world of CNC tools than to hire a highly experienced woodworker who knows how to create timber joinery.

    ftech - could you elaborate more on the moving column machine you worked on? Perhaps pictures or any interesting details?

    mactec - I wonder about the practicality of a vacuum pod design? I am not sure setting timbers, sometimes rough sawn on the pods would create an acceptable seal with enough clamping force? Unless I am missing the approach to this design?

    peteeng - So for the rails on the long axis which are un-supported as you mentioned... I had planned on welding on solid bar stock the whole length of the top of the tube and then machining that down, I would not be putting the rails directly to the 10x10 tube. Even with the extra flat bar welded on would you move the rails to near the outside vertical wall of the tube? My CAD seems to have modal analysis, I am using fusion 360. I am quite fresh to the CAD world, I have never done any analysis like this. Seems very interesting though.
    So I have not thought too much about the table... My only thought has been to start with a torsion box approach. I was thinking if I design an aluminum torsion box (maybe using extrusions????) with an mdf top plate I would end up with a very stiff yet light table. Or perhaps I do a welded aluminum tube table and get the entire thing machined flat after welding? I had also though about most likely increasing the amount of rails as they currently have almost 3 feet in between them. Perhaps 5?
    Right now I have the Y travel of the machine sitting at only 24 inch, so the table right now is also at 24 inch wide. I have been thinking extensively about the type of work I will do on this machine, it will so rarely be above 24 inch in the Y direction that I will most likely land on a Y axis size that somewhere in the 24'' - 36'' range. 48'' was my initial thought because that is a decently easy number to get on a gantry design from what I understand, but seems to be a larger challenge on a moving column design.

    I will post more later today/tomorrow.



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    Default Re: New Machine Build - Massive CNC router for timber components

    Hi George,

    Here are a couple of pics of the machines before I worked on them.
    New Machine Build - Massive CNC router for timber components-dscf0495-jpgNew Machine Build - Massive CNC router for timber components-dscf0489-jpgNew Machine Build - Massive CNC router for timber components-dscf0524-jpg

    You might also want to check out this ad on Kijiji
    https://www.kijiji.ca/v-other-busine...ual/1470184696

    Rick



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    Default Re: New Machine Build - Massive CNC router for timber components

    Hi George - Before too long you will need to find out if your weldments can be stress relieved nearby. If you weld something then machine it especially something like a torsion box design it will warp when you release it from the mill. This is counter to the intent. Stress relief can be heat treat or vibration type. If you can't stress relieve then you need to think about bolting or gluing everything together. Especially long objects, does not take much welding to move them around.

    Yes I'd still put the rails to the edges, much stiffer and much less chance to vibrate. For the long 10x10 members although they are very stiff globally they are not stiff locally in that application in the middle of the section. By the time you leverage 100kg (plus) tool load to the distance you have drawn it will deflect the tube wall quite a bit, even if you use a doubler. If you look at commercial machines like Mactecs GDLs they are on edges or solids. If you are aiming at 0.1mm accuracy (0.004") then you need to design to 10x that to ensure you achieve this figure. So designing to 0.01mm (0.0004") seems overkill but there are so many things that will add up in the machine you quickly erode your tolerance. The structure is the easiest thing to upsize and in your case everything has to be big and stiff. Whether its a moving column or a gantry machine take every advantage you have in gaining stiffness. I design machinery for a living and it takes 200-400 hrs to sort out a new design. Then it takes another 50-100hrs to review it and polish it and document it. You are going to make decisions on the fly due to your timetable and you will have to correct and compromise on the fly. But in the end it will work out, just think BIG and there are enough people looking over your shoulder here that you should miss making a fatal error. No blue screens for you.... Peter

    If you go moving gantry style you will need to allow a parked position at one end. In this way it can be loaded from the long side. This will increase the footprint significantly but if footprint is not an issue then it maybe viable. Plus it puts a rail in a vulnerable position to stab with a fork tyne so it needs to be mounted low which make the columns longer which means they have to be bigger.... so the hurdy gurdy begins...

    Attached Thumbnails Attached Thumbnails New Machine Build - Massive CNC router for timber components-gdl-jpg  
    Last edited by peteeng; 12-03-2019 at 04:40 PM.


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    Default Re: New Machine Build - Massive CNC router for timber components

    ftech: Neat machines you worked on. I saw that ad on kijiji, going to inquire with the owner to get some more details.

    peteeng: I had thought about the warping issue after machining. I am sure there are stress relieving companies near me, I will consider that route although it seems an easier approach on this build would be to try and bolt everything together. Is it common practise to bolt and glue/epoxy metal parts together rather than just bolt? I appreciate your view on my project, I will make sure to document every detail so the professionals on here can let me know when I am making a massive mistake haha!



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    Default Re: New Machine Build - Massive CNC router for timber components

    Hi George - There is a build log in here somewhere of an aluminium machine all glued together. Planes are glued together these days to remove the 100,000 rivets and bolts they used to use. Not sure about machines yet. Epoxy grouting is very common to set machine elements in place. Bolting is good enough for machine frames as the member sizes are for stiffness not strength. I'm a fan of riveted structures aesthetics and they have proved they stand the test of time over welded structures. I've been involved with racing yacht structures for over 30 years and they are all bonded so I have no issues with a bonded machine structure. Adhesives have become very user friendly and effective. You will need to pick a build ethos and stay in that universe. If you try to live in the welded universe and the glued universe it can come unstuck! So conventionally its easier to find a stress relief company then the welded stuff all works. If you can't SR and you weld then you have to be able to cold set or do the best you can. If you pick welded sub structures and bolting to allow alignment then think it through to where you break the structure into bits. If you decide to bolt things together then a blend of welding and bolting can work well.

    Very elaborate structures can be made with bolts (high strength bolts replace rivets these days) its up to you. In some respects SHS, RHS and welding is a very limited design space... square shapes and flats vibrate easily, Curves and bolt friction dampen vibration...Conventional cast machine elements are heavy, thick and rounded so they do not vibrate much. Much emphasis is placed on them being cast iron which is damper then steel but not by much. Its the mass and shape that makes the biggest difference. Relatively thin and flat hollow sections vibrate easily. All of this is a big subject....Breath and Carry on...Peter

    Attached Thumbnails Attached Thumbnails New Machine Build - Massive CNC router for timber components-rivets-jpg   New Machine Build - Massive CNC router for timber components-arches-jpg  


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    Default Re: New Machine Build - Massive CNC router for timber components

    Quick update...

    -I revisited the base of the machine. I switched to 6x12's instead of 10x10's as I have a good opportunity to get a fairly priced 24 foot length of 6 x 12, .375 wall.
    -I placed a 1x4 solid steel bar on top of the 6x12's which I will bolt down, maybe glue/epoxy as well, going to have to look into that. These will then be machined to accept the linear rails.
    -I beefed up the legs to 6x6 tubing, .375 wall. I will bolt these to the 6x12's
    -I have cross members connecting the 6x12's... They are sized at 6x6. I will most likely bolt these to the 6x12's as well.

    So In the pictures I have not included any plates/bolts, I will later once I finalize things a bit more.

    The more I dig into this custom build the more it seems do-able for us, and I am very much enjoying the learning curve.

    More to come soon.

    George

    Attached Thumbnails Attached Thumbnails New Machine Build - Massive CNC router for timber components-base-assembly-jpg   New Machine Build - Massive CNC router for timber components-base-assmebly-2-jpg  


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    Default Re: New Machine Build - Massive CNC router for timber components

    Hi George - Your in the honeymoon phase of the LC. You have just scratched the first micro layer of designing a machine and the creative stuff is flowing. Then you have to build it. Then you have to sort it. Then you have to make some money from it. I say this because you have a commercial objective with this machine. I highly recommend investigating a business case for buying a commercial machine. It will arrive with a warranty, with a service contract, a support network and a resell value. It will work out of the box and it will make money from day dot. It may sound expensive but in the end it may not actually be expensive even if its more then you think. As long as the business case stands up this is your best solution. We are all here to help but its a tough road to travel it will take 2x longer then expected and there will be high speed bumps and emotional ups and dips along the way.... One good thing to do is find a commercial machine that does what you want as a benchmark for your design, then you have a $$$ value and a performance standard and a visual guide to what things should look like. Keep at it...Peter

    Last edited by peteeng; 12-04-2019 at 05:20 AM.


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    Default Re: New Machine Build - Massive CNC router for timber components

    Hi All - There is some discussion about welding vs bolting vs bonding so I thought I'd put some numbers on paper. I've kept it simple. If we take a 50mm (2") wide mild steel bar 6mm (1/4") thick and weld it what do the other connections have to look like to support the same tensile load? Interesting thought. So attached is the calcs, but the summary is the welded joint yields at 75kN so this is the target for the others. If we look up the shear strength of class 10.9 bolts an M12 has a shear strength in shank of 74kN, a 5/8" grade 8 has 84kN. So a single snug fit bolt is same strength as the weld.

    If we try to do this with a friction fit we need 7xM12 Class10.9 bolts to hold the 75kN. This is why aircraft use snug bolt or rivet fits to minimise the number required. Plus its why old riveted structures used so many as they were very low strength rivets and they used conservative approaches to the design.

    Bonded connection. If we use a toughened epoxy or a urethane adhesive we can get 30MPa shear strength glue. There are 40MPa adhesives around as well. 30Mpa gives us a 50mm wide connection for the same strength as the weld. This is why aircraft have steadily moved into bonded connections to minimise the number of holes to make, ream and fit fasteners to. Now machine structures are stiffness driven not strength driven so it would seem that relatively small bonding areas or joint geometry is required to achieve adequate strength connections. Plus a bonded joint is visco elastic so is damper then a welded joint.

    Obviously we can't butt joint an adhesive yet (we probably can with a big fillet) but if we revisit how riveted structures are made out of angles and flats we can bond these easily and use a few bolts for alignment and fixturing while the bondo sets. Then there is no heat and it will be the same geometry as fixtured when cured. Cheers Peter S

    https://www.prosetepoxy.com/standard...bly-adhesives/ 30MPa epoxy to steel

    Attached Thumbnails Attached Thumbnails New Machine Build - Massive CNC router for timber components-joints-jpg  
    Last edited by peteeng; 12-04-2019 at 05:22 AM.


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    Default Re: New Machine Build - Massive CNC router for timber components

    Yes, the honeymoon phase is definitely the most exciting part. Even the first glitch free run seems to pale in comparison. So George, try to make sure you don't let that glow interfere with the business decision(s) you need to make.
    I agree with Peter that you should make a business case for a new machine but also include any used machine(s) you may find. Just make sure you add a bit for the extra maintenance you are likely to encounter.
    Peter, thanks for the comparison of weld vs bolt vs adhesive. It is good that you used the shear strength of the mild steel rather than the weld steel since the weld material is at least twice as strong. I would like to comment on the bolt comparison; try to picture having to put 7 of those m12 bolts into that small area.
    Rick



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    Default Re: New Machine Build - Massive CNC router for timber components

    With bonding, I would think Cleavage and Peel forces would be the most problematic?

    Gerry

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    Default Re: New Machine Build - Massive CNC router for timber components

    Quote Originally Posted by peteeng View Post
    Hi All - There is some discussion about welding vs bolting vs bonding so I thought I'd put some numbers on paper. I've kept it simple. If we take a 50mm (2") wide mild steel bar 6mm (1/4") thick and weld it what do the other connections have to look like to support the same tensile load? Interesting thought. So attached is the calcs, but the summary is the welded joint yields at 75kN so this is the target for the others. If we look up the shear strength of class 10.9 bolts an M12 has a shear strength in shank of 74kN, a 5/8" grade 8 has 84kN. So a single snug fit bolt is same strength as the weld.

    If we try to do this with a friction fit we need 7xM12 Class10.9 bolts to hold the 75kN. This is why aircraft use snug bolt or rivet fits to minimise the number required. Plus its why old riveted structures used so many as they were very low strength rivets and they used conservative approaches to the design.

    Bonded connection. If we use a toughened epoxy or a urethane adhesive we can get 30MPa shear strength glue. There are 40MPa adhesives around as well. 30Mpa gives us a 50mm wide connection for the same strength as the weld. This is why aircraft have steadily moved into bonded connections to minimise the number of holes to make, ream and fit fasteners to. Now machine structures are stiffness driven not strength driven so it would seem that relatively small bonding areas or joint geometry is required to achieve adequate strength connections. Plus a bonded joint is visco elastic so is damper then a welded joint.

    Obviously we can't butt joint an adhesive yet (we probably can with a big fillet) but if we revisit how riveted structures are made out of angles and flats we can bond these easily and use a few bolts for alignment and fixturing while the bondo sets. Then there is no heat and it will be the same geometry as fixtured when cured. Cheers Peter S

    https://www.prosetepoxy.com/standard...bly-adhesives/ 30MPa epoxy to steel
    No stress from not welding this is great, but how do you stress relieve the steel parts once it is all glued and bolted together, all the steel parts have stress from it's manufacture, just gluing and bolting a frame together does not get rid of this built in stress, so when you machine the linear rail and ballscrew mounting points the steel glued and bolted parts will move all over the place

    Mactec54


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    Default Re: New Machine Build - Massive CNC router for timber components

    Hi Gerry - Peeling and cleavage need to be accounted for in the joint design. Toughened adhesives these days cope with these very well. If the connection is symmetric then these issues are minimised. Also many bonded connections use bondlines that are too thin which makes it easy to peel due to the stress concentration at the edge.. The supplier should be able to provide guidelines on ideal bondline thicknesses. A good connection design should have a thick edge. So the bondline maybe say 0.5-1.0mm but at the edge its 3mm thick via a chamfer or some edge feature. this allows the edge to stretch further.

    Mactec - I think the plan would be to machine everything first so any of those effects could be accounted for. I agree that rolled sections have internal stress that does relieve during machining so this has to be accounted for. But transport and SR of a small object is easier then a full frame.

    Lots of commentary is based on failure but a machine frame or component is stiffness dominant. Nowhere near failure!! So strains are small, loads are small. So things like 100% welding is not needed, bonding could be done with low strength economical material not high cost fancy extra toughened adhesive. There would be a few single component adhesives that would work at the local hardware. Just putting forward some ideas on the subject. Hobbyists and Makers need a better frame build method then welded steel or AL construction extrusions. They don't have cranes, access to stress relief, large milling machines for correcting frames etc. So we need to explore these options.

    I've attached a doc on adhesive joints for those interested. It's a Hexcel doc so a bit technical but it covers many aspects of joints well. Peter

    Attached Files Attached Files
    Last edited by peteeng; 12-05-2019 at 01:03 AM.


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