big budget cnc

[pet30]

and if i was to change the gantry to 1600 mm so just flip the design?
could i then use ball bearings etc?

is not my fulltime job , i make kitchens etc after hours. so the machine do's not need to get super fast speeds.

and could i use the same system as this machine? he uses rack&pinion and round rails


http://www.rawcnc.com/

[hanermo2]

Strength is not the issue.
Rigidity is.

All machine tools are loaded, at max, to == 2% of their strength ie yield point.
Machine tools today are lightly loaded stressed-skin structures.

You can make a router with the ball bearings, and it will work. Yes.

It will not be productive vs others, and cannot use modern carbide cutters, due to flex/vibration/chatter, effectively.
Your proposed solution will work fine at 5-10 ipm, feed, where real machines run 100-200-800 ipm.
So about 20x less productivity.

[Ger21]

It will not be productive vs others, and cannot use modern carbide cutters, due to flex/vibration/chatter, effectively.
Your proposed solution will work fine at 5-10 ipm, feed,

This is 100% not true.
Do not listen to Hanermo, who tells everyone that they need to spend $20,000 on a 10,000 lb machine.
I built a machine 13 years ago, out of wood, using skate bearings on round pipe for the linear bearings. It still runs today, and I can cut at 200ipm, with carbide cutters. With better motors and drives, It could cut much faster.

Having said that, your design does have some serious flaws.

Not sure what material you plan on building from, but it looks like a simple aluminum tube?
If you want to use 80x160 for a gantry, it really needs to be a heavy extrusion, not just a tube. That tube you have modeled will easily flex and twist.

While skate bearings can be made to work, there are some things you need to be aware of.
They need to be in very tight contact with what they are riding on, in order to have a rigid structure. And on a flat surface like that, they are not very tolerant of dust and chips, and will bind if dust builds up under them.
You also are only showing bearings in one direction in each carriage. You need additional bearings to constrain the carriages in the other direction.

This is a very large machine. It's easy to build a fairly rigid small machine. But as the machine gets bigger, it gets much more difficult. Everything needs to be bigger and stronger, to achieve rigidity. And rigidity is of the utmost importance.
I think that you will be very disappointed if your first machine is this large. I would recommend building a much smaller machine, which will teach you where you need to improve your design. If you build something similar to what you've shown, it likely won't be worth upgrading in the future. Build a small, inexpensive machine to learn with, and a larger, more expensive machine when you can afford to.

You can not direct drive the pinion on the stepper shaft. you'll have poor resolution, and not enough power.

[Desertboy]

Morning, do you have a budget in mind for this?

[Boyan Silyavski]

Your idea is riduculous. Be realistic and prepare a budget of 6k for simple machine this size or better 8k for a Ferrari

Just copy my second machine and it will do whatever job you throw at it. No need for the heavy duty Z, just 3kw spindle. I have plans for it that i sell to people that know what they want and i offer one to one support for the build.

Tool changer is not needed for kitchen jobs and it costs 3k at least and you need a controller that could do the job.

20k machine will NOT pay for a month. You need to have factory and at least 10 people working for you for that to happen. But then you will not be looking at DIY machine, right.

Maybe a second hand machine around 10k is better for you and will start making money at day 1. You will need 1/2 year at least to build your machine, even if you have the detailed plans of my machine or any other. Its not a one day job. Most people here like what they do and its their hobby, side business or similar so they take their time. Even if i have all pieces i will need a month to build it.


That may answer all your questions. And yes, crappy machines not with proper linear bearings will make you pull your hair off and will be total waste of time and money. MONEY.

[Greeny]

Hi Peter,

If you cannot stretch to linear rails at the moment, you might like to have a look at mechmate design.
http://www.mechmate.com
http://www.mechmate.com/forums/index.php
I'm not necessarily saying use the whole mechmate design as its a little dated, but it has a lot of features you describe in your initial post.
Lots of info for making roller bearing rails, rack and pinion, and other stuff

Personally I would always keep the gantry as short as possible. 3m will offer huge challenges.

Cheers

[pet30]

the beams are 160x80x5 mm steel
they will be perfectly flatten at a machine shop not far.
then i wanted to put a flat steel plate of 120x5 mm and on the 2 side beams so the bearings can ride on this.
on the bottem of the flat bar ther will be 2 bearing that are pushed against the flat bar with a spring so its really thight .

the steppermotors would be nema 23 directly to the rack ( the rack is bolted to the flat bar on its side) and behind the rack ther would be a bearing so the gear can't jump a way
what do you think or what should i change

i was also thinking of using the mechmate V groove rails etc instead of the ball bearings.

[Davek0974]

what do you think or what should i change

Your issue is going to be that massive 3m gantry beam - even at 160x80x5 it will flex and twist like a bitch.

Then there is weight - that beam will weigh about 55kg before adding motors, spindle, guides, motion etc - two nema23's will not do unless you add some decent gear/belt reduction - this will be a slow machine, this size stuff is servo motor territory i feel.

To stop the beam sagging, you add triangulation - a support from end to end raised in the middle and joined with a strut, this will not stop twist though and all this will add weight, I would guess a working 3m beam gantry would weigh in at around 200kg or more - this is silly and would mean using Aluminium to build it.

I'm not bragging on you here - just trying to save your money, i've built some dodgy small machines in the past but nothing this big ;)

[pet30]

no problem thanks for the help

i know this is not easy to build but i think ist the only way i can have a cnc in the garage.

if i was to change the machine 90 °( making the machine 3 meters long and the gantry 1600 mm long) could it work then?

what do you mean with :
you add triangulation - a support from end to end raised in the middle and joined with a strut, this will not stop twist?

and how hard will it drop and twist?
if the cnc is accurate to about 1 mm on the 3 meter then its ok i can live with that
i am using it for shelfholes( 5 mm holes like ikea cabinets) and making some MDF doors , some holes for blum hinges etc.

[Davek0974]

Yes make the gantry 1600 and things get much much easier.

I think for a router you will still possibly need 2:1 reduction on the drives though if using rack/pinion, ball screws would be ideal but much more money.

Triangulation - draw a long thin box - this is your beam, now draw a triangle on top spanning end to end of the beam, from the apex draw a vertical line down to the beam. You now have a box with much more vertical rigidity, triangles are very strong when used right. The trouble is this will not stop twist - you will not stop twist with a single beam that long - it will need two parallel beams with the spindle/z axis mounted between them, this will be very sturdy but 2 x heavier - there is no free lunch here :)

I doubt you will achieve 1mm tolerance in the middle of a 3m beam, plus you have lift - when the cutter plunges into the wood, the beam will lift causing tapered cuts etc.

Big machines need lots of design i'm afraid, and lots of money to make them work.