3' x 4', welded steel frame...critique wanted!


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Thread: 3' x 4', welded steel frame...critique wanted!

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    Member Matthew_H's Avatar
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    Default 3' x 4', welded steel frame...critique wanted!

    Hello,

    I've spent some money so I guess I'm into it now.

    Intro: I'm a recent mechanical engineering grad, which probably means I don't know anything AND I'm too cocky to admit it. I learned a lot about machine design in college but there's no substitute for experience...that much I've learned from experience.

    Anyway, the plans:

    - Welded steel frame, 2"x2"x1/8" tube
    - Linear profiled rails/bearings
    - Double ball screws on the X
    - Nema 23s

    Main goals:

    - Frame rigidity, minimized vibration and flex
    - Accuracy / repeatability
    - Long z-axis travel

    Not as important:

    - Anything happening soon... it will still take me a long time before I see any woodchips flying
    - Cutting speed
    - Precision / resolution. I'm carving wood, not etching a circuit board.
    - Cost. If (when) I run out of money, I'll slow down, save up, and get back to it when I can

    Main questions:

    - How perfect do my rails have to be for the bearings to slide easily/properly?
    - - My plan is to have the X axis rail beds machined both at once at a local machine shop. It took me a while to find, but there's a shop nearby that has the capability to cut 3' x 4' in a single setup.
    - - Is this necessary? Or can I just cut the rail beds on a manual mill one at a time?
    - Are there disadvantages to having the Y axis rails on top of / underneath the gantry instead of on the front? Most machines have them on the front.
    - - I put them on the top and bottom to keep the Z axis closer to the gantry...didn't want it sticking out farther than it had to.
    - - I can machine both Y axis rail beds at the same time on a standard manual mill so they will be perfect relative to each other
    - Are my gantry ends strong enough?
    - - It's 1/4" plate right now...both the horizontal plates and the vertical ones
    - - I have some 3/8" plate if it's worth the added weight

    If there's anything else that seems inadequate or poorly designed, let me know!

    Thanks

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    Default Re: 3' x 4', welded steel frame...critique wanted!

    Hi MH _ going thru this point by point

    1) Look up the manufacturers specification for the rail foundations that's the starting point
    2) good idea to have them cut in one setup
    3) can do it one at a time if the machinist is good and can register one side to the other somehow
    4) top and bottom is good if you can machine the rail foundations to keep them parallel and square
    5) ends could be improved, do you have access to fea? as that gives you clues to what is compliant and what is OK
    6) thicker plate is better for local stiffness. Depending on how stiff you want 3mm is usually too thin for local stiffness

    Before you machine you need to look at thermal stress relief. After welding the frame will distort and then after machining it will distort again. TSR will remove the internal stress that does this so when you machine, the frame will stay put. The long members for the rails will need intermediate braces to limit deflection and to stop vibration. The twin gantry design is limiting in that the members are small and poor in torsion. Look at a large single gantry vs the twin design. Your Z axis plate needs to be thicker, the side flanges help but a thicker one is better especially if its high Z. Using light angle for the saddle to gantry car connection is a bit light on, either add webs to the angle or use solid blocks. These get twisted and bent a bit so the car attachments need to be very stiff

    Its coming along - keep at it - Peter



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    Member awerby's Avatar
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    Default Re: 3' x 4', welded steel frame...critique wanted!

    That looks like a pretty nice design. I'd like to see more reinforcement, like X bracing, under the beams that support the gantry; that will stop some bouncing around. And if you connect the two parallel beams that constitute your gantry with a substantial aluminum plate, which can be bolted on, that will make the whole thing a lot stiffer.

    [FONT=Verdana]Andrew Werby[/FONT]
    [URL="http://www.computersculpture.com/"]Website[/URL]


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    Default Re: 3' x 4', welded steel frame...critique wanted!

    This is a design That I found a Young Man in South Carolina (I believe) who built one for his father-in-law and I absolutely loved his concept...So immediately my brain started working in overdrive on how I was going to ensure it was going to be level on the beams where the Gantry Rails road...There's a video out there on his build and if you watch it he shows the detailed frame parts before they are welded up and you can see his fly cut surfaces...It seems he is building his basic foundation of his X off these fly cut areas then from there after he has that accomplished then he goes on the build his vertical frame for the base and legs...

    I was thinking that those 4 corner supports that held the 2 rails would be machined with welded end caps for sitting on the fly cut frame...Then attach perhaps with bolts ( to reduce head and possibly warpage) to go into the frame and then the supports to achieve a assured flush/flat area for the 2 rails to attach to...
    Now since both the top and bottom of the supports are machined the supports are now hard located to the lower fly cut area,
    then with the X rail being fly cut only where supports are being supported at can then be mounted with bolts thru the rails into the supports...
    Reason being I have now created 2 areas at each corner to be shimmed to fine tune X rails
    For the linear rails the surface of the tubing where the rails sit upon will get fly cut as well for a absolute flush surface to attach the rails to...Doing this seems to be needed to help reduce as many variables needed to accomplish a foundation that will ensure the best possible outcome of what we are trying to achieve for the DIY'er...
    That is since we are not looking for that nano nats ass of pression...it's a machine we are using for the hobbyist...not mass production where we are seeking 4th decimal place...
    Hope this helps
    Paul
    Hope this makes sense
    this is what Im planning on designing
    perhaps what we should do is get together and share processes and materials along with parts and get going on this design and build...



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    Default Re: 3' x 4', welded steel frame...critique wanted!

    Hi Paul,
    An image of the machine would be good. Be aware that a steel structure will move if welded then machined. That's why they are welded, stress relieved then finish machined. Plus makers do get stuck as they can't find a machinist with a big enough bed to do the machining or find they do not have the budget for the machining. Design to detail and cost it out before you actually acquire or physically do anything. There's lots of fences to jump yet. Peter

    its easy to achieve a machine that gets +/-0.1mm accuracy +/-0.01mm takes planning and effort and forget about 0.001mm as you say....



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    Default Re: 3' x 4', welded steel frame...critique wanted!

    Hi,
    my local heat treatment company charge $6NZD/kg for stress relief, and with the price of fuel skyrocketing I would not be at all surprised that the cost has likewise skyrocketed.
    Additionally the max length of the part is 695mm, to fit in his furnace. If my part is bigger than that I have to send it to Auckland, a 2000km round trip.

    If you want to weld stuff then heat treatment is effectively mandatory, so I would suggest you research the heat treatment facilities in your area to get both the cost and the max size.

    I design parts to fit in the furnace (local) and then assemble the parts into a machine. If I absolutely have to make one big assembly then I have to allow freight etc to Auckland and back.

    There is a company locally that does machining. Their biggest machine is a near new Okuma that you could park a car in!!!. It's huge. Great company, great machines and skilled
    machinists, $170NZD/hour. Provided you are aware of what you are facing going in...no problem. Its when you get slammed with a $2000 expense that you did not allow for that will
    sour the build experience.

    I'm a little less inclined to go for CAD straight away, I tend to research the facilities I intend to use and design to fit that capability.

    My new build (well 1 year old now) mill has three second hand ballscrews, 32mm diameter and ground C5 grade, very nice indeed and at a small fraction of the price I would
    have paid new. My design is largely is to accommodate/exploit those ballscrews.

    The idea essentially is that if I chose the parts and materials wisely, and design within the limitations of local suppliers, like my local foundry, and heat treater I can produce a worthy machine
    within a budget. If however you design the machine.....I want this, and I'll do that this way etc, then when it comes to doing it it may well cost a fortune.

    I tend to draw the detailed plan once I've finished building!

    Craig



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    Default Re: 3' x 4', welded steel frame...critique wanted!

    Hi Paul - In another thread I mention this. If you go the path of welding with no thermal stress relief (there is vibrational stress relief as well) consider using silicon bronze wire. Its melting point is less then steel so you do not melt the parent. This considerably reduces the internal stress. If you braze using oxy and tobin broze it would be even better... If you want to go down this sort of path. Peter



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    Default Re: 3' x 4', welded steel frame...critique wanted!

    Hi,

    (there is vibrational stress relief as well)
    Been there, done that, and it's not too bad either. I have no measurements to support my claim, but I found vibrational to be about 50%-75% as effective as heat treatment. The upside is that its cheap,
    $200NZD for a part that would have cost $1500NZD in the furnace and it can be applied to big parts (meters long) for which there is no other choice.

    Craig



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    Default Re: 3' x 4', welded steel frame...critique wanted!

    So this process of silicon bronze is achieved with the acetylene/oxygen and a rosebud tip? if so this would certainly be a method I could achieve...
    Is there a wire that would go into a MIG welder and achieve the results you speak of?
    What about TIG?
    Paul



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    Default Re: 3' x 4', welded steel frame...critique wanted!

    Hi Craig et al - Most of the welded structures I deal with at the moment are too big for ovens. They are vibrationally stress relieved. It does work. Sometimes too well and the vibs can crack the structure. These trailers are made with very high strength Q&T steels. Interesting stuff. I get printouts of the before and after "ringing" signatures and the internal stress is reduced via VSR. Peter

    Attached Thumbnails Attached Thumbnails 3' x 4', welded steel frame...critique wanted!-trailer-jpg  


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    Default Re: 3' x 4', welded steel frame...critique wanted!

    Hi Paul - You can get mig wire and brazing wire. If you have oxy/act then you can braze weld. This is like tig welding. If the fits are good and they should be you could flow braze with a rose tip. If you go down the brazing path with oxy look up in-line fluxing will make your life easy. I highly recommend this process but you can't thermally stress relieve as the braze will melt. But then that's what you want to avoid Paul from your name do you want to make bows? I made a couple when I left school. (so long ago) Peter

    Paul you can TIG braze as well. Ideal brazing system is oxy with in-line flux I feel. But tig brazing is common if you do the searches...

    Hey MH - How you doing with the machine., Sort of hijacked the thread....

    Last edited by peteeng; 06-30-2022 at 06:41 PM.


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    Default Re: 3' x 4', welded steel frame...critique wanted!

    Hi,
    bronzing is traditionally done with oxy-acetylene but you can do it with a MIG. I presume you could do it with a TIG also, but I've never tried.

    We used to supply a customer who TIG welded copper busbars etc, and had to get full depth penetration.

    Bronze is good for thin sections only, you do not get penetration like you do with a genuine weld. The strength/rigidity of a bronze connection is about wetted surface area, not unlike
    soldering. I think to accept bronzing is to accept to many limitations and all to avoid heat treatment. If you weld you need heat treatment, end of story. If you don't want the cost
    of heat treatment don't weld....simple.

    Craig



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    Default Re: 3' x 4', welded steel frame...critique wanted!

    Hi Craig - Obviously you do not get penetration with a braze as you don't melt the parent. But if done correctly you get full wetting across the faying surfaces and a meniscus on the inside. That's all you need for machine parts to work properly. I debate if its only for thin sections, as long as you have enough heat to get to correct temp then its doable. Just like welding you need equipment up to the task. I would not consider anything in this sort of build thick. Peter

    On the point of penetration the braze does penetrate the parent via the intergranular gaps. Its a very intimate connection and does much better in fatigue then welding does. Welding tends to rip the grain structure apart vs brazing that keeps the grain structure intact



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    Default Re: 3' x 4', welded steel frame...critique wanted!

    Hi,
    I personally would not even consider 50 x 50 x 3 section, I would be going to 50 x 50 x 6 for which I think brazing would be inadequate, whereas a full depth weld I could do myself
    no trouble with a a reasonable MIG plant.

    The pic posted earlier suggests to me that the welded structure excluding the gantry would be well under 100kg, even using 6mm thickness. Heat treatment could be
    of the order of $800NZD, which I don't think is out of the way.

    Craig



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    Default Re: 3' x 4', welded steel frame...critique wanted!

    Quote Originally Posted by Texasbowhunter View Post
    So this process of silicon bronze is achieved with the acetylene/oxygen and a rosebud tip? if so this would certainly be a method I could achieve...
    Is there a wire that would go into a MIG welder and achieve the results you speak of?
    What about TIG?
    Paul
    Silicon Bronze welding is normally used with Tig welding

    Just MiG weld your parts as you had planned to do, the steel has stress in it so no matter how you put it together the stress will still be there in the steel, the only way to remove the stress before machining is to Heat treat the parts, the parts you have like the Tubes do not stress relieve very well with vibrational stress relief

    The only methods to weld a frame like this is use Mig / Tig or Stick

    Last edited by mactec54; 06-30-2022 at 07:45 PM.
    Mactec54


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    Default Re: 3' x 4', welded steel frame...critique wanted!

    Quote Originally Posted by peteeng View Post
    Hi Craig et al - Most of the welded structures I deal with at the moment are too big for ovens. They are vibrationally stress relieved. It does work. Sometimes too well and the vibs can crack the structure. These trailers are made with very high strength Q&T steels. Interesting stuff. I get printouts of the before and after "ringing" signatures and the internal stress is reduced via VSR. Peter
    The vibrational stress relief is only suitable for heavy welded parts over 1/2" thick and parts like what you are showing, is no good for RHS or a machine frame like this.

    Mactec54


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    Default Re: 3' x 4', welded steel frame...critique wanted!

    Paul from your name do you want to make bows? I made a couple when I left school. (so long ago) Peter...

    I had not considered making a bow on a CNC platform...Although I have certainly entertained the idea of making a long bow but it would be done with allot of cutting and file work...Old school way...I have felt I wanted to make one for my Granddaughter...I need to go down to the creek and find a bodark tree and cut it down and then glue the ends with wood glue so the tree will dry from the inside out for about 6 months...but being her first one and my first one I will just go down to the Big box store and get a nice piece of white/red oak and build her one just to experience the build part...
    But as the name stated I was big into bow hunting and competition many years ago and the username has stuck...You heard about the OLD KISS Method...
    I don't always follow this logic but from time to time it seems logical...One of my downfalls and I have several is when I build something I always over engineer it for the stated reason but when its finished its very well built and will last forever...
    Paul



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    Default Re: 3' x 4', welded steel frame...critique wanted!

    Hi Mactec - Take that up with the VSR suppliers. They will disagree that there are thickness and size constraints. Peter

    https://www.advancedvsr.com/the-phys...al%20integrity.



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    Default Re: 3' x 4', welded steel frame...critique wanted!

    Quote Originally Posted by peteeng View Post
    Hi Mactec - Take that up with the VSR suppliers. They will disagree that there are thickness and size constraints. Peter

    https://www.advancedvsr.com/the-phys...al%20integrity.
    We have used this process for a number of years, so know what works the best, I say it again, thin section RHS is no good for this type of treatment, you could post links all day long which are meaningless, you are showing what the manufacture wants you to see

    They don't show you the failures, when you weld plates onto thin wall RHS and the cracking that can happen from using this method, this is why they still use regular Heat Treating (Stress Reliving) VSR has its place no doubt, as we use it every day, it not for every application though, it quite amazing how people can get fixated on something but have little to no experience in whatever the outcome or process is

    Note in most of their examples it is all thick solid material they are using.

    I just built a machine frame fully welded and after Heat Treatment it required less than .020" .05mm to be machined Ground off to make it have parallel / true surfaces. this frame could have used VSR as it had plates up to 3/4" thick, it also had a lot of RHS, so the choice was easy to Stress Relive by using Heat

    Their example of the fabricated welded beam was 1/4" over 50 feet after using VSR, our 10m 5 axis machine frames before using VSR are better than 1mm (.040") we have built these machines up to 30m long so there 1/4" 50' beam after stress relieving was nothing special, to our standards was a poor fabrication to start with

    We use VSR on all the large machines 2m and up as there is no part that is under 12mm thick steel used in the builds

    You can buy those pneumatic vibrators they are using and try it out for yourself, just adjust the air pressure to change the frequency amplitude of the vibrations, be aware of any experiment's though as if not put together well (welded) it will come apart.

    Attached Thumbnails Attached Thumbnails 3' x 4', welded steel frame...critique wanted!-mac-10m-png  
    Mactec54


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    Default Re: 3' x 4', welded steel frame...critique wanted!

    I said you could post articles on this all day long, here is one that is saying what I have posted about different materials being used and to two methods
    Note this part, it is not efficient for extruded cold worked materials, as I said RHS is not a good candidate, localized VRS while welding does work quite well, but this does not relieve the stress in the rest of the RHS fabrication

    The method can be used on a wide range of ferrous and nonferrous metals, including carbon and stainless steel, cast iron, aluminum, titanium etc., in a large variety
    of shapes. Sizes can vary from small, welded parts, shafts and gears to large welded and machined steel structures.
    However, it presents some limitations: it is not efficient for extruded, cold worked and precipitation hardened materials.

    https://stressreliefengr.com/stressr...IG%20and%20TIG.

    Mactec54


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