Seeking informations on Big CNC
 

Hi all,
I'm Axel, from France.
I was searching informations for a DIY Huge CNC, for 2,5D milling on various types of raw materials.
Just landed here, and see a lot of interesting informations.
Thanks for all. And please excuse my bad english.
Cya.

Welcome!

Hi all, thanks for the welcoming.
I've read a lot and list all my needs about my final CNC project.
The Mechmate conception match my needs.

I have still serveral questions remaining before to start.
Appreciate I'm graduated engineer in accoustic, not in mecanics. :o

1/ Is light right ?

The Mechmate is based on steel bars.
From chassis to trolley, this is pretty heavy.
Is there any technical benefit of an heavy structure ?
Otherhand, stepper motors may use less torque if mobile parts are lighter.
Last, aluminium profiles may be less expensive in France.
According an aluminium structure offers comparable strenght and rigidity,
is it possible to swap steel for aluminium ?

Heavy is good as far as cutting goes.

You see many homemade CNC rigs filled with sand to add mass and dampen vibrations.

Generally, you need aluminum that is 3 times thicker to have the same bending strength as steel; so you not only would pay more for an aluminum structure (I don't think you will find aluminum cheaper than steel), it might end up weighing the same.

Welding steel with a MIG welder is easy and cheap (anyone can do it), Welding aluminum is much more difficult.

Thanks James.
I don't want to weld aluminium (and nothing else than electronics if possible...).
I thought rivets and corners braces was a fast and nice way.

Throught, the MM main longitudinal beams are able to support 10 tons each (22.000lbs).
Isn't it a bit oversided to carry the Gantry and Car ?

Why a lighter profile can't do the job, especialy a tube profile ?

You are only looking it in terms of static load. When the gantry starts to roll there are a whole lot of new forces around, and it needs a heavy table to absorb it.
My gantry tube is 3mm thick, my friends is 4mm, his gantry moves a bit smoother as the vibration from motors is dampened a bit and added mass keeps it firmly on the rails.

Thanx Danilo. I understand what you mean.

I thought the gravity system of the V-rails was perfectible, especialy with a light gantry.
Otherhand, the cut of the V-rails seems to me leading to unpredictable results,
event with building the special guiding tool. Small variations may produce a wrong result.
So I was about to invest into a stainless steel trolley-rail system witch is not so expensive compared to the needed v-rollers :
http://www.michaud-chailly.fr/custom..._cxx-pmod1.jpg
With the Gantry and Car fixed horizontaly and verticaly, the movement should be as smooth as possible. Appreciate the rails are straight to 0.05mm.

So, the next factor may be, will the structure be stiff enough to absorb vibrations and kinetic energy ?

If you don't like V-rollers or the weight of a Mechmate the whole design will not work for you and you will be forced to make too many design changes, look into cncrouterparts linear carriage and see how they use aluminium for structure.

This feels like Déja vu.

Axel1966

IMHO, the MM design has been worked to the point where no more changes are necessary. You're trying to re-invent the wheel. Anyway, if you do a bit of reading you'll see that you are asking the same questions that have been asked many times before. Sorry but i didn't mean to come down on you like that. :o...just had to say something. I hope to build one in the near future and I will not change one single thing.

Don

Axel, WOW! Stainless steel trolley-rail system that is straight to 0.05mm!!! Do they come in 3m length & still straight to 0.05mm? Can they take 300kg load?
I surely could use many of those for my store room & retractable canopy

I respect your point of view Don. Thanx Danilo, i've checked all the possible drive solutions.

An engineering is an instant vision to solve a problem.
A car is a car. Appreciate the way cars a builded now is not exactly the same than 20 years ago.
One day, the 2006 MM will be out of date. Should we definitely reject evolution ?

An exemple, Some MM are chain drived. IMO it's not a bad idea for many reasons.
First, it works pretty well.
Second, it's unexpensive to find, to build and to maintain.
Third, it's more simple than axis-pignon-belt-gear-rail. Just a chain a gear and two tensors.

I ask questions to the comunity to check principles.
As far i'm not an expert, my questions may be stupid, or not.
Compared to 2006, steel is much more expensive in 2012 (200% here).

I need a good CNC router. I don't have an extensible 10.000€ budget.
Two solutions :
1/ no CNC router = no budget problem
2/ try to find solutions around the MM, to make the build possible

I need to check the relevant possible evolution and minimize the desing changes.
I submit my thinks to the comunity to check where i'm wrong.

Weight means money. Definitely.
Is the weight an indispensable factor or can light but stiff structure can be an alternative ?

Thanks for your reply Ken. Sorry, I was writing, I did not read your post before.

300kg load ? Uh ! It's huge for the gantry and car, I'll use a mill not a V8 ! :D
Do you mean 300 kgf ?
According to the manufacturer informations, a four trolley guidage system can hold 320 daN (witch is comparable to kgf within 2%).
I was wrong. The profile is built with a tolerance under 1/10e mm to be exact
the roller trolley is built with a 0.05mm precision (cf. manufacturer).
I hope both can come in reasonable shape.

don't know whats the problem with rack and pinion, here it costed 22eur /m
you can just stick it up with tape and its finished?
chain on the other side needs tension, adjustment and further adjustment over time and maybe even be more expensive.

Steel tube is still the cheapest building material I know, a 6 meter U-profile 180x70mm costs 110 eur, you can cut it, tap it, weld it. Aluminium extrusion in that size and length cost surely more than 2 times that, and with extrusion you need all sorts of joints etc which you can't make yourself easily.

Please don't be discouraged by no means, find the material and parts and compare the prices, my 2 year experience with machine and the people coming over to see it says... you cant build it easier and cheaper.

Axel,
I'm thinking about having shelves to stow my plywood on a multiple drawers, I now stack all my sheets on the same pile, & pulling selected size sheet from the pile is too much strains on my back... 320kgF is ~32 kg... Can even take my weight... useless for my purpose. But I reckon you can build toy desk top CNC with it. Should be cheap & fast to complete.
If you money is short, time is your friend...
Ever consider hand filing your own rack gear from square bars?
I believe no one here resist evolution... as long as it is an improvement & worth the effort... Ever seen a hammer with 2 handles in your local stores?
BTW, ever cost in the time you spent on looking for a "better" "more Economical" solution? Most likely, one will waste more in opportunity cost than that few thousand bucks you saved on material...

Think "Standing on the shoulder of the giant"....

**PS, Even consider using scrap timber for the table & main beams?

If you want to build a MM, there is going to be welding - there is no way around it. MIG welding is much faster than you can drill and tap holes for bolts and rivets, and a MIG welded joint is stronger than the steel itself.

You can learn to MIG weld steel in a day with a used $500 Miller welder (do they have Miller and Lincoln in France?). Although aluminum can be MIG welded (it requires an expensive spool gun add on and gas), it is usually TIG welded. TIG welding is 3 weeks of classes and a $2500 rig just to get started.

The reason the MM main longitudinal beams are so strong is that with the stresses of the moving gantry and the load of the router being plunged into the material are much greater than you think. You want to hold tolerances to .001" right? The roof on your house is fine until you pile 2m of snow on it...


******************
Today, I want you to call a metal supplier in your town and ask for the same piece of material (lets say 50mm x 50mm square tubing with a 6mm wall, 4m long) in both steel and 6061 aluminum. Report back to us the price difference.
*******************

Hi all, thanx for your awnsers.
I only studdy a CNC router for one year, every advice is crucial to me.

@Dalino
I seached a lot for best suppliers here. I don't have the same prices.
UK or Germany are less expensive than France. Serbia looks like even better !
The best price I get for U-Profile 180x70mm is 26€/m while you have 18,5€/m.
Same for the rack you get 22€/m while I get 32€/m.
For the transmission, pignon, 2 pulleys, belt and axis = +-45€ without fasterners... :(

That's why I turned (at this point) into :
100x18mm renforced aluminium structure at 4,5€/m (can be doubled or tripled if necessary)
Chain 5€/m, chain holders 2€ each, 1 pignon 9€, 2 tensors 6€ each, 2 springs 0,40€ each.
Definitely, it's less expensive.

Otherhand, Aluminium is fast and easy to be cut, just drill holes and fix a rivet, it's all done.
No need of grind, degrease, paint... A rivet cost 0,02€ each, plate or corner braces only 0,60€ each...
With steel, I will need an angle grinder (200€) preferabily a metal chop saw (450€), an arc welding machine (80€)...
And just for the CNC construction because I won't use it in the future...
Aluminium must be faster and easyer and not that expensive. The question is : is it a good idea ?


@Ken
"nani gigantum humeris insidentes" I was born near Chartres and Studied there, I well know this aphorism. ;)
That's exaclty what I'm trying to do... I guess it's at last missunderstood.
I apreciate my request seems ridiculous for your eyes. Ok, duly noted.

Among your inacurate comments, this must be corrected :
Kilogram-force (kgf) is equal to the gravitational force on a mass of 1 kilogram.
1 kgf = 9.80665 N = 0.980665 daN
That means you can hold >313 kg (not 32kg) on 4 trolleys, until 9.8 meters per seconds, whitch is fast enough.
Up to 10 plywood plates (2440x1220x18mm), not that bad.
So it can match your needs. My pleasure to help.

@James
Thanks, it's one of the best awnsers I ever had. I understand what you mean.
I know Welding is strong. Parts have to be cuted and drilled too, and maintained in place while welding.
I dunno if I'm able to do it in a single day. Throught, there's finition to do after that.
We have MIG engines in france, starting @ 180€, I guess a good one may cost at last 500€ (660 US$).
Maybe the solution is to rent a professional one.
It's too late here to have the exact prices you requested. (Week End). I'll get the information on monday.

I'm Sure the kinetic forces of the moving gantry and the car can be calculated.
It should be depending of the speed and the weight of the moving parts.
I'm more comfortable with sound reflexions or isolation calculation,
but I'll study that to know exaclty what amount we're talking about ! ;)

Thanx all for your interest and your comments.
I'm still at the begining of the road and your help is greatly apreciated
:)

There are lots of people on the net who have designed their own cnc routers. Some have used MDF, some Aluminum and some steel. If you want all the benefits of the Mechmate proven design, follow the plans. If you want to do your own design to make use of materials more available to you locally you can do that as well. Your end result will depend on how good of a mechanical designer you are.

Thanx for your interest Heath.

I can not find any information about the gantry and the Y-Car's mass. :(
Of course, it depends of many factors, especialy lenght, accessories and tube sections in use...
No need to have a precise number, just an aproaching value can be enough to have an idea.
Let's plan on 1500mm lenght for the gantry. (as Y-Car's should be closely the same weight for all MM)
Any idea mates ?

Gantry weight including the Ycar and all options, could easily move past the 100kg mark.

Thanks you so much Kim, I make a table with this value :cool:

Note that I said it could easily move past 100kg... So it's not exactly 100kg, it could easily be more...

Yes, I got it kim. ;)

So, a 100kg Gentry+Ycar at 0,170 m/s (400 IPM) makes a kinetic energy of 1,43 Nm.
A 120kg Full Gentry at the same speed makes a kinetic energy of 1,70 Nm.

I wonder if the calculation is right. The kinetic force seems very low... :(
Maybe the MM is able to go faster than 400 IPM...
What should be the good speed to deal with ? (aproximatively, throught...)

Your rapids probably can be a lot faster than 400 IPM, but for cutting, it depends on the bit, the size of your spindle, and the spindle rotation speed.

Thank you James.

Into this post, J.R.Hatcher says his MM max. speed is 1350 IPM :
http://www.mechmate.com/forums/archi...php/t-748.html
So fast! Even with a good spindle and low deepness, maybe too much for safety IMO.

So, let's calculate again with several values !
Ec for 120kg @ 500 IMP = 2.68 Nm
Ec for 120kg @ 750 IMP = 6.04 Nm
Ec for 120kg @ 1000 IMP = 10,74 Nm
Ec for 120kg @ 1350 IMP = 19.57 Nm
In the formula, it's speed². So speed is an important factor.
Maybe more important than weight.
Throught, these values seems to me low...
(If a Mechanic Engineer may verify...)

Let's see with half weight gantry
(aluminium made, according rigidity must be similar... -45 to -65% weight less usualy)
Ec for 60kg @ 500 IMP = 1.34 Nm
Ec for 60kg @ 750 IMP = 3.02 Nm
Ec for 60kg @ 1000 IMP = 5,37 Nm
Ec for 60kg @ 1350 IMP = 9.78 Nm

Even if the calculation is not totaly exact, with half weight,
aluminium will deal with half less kinetic energy.
Interesting, even if it's not the single factor.

What do you think ?

I think you are at the wrong forum - you should go to CNCzone.com instead.

Thank you for your interest Gerald, and for all your work and investment here.

A lot of people think about kicking me out, while I just want to understand principes before to start.

Just a question.
Today, the MechMate is 1.x
Did you ever think about a MM 2.0 ?
What could be the future of this marvelous machine called MechMate ?

Axel

That question have been up many times. The MM community is pretty set on their ways, and by such they are not keen on taking changes and new design ideas into effect.

I have also been one of the few which has been excluded a bit on this site, when I went my own way.

No offense Gerald, I have gotten alot of information on CNC's through this site, and I have put it to good use over the years. So for that I thank you.

What do want to start?:
- if you want to start to build a MechMate, then follow the plans
- if you want to start analysis of CNC machines to design your own, then find some people with better experience, that is at CNCzone.

Thank you very much Gerald.

I have no more questions except those you did not awnser.

Axel,

I think what Gerald is trying to tell you is that the MM is done being designed. It is already version 2.0 (for a while the second version was being called Mamba, now it simply IS the Mechmate).

All of the engineering of whether it is stiff enough, the motors large enough, the weight heavy enough, the V-rails accurate enough - has already be worked out years ago.

Gerald worked for 6 years to help us all build our own MM and is now "retired".


So if you want to build a proven design (there are already well over 150 MM working and making money), that lets you own a $35,000 router for $5000, just download the plans and build the machine.

If you want to talk about re-engineering the plans, making it lighter (which will make the cut quality poorer), using sprocket and chain (gets filled with wood fibers), using ball screws, or any other ideas that were tested and rejected many years ago; then the place where people like discuss those things is the DYI Router Table group on CNC-Zone:

http://www.cnczone.com/forums/diy-cn...able_machines/


Here on the MM forum people just want to quickly build a commercial quality machine from proven plans - not reinvent the wheel.

Thank you very much James.

I personally know of a couple of people that came to my house to look at my MM....then I hear all the KNOWLEDGE poring out...I will change this, I will do that etc.
I warn them and say to them to just stick to the plans like I did.
What happened, most of those start the build, change things and run into all sorts of problems...Bottom line 2 years later they still don't have a working MM.
I am happy with the MM as it is....too stupid to re-design it, and it works for me.;)

Agree with Kobus, we don't have to go far, we are not short of such "knowledgeable" individuals posting in this forum...

I am going to have to agree with Gerald and the others on the building of the Mechmate.
If you want to design a machine,this is not the forum for that. We are here to help you build a MechMate and the reason everyone does basically the same build has also been covered. So feel free to read as much as you like, buy a set of plans and get busy building a MechMate. We will be there for you on those questions but you will find this group not to focused on talking about non MechMate systems.

Oh, come on !

I was friendly and gentle with anyone here.
I studdy CNC router solutions for more than one year, I did not land here with no reason...
to come.

I said it at the start, I'm not a mech engineer.
Like in all forums, you have people of all kind. Sorry to be of an unexpected one.
There's no offense to try to understand the meaning of a complex structure you're going to build during weeks.

I'll have to build a MM with half the comfortable budget needed.
Unfortunately, parts are more expensive in France than in the States, when you can find them. Those are two very important factors to me.

That's why I started to question each point that could have an incidence on budget.
Starting by the question "Is Light Right ?"
Instead of any pertinent awnsers, I had "do not reinvent the wheel" ; "Go to CNCZone". A bit short to understand, especialy, if your English is not realy good.
So I tried to present arguments to see what could be wrong.

An understandable awnser comes at last in message #32, thx James :
Good ! So weight is important to cut quality. That's all I wanted to know at this point.

So I'm now working on my table dimensions. I will make and submit a rough as soon as possible, to valid the global shape. I studdy meanwhile "welding for dummies".

According 6 years is old for technologics these days,
I wish we will not have a new version of the MM in a close future...
I don't want to spend months of work for an obsolete or dysfunctional table.

Thanks again for those who gave their help without judgement.
I promiss to explain better (as possible) the reason of my questions,
to avoid bi-lateral missunderstanding or waste of time.

I try to be a suitable MM builder. ;)

Axel,

Like on a job site, we have to pick on the new guy a little bit - just to make sure he is tough enough to hang around with the rest of us.

Looks like you will be fine, and we look forward to helping you build your MM.

=

Do you have a scrap yard in your city? Or Craigslist on the computer? It is pretty easy to find inexpensive I-Beams that can be substituted for the less common C-beams.

Sometimes giving a couple of bucks to one of the scrappers is worthwhile if he'll set aside material that comes in and call you.

Many thanks James,
Well I make my searches in this way...
A have a contact with a steel provider who cuts for the industry.
So he have 3000 tons of unselled ends, i'll find my stuff there with a piece of time.
I don't worry with the metal.

I guess I'll rent a good MIG Welder for a week end when all the cutted parts will be ready.
I own a dedicated (not so) old computer. This is not to be buyed.

I guess it will be more difficult to find rollers, morors and controllers cheaper.
We'll see. I'm just at the start and I know I must go slowly. :o

Axel,
There are very few MM builders with fewer skills than myself. It can be done. The welding takes practice. There is good info here and on welding forums about welding, but it's all about getting the "feeling" for yourself. One of the nice things about the "heavy" (thick) steel of the MM is that a poor welder can get away with grinding and rewelding (a lot, in my case).

If you're an engineer, then you have the ability to read the plans and figure out the electronics - for me these were the most interesting, but also the most worrying, because that's where the $$ are invested and so you don't want to fry components.

The thing I noticed during the build was that things magically fit together right at the end. If you change something from the plans, you suddenly discover that there is insufficient clearance for a bolt head or something when you assemble things. I've seen this a few times on the forum.

I've also noticed that builders who spend too much time worrying about fancy and "optimised" components often seem to bog down, go quiet, and seldom finish.

I guess I read some threads in the Structure and Mechanics and other parts 10 times during the build. Each time I understood a little more what was being discussed. Also, I found a few local builds to follow (surfCNC and Tony, in my case) because that helped with sourcing components.