i'm new to CNc, and i need help

[acontia]

hi all

i'm new to CNC milling, but i'm really keen in making a machine.
i'm not quite sure what are the important things i'll need to get everything going and working as a whole.

so far i've completed my X and y axis and will be doing the z axis soon. i've also ordered the stepper kit from hobbcnc and should get it in 1-2weeks time. the machine is mostly aluminium, stainless steel for bolts and nuts and also some acrylic parts. everything is hand made so far cuz will need this machine to cnc my future project if i can get this first unit to work.

the Q in my head now would be.... how does the machine know the x,y, and z limits and how do i calibrate it?? do i need to put in switches to stop the movement of all the axis limit.

is the alignment of the rails very critical? so far the x and y axis are smooth but not sure if it's smooth enough. if i tighten all the screws for the rails and support then it feels a little off but just a little.

sorry to sound so daaaa, but i'm really in need of some answer.


cheers

[widgitmaster]

Limit switches send a signal to the controller, then the controller knows when to turn off the motors.

When setting up the software, you tell it the thread pitch of the lead screws. That is the calibration.

Alignment is critical only if you want to make true square parts! If the alignment is off, then:

The axis slide will bind or have tight spots causing lost steps from stepper motors.
The machine will only produce parts as accurate as the machine its self, so making it right the first time is my 1st choice!

If this is your 1st machine, consider it a learning experience for the next machine and have FUN!

Eric

[acontia]

widgitmaster

thanx for the advice!

so in actual fact, u don't really need limit switches and can get by if the machine is calibrated correctly from the start and those limit switch is there for safety reason or more like a fail save????

if the alignment is off by just a bit then work piece may be off a little too.
it will also put load on the stepper motors. so can i say that if i i'm slightly off on alignment, then a higher/powerful stepper motor of at least 200oz might be able to compensate for the difference...

i'll try to post some pics when i go back to the workshop at work and finish up the rest of the machine.

Ho

[acontia]

this are some of the pics. still have some issues with the gantry rails...too flimsy, (need to change to a longer blocks) will never do any solid work. well............ i'm learning as i go along.





here's the z-axis




will post more updates.

pls give me advice as i really need it.

[widgitmaster]

Originally Posted by acontia so in actual fact, u don't really need limit switches and can get by if the machine is calibrated correctly from the start and those limit switch is there for safety reason or more like a fail save????

If you use Servos with encoders, the controller knows where the spindle is, but stepper motors without encoders have no way of knowing exactly where the spindle is other than by counting steps! However, if there are lost steps due to binding, or too heavy a cut, the controller still thinks the spindle is on target, until it slams into the end of travel!

So I would suggest the use of limit switches with steppers!
They can be magnet, or proximity, or micro switches!

Eric

[acontia]

Originally Posted by widgitmaster If you use Servos with encoders, the controller knows where the spindle is, but stepper motors without encoders have no way of knowing exactly where the spindle is other than by counting steps! However, if there are lost steps due to binding, or too heavy a cut, the controller still thinks the spindle is on target, until it slams into the end of travel! So I would suggest the use of limit switches with steppers! They can be magnet, or proximity, or micro switches! Eric

widgitmaster

got it!!! i'll go with micro switches.

where and how do i hook up encoders to intigrate with those stepper motors.....

do those kits from hobbycnc come with it, or can those be incorporated into them??? (i mean the encoder incorporating into the hobbycnc kit)

cheers

[widgitmaster]

Sorry, electronics is not my specialty!
I have been told the stepper motor controllers do not support encoders, so you may not be able to use them!
Don't know how accurate this info is!
Eric

[acontia]

the hobbycnc stepper kit got stuck at the airport customs, so will have to wait for now

here are some updates!

i redo the gantry rail.



this would be the y-axis top made of acrylic.



i'm using wing nut to hold down the work pc



2 sets wing nut, and will add on an angle bar across both



will do more updates when available.

pls feel free to give suggestion, i will need it.

cheers

[Lionclaw]

Looking good Acontia. The acrylic is really a nice touch. Almost makes it look like a piece of furniture

One thing you might consider is adding a second set of bearings on the long axis and creating a bit more structure, sort of like a half A frame on each side, to support the gantry. There are other 8020 builds around that use this, but I don't have links off hand.

[Rance]

Acontia,

[still have some issues with the gantry rails...too flimsy, (need to change to a longer blocks) ]

Looks nice but I notice you seem to only have two bearings for each axis. Longer blocks won't do any good unless you add two more bearings, and they need to be separated. This counteracts the leverage of the moment arm you have in your gantry. Wish I could point you to some good pics. You could look at http://www.cnczone.com/forums/showpo...8&postcount=22 to see a little of what I'm talking about with the separation of the bearings.

Keep up the good work.

Rance

[acontia]

lionclaw

rance

i wanted to do just that, but thought i could save $80sin for two sets of bearing.....well i will go get them today and hopfully fix them on by this weekend including the stepper kit.

thanx a million guys

[Lionclaw]

I know how it feels. I'm just barely scraping my way through college, so I try to skimp as much as possible where and when I can.