DIY VMC Opinions

Hey guys,
What are your thoughts about this build?

The workspace is 300x250x250mm. I would use 20mm linear guide on all axes (how strong precompression?) and 20mm 5mm pitch (2005) ballscrews with antibacklash nuts on all axes. The plates would be rotary ground steel plates. The Y axis "holder" would be filled with epoxy granite mix. Planning to use ER20 watercooled spindle. The motors are nema 34 servos.
Do you have a reccomended spindle or different collet type?
What should I improve on the design?
What controller should I use?
I attached the pics.

It desperately needs some diagonal bracing to prevent the uprights flexing under load.It also seems considerably overpowered with those NEMA 34's,they will just bend it further and faster than a more modest motor.There are some apps out there for Android phones that will calculate the force generated by any motor you specify with the thread you select.I suggest you run the figures and see what kind of force you need to accommodate.If the CAD package you use has a FEA capability,run it to find the weak points with that kind of force applied and then improve it.A couple of tubular steel braces will almost certainly cost less than five or six buckets of epoxy based filler and will take less time to have ready-once it becomes clear where they are needed.

Google VMC frames and have a good look at them.

Look at rail spacing, proportions etc.

Nothing should be a flat plate.

To be blunt, your design is going to be very weak. Start again.

I made a second version, what do you think? It has a 400x300x400 work area. X axis would be about 80kg
The X and Z axis looks waay better, but I'm not sure about the Y axis. Maybe I should made it into a Y shape or maybe I should reinforce the back of it too?

I think it needs to be shown when you are ready for our comments and it isn't visible at present.

sorry, for some reason it didn't upload it. Here ya go

Don't build that.The upright part looks absolutely massive and yet has no lateral support and the height increases the leverage from lateral movement.The extreme length of the spindle mounting bracket gives a high torque loading to the base of the upright and the lower web of the motor mounting bracket may well foul the piece being worked on if you need to produce a deep feature on the side away from the column.It does look like some of the components are now of a size that will give some rigidity,now you need to go through the rest of the mechanism to bring it all up to that level.

If I improve the Z axis, the upright part and the mounting bracket it would be okay? Do you have any good idea how to mount the spindle to the upright part? It is about a 210mm long section.

My reaction is that if you are seeking the challenge of building a machine,you have made a start on the process.There will need to be several more iterations before the design is able to meet your expectations.Did you calculate the force that the leadscrews will generate for the motors you wish to use?I have doubts that the construction you are proposing will maintain is shape under even a quarter of that load.Additionally,high speed machining of aluminium is a specialised field-do you have experience of it?

If the intention is to make components,rather than the intellectual challenge of machine building,I suggest you buy a benchtop mill and equip it with steppers as the machine will have the rigidity and will have been made fairly accurately.If you were to really go to town and add ballscrews,it could be a very useful thing to have.With the advantage that you could use the machine in manual mode to make the brackets and other parts you might need.

I did some calculations and I based most of the drawing on that.
Its more of a challange to myself as I have access to other bigger mills. A conversion seems to easy for me :D

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Originally Posted by routalot

My reaction is that if you are seeking the challenge of building a machine,you have made a start on the process.There will need to be several more iterations before the design is able to meet your expectations.Did you calculate the force that the leadscrews will generate for the motors you wish to use?I have doubts that the construction you are proposing will maintain is shape under even a quarter of that load.Additionally,high speed machining of aluminium is a specialised field-do you have experience of it?

If the intention is to make components,rather than the intellectual challenge of machine building,I suggest you buy a benchtop mill and equip it with steppers as the machine will have the rigidity and will have been made fairly accurately.If you were to really go to town and add ballscrews,it could be a very useful thing to have.With the advantage that you could use the machine in manual mode to make the brackets and other parts you might need.

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I made a "few" modifications here and there. What do you think about this? The new workarea is 500x300x400mm.

Much much much better.

Base is too thin. Looks thinner than column?

Put the y axis stepper behind, hidden below column.

Yes its thinner, because I didnt design the table yet that it will be sitting on. The base will be about at least 2 times thicker than now.

The stepper is a good idea, I dont know why didnt I think about that :D

That version is looking much better.If you added a mounting bracket to hold the transverse stepper off the ends of the ways it would give a larger work envelope,assuming the workshop space allows and the extra length of ballscrew is a comparatively minor expense compared to the entire project.The steppers only need to resist torque and support their own weight.

From my experience 20mm rails are quite fragile, I'd opt for 30-35 size from some high load series, they dont cost much extra until you get to size 40.
Also for DIY I might suggest macing column hollow and fill it with concrete, since casting most likely is not available for you

Fill it with class C CSA grout.

That bracket is a quiet a good idea, i will design one in a few days.
As for the linear rails is it worth going for a 30mm?
The column will be a welded with 14mm thick laser cutted iron, the inside will be filled with granite epoxy, as the whole machine would be from this it would be a lot easier to buy a few more kg of that.