time to gather parts for new machine

[deannos]

If i wanted a cnc with a cutting area of 4' x2' what length rails and ball screws would i require for all axis. I like the look of the low gantry designs, i.e Jonathan's etc. I have decided to go with a frame made from steel box section. But that is as far as my knowledge goes. So plenty of help required and desired

[JAZZCNC]

Hi Dean, What your asking is very hard to answer accurately without knowing the design and will change with different design.!
That said I'm soon going to be building for someone a steel framed machine with very nearly the same dimensions.! . . . .So to give you an idea i've just quickly changed the Cad model to give the length you want, width was the same or slightly more anyway.

With a design like the one in the pics below the X axis screw would be Approx 1400mm and the Y axis 825mm. The rail lengths would be approx 1475 and 850mm.
The model is just at a very rough concept stage so nothing is aligned or setup and things like gantry sides will change shape, position etc with more work on the frame and more trimmings will be added like covers for screws and igus chain etc but it should give you an idea of how it would look.

Every thing is 1/1 scale so motors, spindle etc are all correct and all materials can be got or cut from products that are available of the shelf, IE gantry sides (as can most of the gantry and Z axis) be got out of 200x20mm plate from Aluminium warehouse, 80x40x3mm Box section from local steel merchant etc. The adjustable bed is steel frame with KJN's 90x45 profile but could easily be replaced with MDF to save money.

Hope this helps and just ask if you want to know anything.

[deannos]

Thanks for that Jazz, that design is what i was thinking of. The Aluminium warehouse is also 1/2 hours drive away. How would i work out the cut lengths for the steel etc

feel stupid now, the lengths would be the same as the rails

[JAZZCNC]

Some good advice is get a decent cad program and start designing the machine before you start cutting anything.!
It really does help with checking fit etc and finding dimensions etc.
The time invested designing will be repayed as the build progress's because It helps keep the build on track and has time goes by having an accurate reference to look back upon really does pay back. . . . It's also a good motivator because you can visually see what your going to have at the end.:dance: (Amazing how several days or weeks of grinding,drilling etc can De-motivate.)
Not only will it save you time but it will save you money because you'll not waste material making parts that don't fit or work how you thought they would.
You can also work out accurately easily if several compnents can be got from a single length or stock or if you'll need an extra length.! . . . . Nothing worse than buying Stock you don't require when your on a budget.!!. . Equallly nothing worse than running short by 3mm because you "thought" it would fit.!! . . .If you use the suck it and see method Sod's law nearly always bites you when you don't need it.!!

[deannos]

Am i right in thinking that 300mm rails and 300mm screw would be ok for the z

[Jonathan]

Am i right in thinking that 300mm rails and 300mm screw would be ok for the z

Draw it and you'll find out.

It depends what travel you require, but it's probably fine. Ballscrew isn't necessarily the same lengths as the rails.

[m.marino]

Not free but a very good CAD program for the money is ViaCAD 2D/3D V8 as it not only let's you design it but you can then extract 2D drawings from the model. I used it on my model and it really helped make designing and the build much much easier. Also I knew what materials where needed. Still ended up with a few tweaks here and there but that is better then major OS moment. Good luck.

Michael

[Jonathan]

Lots of people use google sketchup.

[jcb121]

Sketchup is in my eyes, the best program ever for designing. have you considered what parts you are going to use? Supported rail from Linearmotionbearings2008 etc?

[MikeyC38]

Hi Deano.
I thorughly agree with JazzCNC and Jonathan about drawing out your design with a CAD package. You can see this from my thread here http://www.mycncuk.com/forums/showth...gn-Build/page4 and it allowed me to get good advice from the guys here on the forum who have learnt the hard way! A picture tells a thousand words!! A 300 mm ballscrew does not have a thread length of 300mm - it is about 200 once you take into account the end machining to fit the bearings at either end. On my Y axis, this clearly showed up when I did the drawing. I use TurboCAD Platinum Pro 15 which I got from Paul Tracey http://paulthecad.co.uk/ at the Model Engineer exhibition some years ago for a fantastic price (very much less than retail!!). It does solid modelling which means when you draw the ballscrew, bearings etc, you can "assemble" them together just like real objects. Some of the stuff like the BF/BK bearing blocks, stepper motor couplings I got off the internet already drawn as 3d objects, so it was easy just to use them. Also as CAD is / will be part of my workflow to use the machine i.e. CAD draw object send to CAM software to produce toolpaths and tool selection then to CNC, then for me it is time well spent.

There is quite a step learning curve in using these programs (Google Sketchup is easier to get to grips with) so unless you are in a hurry, it makes you think through every stage. My mantra is "measure twice cut once" so doing the drawings etc will hopefully help me avoid some expensive mistakes.

All the best with you new project!

Mike

PS Also got my rails, ballscrews, bearings couplings from Chai at Linearmotionbearings2008 on ebay. Fantastic price and great service. Everything turned up within 10 days and was straight.