So I am yet to see anyone attempt this proably because it's just not that cost effective but I think its the route I am going to take. I am designing a 1500 x 1500 vslot cnc that uses dual 5 pitch ball screws for the base and single 5 pitch ball screws everywhere else. I want to drive it with nema 34s as I'd like to be able to cut thick aluminum even if its not terriably fast doing it. The main use will be mdf and hardwoods though. The z potential is important to the gantry runs fairly high but I have done some things to eliminate the extra stress on it. I am still very much not done with the design process so any attached pictures are very early stage but I think I have worked out a lot of the issues. Please good or bad tell me what you think. I am really hoping when all is said and done this is one of the best cnc s to come out of the openbuilds product line and I hope to see some others going the same route.
If you are planing on a 1500 x 1500 bed, then you really do need to build it with an awful lot of strength in it. Particularly the cross member, i.e. the "X" gantry. Although you don't show it on your plans, it might be good if you do, so we can offer any advise. Have a good look around the Forum, and check out the various builds from the guys on here, and they really do vary in style, performance and weight. For the best ideas, read, read, read. Good luck in the mean time, and welcome to the world of CNC! Cheers Gray
The gantry I'm still working on but,it will be 4 20x80 beams as such 2 beams 80mm gap 2 beams the ball screw will go through the middle the side supports are either going to be 1/2 steel or 3/4 6061 aluminum
You will need to, if you hadn't planed to, bolt each pair of v slots together to get maximum strength. I don't know if you plan to have those v'slots in a horizontal or vertical position, but how about, for additional strength, use a good sized piece of aluminium channel for the screw to sit in, and then bolt the v'slot to that. Now that would be strong! Please don't underestimate the possibility of judder and twist on a machine of this size when milling aluminium. Gray
I planned on putting a bolt every 3 inches and as far as gantry position it would be horizontal. The ball screws. Would be bolted to 3\4 inch aluminum sandwiched between 2 2060 rail pieces. Like I said I'll have more soon just working on it slowly
Also each side of the y will be independently drive by nema 34 motors and they will be self aligning not sure of the best sensors to,use for,this yet but I was thinking cncrouterparts switches. They seem pretty accurate
Bolt, weld glue it, still won't be enough over 1500 for routing, I know this because I have one. Really it needs another twin set of profiles spaced above with a ballscrew between the two., debating wether to cut mine down or add Erwin carriages instead of v wheels or dedicate it to plasma only. In which case I'd still need to get rid of the belts. To put this in perspective.. If I bore a holes say every 100mm in x direction I will find the end ones will be bang on and round, the holes gradually getting more and more elliptical as I get towards the center with around 2mm difference in width. Really these aluminium v profiles just arnt up to it. If your going to go ball screw use chunky standard slot profiles say 80x80 with Erwin carriages and 9mm steel gantries. Wish I'd thought of it before I went down the route of the ox, I'm sure they are fine for small stuff, but you can do something like what I just said for the same money. Kicking myself really
So even with the 40 mm on bottom doubled and the 80 above the screw doubled and 20 wheels on each side,you don't think,it will be strong enough? This was the info,I was looking for,though so please keep,it up
No I'm afraid I dont. Problem is vibration aswel as flex and this design with the y profiles un supported over that distance, doesn't take a lot to make em shake. in my case I keep looking at the modification I could do to it to strengthen it, but I'm convinced the nature of the beast it's never going to be cured completly. Think the best investment for me with mine would be a fresh abrasive wheel for my chopsaw. And take it down to 1000x1000 and see what it's like then.
I really need to get the model finished so you can see what I am doing I really think I engineered a lot of these issues into a more acceptable tolerance. I'd love to chat with you Johnny and pick your brain on your build. This will be bolted to a solid welded steel base if that makes a difference. I am proably looking at the 3000 Mark for the build but with ball screws and really high end electronics and hardware I cared about accuracy over speed. Well like I said I can see the core issues with a build this size. Originally I had planned on using 3 rails for the x think this might make a diffrence
Hi, why going thorugh the trouble of "bonding" two/ three / four insufficient extrusions togehter while still not achiving the desired? designing a machine without accurat data isn`t engeneering - it is siply guessing. with all its potholes... Like said above, lookout for standardt profile aluminum extrusions... (i do prfere "item" or "bosch" compatible). there are sices like 160x80 mm in reg and strong availible... even bigger if desired. Like this for ex: http://www.smt-montagetechnik.de/produkte/98.htm at least you get guaranteed strenghes and their data - so that you can at least start to design your cnc. pricy?- yes worth it- definetly btw: welding a frame will get you strain/ tension into the system that will cause your frame to wrap. Without heat curing that afterwards all your desired accuracy will be spoiled by the welding - completely. Read the forums - all steel welded cnc´s are beeing heat treated afterwards ( at least the succesfull ones) - one reason most hobbyists build in aluminium extrusions... greets flo
Check out http://cncdiaries.com/blog/category/step-1-design-phase/ I've priced up a 2600x1500 version of this using 90x90 profiles at £3100 with hIwin carriages (not Erwin sorry about that) and ballscrew off the shelf z kit, and everything needed, all descent quality nothing Chinese. Which is a lot but considering I've spent half this on an ox. This is the style design used with most comercial Cnc machines
I'm actually in the process of having some 90mm thick aluminum y gantrys with internal triangular comb reinforcement cast that have a similar shape to the ox gantry but excepts two 90x90 profiles on top of each other, that slot in and nema mounts, ballscrew bearing mount, and hiwin carriage mounting plates built in. Should make for a lot stronger aluminum build without going down the road of using steel.
Yea I didn't mean the frame was steel. The table is and it is heat cured it's an old industrial base I picked up. But yea I get it this was the whole point of putting this up here I had a feeling it wasn't going to cut it. I think I am going to end up back at standard 30x60 tslots with either rolled steel v rails or thk sliders. :/ so much for the simplicity of vslot. Lol. Honestly the cost won't be much more using 3060 over vslot since I doubled tripled and quadrupled sections up. I am going to 're design the end plates for 3060 tonight and I'll put some pictures up. What did you think of the x design though with maybe a 3030 on the bottom the ball screw and then a 3060? Something like this.
Joseph is that the x or the z? looks like you have 10 v wheels there.. whats the cost of those? around £4 each for the hardened version here, i wouldn't use the cheaper ones, they wear real quick. if that's about right you looking at £40, you can get round rail kits for £44 and they are much better. You will find some here: http://www.cnc4you.co.uk/Linear-Rail/Round-Rail-Kit/SC16UU-Rail-Kits-with-SK16-Supports or alternatively they sell z axis kits A pic of a design of mine and most certainly my next venture. 90x90mm profiles, 90mm thick aluminium water jet cut gantries. 140mm z range, x is 1500mm between inside of gantries and y to be 2900 for 8'x4' cutting with tool change table , x profiles are rebated into the gantry's, inbuilt nema and ballscrew support mounting holes, with recess for coupling, hiwin carriages for x and y and an off the shelf z axis kit, slot for cable carrier at the top, gantries mirrored so x motor can be mouted either side.. frame is also 90x90mm. Everything else that is needed to make frame and all running gear and z kit is all available from one single UK supplier.
I like the integrated web design concept. A great combination of strength & lightness. Water jet cutting is an amazing process but expensive when cutting this thickness of aluminium. But when you consider your looking at building a large machine expensive is a relative term!
Yes lets hope so I have heard that even a solid 90mm gantry will vibrate and even flex!! so i said to this person about the lattice reinforcement and they, and i trust his judgement here, says he has used lattice work in simular applications and its worked really well, that he hadn't thought of it in a gantry plate and that he expects it would actually be a lot stronger with the lattice work than just a solid sheet. lets hope hes right. but like you say lightens it also, though the hiwin gantrys are rated @ two tons load capacity, should make it easier on the motors. "Relative" yes indeed, well with cnc you get what you pay for i suppose. and unfortunately quality isn't cheap. I'm estimating total build at £4000 so not far off a shop bought machine, but fingers crossed it will be comparable in its ability. though saying that you cant get a lot for that price and this is shaping up to be pretty hi spec.. and the upside to this is i wont need to shell out all in one go. And sorry Joseph, kinda hijacked your thread.
