Fixed gantry opinions/possible new build

Hi,

Long time reader, first post! Have enjoyed reading this forum for many years.

I am looking to build a machine for specific duties and one-off jobs. Majority will be 6061, but occasionally acrylic and possibly steel. Aluminium parts are generally 800x80x30mm in size.

I currently have a retrofitted Bridgeport running steppers and LinuxCNC. It was a great learning experience, but it isn't suited to my current needs. I am looking to build something that can handle the high feed rate 3d tool paths that Fusion360 can generate. The slow moving steppers and 3.6k rpm spindle of the retrofitted Bridgeport is not cutting it!

So, I was thinking of building a fixed gantry router. So far these are the parameters I would ideally meet with the machine:

900mm X travel, 400mm Y travel, 200mm Z travel

400ipm/10,000mm/m feeds

High speed spindle 20k plus

Ideally hold under 0.05mm tolerances. Aim is speed of machining. This will be used in a small batch production scenario.


I run a little job shop, so I have access to cold saw, Bridgeport, mig/tig for fabrication. Hence I was thinking a box steel frame with faced mating surfaces would be a good design direction. So far the hardware spec looks something like this:

hgr20 rails in all axis

1605 double nut ball screws (perhaps these should be 2005)

Clearpath SDSK3432P servo motors. Continuous torque of 1.5Nm, peak torque 5.0Nm and max 2380rpm

100x100x5mm SHS construction. Gantry to be 200x150x5mm.

Spindle currently unknown. Open to suggestions.


Would love any input on the proposed specs, any advice on machine design and also feasibility of my parameters.

Many thanks,

J

For a new build, DMM Technologies servos would be my first choice. https://store.dmm-tech.com/

Very competitive with ClearPath pricing. I'm using 4 of their 1.8KW units on my lathe and have been very happy with them, they have many options to choose from.

Repowering your BP with these would make a world of difference also, would be like a new machine.

You want 10mm-25mm pitch screws if you want speed. 5mm pitch screws will be sloooow.

Thanks for the input Jim. I will check out those servos.

I thought about repowering the Bridgeport, infant it is still an option. The thing that bugs me about it is the 600mm x-travel and the slow spindle. It's also pretty tired. Still the best drill press and tube notcher I have though...

Quote:

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Originally Posted by ger21

You want 10mm-25mm pitch screws if you want speed. 5mm pitch screws will be sloooow.

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Thanks ger21, I will look into what is available in those pitches. I was worried about losing too much power through a steep pitch, but maybe I'll run some more calculations.

Don't worry about the power on a steep pitch. My 4x8 fixed gantry router had a 4040 on the table axis, and a 2525 on the cross axis. Both powered by 1200 oz/in NEMA 34 steppers, 1:1 on the cross axis, and 1.3:1 on the table. 600 IPM max rapids. The moving table weighed in at about 700 lbs. 1 or 1.3KW servos would have been better, but I didn't know any better at the time. Positioning accuracy was +/- 0.001

Hi Laundro - I'd go at least 200x200x6 for the gantry as you are mainly metal. I presume you are going 200mm high ? You need the size for plunging/drilling and for XY cutting. Being fixed gantry I'd go thicker as well 200x200x12.5 say. Can't have too much stiffness plus gives you threading depth and a machining allowance. Cheers Peter s