Newbie CNC Build

[JunkieHobbo]

Hi Guys,

Thanks for ALL the advice, after the whole weekend doing some research and messing with the designs and Ideas I have come to the point where I would like to know what hardware Sizes I should be going for.

I am looking at a design with a raised X-Axis, similar to JazzCNC design mentions earlier.

To complete my design work I need to know some things, only a few questions I promise!:whistling:

From my understanding Linear Profile Rails are the way to go as they are the "Most Stable/Accurate" option. What size would be best for the X-Axis and Y-Axis? Should I use them for the Z-Axis? Also how many bearing blocks per Axis? Is there a calculation to work it out?

Now onto the Subject of Ballscrews, again from research the "Most Stable/Accurate" option would be to have a Stepper running a Ballscrew on each side of the X-Axis, is this correct? Again, What Size ballscrew for each axis? Is there a Calculation to work it out?

@JAZZCNC: Some very good Advice, kept me busy for the weekend. Regarding the Budget, you are correct, I would rather Plan and Plan and not waste money as the budget is tight. When you say beef up the Y-Axis, could you elaborate a little?

@m.marino: Yes, some very Good Advice from JAZZCNC, regarding the Switches, I have added them to my notes as a Priority!

@kylelnsn: Yeah, JAZZCNC sure looks like he knows his stuff, not sure about all this Vertical talk though!

@motoxy: LOL! :lol::lol::lol:

Again, thanks all for your Help, Time and Patience!

[JAZZCNC]

From my understanding Linear Profile Rails are the way to go as they are the "Most Stable/Accurate" option. What size would be best for the X-Axis and Y-Axis? Should I use them for the Z-Axis? Also how many bearing blocks per Axis? Is there a calculation to work it out?

15mm Profiled rail will be sufficient with 2 bearings per rail. Regards calculations etc you could do them but profiled rail & bearings, even 15mm bearings, are designed to hold a huge amount of weight far more than your's or most DIY machines will ever need so I wouldn't concern your self too much in this department.

With profiled rail there's different types of carriage, usually 2 lengths standard and long, then there's slim and wide type carriages.
Think of the bearings as a foot print the wider and longer the more planted the foot, if using 2 ballscrews to move the gantry the length can be reduced slightly because of it being driven and held both sides but longer and wider is better than fine n slim, trade off being extra length rails needed for same cutting area.

Use them on all Axis but with the Z axis mount the rails on the front plate and bearings on the rear plate, this will give the maximum strength when the Z axis is extended.

Now onto the Subject of Ballscrews, again from research the "Most Stable/Accurate" option would be to have a Stepper running a Ballscrew on each side of the X-Axis, is this correct? Again, What Size ballscrew for each axis? Is there a Calculation to work it out?

Yes driving the gantry with 2 ballscrews is much stronger than using a single screw because it reduces the racking or skewing affect when cutting at the outer edge's of the machine, more so the wider the machine.
Regards size etc then you have a few options.!! It's not rocket science but does revolve slightly round the type of use of the machine and the length.
Basicly you choose the screw by pitch and diameter and length.
If it's going to be used as a general purpose machine IE, wood, plastic's, soft metals then a good all round pitch is 10mm. This will give a good balance of speed and resolution.
If it's to be used for very detailed work Ie: Engraving etc then you will want a lower pitch like 5mm or less, the advantage being higher resolutuon. The trade off being slower rapid and cutting feeds.

The diameter is often determined by length and what's pitch is available in that diameter. Long screws 1300mm and above need to be thicker to handle the whipping affect unless some other method is used like rotataing the ballnut and keeping the screw fixed in tension at both ends.!
Again there's a trade off.!! . . Larger ballscrews weigh more and therefore take more energy/force to be accelerated they also produce more inertia which as to be de-accellerated the net affect is this requires larger motors which require larger drivers which require larger PSU's all this add's to the expense.

Depending where you buy the screws(Probably from china for cost reasons.!!) you'll find 10mm pitch is often only available in 16mm or 25mm dia for some reason.?? 20mm is nearly always 5mm pitch.?
For an all round machine Upto 1200-1300mm then 16mm Dia meter with 10mm pitch is a good choice.

For higher resolution but with less speed then 5mm pitch is a good choice, would will also be ok regards whipping upto around 1500-1600mm with 20mm due to less rotational speeds. (my machine use's 150mm 5mmpitch 20mm Dia with no whipp upto 12meter/min)

Another option and something I like and know Jonathan likes to use is connecting the motors to the screws via a short timing belt.
Doing this gives a few advantages.! . . It reduces resonance which direct drive can suffer from and it also allows for easy gearing to either increase speed or resolution/torque. Makes a machine that bit more versatile.

When you say beef up the Y-Axis, could you elaborate a little?

Yes very simple really.! When cutting metals, even soft metals like Ali or brass the machine needs to be very very strong if you want to have any kind of resonable depth of cut (DOC) and feed rate(FR) with a nice finish.
To be honest most half decent built machines can cut Ali or brass. . BUT . . There's cutting and there's cutting.!!
Lighter less ridged machines will have to take far less DOC and often go slower, thou less DOC does mean you can go faster on the FR but the machine becomes the restriction. Less ridged machines suffer from resonance which transfers to the finshed cut quality, the faster FR or deeper DOC the worse the finish due to resonance.

Basicly if you want to soley cut metals then build it strong and heavy in all departments, don't be affraid of weight, the Mass helps massively with quality of cutt.
Again the down side is more power and bigger components required to handle the weight etc. Plus an often over looked but again massively important area is the Z axis and Spindle used.??
No point building a strong framed machine with the best components etc if the Z axis is under built and flexing around or there's a weedy spindle attached that can't handle the DOC or FR.
If you want a decent machine just for Metal be prepared to build strong and spend money. . .OR . . . Some times easier/better to Convert a milling machine.

@kylelnsn: not sure about all this Vertical talk though!

Why would you say that.!! . . . When you have used a machine for a while you'll inderstand better and defiantly see/appreciate all the advantages.!
With a few weeks experience using it in the vertical position I can absolutly say 110% it's the best thing I've done to the machine since I first built it, and with the excepton of slightly more awkward clamping which I've fully adjusted to know i've made some little rest aids there's absolutly NO down side only big positives.
I would recommend anybody building from scratch to think long and hard and not be put off by the unusual positioning.!!. . . There are virtualy no down sides only positives..:dance:

[kylelnsn]

Why would you say that.!! . . . When you have used a machine for a while you'll inderstand better and defiantly see/appreciate all the advantages.!
With a few weeks experience using it in the vertical position I can absolutly say 110% it's the best thing I've done to the machine since I first built it, and with the excepton of slightly more awkward clamping which I've fully adjusted to know i've made some little rest aids there's absolutly NO down side only big positives.
I would recommend anybody building from scratch to think long and hard and not be put off by the unusual positioning.!!. . . There are virtualy no down sides only positives..:dance:

I didn't say that? Lol? Confused!