Effect of Forces on Gantry Cross-Sections?

[JAZZCNC]

am i reading this right that mounting on steel box section is a no no?? if so how big of a problem are we talking here?

Depends which world you live in.? The theoretical or the real.!! . . . . . FFS wish folks would stop over complicating things.!!

Here's the real world deal.!! . . . Irving is absolutly correct that unless you can surface the two sides parallel and flat then you can't be 100% sure every things correct.! . . . BUT . . . This is true in one way or another for ALL the surfaces the rails mount onto whether they be 1 rail on top & 1 on front, or both on front etc and unless you can put these surfaces complete and assembled onto a milling machine and accurately machine all surfaces flat and parallel or perpendicular to each other then you are going to have to accept they will need some adjustment or tweaking.!!

How you do this will depend on the design But having the rails on 2 separate sections, no matter if that be profile, boxsection, ali plate will make very little difference and It's FACT that some shimming or filing or grinding will be needed to bring the rails into perfect alignment and parallelism either way.!

Now I'm not going to blow smoke up your arse's saying this is easy and quick because it's not and doing this takes patience and a lot of measuring and masses of time if you want good accuracy.!. . . BUT . . . If your just cutting wood,foam and bit of plastics then even box section will be close and with slight bit of clean up and shimming you'll be there in no time.!

I know it's hard if you haven't hands on experience of the forces cnc impart on frames and accuracy required but really for the application of mainly wood use then any of the designs shown here would be plenty strong enough.!! . . . For real meaningful Aluminium and steel work then all of them are not really up to it.!!

Don't fry your noddles trying to create the perfect flex free gantry for cutting woods etc because your just wasting braincells and time when it's not needed.!

[Iwant1]

. . . If your just cutting wood,foam and bit of plastics then any of the designs shown here would be plenty strong enough.!! . . . For real meaningful Aluminium and steel work then all of them are not really up to it.!!

Don't fry your noddles trying to create the perfect flex free gantry for cutting woods etc because your just wasting braincells and time when it's not needed.!

Thanks for the comforting post Jazz. Since this thread started, I've been thinking I got my machine drawings all wrong, and thinking about it day and night. I'm building my machine for general use and for a multitude of materials. I definitely won't be cutting steel, but would like to know it could do the odd bit of aluminium such as the 'Aztec calender', lol.

Is there any chance we can see your machine's gantry or get a description, as I know you mostly work with aluminium.

Thanks

[WandrinAndy]

Since this thread started, I've been thinking I got my machine drawings all wrong, and thinking about it day and night.

Blame it on Jazz... lol... It was he who got me questioning that my drawings were all wrong, although I thought I had roughly copied my gantry design from your gantry design.

But... I am extremely pleased that he sold me his simpler green design!

LOL and night night.

[JAZZCNC]

Blame it on Jazz... lol... It was he who got me questioning that my drawings were all wrong, although I thought I had roughly copied my gantry design from your gantry design.

It's OK my shoulders are broad has well as my stomach.!! . . . .But never said wrong just could be better with wider profile.!!

Is there any chance we can see your machine's gantry or get a description, as I know you mostly work with aluminium.

Well actually this will seem ironic in that my gantry is kind of like box section.? I'm a bit of "Womble" and hate waste. So It's rescued from scrap bin and started life has a Stanner stair lift real HD bespoke aluminium profile that the chair rails ran along.
It's shaped like an "H" but imagine the bridge being box section with the sides sticking above and below about 30mm. Cant show pics because I'm not at home and my pics are on external drive.
The void the top and bottom sticking up bits create have had 60x30mm profile inserted and bolted to gantry which the profiled linear rails fasten onto.
The boxsection void is filled with sand to dampen resonance.! This was done afterwards because I wasn't happy with the tune it was Singing.!!

I wouldn't recommend anyone copy it because it's a rubbish why to do it and I only did it because I had the profile for free. It took me along time "Shimming" to get it working to an acceptable level of accuracy and I'm still far from happy with it regards strength and vibration so while It's strong there's easier and better ways to do it.

The secret to cutting aluminium successfully on a "Router" type machine is to limit tool and Z extension to the minimum possible and reduce resonance/vibration to minimum thru using dense gantry/machine materials.
That's why box section is not ideal for gantry's cutting aluminium unless filled (Made denser) but for woods then it's not really a problem if a decent wall thickness is used and like I say the rail alignment/parallelism etc has to be dealt with thru shimming or surface adjustment regardless if rail mounting surfaces are on individual pieces of profile/B-section or one big boxsection/profile.!!

If I was in the position lots are where they have to use off the shelf materials that can only be worked with hand tools then for a "Gantry" I'd choose Profile over box section every time.!

[irving2008]

Well actually this will seem ironic in that my gantry is kind of like box section.? I'm a bit of "Womble" and hate waste. So It's rescued from scrap bin and started life has a Stanner stair lift real HD bespoke aluminium profile that the chair rails ran along.
It's shaped like an "H" but imagine the bridge being box section with the sides sticking above and below about 30mm. Cant show pics because I'm not at home and my pics are on external drive....

This made me smile Jazz... I have nearly 7 metres of the stuff, in two 3.5m lengths, rescued from my late fathers house, had to cut it into two bits to get it in the car. I had plans to use it for 'something' but never did figure out how to get round the odd shape, I'd describe mine as like two round rails attached to a box section with fins (see the pic below, the end cap is roughly the shape of the profile). I keep thinking about chopping it up and turning it into ingots for future needs but its just looks too good as a profile. Also got the rack (that was already in 2 lengths) and pinion and the original drive motor and batteries still.

[JAZZCNC]

This made me smile Jazz... I have nearly 7 metres of the stuff, in two 3.5m lengths,

Yes I've seen this type on the newer models Irving but it's completely different to the stuff I had given, it was 3.5mtr thou and yes I cut it In half to get into car that's why my machines 1500mm wide. . Lol . .. . I actually didn't have a use for it when given just knew it was too good to go in scrap bin.!!
My machine came about by watching A U-tube vid and thinking "I can do that.!!" then looking at this piece of profile and pile of spare box section and hey presto 6hrs later the frame was roughed together.!!

The materials for whole main frame including gantry of my machine (1500mm,sq) cost £77 and that includes Ali for sides and profile on gantry, Z axis Ali cost £25. The complete thing including Z axis but excluding Ali bed cost less than £102. The profiled linear rails cost another £175 second hand of ebay. The ballscrews from chai/ebay and for roughly £500-600 I'd got a working machine that after plenty of tweaking cut's Ali fine and doesn't even know it's cutting wood.

[WandrinAndy]

. . . For real meaningful Aluminium and steel work then all of them are not really up to it.!!

The trouble in my case is that my (human-oid) mind, although not (and maybe because of not) having any experience of this field, wants to understand at least the basic concepts of why some things are bad and others good.

Quite sure that I will get a massive buzz with the first proper movement of the cutting tool... maybe just scribing something... but the REAL joy for me is in learning new stuff and putting ideas together, albeit mostly cribbed from others!

My journey started with the intention of only machining wood, and then the idea evolved to...

- maybe it could also be used for at least accurately marking layouts on aluminium parts which would surely be better than marking them manually

- and maybe it could be used to machine aluminium parts like the guys on here have made for the next upgraded version of their machine, albeit at slow speeds and not to the greatest levels of accuracy

Don't think it will evolve further than that... certainly not on the initial machine.

[wilfy]

Depends which world you live in.? The theoretical or the real.!! . . . . . FFS wish folks would stop over complicating things.!!

Here's the real world deal.!! . . . Irving is absolutly correct that unless you can surface the two sides parallel and flat then you can't be 100% sure every things correct.! . . . BUT . . . This is true in one way or another for ALL the surfaces the rails mount onto whether they be 1 rail on top & 1 on front, or both on front etc and unless you can put these surfaces complete and assembled onto a milling machine and accurately machine all surfaces flat and parallel or perpendicular to each other then you are going to have to accept they will need some adjustment or tweaking.!!

How you do this will depend on the design But having the rails on 2 separate sections, no matter if that be profile, boxsection, ali plate will make very little difference and It's FACT that some shimming or filing or grinding will be needed to bring the rails into perfect alignment and parallelism either way.!

Now I'm not going to blow smoke up your arse's saying this is easy and quick because it's not and doing this takes patience and a lot of measuring and masses of time if you want good accuracy.!. . . BUT . . . If your just cutting wood,foam and bit of plastics then even box section will be close and with slight bit of clean up and shimming you'll be there in no time.!

I know it's hard if you haven't hands on experience of the forces cnc impart on frames and accuracy required but really for the application of mainly wood use then any of the designs shown here would be plenty strong enough.!! . . . For real meaningful Aluminium and steel work then all of them are not really up to it.!!

Don't fry your noddles trying to create the perfect flex free gantry for cutting woods etc because your just wasting braincells and time when it's not needed.!

thats a really great post and it goes someway to help people realise what they need. thank you :D