Thread: Hello and here I go
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09-11-2012 #1
So nothing positive about my design then....perhaps my sketchup drawing was nicely coloured
Seriously though,
C Channel was chosen over Box section because I thought it would be easier and probably better for fixing and it would also provide room for adjustment later when getting everything aligned.
Cost wise, never really compared the C to Box. But, looking at Box it's double the cost of C - web prices of course. C was chosen purely because I thought it would work better.
So what you're saying is that 2900mm fully supported rails and ballscrews will work out cheaper in the long run.
Would I need 2 rails for each side?
So is it safe to assume that parts would be:
4no 2900mm fully supported rails for the long axis
1no Ballscrew 2900mm long
What do you think a rough cost of these items imported from china would be including any import duties?
I have welding experience and equipment so a metal base doesn't worry me. Just thought there was no advantage of using metal over wood for the base.
Please bear in mind, that this is a build for home not commercial use. The reason I'm building this is to learn about the processes of making a machine and to have some fun along the way. Of course, I'm going to fall over on some things but this is part of the learning process.
Thanks for taking the time to reply.
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09-11-2012 #2
Ye nice colouring.. . Lol
Sorry to be negative but I'm just trying to save you some pain and money.
Being completely honest with you this size machine is not a wise choice for a first time build.? . . . Thou That does not mean it's not do-able because it most certainly is.!
Large machines change the game quite considerably when it come to linear motion and it becomes very important to success that the right choices are made. First time builders while they may have the skills required to accomplish the build don't always see or realise the importance of some of the things needed for success.!
The choice of linear rails and linear motion system like R&P etc become very important. Both these things are important to any successful build large or small but over a certain length, approx 1500mm, the choice and implementation raises the stakes and chances of failure rise greatly. This is why avoiding the weak designs like Angle iron/bearing linear rails becomes so important.
But the bigger issue over this length is the choice of linear motion becomes a much less simple affair.?
The usual simple choices like lead or ballscrews are suddenly very complicated.! The alternatives like R&P while more suited come with there own set of needs and things that have to be correct for success. . . . It's these that I was trying to point out before.
Now to answer some of your questions and hopefully set you down the right road for your needs and wallet.!
Seen has you can weld then it will be far better machine and easier to build from steel so that's the route I'd suggest every time.
Without seeing the full design then the use of C channel I can't fully comment on but IME box section works much better and far stronger. C channel is rarely flat or square on the inside and using the outside to have a decent level of strength requires a much thicker wall thickness which then makes it costly.
You only need 1x rail 2x bearings per side. 25mm supported round rail will be fine for this length and about the cheapest way to do it correctly.
To be honest the building of the frame is the easy part it's this next bit where it gets funky.!!. . . . . R&P or Ballscrews.?
Ball-screws are far far better than R&P but at this size they need a special attention and implementation is needed.! . . . Namely they need a rotating ballnut design.
This will mostly be beyond the first time builder to DIY build them selfs and far to costly to buy from a ball-screw supplier. The other option is to have another person make the rotating ball-nut assembly, Jonathan on here has a good design and I'm sure will gladly make for the right amount of beer tokens.!!
R&P then becomes the next choice has that doesn't have some of the issues long ball-screws have IE Whip but like I pointed out before they do have there own set of needs. Again Namely they need correct gearing ratio's, careful and accurate alignment of rack, usually larger motors due to inefficiency, larger drives and PSU to run the bigger motors.!! It also requires more maintenance than ballscrews and requires that the rack is kept clean and free from debris. . . Try to skimp and it will bite you with binding, racking, stalling and generally frustrate the hell out of you.!!
So has you can see not simple or ideal for a first build.!! . . . If you take the cheap route then be prepared to be frustrated and constantly chasing problems and unless you have a good grasp on what a CNC machine needs and the traps involved then not something I'd recommend at this size.
Do it correctly with the right components and careful selection of methods then YES it's very much do-able for a first time, easy NO but very possible.
Good luck.
PS The prices from china I don't know but the duty's will be VAT on the rated value on the shipping paper work plus a shipping handling fee of about £10. Often the supplier will put a lower value on the paper work so the Vat payed will be lower.! IE My last bought was £460 and I payed £20 vat. .Last edited by JAZZCNC; 09-11-2012 at 11:56 PM.
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