Im new, am a 3D designer. Need a New cnc machine and need advice and guidance

Not at all :) If the design isnt up to the job then its not up to the job. Criticism is how all novices get to a good stage...just like RC haha. I have the CAD files for all th parts I need now, with a number of them provided by Jazz...so the rest is just making a new frame which can still utilise these parts :)

The one thing i really dont understand is how something has to be so strong and precise but are hand welded most often by people who have a mig and no jigs...

Is it possible that the design I have done can be beefed up? with no real change to the machine? Just to save going back and forth...I dont mind, I have taken everyones advice onboard...I know it looks like im rushing into everything but I hav been doing allot of studying on the forums with build logs, The questions I ask which seem similar to other peoples questions are because I want to put it in my own words so I understand it better...

The criticism is good though, didnt show as unfriendly at all, no worries there :)

Good man...things can be welded by novices (me!!!) but still precise as long as either some form of adjustment (shimming the top rail on the x axis for exampke) or the epoxy method is employed.

Yes you can still use your design if you look into the gantry a bit more. Bracing is your friend as wood needs to be cut quick so on full chat your machine will be dancing about (how you fixing it down by the way?) all over the place...

The best way to get stiffness in your gantry is to keep the sides as short as possible with the best being to mount it directly on the linear carriages...this needs raised rails.....

Sent from my Galaxy S5

Quote:

---

Originally Posted by FlyHighRC

The one thing i really dont understand is how something has to be so strong and precise but are hand welded most often by people who have a mig and no jigs...

---

The trick is to be creative about how you get the accuracy. Making a reasonably accurate (+/- 1-2mm) bed is possible with a reasonable amount of skill and care. If this is properly designed it can then be made very accurate using epoxy to level the important faces. On to those now accurate faces you bolt bought in accurate components (the linear rails) and so on.

So, you don't have to worry (too much) about accuracy of the welded frame but you do have to consider its stiffness - it would be worth you reading up on some basic engineering - in particular stiffness of beams. This is not just a 3d design problem, it's also an engineering problem and although you don't need to be able to do accurate stiffness calculations for each part of the machine, you do need to appreciate how the material responds to stresses.

Thats good then. If i can still use this general design that would be nice. In terms of the gantry, where the two braces are connecting the two sides, is that where I need to brace? I,e Add vertical members between the two?

Are you a Solidworks user Neil?

Yes you can still use your design if you look into the gantry a bit more. Bracing is your friend as wood needs to be cut quick so on full chat your machine will be dancing about (how you fixing it down by the way?) all over the place...


Sent from my Galaxy S5[/QUOTE]

I didnt include it on the solidworks model since i didnt feel the needs but there will be 6 tabs around the bottom of the machine with m6 bolts to bolt it to my other workbench, depending on how much vibration there is i might replace m6 vibration isolation...i use m3 equivalents for quadcopters

maybe if this all works out well i can make it an early last year uni project :D

Quote:

---

Originally Posted by FlyHighRC

Thats good then. If i can still use this general design that would be nice. In terms of the gantry, where the two braces are connecting the two sides, is that where I need to brace? I,e Add vertical members between the two?

Are you a Solidworks user Neil?

---

Got SW but not installed it...I've got Geomagic Design on my PC at work so trying to get used to that at the moment so won't install it as I don't want to confuse myself (easily done!!)

You need to put in vertical and also cross bracing....like you would in a CF quad arm...

Neils bluntness was required here because if you are looking at other builds, esp those built from steel then your not paying attention because you'd have seen NONE are built flimsy regards the Gantry and 99% are done using timing belts and pulleys for connecting to motors. Your design at best is medium duty wood use only.!
Reason for Pulleys is Resonance handling, I'm not getting into how's and why's because it's been covered in many threads so go check some out, But will say it's an important thing on steel framed machines so wouldn't skip it.

Gantry needs to be much more beefed up and braced with plenty of thought to rail alignment and Ballscrew Fixing/adjustment/access. Your design severly lacks here, esp on the Twin axis area. Ballscrew alignment and fixing needs to be strong and easy to setup, if the ballscrew end bearing mounts are flimsy then the screw will resonate which can cause whip and affect performance. If bad then it will also have the similar affect has backlash and causing inaccurecys so design these areas strong and adjustable.
Just remember you have two goals Strength and accurecy, and you can't have one without the other. Build in has much adjustment as possible to allow for the DIY factor, this is KEY to successfull DIY build and stress free build.

Don't be afraid of weight it won't be a problem at this size and will actually give positive affect not negative.

One more note.? . . You've drawn the Gantry bearing plate as Angle iron, this won't be strong enough or accurate enough unless Thick material and prep'd. What you have drawn is has much use as tissue paper.!! . . . The Profiled linear bearings are very intolerent of uneven surfaces and will cause binding if fastened to one. Angle iron isn't flat so it would need surfacing and it will need to be thick material to reduce resonance. Just Fastening to the bench won't stop resonance from weak frame material.
Also beaware it's not a good idea to bolt the machine to the bench unless the bench is perfectly flat and true other wise you'll pull the frame into twist and force the rails out of plane. To be honest this machine won't be light so you won't need to fasten down anyway just level bench and put some buffers to stop machine rocking off the bench.

Jazz - I know you seem to favour single X motor and belt drive to two screws (for this general size machine, anyway). For a steel machine where resonance might be a problem, is it still better to have a single motor, or two motors with their own drivers to give the drivers the best chance of controlling resonance - and still having motor/screw coupling via belts?

Quote:

---

Originally Posted by Neale

Jazz - I know you seem to favour single X motor and belt drive to two screws (for this general size machine, anyway). For a steel machine where resonance might be a problem, is it still better to have a single motor, or two motors with their own drivers to give the drivers the best chance of controlling resonance - and still having motor/screw coupling via belts?

---

Actually Neale the reason I like Single motor connecting two screws has nothing to do with resonance really just I prefer because of keeping screws in sync.
In either case single or Twin motors belts to motors are best on steel machines and to be honest I fit them on machines I build from aluminium profile and Ali plate for same reason plus they allow flexabilty with ratios if required.

One thing I will say thou is that the newer Digital drives are getting so good at handling resonance or allowing it to be tuned out that it's becoming less important but I still prefer to have them for reasons above.

Edit: Just realised I didn't actually answer your question did I.? Not a politician honest. . Lol

Well one motor is best really due to not having to worry about sync and each drive keeping perfectly together or resonace just affecting one motor/drive not the other etc plus less to go wrong etc. . . .BUT. . . here's the crux with one motor.! . . . It means larger motor is needed and often this throws you into Nema 34 country and with that comes other side affect's like Larger PSU required more expensive drives etc. In reality It doesn't often work out any cheaper than 2 motors/drives really but it does give piece of mind the machine won't tie it's self in knots if one motor stalls and it NEVER Racks or one side loses position if motors are tuned in-correctly.!

Again thou modern Digital drives are helping here with Stall detect and fault signals to help E-stop the system if happens so not so big an issue really. I only Use Digital drives know and Motion control cards which really do help with good fast quality pulse signals so because of this I'm using more 2 motor setups for simplicity sake and avoiding long belt runs.!