[Chmfhm]

I want to make diy cnc milling machine for steel and really confused to choose Bridge Type or Single Column Vmc Style

KINDLY SUGGEST me which one is better what are pros and cons of both type.

Your Views are valuable for me.

Thanks

[awerby]

If it's a small machine with a relatively narrow table, you can build a "C" shaped column mill from available steel shapes and get acceptable rigidity. But as it gets larger, or the overhang increases, it starts needing massive castings for rigidity. A bridge design with a moving table can span a larger area widthwise, since the spindle's not out on a canteliever, It's an easier kind to build if you don't have a foundry, but eventually the twisting moment from an extended Z axis with the spindle on the end gets harder to constrain as its length increases.

[peteeng]

Hi CHM - It comes down to the size of the machine you want. Look at commercial machines with the table size you want and that will tell you the answer. You will need to make a machine with similar component sizes to the commercial machine. Single column VMC's can be very big so I expect that will be your answer. This removes the issue of synchronising two axes and the cost of the slave axis and minimises the footprint of the machine. Unless you want wide and deep parts, then you will need a bridge configuration. Good luck, making a mill is not for the faint hearted!! . Peter

[joeavaerage]

Hi,
the rigidity required for milling steel is very high indeed, and as others have posted it not easy to make your own.

I have attached a pic of mine, and while I'm quite proud of it....its still only just rigid enough. For 95% of the jobs I do its perfect but when it
comes to larger steel and stainless jobs I have to take it easy.

I had the axis beds cast in iron, 115kg each. The frame is laser cut 32mm med tensile steel. The cantilever is 100 x100 x 9. The cantilever is too flexible for my liking and I will have one cast
in SG iron....when I can afford it. All-in-all I'm glad that I built it, but the cost and energy required to do so is high, certainly higher than buying a secondhand machine, even if its less than a new machine.

Craig

[Chmfhm]

Hi,
the rigidity required for milling steel is very high indeed, and as others have posted it not easy to make your own.

I have attached a pic of mine, and while I'm quite proud of it....its still only just rigid enough. For 95% of the jobs I do its perfect but when it
comes to larger steel and stainless jobs I have to take it easy.

I had the axis beds cast in iron, 115kg each. The frame is laser cut 32mm med tensile steel. The cantilever is 100 x100 x 9. The cantilever is too flexible for my liking and I will have one cast
in SG iron....when I can afford it. All-in-all I'm glad that I built it, but the cost and energy required to do so is high, certainly higher than buying a secondhand machine, even if its less than a new machine.

Craig

Thx for your input. I will upload design of mine soon based on epoxy granite

[joeavaerage]

Hi,
the problem with epoxy granite is that its about as stiff as a limp noodle. As a hobbyist you can expect no better than a Youngs modulus of 30-40GPa,
compared to cast iron at 110GPa and steel at 205GPa. So you can make an epoxy granite machine arbitrarily as stiff as you want ONLY by using huge sections
and consequent volume of epoxy granite. Whatever cost savings you had hoped for by using epoxy granite are seen disappearing in the rear view mirror.

Craig