Effect of Forces on Gantry Cross-Sections?

[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.