marker pen driven over an 8x4 sheet help.

[JAZZCNC]

Is this possible ?
What should i buy?
Can i make this happen on a shoestring?

Nobody can truely answer this accurately without knowing the length of the shoe string.!! . . .If your thinking £300-£400 then forget it it's NOT do-able and don't let anybody tell you it is because there just pissing up your back.!!. . . . but . . . If you set a sensible realistic Minimum budget of around £800 - £1000 drivers etc but NOT PC or software then yes it's easily do-able.

Like Jonathan says timing belt driven machine will work out the cheapist option to do what you need, but he's wrong(Sorry jonathan) about the resolution not being a problem with belts.! . . I've built a few belt driven machines to do similiar light weight jobs (cutting out Hypalon for RIBS) and without gear reduction the low resolution becomes a problem with tight radius and medium to intricate detail work.
The problem without reduction when cutting/drawing small Radius,circes etc or intricate detail the feeds needs to be low otherwise the corners get clipped and because of the high effective pitch using direct drive it makes the motors work in a low speed range they don't like. This cause's them to run rough also because of the Low resoulution the action is jerky.
The amount of reduction will depend on the diameter of pulleys used but from expeinece at least 3/1 is needed to be usable and keep the motors working in nice range they like.

Must say thou if your going to the trouble/expense of building a machine then it's a absolute no brainer to let the machine cut the plywood rather than draw it.? . . . Belt drive will easily be upto the job of cutting ply wood if a decent design and job is made of the build.

[Danny]

Hey thanks for all the good feedback, my shoe string is around £500 quid at the moment ,

The reason for pen plotting is because the type of shapes i am interested in cutting are to be faired on the job (clinker boat planks).

Being able to draw on an 8x4 accurately has great DIY potential for allot of budding designers, you also have the option of plotting on paper laid onto the sheet, this then allows accurate patterns for cutting out all kinds of materials, im an upholsterer by trade and have sewn up anything from car headlinings to tents, boat hoods bla bla , i work in the furniture industry where allot of money is thrown at big cnc kit often burdened by service contracts and sytem updates, cat and mouse situations with sofware compatibly, Journeymen asking why they cannot just pick a hand tool up and crack on happens too. extraction of cad patterns and lines into the real world is more the issue for me, i can see low a cost cnc plotter going into all kinds of projects and small business solutions allowing the craftsman not be be burdened with the chance of
measurement mistakes.

Funny enough i have too considered image projection but came to the same conclusion about scaling and accuracy.

I have one last idea id like to put forward that may keep the cost down if only i knew how to achieve it , how about a small robot plotter that runs over the surface on a sheet , although you would have to lay you sheet down it would perhaps be compact and portable! so the sheet could be anywhere temporarily , onsite cnc plotting for builders shop fitters now there's an idea!
Printing out detailed lines onto floors..

Could i convert an old scanner to move and draw lines perhaps.

Thanks guys for all the advise, its good to purge the mind of mad ideas!

[Jonathan]

Minimum budget of around £800 - £1000 drivers etc but NOT PC or software then yes it's easily do-able.

This is only 2D or 2.5D so the free version of Cambam should be fine. I used it a lot.

but he's wrong(Sorry jonathan) about the resolution not being a problem with belts.! ... the low resolution becomes a problem with tight radius and medium to intricate detail work

I meant not a problem with belts for a plotter, but if you've done a plotter and it's wasn't then fair enough. There was a plotter at school we dismantled that was belt driven without further reduction...and the rapid prototyper, laser cutter.
Hmm, a cheap low power laser to burn the outline into the wood would be a snazzy way to do it! Might be easier than finding a pen that'll work consistently?
Given these parts seem to be for a 17' boat/canoe (?) I doubt there's going to be many tight radii or engraving! But still there's no point theorising unless we actually know, and it's clearly better to do it as well as you can afford to start with.

[JAZZCNC]

I meant not a problem with belts for a plotter, but if you've done a plotter and it's wasn't then fair enough. There was a plotter at school we dismantled that was belt driven without further reduction...and the rapid prototyper, laser cutter.

Yes on small printer type plotter this would probably be fine because of the small Diameter pulleys but on a machine this size the diameters get large so obviously the circumference does giving a very large pitch.!
Take for instance a 20T pulley which really for 8ft machine is about as small has you'd want to go then direct drive pitch is 97mm. . . . . It's bit like putting F1 engine in a dumper truck, it will carry what ever you want and go like fuck but the bastard won't stop or go round corners. :dance:

[Jonathan]

You could try the method where the board is supported with it's longest edge on the floor and a cable, up to 8+4=12' long supported at the top corners with a motor and pulley. The pen is suspended in between, so the cable makes a V-shape. By adjusting the length of the cable by spinning each of the motors you can get the pen to move to any position within the board. It's simple trigonometry to work out the relationship between pen position and motors. Then you enter those formula's into mach3 and it will run it as normal...
A standard belt driver plotter will probably be better, but since you're going to have to buy steppers and drivers for either you could try this initially as you only need a piece of string and a pen...

Edit: Wrote this post 2 days ago but forgot to press send!