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Robert Millard
13-02-2016, 05:48 PM
Hi everyone
here's my 8x4 mdf CNC with vacuum table build
its a little agricultural but hopefully I'm getting there!!
I have some Vee bearings on order so once the vacuum table is finished I'll be on that next
feel free to comment and any heads up before I make any costly mistakes are more than welcome
😃

Boyan Silyavski
14-02-2016, 07:57 AM
Hi everyone
here's my 8x4 mdf CNC with vacuum table build
its a little agricultural but hopefully I'm getting there!!
I have some Vee bearings on order so once the vacuum table is finished I'll be on that next
feel free to comment and any heads up before I make any costly mistakes are more than welcome


Hi,
no offence, but most people here would say the costly mistake was making this from MDF not steel. And i am first on the list usually :wink:. Hence nobody commented till now.

What motors and setup you are planning? Cant you at least make the gantry and Z from somewhat more permanent material? What are you plans there?

JAZZCNC
14-02-2016, 11:19 AM
And i am first on the list usually :wink:. Hence nobody commented till now.

Err you sure about that Boyan.? . . . . On this occasion I didn't post because he's obviously not done much research otherwise wouldn't be using MDF/V bearings also know when man's gone to this much effort and trouble he's not going to listen to anything we say So why waste the effort.!!

Robert Millard
14-02-2016, 09:36 PM
Hey peeps why all the negative vibes???
I'm just playing at this anyway... We all can't afford the expensive linear rails
plus this isn't something I'm building to last I just wanna cut a bit of ply

I've seen plenty in mdf that work perfectly well. If I wanted to spend 3k plus I'd be building from steel but I don't. I have a wood work shop and all of this was stuff I had kicking about damaged boards etc so it's free so far. If it doesn't work I won't loose much sleep about it. If at the end I fancy a posher job I'll design something I bit better. So please don't shoot me down this is supposed to be a friendly forum not cocks are us!
Hi boyan I'm going to use 25mm ball screws for the main gantry 30mm would of been a bit better speed wise but as its a mdf build I won't be running a very high speeds I've yet to spec the steppers which I'll do when I've done the calcs. I agree I may need to stiffen things up a tad and Vee bearings were my second choice but cost wise I couldn't knock them as I found a job lot for 45 quid
Ive got a job I thought it would be handy for so as long as it does a decent enough job cutting some shapes from 18mm ply it's saved me having to sub the job out. If it doesn't it'll keep the boiler burning for a month or so!

Neale
14-02-2016, 10:30 PM
Hey peeps why all the negative vibes???
Ah! You used the M word! Forum members around the country will be hanging up sprigs of garlic over their keyboards to keep out the wicked spirits of MDF!
Now, I'm probably the only forum member (or, at least, the only forum member prepared to admit it) to have built and still use an MDF CNC router. Personally, the experience of using this close relative of cold-rolled cow dung has somewhat influenced my views, but the machine works. In fact, I've just popped into the warm to do a quick CAM update of a design I'm cutting on the machine this evening. For reference, my machine has a cutting area of something like 600x400mm. Over the three years I've been using it, it has gradually been sagging and warping its way into oblivion, and while it wasn't that great to start with, it's worse now! I've had to bolt square steel tubes along the sides of the bed to try to keep it somewhat flat but still end up machining spoil boards or spacers for any job that needs halfways decent accuracy. The Z platform is sagging and is now a few degrees off vertical, and I've fudged it by packing out the spindle supports so that the spindle is vertical, but I can't make significant depth cuts in multiple passes as the cuts don't line up accurately enough. At the moment I'm cutting 3.6mm ply with a 3mm cutter, and running at about 500mm/min. I can hear the laughing from here - that should be around 10x faster but the structure of the machine won't take it.

More to the point, though, and assuming that you can build a torsion box structure, maybe judiciously reinforced with steel, that is strong enough to do the job, you still need to think about the subtleties of the design. For example, using ballscrews or whatever. I'm using cheap threaded rod as leadscrews on my machine, and that limits me to 900mm/min max. That's because of the leadscrew critical speed, which is the rotational speed at which the screw starts whipping and shaking things to death. I've just looked up an online critical speed calculator which suggests that the critical speed of a 25mm ballscrew, 3m between bearings (which is about what you are looking at) is just under 300RPM. If you use 2510, that means about 3m/min max speed. That might be OK, but most new builders are surprised to find that things like ballscrew inertia are critical to machine performance as this limits acceleration, and that's a big ballscrew you're planning. There's a reason why big machines often use rack and pinion or ballscrew with rotating ballnuts. There are plenty of other non-obvious design decisions and trade-offs.

Personally, I'd be surprised if you can build a very successful machine of this size in MDF, but in any case bear in mind when you are buying the more expensive bits that you might want to use them on the Mk2 when you get dissatisfied with the Mk1! That's what I did with my own machine, and I'm halfway through building a bigger machine in steel at the moment. But I won't say don't bother with the MDF machine, but be prepared to be disappointed. However, as a hobby machine, MDF gives quite a lot of fun per pound. I've learnt a lot from mine but based on that experience, you are being pretty ambitious with yours.

Robert Millard
15-02-2016, 08:07 AM
Hi thanks for that wow 3yrs!! I only need mine to last 6 months so that gives me a positive. My whole machine is 3m long but the ball screws will be 2.6m which makes a fare difference to the critical speed
I may rethink the gantry sooner rather than later and swap out the bearings for a better option in time ... Just see how it goes
i did give sagging a fare bit of consideration when I built the table which is why I made the 2 sides as separate load baring structures in there own right and joined with supports from 25mm plyI agree though the expensive pieces I may wish to reuse
thanks for your input :)

JAZZCNC
15-02-2016, 02:09 PM
So please don't shoot me down this is supposed to be a friendly forum not cocks are us!

Yes it is and I'm sure you'll get lots of help with comments like this.!!!

If you just want to shapes in Ply wood buy good Jigsaw it will be quicker and do better job. .:whistle:

njhussey
15-02-2016, 03:12 PM
Hi everyone
here's my 8x4 mdf CNC with vacuum table build
its a little agricultural but hopefully I'm getting there!!
I have some Vee bearings on order so once the vacuum table is finished I'll be on that next
��

Hi Robert, firstly welcome to the forum :eagerness:, you might not believe it but there are some supremely helpful guys on here (the ones who have answered you are some of them!!) who will gladly help you out with any questions you have.

Where things have gone a bit pear shaped from the start here is that you didn't state that it was for a one off job so had to be done on the cheap using what scrap wood you had etc. etc.


feel free to comment and any heads up before I make any costly mistakes are more than welcome

Generally wood (and MDF specifically) is not a good medium for a CNC machine that looks as though it's needed for production (which is all we have to go on looking at your pictures of your workshop) and when you couple it to Vee bearings everyone on here immediately ducks for cover :cower:. Yes wood machines can be made to perform OK but at this size and for cutting wood you need speed and to get speed from ball screws you need large diameter ones with a large pitch and these need Nema 34 motors at a minimum with 230V AC drivers which starts to get expensive....even from China.

If it is truly for a one off job then have you considered belts and pulleys? You could use smaller Nema 23 motors and smaller drivers then and the cost will be minimal.

If it's not for a one off and you're thinking of using the mechanical and electrical components for CNC Router V2 then (normally designed when you're 1/2 way through the first build) what the lads are saying (and will continue to say) is do it once properly rather than as a compromise this time and then properly next, that's all :biggrin:

Boyan Silyavski
16-02-2016, 07:35 AM
The way i see things, so its not a waste of money, is to make the gantry right and also the Z. So if you get into it, you will have good components for upgrade.

Go find 2-3 meters of steel profile 200x100 or sth similar and make gantry portal from 1 beam. You will need ~2m for the gantry and could use the rest for gantry legs. The other way to go is from aluminum profile but anyway you have to reinforce it with steel plate, so first option is cheaper.


As for movement, you will need ball 2510 ball screw to move the gantry and rotating ball nut, but as thats out of question here, better go with rack and pinion. 1610 ball screw for Z left right and 1605 for Z up down.


You could incorporate also 2 flat steel bars or simple frame so gantry moves on steel. Say if you buy 6m of gantry profile, you could use all that and have much more better machine, even if rest is MDF. We are talking ~50-100euro here. not 1000.

So hope still is not lost.

JAZZCNC
16-02-2016, 04:23 PM
The other way to go is from aluminum profile but anyway you have to reinforce it with steel plate, so first option is cheaper.

Profile doesn't need reinforcing with steel at all Boyan. Provided it's sized correctly the it's perfectly strong enough for any wood router and it's much easier to work with than steel. It's also more accurate from the start and can be used without any other treatment which often isn't the case with steel.

Wood router doesn't need the Silly levels of strength your promoting with encouraging people to use steel. Infact it's wasteful and often negative to performance because the rest of the machine doesn't match.
Machine with heavy gantry needs more power than steppers can provide so everything goes to another level with servos etc and often people can't go to that level. Then the strength which isn't needed anyway just cripples performance.!

People need to start getting real and realise while it's Daft to build from weak inappropriate materials there becomes a point where over building is just has daft if the rest of the machine doesn't match.!

Boyan Silyavski
16-02-2016, 04:55 PM
Profile doesn't need reinforcing with steel at all Boyan. Provided it's sized correctly the it's perfectly strong enough for any wood router and it's much easier to work with than steel. It's also more accurate from the start and can be used without any other treatment which often isn't the case with steel.

Wood router doesn't need the Silly levels of strength your promoting with encouraging people to use steel. Infact it's wasteful and often negative to performance because the rest of the machine doesn't match.
Machine with heavy gantry needs more power than steppers can provide so everything goes to another level with servos etc and often people can't go to that level. Then the strength which isn't needed anyway just cripples performance.!

People need to start getting real and realise while it's Daft to build from weak inappropriate materials there becomes a point where over building is just has daft if the rest of the machine doesn't match.!

We all have right of opinion. I dont promote anything. My opinion is that when you spend 3000 on a machine is false economy to save 100 more on material which will raise your machine to whole new level. You call that overbuild, i call that "ability to make more juice from one orange"


But we are here not to argue or police each other. Right? The man has a question, trying to make a cheap machine and i am giving suggestions as to how to make it without loosing money in future.

So what aluminum profile exactly you suggest for 1300mm travel that will not bend and what is the price of the beam? How much the gantry +sides will cost ?

JAZZCNC
16-02-2016, 05:45 PM
We all have right of opinion. I dont promote anything. My opinion is that when you spend 3000 on a machine is false economy to save 100 more on material which will raise your machine to whole new level. You call that overbuild, i call that "ability to make more juice from one orange"

That's my whole point.!! . . . It's not just the material is it.? . . Lets look at You monster which is using servo's correct.?

Even the cheapest servos are 2 or 3 times the price of stepper motor and drive. Then you have the fact that Servos require high pulse rate to get there full speed and resolution. If not then your using electronic gearing which is wasting resolution of the encoder which you paid for and lessens the advantage of servos.
This then means a good external motion control card with at least 500Khz frequency for typical 2500ppr encoder is needed. Far more than the lower end ones like Pokeys, usbcnc or even Cslabs IP-M can offer. This also then means a quality BOB which can process high pluse rates, lots of the cheaper ones can't do this.
You also have the fact servos are very much more affected by electrical noise and require much higher attention to detail on the wiring side. Quality cables are needed and filtering for power etc and the list goes on and on.!! . . . . This is the TOTAL cost of over building.

Many won't do this and will suffer the price in some form or another. Often it's low speed/accuracy or unrelaibilty.!

Profile I DO USE for machine this size is 120 x 80 or 160 x 80 and arranged in "L" shape and can tell you now it doesn't bend even in Heavy use. Yes like anything it will bend if enough force is applied but still it's more than strong enough for any wood router or even one that's cutting aluminium.

It's also nearly 1/3 the weight of 200 x 100 x 5 RHS and not nearly has resonant. Initial Cost is more than steel but the time saving and less treatment required balances this out in the end.
Gantry sides etc are irrelavant even a steel machine will need these if designed that way.!

Also just to clear things up I'm not trying to stop you having an opinion. I'm putting my opion across and saying that what your promoting with your "Must use Steel to be strong" opinion isn't exactly true or even correct if not properly implemented and follwed up with correct components through out the machine. This you don't seem to mention often when preaching use steel.?

So I say what I do for the sake of those who see your posts and hopefully don't go blindly into something they haven't been made aware of by the preacher.!!

longy
17-02-2016, 06:51 PM
Welcome to the forum, I would suggest adding some corner bracing and beefing those legs up or you may just find your frame on the floor after a short while. Having read the others comments using the dreaded "m" stuff is a no no, but if you sheet material Baltic birch ply is much stronger but 4 -5 times the cost and won't swell up as much. The guys on here will help with the other stuff but not happy to help with the "m" stuff. m has it uses like the burner to keep you warm in the workshop.

routercnc
17-02-2016, 10:51 PM
Hi Robert,

My very first machine used plywood for most of the construction. It worked in that it moved around according to the g-code it was being given, and it did cut thin wood. Like you I built it out of stuff I had lying around to see if this hobby was for me. I actually just wanted to cnc cut a few bits for my model aircraft instead of by hand, and if you were careful this was possible.

However, it did go a bit oval on the circles and you could actually see it twisting a bit when cutting and changing direction. So in the end I stripped it down, chucked the wood out, sold the unsupported 20mm rails on ebay and kept all the 'good bits' for the next machine. These were the 16mm ballscrews and the 3Nm low inductance stepper motors. The following machine used more metal bits and was an improved design all round. As you can see in my signature it went on from there as you reach the limits of each machine and build a better one.

The negative tone on here is not meant maliciously - most guys on here have been there and done that and just can't recommend starting with wood / MDF. Especially when you see problems even when using all metal machines. In the end these machines fly around with lots of vibration over long periods of time and if they are not robust they can let you down just when you need them or be a pain to keep maintained / true.

As has been mentioned if you can buy some quality running gear you can keep them for the inevitable next machine once you realise just how much you can do with these new toys. Any metal you can add this MDF base will be a big help. For example metal parts for the gantry, and box section down the sides to mount the V-bearing plates to.