Epoxy resin to strengthen the gantry


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Thread: Epoxy resin to strengthen the gantry

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    Default Epoxy resin to strengthen the gantry

    Hi, I'm plodding away with my first router build and am getting close to mounting the gantry now. I got my spindle last week (2.2kw) and weighed it with the mount at 6.5kg's. Add Z axis and motor we're getting over 10kg's. I have 50mm*100mm heavy duty bosch profile as my gantry. My gantry will be 1650mm long, I'm going to embed the gantry 5mm into the mounting plates (25mm tooling aluminium) for extra support.

    Epoxy resin to strengthen the gantry-cavity-png

    The plan is to fill the cavities with a mix
    50% aluminium filler powder
    35% Epoxy resin
    15% Carbon Fibre powder

    then cure in a water bath to stop it overheating and warping.

    It's a simple cure the resin I am going to use would benefit from a 2nd cure but much more difficult to pull off so for my first gantry I will only do the simple cure. If this works well on my next build I will do the 2nd cure and the strength should be comparable to a solid steel core, with the simple cure it should be stronger than a solid aluminium core but weaker than steel which for the 4.2kg's it adds in weight will be a good trade off.

    I was wondering has anyone else ever tried to do this? Does anyone see any issues with this?

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    Community Moderator ger21's Avatar
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    Default Re: Epoxy resin to strengthen the gantry

    The only issue is that it won't add much strength, if any.

    Gerry

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    Default Re: Epoxy resin to strengthen the gantry

    Quote Originally Posted by ger21 View Post
    The only issue is that it won't add much strength, if any.
    Hi, I was wondering if you could tell me why?

    I have no experience with resins I'm just going on what the resin people told me, I'd like to understand why casting a resin that cures to almost the hardness of steel (With the right fillers) won't increase strength? Is it because of flex or is there something I'm not getting here? This is why it's always good to ask before doing lol.

    I was intending to cut 2 identical gantries one with resin and one without and they do some flex tests on them. I pay very little for bosch extrusion (Recycled), the last 10*3.6m pieces I got cost me ~$30 my only real cost here is the resin, filler and carbon fibre.

    I originally planned to encase the aluminium in angle steel (Which is cheaper) do you think this would be a good option to strengthen it up?

    Or what about if I fill the cavities with threaded bar then cast the resin around the threaded bar? (This would be good as I can this for free)

    Thanks
    Tutu



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    Community Moderator ger21's Avatar
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    Default Re: Epoxy resin to strengthen the gantry

    Because the strength is only in compression. There's no strength in tension. Epoxy is brittle in tension, and the fillers don't add anything to it's strength.

    Gerry

    UCCNC 2017 Screenset
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    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


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    Default Re: Epoxy resin to strengthen the gantry

    If you need a stronger gantry, you really need to upgrade to a larger, more rigid extrusion. The profile and wall thickness of the extrusion is what adds the strength and stiffness When you look at the properties of a specific extrusion most manufacturers list structural strengths, deflection, weight limitations etc, etc so users can determine the proper use for each size/profile. You can only get so much rigidness based on a size, wall thickness etc. What may be sufficient for a 1 foot length may not be for a 4 foot length. One thing your idea would do is add weight. That can be good as long as your drive/motor setup can handle it. Additional weight helps reduce resonation and vibration but may actually decrease load capacity of the extrusion simply because you're adding more weight to the overall design that may not be engineered into the specs.. One thing that makes aluminum extrusion good for some structural designs is it's light weight vs it's structural strength characteristics. If you want to add weight simply fill the tubes with sand and cap them. It will do about the same as the resin and cost a lot less.



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    Default Re: Epoxy resin to strengthen the gantry

    Quote Originally Posted by ger21 View Post
    Because the strength is only in compression. There's no strength in tension. Epoxy is brittle in tension, and the fillers don't add anything to it's strength.
    Hi, thanks that makes some sense to me, I guess using a high tensile epoxy makes no difference?



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    Default Re: Epoxy resin to strengthen the gantry

    From an engineering perspective, the resin will help with some damping and noise, but won't provide a noticeable difference in deflection if that is what you are going for. As suggested before if you go with a larger cross section, that exponentially adds more rigidity and strength.

    Sent from my SAMSUNG-SM-G900A using Tapatalk



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    Default Re: Epoxy resin to strengthen the gantry

    I haven't tried this specifically but I have done a lot of part reinforcement using epoxy and carbon fiber.

    I think you would be better off filling it with chopped carbon fiber strands cut at 1/4" wetted out with epoxy in a 50:50 ratio if ultimate rigidity is the goal. I think that adding aluminum powder and carbon fiber powder will make little difference. It might increase the surface hardness / scratch resistance of the resin but that won't matter when it's inside an aluminum cavity.

    For the costs involved though, you could probably replace the aluminum with steel square or rectangle tubes unless you are using the aluminum extrusion as a linear rail.



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    Default Re: Epoxy resin to strengthen the gantry

    Couldn't you hire the best welder in town (to make a nice steel frame) for the money you're putting in the extrusion and epoxy?

    Steve



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    Default Re: Epoxy resin to strengthen the gantry

    Quote Originally Posted by sajurcaju View Post
    Couldn't you hire the best welder in town (to make a nice steel frame) for the money you're putting in the extrusion and epoxy?

    Steve
    Extrusion was free so for now I've increased the amount of extrusion in the gantry, I also embedded the extrusion into the mounting plates 5mm and increased the thickness of the plates by 5mm



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    Default Re: Epoxy resin to strengthen the gantry

    Quote Originally Posted by Tutu View Post
    Extrusion was free so for now I've increased the amount of extrusion in the gantry.
    Can't argue with that!

    Steve



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    Default Re: Epoxy resin to strengthen the gantry

    I think that some of the confusion about what people are using epoxy / sand mixes for is that they aren't using it fill the cavities in aluminum extrusions. It's the opposite. They are using epoxy / sand mixes to create a machine base around an aluminum or steel skeleton. They use this term "epoxy granite".

    The purpose of the epoxy granite machine base is vibration dampening and weight. They increase the thickness of the epoxy walls to make up for the reduced strength compared to aluminum or cast iron etc.

    Anyway, the key point is that aluminum is the filling, not the thing being filled with this design. A lot of the structural strength still comes from the metal.

    Sand is added because it's a lot cheaper than epoxy. It would cost a fortune if pure epoxy was used for such a large structure.



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Epoxy resin to strengthen the gantry
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