Build Log for first CNC Router .:|RoboTooth|:.

NastySpill · #1 11th Feb 2010, 11:17 PM

Hi All,
cnczone is a nightmare to navigate, and being a Melburnian I thought I'd post my build log 'locally'. I will be implanting loads of links as I find many people forget that not everyone knows what your talking about. Please feel free to ask me to clarify anything.

For those who have come before me thankyou documenting your work online. I read in initial research for this project that "there is more to it than meets the eye".. bahhhhhhhh what can there be to it, a few motors, a pc interface, and some rollerskate bearings. I'll be done by Monday.

Almost 2 years later I am confident that I am ready. I am embarking on the construction of 'RoboTooth' X slides - 600mm Y-400mm Z~100mm.

I had planned on building 'Joe's 2006' then his R1, I have now settled on his Hybrid 4x4 design, with a few of my own "improvements". I figure he has gone through all the blood sweat, tears and money, so I may as well trust his final design as being the best compromise.
Links to Joes CNC plans 2006 - CNCzone.com-

Here is the hybrid I aim to ultimately build.
Joe's Hybrid 4x4 CNC Router

I paid for the hybrid plans, and then got the Bill of Materials and priced all the components.. Coming in at ~$1300USD + steppers + stepper driver + router + software + a few other things I have not thought of yet.. Thats over $2k I don't have.

So with a budget of $1000 and some scavenging I thought it best to build a mini CNC to learn with, and use that to build a larger machine should I justify it.
Henceforth known as RoboTooth. RoboTooth will be the parent of RoboFang, the full size Joes Hybrid. I aim to make RoboTooth fund RoboFang with some services I will be flogging round these woodwork parts of the intraweb - if all goes well. I have BIG plans for these machines.

What follows is my log of the build and I'll try and provide details for those interested in following in my footsteps.

I have a substantial junkbox of laser printer parts, medical equipment salvage and odds and ends I picked up.. But sadly I have learnt that to do this right it's best to 'buy right - buy once' Only the wealthy can afford cheap components. I do luckily have some very high quality power supplies.

Onto my design.
I cannot recommend Google's FREE 3d application 'Sketchup' highly enough.
Google SketchUp
That is what I have used to model all 5 of my designs. Slowly but surely I have simplified things down to as few parts as possible. My aim is to get operational, then use RoboTooth to 'bootstrap' itself up into a better machine by creating new more accurate parts for itself. A constant self upgrade.

Ultimately RoboTooth will make parts for RoboFang.
One last bit.. tools at hand..
I have all the basic hand tools, a router, circ saw, cordless drill, grinder, welder and ahhh thats about it. I don't plan to use the welder, but it comes in handy. So if you have those tools then you can feasibly follow along and make one yourself.

RoboTooth R2.png

Ugly ehh?

I have some nice furniture plywood handy which will be the majority if not the entire structure of RoboTooth.
I have ordered 4 x 20 sliding bearings from ebay. And have also ordered 2 x 600mm & 2 x 400mm 304 stainless steel rod from Moorabbin Steel.
Moorabbin Steel
I also got a GeckoDrive G540 on ebay for a slight discount. after shipping it was a little over $300. For its features I think its the best value driver around..

So! So far I've spent;

Plywood - free
GeckoDrive $340
Linear bearings $50
ss rod $62
Total so far $452..

I need to locate a z axis. I have decided to lash out on this part and buy a complete assembly.. Then donate it to RoboFang later. On the hunt for a 100>200mm travel ballscrew linear actuator.
The X and Y axis at this stage will be either belt drive or threaded rod.

I hope to be operational in March.

Ch4iS · #2 12th Feb 2010, 01:08 AM

If you can spare a few hundred I believe you can upgrade to ballscrews which are much better. Theres a fella in china who can supply and machine them for you, I dont have his link ATM but I can find it for you if wanted.

Not to put you off building a wood router but have you had a look into using aluminium extrusion, a machine that big you would only need the light stuff and it goes together so much better and quicker.

Im not sure how strong the Gantry sides will be but it looks like you might have a issue with a twisting Y axis with that design.

Single Slide Trucks I believe is really pushing it also.

NastySpill · #3 12th Feb 2010, 07:58 AM

I should have clarified. This first machine is to be used mainly with acrylic and a dremel. Just light cuts. And yes the Y side supports are a bit of a concern, but this'll be a learning testbed.
I know ball screws are the way to go. I may upgrade to those in due course. Are you thinking of the ebay seller 'LinearMotionBearings2008' ?

http://stores.shop.ebay.com.au/linea...__W0QQ_armrsZ1

I figure 20mm dia slide trucks should cope with what I want to do. The side supports may get bumped to steel.

Thanks for looking and for the feedback!
Martin.

NastySpill · #4 13th Feb 2010, 06:36 PM

Chris,
Your right. I just assembled my X-Axis bearing rods and trucks and it could be my sloppy joinery, but it is a bit skittish and prone to racking with just one truck. The sc20uu linear bearing assemblies are not as tight as I had hoped.
I can't tell if the rod is slightly loose in the bearing or if the bearing is slightly loose in the outer housing. I'll pull one apart soon and find out. Hopefully its the bearing in the housing and I can shim or cross drill the body and install set screws.

I have ordered another pair for the x axis and will modify my y axis side supports to allow for two trucks.

Is anyone aware of a suitable minimum ratio of bearing spacing to axis width?
For example my Y axis has a span of 400mm, would a x bearing span of 100mm be enough? Obviously the greater the better, but there has to be a happy comprimise.

I have also bought a KR33 linear actuator to use as a z-axis.

NastySpill · #5 16th Feb 2010, 10:43 PM

Hi,
I've got motion on my Y axis! But the tuning is out and I can't figure it out..

I have a stepper turning a 13mm dia toothed wheel, direct driving a toothed belt. The motor is attached to the y stage.
It being driven by a gecko g540.

So unless I'm mistaken, one rev will give me (d*pi) 40.84mm of travel.

I dont know the spec of the motor as it came out of a laser copier, but will assume its a 200 step. Nema 23 round body. P/N 23LQ-C255-G2V

In MACH3 motor tuning I have the native unit set to mm.

the G540 driver is I believe a 10 microstep. There is no way to configure it in the manual, and the spec says 10microstep..

So 200 x 10 = 2000 steps per rev
40.84 mm travel per rev.

2000/40.84 = 48.971 steps per mm.

When I enter that into mach3 motor tuning then set a very low accel (300) and velocity. (150)

I then enter g0 y 40.84 in the MDI window and expect 1 revolution.. but instead I get 4.5 or 4.7..

I had my current limit resistor set to 1k which is 1 amp. Maybe that was too high and I cooked the motor? It just seems to be getting more and more erratic.

My kernel speed is set to 25,000hz too.

Anyone got any ideas on where Ive gone wrong?

rodm · #6 16th Feb 2010, 11:35 PM

The steppers can take quite a bit of heat. If the motors can still be touched when hot and no smoke is getting out then they should be ok. The resistor only comes into play at standstill and reduces the idle motor current.
Your stepper timing will have to be worked out by the tooth pitch not the diam of the pulley.
In any case if you do this in Mach3 it will automatically set up you steps.
Press the "Settings Alt6" button.
Just above the reset button press on the "Set Steps per Unit" button.
Select "Y" axis and press "OK" button
From here in it is easy to follow. Just mark your Y axis start position on the machine. Make the move and measure how far it travels. Enter that into Mach3 and accept the calculated steps per unit.

NastySpill · #7 17th Feb 2010, 09:56 AM

Great I'll try that. I dont undertand what belt pitch has to do with motor travel though..

NastySpill · #8 17th Feb 2010, 09:57 AM

ahhh a 15 tooth drive with a 1 tooth per mm belt will give a 15mm travel per rev.. ?

rodm · #9 17th Feb 2010, 12:41 PM

You got it.

NastySpill · #10 17th Feb 2010, 01:31 PM

So the motor is getting pretty hot after 45 minutes of testing I wouldnt want to hold my hand on the motor body - its getting up near burning hot. I'll drop down to 500mA.
I tested the resistance of the coils and they are still the same as before I started 3.3 Ohm.

NastySpill · #11 17th Feb 2010, 07:55 PM

Something funky is going on..

I followed the calibration in the settings window, but it didnt work.
i said move 10 units.
it moved 11 mm
i accept its settings.

I reset my ruler so its zero at the side of the y stage.
restarted mach3

enter g0 y10 under mdi
it moved 10mm spot on.
g0 y-10 and it over shoots zero to

.. ahhhhhhhhhhhhhhhhhhhhhhhh
Its a co ordinate - not a shift!

I thought by entering g0 y-10 it would move -10mm.

I'm learning more every day!!

rodm · #12 17th Feb 2010, 10:51 PM

Use G91 if you want to move in incremental.

NastySpill · #13 23rd Feb 2010, 12:09 PM

Even though its in a tangle of wires it is alive!
I did my first route last night with a 130watt Ozito dremel lookalike. I've been so focused on getting this thing moving in 3 axyceciss.. now I need to learn Mach3.. or more realistically emc2.. given my budget and thirst for learning i'll try the later..
Also the demo version of mach3 only allows 500 lines of code which is much less than I thought it'd be.

What I would like to ask for is some guidance on determining feed rate and such. This contraption I built is (photos to follow when my camera charges up) using ss threaded rod, so its slow, but it's just a test bed so I dont care if my feed rates are slow too. I would prefer a nice finish.
Can anyone point me to some good online resources for getting to know the important variables in using a cnc router..

Initially I would like to try some of these "image to g-code" applications.

Can someone verify my approach and let me know if I'm missing anything?

I create my g-code.
Move the cutter to the corner of my work piece.
Set the cutter to the surface of the workpiece
Offset cutter by correct amount in line with gcode
Run.

In that process I am not sure where I define my feed rates..?
Is it in the gcode or in the control software?
If so where?

Also in mach3 where is the estop over ride button? I have micro switches at the end of each axis of travel and have it set as home x++ x-- and so on. So when it homes its fine, but if I drive it to the end I have to switch off the driver, and manually wind it off its microswitch.. which is a pain.
I can't for the life of me find over ride in mach3..

rodm · #14 23rd Feb 2010, 12:44 PM

Click on the setting button in Mach3 and in the left hand column there are the override limits controls.
You seem to be jumping between EMC and Mach3 which might confuse you.

You are nearly there on the process. The cutting tool offset should be calculated in the Gcode. Imagine you are cutting a box. If you just set up your machine for a cutter offset on one side then when it gets to the other side it will be a full diameter of the cutter on the inside of the line. I might have interpreted you wrong there.

Feed rate is in the Gcode
eg F600 sets the feedrate at 600mm/min if your control software is mm native units.
It will remain this speed until you issue a new F rate.
Rapid moves ( G0 ) override feed rate.

NastySpill · #15 24th Feb 2010, 09:54 AM

Thanks again Rod.

I am using mach3, but once I setup my pc to dualboot into linux (which i know isnt difficult) I'll have a try at EMC2.

So I did a little reading on feed rate calc last night as a distraction from staring at the cnc go back and forth aimlessly.
Speeds and feeds - Wikipedia, the free encyclopedia
I have what appears to be a 2 tooth climbing end mill bit in the dremel - it came with it.. It is a straight shank directly into the collet so I think it'd be ~3.2mm dia. What would a reasonable chip load be?
It seems I need to know that to get a feedrate. All the others can be guessed or estimated.
I'm thinking somewhere around 0.05mm ?