Im looking at building a 1250mm x 1250mm x 300mm (cutting capacity) cnc router / miller from scratch. Will be cutting the usual MDF, ply and occasionally aluminium.
ive read through millions of posts on the forum (very useful!) but I still have a few questions before I get started on the CAD model.
as the x axis will be fairly long I am undecided whether to have 2 ball screws or one and this leads on to the next question 1 stepper motor or two. I think the two ball screws will be beneficial but if I use two steppers is it easy to get them in sync (via a slave) or would it be better to power the ball screws via 1 motor all linked by belt drive or should I just go for the 1 balls crew in the centre and power off 1 motor?
next question is the controller. As times are moving on is it best to go with USB connection or parallel, again pros and cons for both with the parallel port being tried and tested and most popular or to go with USB as it will probably go down that route in the future and I will be able to connect my laptop to it.
i don't mind going parallel and mach3 but would be good to connect via laptop.
also generally what size aluminium extrusion do people typically use, would 80 x 40 be too lightweight for the size of the router?
Is there much difference in accuracy and life span between flat supported rails and round supported rails and are the ones sold on eBay from honk kong etc ok or is it best to go with UK suppliers?
finally, may need a few parts machined and more advice so any help would be appreciated.
Will get some images up of the concept model one these few queries have been answered so feel free to give your input.
Il answer what I can, however Im no pro...
*You want 2 ballscrews driving the X on a gantry that wide, to stop it crabbing
*in regards to one stepper or two, this is a bit of a sore subject on this forum. Both methods have their advantages comes down to personal choice. Im going for one stepper driving two screws.
*(controlelr/breakout board) This is talked about in lots of different threads by people far cleverer than I. So I wont comment.
*extrusion...get a design drawn up, its the design stage that will answer that question. Its all very well me saying yeah 80x40 but it depends on your design. Mine uses two peaces of 100x50 box 5mm thick in a L setup
*The HiWin type cartridge rails are the ones to get.. They are expensive but from what I read are about as good as it gets.
The supported round rails from china are what I went with, which I understand are good enough (so long as you pick the supported ones) but nowhere near as good as the HiWins
I would read ALL the build threads... If you had done this prior to the above post you would of been able to answer all those questions yourself, from the wealth of information you gather from reading them. Then get some designs uploaded and be prepared for them to be picked apart!!!
:-D wish you all the best with your build. make sure you keep this thread updated as there are some sad individuals (me) who regularly check for updates to build threads!!!
Thanks for the reply / info.
just working on the CAD model now so will hopefully have a few images up here soon for everyone to give their input.
I have decided to go with two rails on the x driven by 1x motor via toothed belt. I have read a few more posts and learnt tons more and have seen quite a few heated debated over that issue but think the belt will eliminate any room for error as its mechanically sound.
I will have a read up on the controllers, I can see the ads / dis ads of both but I guess i just have to make a decision and stick with it.
Will keep you posted on the progress.
Got quite a bit done on the model today but still a few bits to do before the pics go online.
Just want to confirm a few things before i progress any more. My shopping list for rails and ball screws are as follows (all lengths TBC):
Ball screws (machined with ball nuts)
X = RM1605 (400mm)
Y = RM1610 (1500mm)
Z = RM1610 (1500mm)
Linear round supported rails (with SBR20/25UU bearings)
X = SBR25 (1500mm)
Y = SBR20 (1500mm)
Z = SBR20 (400mm)
Looking at getting these from the famous ebay guy, does he machine the ball screws to accept pulleys to or just couplers? can the length machined for couplers be used for pulleys? has anyone used pulleys from cnc4you or does everyone generally use HTD pulleys?
On the X and Y's is it best to have BK15 bearings on both ends of the ball screws for extra support and BF and Bk on the Z or will BF and BK's all round be ok?
I was looking at using dia 20mm ball screws originally but after reading posts on here, will probably go with 16's.
As feed rates and resolution are always discussed regarding ball screw size is it just down to what the machine is used for, as to what to go with. Are the 16's a good all rounder for both?
Last edited by Danielroyal25; 02-02-2013 at 01:15 PM. Reason: Update
Ok, il try and answer what I can...
First off, I think you are referring to Chai. http://http://stores.ebay.co.uk/linearmotionbearings
Next, have a look at this...
When wording your email to chai, you need to specify your ballscrew dimensions carefully.
For example. I wanted 1500mm of actual travel, I wanted BK type bearings at BOTH ends. and then I wanted to put a pulley on. So I actually ordered
**1603mm Total length so 1500mm PLUS one end machined to type A (except dimension F to be 25mm instead of 15 (to accept pulley), and the other end machined again to type A, but without any F
I personally used HTD bearings from bearing station. However the guy at cnc4u is an extremely nice and helpful chap. In hindsight I should of ordered everything from him! that way I could of just kept ringing him with my questions rather than all the reading ive had to do.
remember; its all in design. dont rush into buying your linear gear until you've got it weighed up properly.... dont design around bearing sizes!. I wish I had spent longer designing as there is an amount of waste on my machine due to my inpatience in the design stages... Look at wilfy's build thread... that boy can design!
hope this helps look forward to seeing design.
Bit of a novice myself but you might find that 1605 would be a better choice for the Z axis, no doubt one of the experts will give you some sound advice before you reach the stage of ordering anything.
As for the pulleys have a search on the forum as it's been talked about a lot. Just make sure when you do your design you are going to have somewhere to run the belts, the X axis one in particular because this is quite a wide machine so you are looking at a belt a bit over 2.5 mtrs in length.
Yeah definitely want to get the CAD model 100% before ordering anything, as it will be a costly error! Thanks for the info and yes i was referring to Chai - he seems to be well recommended.
Correct with the Z axis it was a typo, X & Y should be RM1610 and Z should be RM1605.
Ive uploaded a screenshot so everyone can get an idea of the design when its being discussed. Its a long way off being finished tho. Please let me know your thoughts.
Also i have started to research controllers and wiring etc and am a little daunted by it all, does anyone know of any good links that talks through it step by step and any recommendations for controller (makes and model) - think i will go with a parallel controller and Mach 3 rather than USB / bespoke software. Is it best to go with separate drivers rather than built into the controller?
I looked at buying a board with plug in driver boards but couldn't find one that worked above about 36v. You might find that that is not enough for your choice of motors. The motors I used would have operated at 36v BUT I would never have got the best out of them so opted to go with 3 separate drivers that could handle a much larger voltage.
You will get lots of help with control box set up from members on the forum so don't let your lack of knowledge (at the moment|) put you off. Quite a few of the build logs have most of what is needed covered so reading them will give you a good start for your own system.
Unless you have used models that have very accurate dimensions then your much better ordering important or components with critical dimensions has you go along taking measurements direct from the frame and machine has it's coming together.
Often you'll see people buy everything before starting only to find something is too long or too short or completely wrong and won't fit.!!
Components from Chai usually arrive in about 12days and within a day or so of starting the frame you'll have enough information to confidently measure from and order parts knowing they will fit exactly with no guessing or nasty surprises.
By the time you have finished welding or bolting the frame together they will have arrived and ready to fit.
The motors and drives I would buy from Zapp or cncdiy because you'll have backup and easy UK return if faulty. Again don't buy until your ready and need them.?
While it's seems nice to have them and spin them up on the bench etc in reality all your doing is wasting warranty and the Electronics are one of the last things you need. There's also the chance of new or better models being available for the same or less money by the time you actually do need them. The digital drive market is constantly evolving and getting cheaper each month.
DONT BUY the cheap 3 AXIS boards from Ebay you'll just be buying trouble and rubbish performance.
You want separate drives and if you can afford them I'd recommend digital drives. Also very important that you match the power supply(PSU) to the motors and drives.
Watch out for Kits that are sold because they have a nasty habit of bundling low voltage PSU's. Often it's cheaper and better to build your own if needing more than 50-60V
Getting the Voltage right is the key a to good running machine and often folks use to low PSU and don't take advantage of the machines full potential.
Also don't be afraid to over spec on the drives.? By this I mean if you can afford 80v drives over 50V then do so. You don't have to run them at 80V and having the overhead gives advantages. Firstly you have upgrade ability but more so they are not being constantly run close to there maximum capability's so are under less stress and will last longer.
Often folks will buy 50V drives and correctly run them at 45-46V but that means the internal electronics are constantly near there max ability with only a small margin of over head. Anything that easily handles the loads they carry will last longer, yes initially they cost more but it will be returned thru reliability and longevity in the long run.
Another often done thing.?? . . Don't go buying massive motors like 12NM nema 34's etc 3Nm nema 23 will be more than enough for this size type machine and cheap.
Regards the frame then it needs some diagonal bracing and if it's an adjustable bed which it looks then it needs much more support for the sides. Don't rely on the bed to for rigidity or strength, which it will do anyway, because when you come to adjust the bed the frame will move and flex knocking alignment and setup out every time.
This will be a real pain, also the frame will be flimsy and resonant which will affect cut quality.
Don't be skimpy on the frame Chunky is good, same with gantry don't be afraid of bit of weight it helps with cut quality and you'll be surprised how powerful the combination of ballscrews and steppers can be.!!
Hope this helps.
Thanks for the info guys!
Just wanted to give some more info on the use of the machine and the design so far.
Im hoping to cut mainly large ply / MDF sheets on it so wanted it to accommodate the maximum capacity sheet (standard size: 8ft x 4ft).
i didnt want to build a router to this overall sheet size as i it will be a bit of a beast and also the cost comes into play. my thoughts were to make it accept the width of the sheet (4ft / 1220mm + a little) and then the length of the board could be machined in two halves by either feeding the material through of turning it through 180 degrees.
Does the length of the gantry pose a problem for general machining and would it be able to handle cutting aluminium? As long as the strength is there will it be ok and will the precision still be to a fairly high standard. If cutting aluminium or harder woods is
Will be looking at getting the water cooled spindle so im guessing the weight of the gantry and Z axis will be a fair bit so the gantry will have to be fairly substantial.
The bed is going to be in a fixed position so this can be bulked up with diagonals for strength and like suggested heavier gauge extrusion, just difficult to balance the desired design with the cost of parts.
The support in the Y direction behind the gantry was to mount the motor in the centre with pulleys to the X ballscrews, so didnt really want to add a support the other end as this was to allow material to be fed in / out but if i can position it in a way that the material can be slid under the support i may add this in.
That doesn't mean you can't have long gantry but it does mean it will have to be very strong and substantial to resist resonance and flex which are the enemy of finish quality.
Take this strength to another level if you want to cut Aluminium and achieve good Finish quality. Really unless your only cutting Thin Alu sheet or Profiles etc that don't need good finish then forget cutting Aluminium on such a wide or long moving gantry machine. Yes it will do it but not very well.!!
If your into wood can I suggest you have the rails slightly overhang the end of bed. Doing this simple thing will give you some nice options easily achieved.
Namely will allow end machining of boards etc for hinges, locks, Dovetails and oversize or oversize awkward parts by clamping to end of machine.
Also if you want a 4th axis makes it very easy to add one see pics for some idea of what I mean.
It's only a cad mock up so pay no attention to details like gantry has thats actually a design I use the other way round it just saved me some drawing time for showing the person it was intended for. It could be used that way round thou.!!
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