big budget cnc

[pet30]

what are the mistakes?

and do you reccomend someone else's design?

[mekanik]

Hi pet30
Welcome to the forum
I can't see any logic in having your gantry that long the machine would normally have the gantry spanning the shortest width.
trying to construct a gantry that length you are on a hiding to nothing, have a look through some of the build logs.
Enjoy the forum.
Regards
Mike

[hanermo2]

Forget the round rails and bearings.
I tried it circa 2006..

Steel frames, sand for smoothness / non-binding,
increase section sizes 2-5x,
glue in with industrial goops and bolt if you want, ..

For accuracy, a steel or granite machinists reference edge/plate, vertex 1000 mm is cheap to 0.04 mm / m,
sand with wide belt sander to remove most of the bend/curve.
Then assemble/build, with non-binding free-running linear guides.

You probably cannot make a good commercial-level cnc router for cheap --
no-one can.
Look at mechmate. 8-10k for parts.
I will likely make one for a local business for full-sheet 2.5 x 2 m size .. and will charge 20k€ or so.
It MUST have a toolchanger to be useful/profitable.
Likely, it will be horizontal, like the more productive modern CNC machining centers.

Most likely, the 20k€ cost is paid in 1-2 months.

[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?

[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.

[pet30]

Hi pet30
Welcome to the forum
I can't see any logic in having your gantry that long the machine would normally have the gantry spanning the shortest width.
trying to construct a gantry that length you are on a hiding to nothing, have a look through some of the build logs.
Enjoy the forum.
Regards
Mike

i need the gantry to be this way because my workshop( ist at my parents house) and if i go home then my mothers car is parked in the garage so i this way i can still have a cnc .

[Desertboy]

i need the gantry to be this way because my workshop( ist at my parents house) and if i go home then my mothers car is parked in the garage so i this way i can still have a cnc .

3m's is just too long though and you will be creating yourself a world of trouble, there are plenty of machines out there with 3m gantries they are very very chunky and use serious slides the cost of the gantries are far beyond what most of us spend on our entire cnc machines.

If you build it like you suggest it will not work very well at all and you will spend a lot on a frame you can't use.

https://www.kickstarter.com/projects...foot-cnc-machi

This seems like it might be more useful to you although I would never consider this suitable for real production (I thought it looked crap but mate thought it was ideal for a small workshop for occasional jobs.) It might be something that ticks your boxes given the lack of space and tight budget.

There is another choice you could make the gantry 1.5m's and mount the CNC so it folds to the wall when not in use you can get more space and only use when the cars is not there.

You probably don't want to cover your mum's car in sawdust anyway if you still want the cnc machine their in a months time ;)