What is the max Gantry width allowable
 

Gerald,
What is the the Max. allowable gantry width?
I may want to build a "small" form factor machine and need to place sideways so the open side is really the y-direction, thus making the x - 48" and the y - 96" inches (or 3Meters). Would this be allowable?

Thanks,
Sean

I don't see a big problem with that, but I would probably go to 2.5mm wall thickness in the pair of 100x50 box-sections. (Our tables are already at y=75" cutting width)

Great news,
Not that I published in my past 2 builds, but I did use 4.75mm (3/16") wall tube. It was (and is) readily available and the extra mass has not been an impact at all yet.

With your gearing (small pinions) that extra mass is easily handled for accel/decel. The V-rollers are rated for way more than that mass. Maybe we need to look at a hardened rail . . . (How are your current rails holding up?)

But 3/16" wall is going to give you the stiffness over that length.

That's great news for me too, as i'm thinking of a similar configuration.
If I went for a 4mm tube, would a 3m Y work area i.e. 3500mm long cross member tube be pushing too far,
or is it just a question of having realistic X gearing & acceleration settings?

The rails are holding up pretty well, I can see visual wear, but nothing significant that would alarm me. At the current duty cycle, I would assume another 3 years on these rails before I have to be thinking about another solution.

Greeny, I don't know about 3.5m, just because it is so much longer than what we have experience of. In theory, the static flex of a 4mm thick 3.5m tube is less than the static flex of a 2mm thick 2m tube, but I suspect that it will resonate at a lower frequency.

Ok, thanks.

Either, I'll tone it down to 3m overall Y (2.5m working area)
Or swap the X and Y axes back to a more 'normal' configuration.

Did anyone try a longer gantry? I am curious because I have been contemplating building a 10 ft gantry so I can have a long fourth axis.

Thanks

I'm no expert but I don't think so. I'm going to build this way but only max span of 8ft (the established norm for the X axis) as far as going longer see Geralds comments in post #7 above. this doesn't proclude a longer 4th axis though there are examples of people planning recesses allowing the 4th axis to run parallel to the x axis.

Are you building the machine so that the gantry spans the long side of the material?

Post 7 is why i thought i should ask if anyone had experience with a long gantry? I am not worried with deflection but the resonance could be a problem.

If a long gantry was feasible it would allow the two long sides of the 4x8 sheet to be completely open. The two beams at either end of the table, that hold up the gantry, would be extended past the table on one side. The fourth axis would mount under the extended rails, on the side of the table.

Yes I am, I'm building the machine primarily for cutting surfboards, my thinking is that I may be able to run the machine faster with the Y car running the length of the machine rather than having the high mass gantry doing lots of direction changes, it's also more convenient for loading blanks with this orientation. Having said this I'll be sticking to the 3m limit that Gerald discussed, I would rarely cut anything over the ~8ft cutting limit at this length. I'm also just ordering my steel so am a way from having it built.

There aren't any build logs to suggest it and if it has been done it's owner is not advertising at least not on the Forum; hence my comment, I don't think so.

Consider the max length in which TS is available. In the US, the standard length is 20'.

I *think* that a gantry suited for 8' carriage travel will be just under 10' long.

Jeff you are correct I believe, I probably wasn't clear in my first post on this, the 8ft discussed was intended as cutting width not gantry width (i.e 8ft cut requires 10ft, 3m, Gantry).

My point was mostly to consider the materials length if anyone was planning to exceed that length. 3m cutting width would require TS greater than 10' in length.

Reply to post #6 If the wear became too much could you convert the ground to the bolt on hard rails at that time? Regrind?

Why not wax/parafin as a lubricant on the rails.

Using a wide gantry for cutting 2050mm wide boards, would be an 100x50mm or 100x60mm 3mm thick wall tube be enough?

100x50x3 would be enough

Has any one completed and tested the longer gantry? I am very interested how it went.

I used 100x50x3 tubes for my wide gantry, Milan used 100x50x4 , we both have no problems but I think his gantry is more solid. Both gantrys are for cutting 2050mm wide boards.

Cheers Danilom, That boosted my confidence.

I'm planning on a 2400 * 1200 cutting area. So the span would be 2600 and 1400 respectively. I will use the 4mm.
Any photo's?

You have photos in my build and also milan's here
http://www.mechmate.com/forums/showthread.php?t=2704

2940mm for gantry beams
 

Hi all.
My needs are gantry beams of 3m (2940mm) long.
I did not see the Greeny project in the "already cutting MM".
Is it technicaly possible while preserving a nice cut quality ?
I guess I must use a belt reduction to save on torque (7.2:1 ?). Speed does not mater.

What should be the best option ?
- go to some 4 mm thick beams ? Greater ?
- go to 150x50 beams with standard 2mm thickness ?
- stop asking stupid questions Axel... :D

Do motors be different than standards MM specifications ?

I got the anwser by myself, it's option 3 : Stupid questions = no anwsers... :o
Nerver mind, I'll use 150x30x3mm. Or 150x50x3mm. Or 100x50x5mm...
Well I realy don't know... :(

Axel, if we really don't know, then we cannot give an answer. We don't judge your question as stupid. We cannot give a definite answer if it has not been tested.

I understand. And it's wise.

I post here my hazardous conclusions, maybe someone will find it useful someday...

I'd tryed to get a partial anwser with L4 (we say "moment quadratique" ou "moment d'inertie" in french) of rectangular profiles sections...
I started to list some possible tube sections to compare different factors.

http://giemastruc.free.fr/Forums/CNC-calculs-7.png

The goal is to get the best deflection factor, and mimimized vibrations.
According to the informations I own at this point, the gantry beams should not exceed 78kg.
And up to 3mm thick, the flex will be under 1mm (4 points of 20daN at center of the beams, spaced of 50mm).

So, UPN Profile gives more, but I've read somewhere UPN profiles vibrates too much compared to rectangle or square profiles.
May an expert confirm that point ?
As KenC says, higher sections increase greatly the profiles purposes without increasing dramaticaly weight or cost.
A 120x60x4mm profile is close to double the abilities of a 100x50x2mm (which is MM standard).
BUT ! (it's a big 'but':D) Some parts of the mechmate should be transformed.
I'll see precisely with the plans in hand, but I'm realy scared about that.
Each mistake done might cost a lot or induce stunt modifications. I realy know that.

So... Comes another Axel's stupid idea... What about welding two 50x50x2mm together ?
The final shape should be 100x50mm so will not need customised parts.
It's a huge work to weld the two parts together (hours for a 12 meters linerar welding).
With what benefits ? Theorycaly, it should be better than a 100x50x5mm
with lx > 200 and l/v > 40. Saving 20 kg throught.
I realy don't know... The only thing I know : vibrations should be greatly ducked.

Another stupid idea : fixing the Y rails with 120mm bolts throught the Y beams to make bridges reinforcements all along the profiles.

I walk in the dark. If you have any think or feeling about that, feel free to tell. :o