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

[JAZZCNC]

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.

[FlyHighRC]

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...


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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

[FlyHighRC]

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

[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?

[JAZZCNC]

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.!

[Neale]

Many thanks for the comments. I'm still building the frame for my new machine, and haven't reached the stage where I have to worry about single or double motors. It brings up a bunch of related issues, so I'll stop hijacking this thread and start another one.

One last vaguely relevant-to-the-thread point, though - I started out a couple of years ago with my MDF JGRO machine in order to make an engraved presentation plaque (immediate need) and the thought that I would be able to cut things like wing ribs, fuselage sides, etc. Haven't done any of the latter yet, but found lots of other uses for the machine that push the (admittedly very modest) limits of what I have. Spent the last couple of days profile-cutting 6mm and 9mm ply components for a slot-together architectural model, and watching the wheels go rounds at a mind-blowing max cutting speed of 700mm/min was tedious. The moral of the story is that if you are happy to cut modest amounts of material at slow speeds, you can get away with a real junk machine. But if you want to be able to do a good job at proper speeds, do it properly first time!

[FlyHighRC]

Well for me right from the outset I wanted a mchine that is future proof for me (Hence why these guys are pushing so hard ;) ) so that way i can cut plastics,woods and do so ali work in the future and have a machine capable for it all. I was first introduced into CNC at school and was quickly dissapointed with the machines they had... werent very good. Then I got to start using a Roland MDX-540 as part of a young engineers thing.. that machine was better and could chew through plastics...struggled with carbon fiber and did aluminium at 400mm/min, not sure if it could go quicker or the company didnt want to push it but it was annoying to watch frankly.

[FlyHighRC]

Would this be a better frame? Following a design more towards what other people are making...

[FlyHighRC]

Oh building a machine to now combat resonance..meaning pulleys..those pulleys will need a special mount t fix onto the ballscrew right? This is now sounding more and more expensive... Please try to remember my budget :D

[JAZZCNC]

Oh building a machine to now combat resonance..meaning pulleys..those pulleys will need a special mount t fix onto the ballscrew right? This is now sounding more and more expensive... Please try to remember my budget :D

Nothing special needed for using pulleys and the only extra expense are the pulleys & belts roughly £15 per axis. Which isn't much more than direct mounting by time you have bought correct couplings.