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  #1  
Old Mon 28 March 2011, 15:24
Axel1966
Just call me: Axel
 
Paris
France
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.
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  #2  
Old Mon 28 March 2011, 18:17
domino11
Just call me: Heath
 
Cornwall, Ontario
Canada
Welcome!
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  #3  
Old Thu 16 February 2012, 12:34
Axel1966
Just call me: Axel
 
Paris
France
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.

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 ?
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  #4  
Old Thu 16 February 2012, 12:41
WTI
Just call me: James
 
Detroit (Michigan)
United States of America
Heavy is good as far as cutting goes.

You see many homemade CNC rigs filled with sand to add mass and dampen vibrations.
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  #5  
Old Thu 16 February 2012, 12:46
WTI
Just call me: James
 
Detroit (Michigan)
United States of America
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.

Last edited by WTI; Thu 16 February 2012 at 12:57..
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  #6  
Old Thu 16 February 2012, 15:41
Axel1966
Just call me: Axel
 
Paris
France
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 ?

Last edited by Axel1966; Thu 16 February 2012 at 15:44..
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  #7  
Old Thu 16 February 2012, 15:50
danilom
Just call me: Danilo #64
 
Novi Sad
Serbia
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.
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  #8  
Old Thu 16 February 2012, 17:01
Axel1966
Just call me: Axel
 
Paris
France
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 :

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 ?
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  #9  
Old Thu 16 February 2012, 17:05
danilom
Just call me: Danilo #64
 
Novi Sad
Serbia
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.
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  #10  
Old Thu 16 February 2012, 18:08
bozona1
Just call me: don
 
New Brunswick
Canada
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. ...just had to say something. I hope to build one in the near future and I will not change one single thing.

Don
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  #11  
Old Fri 17 February 2012, 03:09
KenC
Just call me: Ken
 
Klang
Malaysia
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
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  #12  
Old Fri 17 February 2012, 04:41
Axel1966
Just call me: Axel
 
Paris
France
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 ?
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  #13  
Old Fri 17 February 2012, 05:10
Axel1966
Just call me: Axel
 
Paris
France
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 !
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.
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  #14  
Old Fri 17 February 2012, 05:14
danilom
Just call me: Danilo #64
 
Novi Sad
Serbia
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.
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  #15  
Old Fri 17 February 2012, 07:15
KenC
Just call me: Ken
 
Klang
Malaysia
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?

Last edited by KenC; Fri 17 February 2012 at 07:23..
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  #16  
Old Fri 17 February 2012, 10:03
WTI
Just call me: James
 
Detroit (Michigan)
United States of America
Quote:
Originally Posted by Axel1966 View Post
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 ?


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.
*******************
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  #17  
Old Fri 17 February 2012, 10:38
Axel1966
Just call me: Axel
 
Paris
France
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
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  #18  
Old Fri 17 February 2012, 13:40
domino11
Just call me: Heath
 
Cornwall, Ontario
Canada
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.
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  #19  
Old Fri 17 February 2012, 15:03
Axel1966
Just call me: Axel
 
Paris
France
Thanx for your interest Heath.
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  #20  
Old Fri 17 February 2012, 15:36
Axel1966
Just call me: Axel
 
Paris
France
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 ?
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  #21  
Old Fri 17 February 2012, 16:13
IN-WondeR
Just call me: Kim
 
Randers
Denmark
Gantry weight including the Ycar and all options, could easily move past the 100kg mark.
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  #22  
Old Fri 17 February 2012, 16:36
Axel1966
Just call me: Axel
 
Paris
France
Thanks you so much Kim, I make a table with this value
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  #23  
Old Fri 17 February 2012, 16:39
IN-WondeR
Just call me: Kim
 
Randers
Denmark
Note that I said it could easily move past 100kg... So it's not exactly 100kg, it could easily be more...
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  #24  
Old Fri 17 February 2012, 16:52
Axel1966
Just call me: Axel
 
Paris
France
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...)
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  #25  
Old Fri 17 February 2012, 17:20
WTI
Just call me: James
 
Detroit (Michigan)
United States of America
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.
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  #26  
Old Sat 18 February 2012, 05:32
Axel1966
Just call me: Axel
 
Paris
France
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 ?
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  #27  
Old Sat 18 February 2012, 06:07
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
I think you are at the wrong forum - you should go to CNCzone.com instead.
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  #28  
Old Sat 18 February 2012, 06:18
Axel1966
Just call me: Axel
 
Paris
France
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 ?

Last edited by Axel1966; Sat 18 February 2012 at 06:21..
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  #29  
Old Sat 18 February 2012, 06:28
IN-WondeR
Just call me: Kim
 
Randers
Denmark
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.
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  #30  
Old Sat 18 February 2012, 08:27
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Quote:
Originally Posted by Axel1966 View Post
. . . .I just want to understand principes before to start. . . . .
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.
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