[Vilyoo]

Hello everyone,
this is going to be my second machine, way bigger than the frist one. I want to see ur opinions about the design.

I dont really like the Z axis, can u check it? both plates are 30mm aluminium. Maybe steel would be better but im not sure if more weight is good? What about Z version 2?

Main frame weights 1200kg Tube 250x150x10 and 150x100x6mm
Gantry with Z is 300kg
working area is 2500x1500x250mm.

Im going to use helical rack with M2.5, For pinion they have 22, 24 or 26 teeth. . I can put bigger rack they are pretty cheap if it helps. X and Y cars are 30mm.

for motors i think 12nm closed loop steppers direct attached to the pinion 1:1 without belts or gearbox.
Spindle... 5-6kw 18-24k rpm
Controller mach 3

The machine will be used mostly for wood and some aluminium. The whole frame will be machined on a big cnc.

What about the distortion after welding? I dont have access to big oven to heat it. I heard about vibration stress relief, how to do it?

Any help appreciated.

[ardenum2]

in theory its simple, you need a vibration motor, which is a motor with an uneven weight attached to the shaft and you need to achieve resonant frequency of the welded part and keep it there. in practice its much harder and I don't think it's ever been done with a self made equipment. you'd need a bunch of sensors(maybe accelerometers) to measure frequency that's being generated and you'd need to know what frequency to hit(via FEM), then there's the question of amplitude(no idea about this one)

https://en.wikipedia.org/wiki/Vibratory_stress_relief

[Vilyoo]

I also heard that i can put the frame outside for 1-2 months on rain and sun, that way it will also stress relief a bit.

[ardenum2]

whats your budget? maybe you could buy something like this eg.

https://allcncrouter.com/collections/cnc-router

[Vilyoo]

budget is 10 000 euro but i prefer to make it

[ardenum2]

budget is 10 000 euro but i prefer to make it

without stress relief you're going to run into all sort of problems with a twisted frame, how much of that budget is the machining price?

[Vilyoo]

without stress relief you're going to run into all sort of problems with a twisted frame, how much of that budget is the machining price?

They will machine it for 500$

[peteeng]

Hi Vily - Leaving steel outside won't stress relieve it. It will go rusty and that's all. You can leave cast iron and some aluminums to natural SR as there is ongoing metallurgical changes going on that helps with the SR. But its faster to do all of this in an oven hrs vs months or years.

You can take the punt on welding then machining. Lots of people do that. If there is enough material allowance you can take away small amounts at a time and then release the part from the mill then measure it and see how its going. You can also braze weld it and since the parent does not melt/solidify it would not need stress relief. Brazing can be with a TIG torch or an oxy torch and a bronze rod. If you laser welded it I doubt it would warp. You can bolt it all together so you can adjust parts as you go. Friction is a good damper and 1000's of structures are bolted together. Ard is bolting one together at the moment and it looks solid...

Regarding VSR you would need to work with someone that has the right equipment so you can measure the frames response to the vibration and then you know its relieved. $500 seems cheap, if they are that cheap consider billet machining parts like columns and bracketry and Z axis. If you have to put it in a machine to finish machine it you may as well billet it. Billet machine in aluminium as it machines faster... Easy to get a price to compare. Peter

[routalot]

That looks like a very rugged design.What are you planning to machine with it and how are you planning to hold the material in place?Many of the problems will disappear if you can be certain that the two longest rails (X or Y as you have selected) are totally co-planar.If you use a spoilboard it will be machined flat relative to those rails and any bumps or dips will be removed.If you are intending to use zoned vacuum you may need to design a bit more detail of the plumbing arrangements and perhaps relocate some of the bracing.I suggest you also add some trays for the drag chains to the design to give a fuller idea of the space required.If you have plans for a tool length sensor,and they are a very good thing to have,you might give some thought to where it might be located.

Will you build a control cabinet or will the hardware be located under the table with a connection to a computer that is not too far away?

[Vilyoo]

Thank you Peteeng, I will read more about braze wielding, I think this will be the easiest. Do I need to do all joints like this or only for tube to tube conection.

Hi routalot, I will use the machine 99% for wood. But I want it to be able to make shallow cuts in aluminium or even steel if it is possible. I think to make holes and threads on the 5 steel sheets on the top of the table.

The electronics will be in an enclosure under the table, and connected to pc near.


I'm not very big fan on rack and pinions, what do you think for ballscrew 2800mm long 2510 for example. With normal nut, not rotating nut. I can add support in the middle for the screw so it will not bend much.

[peteeng]

Hi Vily - 2.8m will be far too long for a D25mm screw. It will vibrate horribly even supported in the middle. Have a look at the Hiwin ballscrew design manual. They publish eqns that predict this sort of thing. Use helical R&P not square cut and you will be much better off. I'm about to make my first R&P machine similiar size to yours. But it is a lengthways machine so the gantry goes along the machine not across. So the gantry is nearly 3m long. This is so the machine can be front loaded easily.

All connections that you would normally weld can be braze welded... You need a good oxy/acetylene torch or big tig welder to do the heavy runs on your machine. Peter

Also you can use silicon rod wire in a mig welder. Make all your fits tight...

https://youtu.be/fvR2q-NuZB0

[ardenum2]

They will machine it for 500$

that's a great price, is the company in europe by any chance?

[peteeng]

Hi Vily - To answer your Q's. I'm up to version 11. Plus some unofficial versions! I mucked about with the conventional arrangement for quite a while and decided the technical stretch of the long gantry on walls was worth the shot vs the conventional short gantry on columns. V11 is still really a visualisation model not a detailed model. I have started building the bench's, one more to go then onto the machine base. I have been playing with UHPC (concrete) and want to build the saddle out of this material. The walls maybe lightweight concrete. The rest will be laminated plywood and aluminium. I have found this sandwich to be very stiff and damp & I can easily machine it on my medium sized router. My last machine was made mainly from plywood & Al laminated on plywood & it cuts aluminium/plastic/timber easily. I've also decided to make the machine base in one piece vs the three pieces as shown. Various elements have come together in my head and now I have to get them into CAD then build it!

One design rule is that it has to be able to be assembled and disassembled by myself (or a person) and no part can be over 45kg... This drives a lot of choices... Peter

[Vilyoo]

Yes in bulgaria, actually 500$ is a lot of money for my country. Almost one average month salary.

Peteeng: interesting design..

[ardenum2]

Yes in bulgaria, actually 500$ is a lot of money for my country. Almost one average month salary

that's a much better situation than here in germany $5000 for machining but that's 4x the average monthly income.

[ViS-motion]

If you constructively make it so that there are only closed structures and do the welding correctly and you do not need high processing accuracy (0.0001 mm), then annealing will not be required.

[Vilyoo]

Actually I would be happy for 0.01 to 0.02mm accuracy of the machine

[ViS-motion]

Actually I would be happy for 0.01 to 0.02mm accuracy of the machine

To be honest, it will be very difficult to achieve a movement accuracy of 0.01 mm on this machine. And when processing will be even lower accuracy. Because you still need to remember about the coefficient of thermal expansion at such lengths.

[peteeng]

Hi Vily - You need to understand what "accuracy" is. +/-0.01mm accuracy means that the machine can go to anywhere in its envelope and be within that spec. For a hobby-built machine this is quite a mission. It means the final machining must be done to better than 0.001mm and all motion components must be good to better than 0.001mm over its length. This means very high quality and precise parts are needed. Repeatability maybe good at 0.01mm but accuracy is another very large rabbit hole. Is this a commercial machine or a hobby machine? Peter

[Vilyoo]

It is for hobby use, after a bit thinking, 0.1mm accuracy through out the whole area would be perfect for me.