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    Default Benchtop Bridgeport Clone Origin

    How's it going,

    I've been on a semester long journey to attain a mill that fits in a small space but can easily mill ferrous metals. Recently I picked up a steel base that supports a Bridgeport J head and was given a ENCO J-head to attach to base (See Pictures). There's no z-axis other than the quill so a buddy of mine helped me weld a table together to bring the XY-Table closer to the spindle. My question is the following: Was this base custom built by someone who wanted a benchtop Bridgeport or was this some sort of option that you could get with a Bridgeport clone. If it helps, the original head on the mill was a MillPort. Also before anyone bashes on the current progress of this machine, I will be making a more rigid motor mount for the 1.5HP DC motor and I will be adding more supports to the table to reduce the maximum deflection to around 0.0004". I will also be replacing the cheap Chinese XY table with a Gilman cross slide which should eliminate the deflection problems I was having with the current XY table. Any other suggestions are well appreciated.image2enco.jpgimage1enco.jpg

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    Quote Originally Posted by Vincevol View Post
    How's it going,

    I've been on a semester long journey to attain a mill that fits in a small space but can easily mill ferrous metals. Recently I picked up a steel base that supports a Bridgeport J head and was given a ENCO J-head to attach to base (See Pictures). There's no z-axis other than the quill so a buddy of mine helped me weld a table together to bring the XY-Table closer to the spindle. My question is the following: Was this base custom built by someone who wanted a benchtop Bridgeport or was this some sort of option that you could get with a Bridgeport clone. If it helps, the original head on the mill was a MillPort. Also before anyone bashes on the current progress of this machine, I will be making a more rigid motor mount for the 1.5HP DC motor and I will be adding more supports to the table to reduce the maximum deflection to around 0.0004". I will also be replacing the cheap Chinese XY table with a Gilman cross slide which should eliminate the deflection problems I was having with the current XY table. Any other suggestions are well appreciated.image2enco.jpgimage1enco.jpg
    Looks home fabricated....by someone that doesn't understand machine design....

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    Quote Originally Posted by digger doug View Post
    Looks home fabricated....by someone that doesn't understand machine design....
    What do you think is wrong with the design lol?

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    Quote Originally Posted by Vincevol View Post
    What do you think is wrong with the design lol?
    How is the original column ?

    it's a hollow box.

    All the gussets in the world on that claptrap will not help torsional rigidity.

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    Quote Originally Posted by digger doug View Post
    How is the original column ?

    It's a hollow box.

    All the gussets in the world on that claptrap will not help torsional rigidity.
    I think you have the right idea, but the words came out backwards.

    No, it is not a hollow box column, it's a kind of I-beam, with relatively low torsional stiffness.

    But it needs to be a big hollow box beam, fabricated by welding. Bolting will not suffice.

    This can be fixed by welding a 0.25" thick steels plate to each open side, yielding a hollow box with internal stiffeners.

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    Quote Originally Posted by digger doug View Post
    How is the original column ?

    it's a hollow box.

    All the gussets in the world on that claptrap will not help torsional rigidity.
    Thank you for following up, yes I'd agree that the whole setup is not the most rigid thing in the universe but I ran simulations on inventor and there should be practically no movement <0.00001" in the column (steel frame holding the J head) as it's built out of 3/4", 1.5" bars alongside a 6" solid steel cylinder at the top. I feel like the biggest weak point is the unrefined build of the table which I think with the correct supports can do an ok job. The table is welded 2in tube steel alongside 1" and 1/2" steel bars

    Again, I really appreciate the swift reply, and take what I'm saying with a heavy grain of salt as I'm a chemical engineer not mechanical and only a 3rd year college student lol.

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    Quote Originally Posted by Joe Gwinn View Post
    I think you have the right idea, but the words came out backwards.

    No, it is not a hollow box column, it's a kind of I-beam, with relatively low torsional stiffness.

    But it needs to be a big hollow box beam, fabricated by welding. Bolting will not suffice.

    This can be fixed by welding a 0.25" thick steels plate to each open side, yielding a hollow box with internal stiffeners.
    Hey Joe,

    I see what he was saying now, would you have any recommendations for the table supporting everything as well? I'm still trying to find the best way to stiffen it, to both support the 500lbs column alongside resist movement going from the xy table to the column.

    Thanks

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    Quote Originally Posted by Joe Gwinn View Post
    I think you have the right idea, but the words came out backwards.

    No, it is not a hollow box column, it's a kind of I-beam, with relatively low torsional stiffness.

    But it needs to be a big hollow box beam, fabricated by welding. Bolting will not suffice.

    This can be fixed by welding a 0.25" thick steels plate to each open side, yielding a hollow box with internal stiffeners.
    Please re-read my quoted.

    I didn't type anything backwards.

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    It looks like the Y travel will be extremely limited.

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    It may have originally been a fixture to facilitate mechanical repairs.
    Like an engine stand for BP heads.

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    Quote Originally Posted by digger doug View Post
    Please re-read my quoted.

    I didn't type anything backwards.
    Well yes and no. Today I see that by "original" you meant the now missing cast-iron base tower that came with the mill. But is not what first came to mind. A few more words would have helped. And knowing that the original was a hollow box does not explain why that is important to torsional stiffness.

    But we all seem to have gotten there.

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    Quote Originally Posted by Vincevol View Post
    I see what he was saying now, would you have any recommendations for the table supporting everything as well? I'm still trying to find the best way to stiffen it, to both support the 500lbs column alongside resist movement going from the xy table to the column.
    I cannot really tell from the photos.

    Nor are steel weldments a particularly good way to build the frame of a machine tool, because steel is too good a spring. Cast iron works way better, because the metal inherently damps vibrations, reducing the tendency to chatter. It can be done, but it isn't easy, and for small machines (anything that will fit in a small shop for sure), it isn't worth the trouble.

    So I suspect that you are about to fall down a rabbit hole here. It's probably far cheaper to buy another B'port clone and assemble one good machine from the pieces. It's certainly way faster.

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    Quote Originally Posted by Joe Gwinn View Post
    I cannot really tell from the photos.

    Nor are steel weldments a particularly good way to build the frame of a machine tool, because steel is too good a spring. Cast iron works way better, because the metal inherently damps vibrations, reducing the tendency to chatter. It can be done, but it isn't easy, and for small machines (anything that will fit in a small shop for sure), it isn't worth the trouble.

    So I suspect that you are about to fall down a rabbit hole here. It's probably far cheaper to buy another B'port clone and assemble one good machine from the pieces. It's certainly way faster.
    I cannot tell if the website uploaded my reply or not so hopefully you won't see this message twice haha. But yes I'd agree that this is a rabbit hole of sorts and that there are better setups out there for sure. Unfortunately I've already dumped a lot of money into trying to throw together a respectable machine on a budget and on a space constraint. This machine currently sits about 5 or 6 feet away from my bed and therefore I cannot afford to fit an entire knee mill in my room. That being said I followed up on the comments regarding the column lacking rigidity and ran simulations using 270 ftlbs of force in both the x and y directions with a max deflection at the cutter/ vise being 0.0003". Assuming this setup lays the groundwork for whatever final iteration this machine will take, will 0.0003" be low enough and would it still be worth adding the steel plates?cd-y-axis.jpgcd-x-axis.jpg

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    Quote Originally Posted by Vincevol View Post
    I cannot tell if the website uploaded my reply or not so hopefully you won't see this message twice haha. But yes I'd agree that this is a rabbit hole of sorts and that there are better setups out there for sure. Unfortunately I've already dumped a lot of money into trying to throw together a respectable machine on a budget and on a space constraint. This machine currently sits about 5 or 6 feet away from my bed and therefore I cannot afford to fit an entire knee mill in my room. That being said I followed up on the comments regarding the column lacking rigidity and ran simulations using 270 ftlbs of force in both the x and y directions with a max deflection at the cutter/ vise being 0.0003". Assuming this setup lays the groundwork for whatever final iteration this machine will take, will 0.0003" be low enough and would it still be worth adding the steel plates?cd-y-axis.jpgcd-x-axis.jpg
    Strain gage the thing up and report back here.....

    It's obvious your not wanting to accept any criticism of your "design".

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    Well, I think your actual forces will be considerably higher due to using screw motions to move the table etc. Your overall play is going to be more than the deflection simply due to the fact that things have to be able to move in order to be useful.

    That said, I think the setup you show can work OK, just less than optimal. Believe it or not, there are many guys building CNC machines using a mixture of sand and epoxy instead of cast iron -- it gives the required damping properties on a home shop budget. If it were my project, I would want to enclose the column with steel plates and pour it full of epoxy-sand mixture. Mass, damping, and rigidity are your friends.

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    Quote Originally Posted by Vincevol View Post
    ... But yes I'd agree that this is a rabbit hole of sorts and that there are better setups out there for sure. Unfortunately I've already dumped a lot of money into trying to throw together a respectable machine on a budget and on a space constraint. This machine currently sits about 5 or 6 feet away from my bed and therefore I cannot afford to fit an entire knee mill in my room.
    I would suggest considering a Clausing 8520 vertical mill then.

    Don't cling to sunk costs. Write them off to education.


    That being said I followed up on the comments regarding the column lacking rigidity and ran simulations using 270 ft-lbs of force in both the x and y directions with a max deflection at the cutter/ vise being 0.0003". Assuming this setup lays the groundwork for whatever final iteration this machine will take, will 0.0003" be low enough and would it still be worth adding the steel plates?
    This is not the whole story. The issue is chatter. You need to figure out the frequency and damping level of the lowest frequency torsional vibration mode, which will be excited when milling an edge or slot, yielding chatter, which can become quite violent.

    You can often also tell a lot by smacking the tool bit sideways with a wooden mallet while listening. A contact mic and oscilloscope is also helpful. Basically, if it rings, there will be big problems. It should instead go thunk.

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    Quote Originally Posted by pavt View Post
    Well, I think your actual forces will be considerably higher due to using screw motions to move the table etc. Your overall play is going to be more than the deflection simply due to the fact that things have to be able to move in order to be useful.

    That said, I think the setup you show can work OK, just less than optimal. Believe it or not, there are many guys building CNC machines using a mixture of sand and epoxy instead of cast iron -- it gives the required damping properties on a home shop budget. If it were my project, I would want to enclose the column with steel plates and pour it full of epoxy-sand mixture. Mass, damping, and rigidity are your friends.
    Yes. For those wanting to go this way, I recommend the works of MIT Professor Alexander Slocum and his students regarding Precision Machine Design. The open course goes into the use of epoxy concrete as a damping material.

    Precision Engineering Research Group (PERG)

    Precision Machine Design | Mechanical Engineering | MIT OpenCourseWare

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    Quote Originally Posted by Vincevol View Post
    Hey Joe,

    I see what he was saying now, would you have any recommendations for the table supporting everything as well? I'm still trying to find the best way to stiffen it, to both support the 500lbs column alongside resist movement going from the xy table to the column.

    Thanks
    Concrete base. Also, non-shrinking grout can be used to fill in the side areas after plate is welded on. Adds mass and rigidity to hollow members.

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    I'd be more worried about having steel chips all over my floor, desk, bed, dinner etc. than any aspect of machine design.

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