Requesting some feedback on steel frame design.

Hello everyone

I have been lurking here for more than a year and have finally decided it's time to start designing a machine of my own.
The machine is intended mostly for hobby use, cutting aluminium but also wood and maybe even a very slowly cut steel part. That being said I try not to have
any unrealistic expectations about accuracy or speed, but i do want to do the best i can within my means.

The machine is designed with these constrains in mind -

• My shop space is very small 5m² (54ft²), so a 100x70cm (40x28 inches) footprint in a corner is all I can reserve.
• In such a confined space dust and chips must be kept to a minimum, so an enclosure is a must.
• The x-axis must run along the short (70cm) axis or access to the machine will be too hindered. So the gantry
  will span be across the 100cm axis which is not desirable but sadly seems unavoidable.
• The shop has neighbors close by so noise should be kept down as much as possible - via enclosure.

This is a rough sketch of the frame. I decided that feedback was needed before moving on.


http://www.mycncuk.com/attachment.ph...id=14027&stc=1http://www.mycncuk.com/attachment.ph...id=14028&stc=1

The tubing is 50x50mm 5mm wall thickness. I am contemplating 60x60x4mm or 70x70x3mm since I remember reading that deflection is related to cross section. Also a NEMA23 stepper motor is around 55mm wide and with a larger pipe it will sit "inside". To keep weight managable I lower the wall thickness as i increase crosssection.
The plates on the back and sides are there to add structural strength and to act as splashguard and enclosure. I have dimensioned this to a thickness of 4mm at the moment in hopes that this will make it less likely to bow and induce deflections in the tube when it is welded. I have not added bracing yet at i was hoping these plates would make up for it, but is this a reasonable thought?

On a whole i know that welding is going to distort everything, but i do feel that the strength is needed for my purposes.
I have not drawn the linear rails yet, but they go on top and will be leveled using the epoxy method.


Any feedback is appreciated.

/Misc

You need to draw in roughly, just using rectangular boxes, the gantry, ballscrews, energy chains, motor mounts, because you will end up with one of two things, a machine with a bigger footprint than you expected, or a machine with a smaller cutting area.

I wouldn't weld the plates to frame.! Brace the frame using normal triangular methods and bolt the sheet/plates to the frame.
This will reduce chances of heat from welds pulling the frame plus be easier, quicker and more flexible regards building enclosure. The bolted sheet will still add strength and allow better access for working on etc. Also you'll be able to dampen the sheet to lower noise and resonance by using rubber gasket between frame and sheet.

Thank you for the feedback, the design has been redone from scratch. I have decided how the gantry should be mounted, but not how the gantry itself should be built. A slim gantry is not easy to design (if at all possible) while also being inflexible.

http://www.mycncuk.com/attachment.ph...id=14052&stc=1
I am planning on adding a center tube to support the middle of the bed in the front.




http://www.mycncuk.com/attachment.ph...id=14053&stc=1
The bed is supported by 3 tubes of 50x50x3 tube in the middle section, the sides rest on a 5mm thick piece of angle iron.



http://www.mycncuk.com/attachment.ph...id=14054&stc=1

Steel tube sizes are as follows

• Green: 50x50x3mm
• Yellow: 80x30x3mm
• Pinkish: 70x70x3mm
• Plates: 10mm Aluminium on the carriages, not sure if i should switch to steel?

At the moment the gantry has 500mm travel are the linear carriages are spaced so they are 230mm end to end, I read later that these should be a minimum of 250mm. So maybe i should widen the gap?

As you can see the wall thickness is 3mm all around, I am considering 4mm to make it stronger; But it is already quite heavy, so is there any parts that will benefit more than others from extra wall thickness?

Looking better but I'm not a fan of ballscrews being up above the rails due to being easy to damage thru leaning on or when loading material etc.

Also if those black things connected to the screws are steppers and your thinking to mount them like that then your in for massive troubles.?
Try to build in some adjustment for things like ballscrews to ease alignment.

The bearing spacing isn't too critical when using twin screws so your size will be fine if it fits better. Thou more won't hurt if possible.

your bracing can be much smaller , as the forces are compression and tension
also try brace into the very corners as this maximize's the strength of the brace , and makes welding easier as there will be even less warp

just a comment :D

Quote:

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Originally Posted by JAZZCNC

Looking better but I'm not a fan of ballscrews being up above the rails due to being easy to damage thru leaning on or when loading material etc.

Also if those black things connected to the screws are steppers and your thinking to mount them like that then your in for massive troubles.?
Try to build in some adjustment for things like ballscrews to ease alignment.

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You are correct, they are 280oz Nema23 steppers. I will change the mount for the steppers to something more "traditional". Is there ready made adjustable ball screw mounts or is this simply achieved by drilling oversized holes for a simple mount?

Quote:

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Originally Posted by JAZZCNC

The bearing spacing isn't too critical when using twin screws so your size will be fine if it fits better. Thou more won't hurt if possible.

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Okay, ill keep it as is for now then.

Quote:

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Originally Posted by Blackrat

your bracing can be much smaller , as the forces are compression and tension

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This makes sense, I will lower the dimensions where possible but since Im forced to buy the steel in sections of 6 meters, so I will change what i can to lower dimensions.

Quote:

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Originally Posted by Blackrat

also try brace into the very corners as this maximize's the strength of the brace , and makes welding easier as there will be even less warp

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Do you mean like this?
http://www.mycncuk.com/attachment.ph...id=14072&stc=1

I was under the impression that this approach would distort the joint more as that small section is subjected to more heat and will also have more weld material causing contraction?