Need HELP with Design and Parts

[joeavaerage]

Hi,
where is the sense in making a rigid steel frame only to throw it all away with an extruded gantry? The gantry is the single hardest piece to make rigidly.

Extruded aluminum is about as rigid as a soggy noodle. Filling the internal void may help a little with damping but do nothing about rigidity. The rigidity of
a hollow section is determined by the wall thickness and the size of the section not by what you put in the middle.

Craig

My apologies, I thought I was replying to a different thread, for your purposes an extruded gantry is adequate, although I would not bother filling it.
Steel is very much more rigid than extruded aluminum, but then your back into the heat treat/machining conundrum again.

[Texasbowhunter]

Seemingly there are allot up guys using this extrusion as well as manufactures and watching their videos they are able to do what I would be asking of this router...Wood and from time-to-time aluminum...Again I'm not looking for .250 plunge in aluminum and cut, but if it will carry .05 or even .10, I believe I would be happy...
Steel tubing will certainly be an option however It gets into more welding with the end caps so they can be drilled and tapped to secure to the gantry support and then possibilities on distortion and then stress relief may have to be factored in...
Hence for simplicity the Heavy 80160 extrusion was the option...If I go steel tube frame and steel gantry I hope that the other parts that support the gantry and the mounts thru out the Z will be adequate for the use of aluminum...I have a sufficient amount in 1/4", 1/2", and 1" in my stash and I need to use it to keep cost down...If not then steel gantry will not be factored in
If steel was used for gantry, what were you visualizing? I open to thoughts hence the reason I joined...
I am open to suggestions to resolve my design...
Paul

[joeavaerage]

Hi,
200 x 100 x 9 is a common size that could be bought locally.
200 x 200 x 9 is less common but still available, whether you can buy a short length is a bit questionable
You might find some 200 x 200 x 12.5, its not common here in New Zealand, but maybe more so in your area.

The bottom line is the bigger the section and the thicker the wall the better it will resist both bending and torsional flex.

Craig

[Texasbowhunter]

I could possibly find a piece of scrap in the scrap yard of perhaps a 3 x 6 maybe on the outside chance a piece of 4 x 8 or even a 8 x 8 with a 1/4" wall but I doubt I'll find anything with the 5/16 .312 or 3/8 .375 in either size laying around...
I would probably have to buy an entire 20' piece
You would build a hobby unit with this heavy material? just asking
Ill check scrap yards next week and see if there's anything there
Seems like a beast
thanks
Paul

[joeavaerage]

Hi,
you might be surprised about whats out there, the thicker wall sections are commonly specified for supporting columns to resist buckling.
Same deal applies, the bigger the section and the thicker the wall the better. Say 4 x 8 x 1/4 is still probably stiffer than aluminum extrusion, and if you can
find an offcut likely cheaper as well.

Even an RHS section will have stress in it from hot rolling when it was manufactured, but unless you weld it subsequently you might get away without heat treatment.
The only pinch is that if you machine one face flat it may move as the thin layer is taken off the surface. Heat treating first would all but eliminate that propensity
and is recommended. That would mean that all fittings would have to be bolted on, but it might be an option.

Craig

[joeavaerage]

Hi,
my mill, about a year old now, has three cast iron axis beds, 115kg each. The frame is two 'L' shaped pieces of med tensile steel 32 mm thick with 20mm thick plates in between. The legs of the 'L'
are 1300mm and 1750mm long. Yes, I used heaviest material I could afford, and wished I gone up a size or two. Having said that its still the best machine I've ever had. There is no such thing as excess
rigidity. if you have 'R' rigidity, then the day will come that you want '2R'.

Craig

[peteeng]

Hi Paul - Heres a good summary of cnc machines. Peter

https://mattferraro.dev/posts/cnc-router

[Texasbowhunter]

Thanks Pete
Read the most part...informative...
Paul

- - - Updated - - -

Hi,
my mill, about a year old now, has three cast iron axis beds, 115kg each. The frame is two 'L' shaped pieces of med tensile steel 32 mm thick with 20mm thick plates in between. The legs of the 'L'
are 1300mm and 1750mm long. Yes, I used heaviest material I could afford, and wished I gone up a size or two. Having said that its still the best machine I've ever had. There is no such thing as excess
rigidity. if you have 'R' rigidity, then the day will come that you want '2R'.

Craig

Pictures?
Paul