4R8's table build

[4R8]

This isn't posted anywhere else of yet so you guys are the first to see it's progress. *****Edit: Now on BegginerCNC.com*****
I'll update this thread over the next few days to catch up on the details and parts.
Doing it this way will hopefully spark some discussion and questions on the components built/machined/used.

Always open to suggestions and criticisms so feel free to chime in with any ideas or clarifications.

For now I'll start of with basically where I'm at with a few components and reasons for the direction I've taken.

Basic details:
-The table is 5x5ft using 425oz Nema 23 stepper motors with reduced ratio (5mm pitched HTD timing belts and pulleys @15mm wide) the is a dual drive on the Y-axis meaning both sides of the gatry are driven together.
-The table surface will be slatted with a water tray beneath and holding tank below. The table height itself will be height adjustable on the odd occasion an object taller than 50mm needs to be cut. This also allows me to add a rotary axis down the track and store 4x4 sheets below, above the tanks.
-I'll be using Mach3 for the control software, SheetCam for the CAM (licenses already paid for) and various programs for the CAD depending on application.
-Torch height control will be taken care of via CandCNC.com's MP3000.
to increase cut quality and lower collisions / torch dragging during thin sheet warpage. it also means the table surface doesn't need to be 100% level.
-Magnetic breakaway for the torch mount is to be used in case of a collision to minimise / remove risk of damage.

So...... this is where the table sits at the moment





P.S.
Don't mind the mess, I currently also have my brother building a car in there so space is of a premium!

[4R8]

I started of building the side frames, they use 50x50x4mm SHS uprights and 40x40x2.5mm cross pieces, these were than filled with 1.6mm sheet. being all butt joints, keeping them square was easy.



The top rails and support channels were then drilled and tapped where required. The channel is used to hide / protect the motors and gear racks, more on that later.



Next the V rails were drilled



at that stage, i was pretty much over drilling holes but wasn't even half way through. Still had to drill and tap the sandwich plates between the v rails and top frame rail, another 120 holes to drill and 90 of those to tap. see the pics in the first post for details, Ther'ee be a closeup in a future post.

[f350ca]

Looking good.
When you say the Y axis is driven from both sides, does that mean two motors?

[4R8]

(11-13-2012, 10:31 PM)f350ca Wrote: Looking good.
When you say the Y axis is driven from both sides, does that mean two motors?

In this case it does.
There's basically three options for the Y, all of which have their pros & cons.
1: single side drive. Cheaper on the electronics & easier to setup once built but lacks rigidity and risks of wobbly cuts during direction changes when cutting at the far end from the driven side. Also requires a bulky driven end which means rails on that side longer than the usable table space. Usually ends up in a gantry heavier than other designs to try build in the required stiffness.
2: both sides driven with one motor. Again cheaper on electronics but requires careful planning to include a method of supplying drive to both sides, usually by a shaft or center mount, dual shafted motor driving a shaft to each side. Depending on design, this can lead to the lightest assembly but can be a pain to setup square to the X-axis.
3: Both sides driven and having a motor dedicated to each side. more pricey to build in most aspects, generally slightly heavier. However can be setup to Automatically Square itself when the axis is sent "home", is rigid and doesn't require a means of transferring drive to the other side.

As you'd already be aware of there's also the option of direct drive- cheap and nasty, reduction belt assembly- mid price and tuneable swapping pulleys, finally gear reduction drives- simple but pricey for minimal backlash.

[4R8]

Ok, up for my next shift of newborn care. 6 weeks old and still has day/night mixed up.
The partner sure is glad I'm in a position to have 9 weeks off!
It's currently 1am and the poor little guy has a runny nose and a slight cough

Next installment of build.
Here's a couple of pics of the torch breakaway mount so far. I wish i took a few more pics during it's construction. I've got a few countersunk rare earth magnets which i still need to be epoxied into the back once matching pockets are milled. The magnets i have may be a little strong so i need to wait for some smaller ones to arrive. The idea here is to epoxy them in with the counter sunk face being open, these faces will the locate over some button head screws bolted to the tool plate. In the event of a torch collision, the torch and mount will come away from the tool plate without torch damage. It'll then be a simple process to re-install as the assembly will self locate over the button heads.

Well that's the theory......

A shot mid way through parting off the clamp, I wish i had a thinner parting tool capable of the depth required of an interrupted cut.


I basically started with a chunk of 65mm aluminium, grade unknown. which was bored across it's length, a flat milled on one side to aid in clearance later, and a large chamfer milled on the opposing side.
It was then place end up on the table so the clamping holes could be drilled and counter-bored.
Once finished on the mill, it was placed in the lathe, the end chamfered and the cap parted as per the photo above.



I'll probably shorten the base once I know what magnets and how many of them will be used. I'm also contemplating the idea of mounting a cut-off switch inside a pocket for protection in the back, while making the whole unit "plug 'n' play". The switch type and size may determine how much length is required. This is the reason, the whole base hasn't been milled flat yet and is only roughed out.



I hope all this makes sense

[4R8]

now, computer, console and electronics so far? or a bit on the drive next?

feel free to ask for further pics and clarification.

[Mayhem]

(11-14-2012, 10:13 AM)4R8 Wrote: now, computer, console and electronics so far? or a bit on the drive next?...

We have to choose? Bugger that - post it all Jason, post it all!

A micro switch in the base to cut voltage to the torch would be a good idea, as you don't want the torch to still be cutting if it breaks free. You would need to ascertain what effect (if any) the magnets would have on the switch.

[4R8]

(11-14-2012, 10:14 AM)Mayhem Wrote: We have to choose? Bugger that - post it all Jason, post it all!

But the longer I drag it out, the more time i have to make progress to show, otherwise there'll be a loooong period without updates.

Well that's how I justify it

(11-14-2012, 10:14 AM)Mayhem Wrote: A micro switch in the base to cut voltage to the torch would be a good idea, as you don't want the torch to still be cutting if it breaks free. You would need to ascertain what effect (if any) the magnets would have on the switch.

Indeed. I had thought about that but thought I was over thinking it. I guess it'll be an easy test offline prior to any machine work to see if there are effects on the reed.

Also need to install some form of retaining strap or cable to stop the torch dropping into the water table Probably a short bit of stainless cable?

[f350ca]

Great explanation on the Y axis drive. On the two motor drive how does it self square? against limit switches .
Hadn't thought about needing a breakaway on the torch, will the motors your using develop enough force to do any real damage?
Your light years ahead of me on the build so carry on in any direction you want, we need to know it all.

[4R8]

the Y axis is essentially using two axis's (what's the plural of axis?) rather than a single signal being sent.
In Mach3, you slave the A-axis to the Y. During normal operation, the 'A' receives the same signals as the 'Y'.
As you guessed though, when homing, each axis gets driven until it reaches it's own respective home switch. Using quality, repeatable switches is a good idea here.

A breakaway isn't (IMO) a true necessity but is a good piece of mind. Many people run successfully without one. For me though I'd rather control the risk as replacement Hypertherm parts are bloody expensive! Not to mention fairly scarce in Aus.
I'll just be using a hand torch for the time being which isn't as susceptible to damage as it's protruding parts are short from the mount. I plan on updating to a dedicated machine torch in the future which when mounted will have more length protruding, meaning easier breakage. If I don't build the option now, my history says, I never will.

It'll be interesting to see if I manage to get off my butt once the table is done to properly paint, powdercoat and anodise the parts rather than run it as is