[I want to reserve the first post for the actual build log]
[I want to reserve the first post for the actual build log]
Hi folks!
I have not designed anything yet as I still struggle to decide which design route to take. Your help here will be really appreciated!
What I want:
- a machine capable of milling aluminium with a decent speed and surface finish
- a cutting area of about 600 x 900 mm
- to be lightweight, with a small footprint. To be able to move through a 80 cm door (partly disassembled).
I was starting from Jonathan and Routercnc designs. Then I tried to find ways to add damping and gantry stiffness without adding a lot of weight.
The easiest and fastest design to build is Jonathan's frame http://www.mycncuk.com/attachment.ph...d=9811&thumb=1 with Routercnc's gantry http://www.mycncuk.com/attachment.ph...=17240&thumb=1, all welded RHS steel and epoxy levelled. But those RHS left empty look so... 'not professional'. The stiffness isn't great and they ring like a bell.
For the frame, filling it with sand (after moving/assembling) looks like a good idea.
The gantry needs to remain lightweight. What could be used to fill the RHS to add damping, stiffness without adding to much weight?
This aluminium foam looks so sexy.. But how is it produced? How complicated/expensive? I couldn't find an answer yet.
Attachment 25162
And here's an article about it: Vibration Damping Analysis of Lightweight Structures in Machine Tools
Another idea is filling them with foam concrete.
But in both cases the filler will shrink by cooling/curing and maybe detach from the steel walls.
There are other damping techniques/materials but do we have access to them? http://www.aspe.net/publications/Ann...IS/BAMBERG.PDF
Then I compared the stiffness of rectangular hollow section steel vs. aluminium t-slot profile.
Adding a 500N force in the middle in a supported two ends configuration, 160 x 80 x 5 mm x 1 meter RHS steel (18 kg) will deflect 0.1 mm and the 160 x 80 mm x 1 meter aluminium t-slot profile (13.5 kg) is deflecting only 0.012 mm. I have no idea which of the two is better at vibration damping. The only advantage that I see for using steel for the gantry is the price, 5-6x cheaper than aluminium extrusion.
Most of the 'real' metal cutting machines are using grey cast iron which has 20x or more vibration damping capacity than steel. And it won't bend but break.
Iron casting with lost foam technique isn't that complicated/expensive. But how strong should a 1 meter gantry be? How heavy will it be? I couldn't find any information on cast iron gantry design...
I am just wondering what material is Datron using for the gantry of their M8Cube CNC?
Here is another way to add damping but the cost is far beyond the budget of a DIY cnc. https://www.machinedesign.com/bearin...on-linear-axes
What do you think? Any comments are welcomed as I'm lost in so much technical information/alternatives!
Paul
I'm intending to add a layer of foil-faced Tecsound damping sheet inside my gantry extrusion, I've found it very effective in the past on metal enclosures. I may also try some expanding polyurethane foam, either on it's own or in conjunction with the Tecsound: just need a bit of time to experiment!.
The answer is easy, the implementation of it is not, you set up a factory to make the Aluminium Foam filled parts of your choice, it is not an "Aftermarket Filler" choice.Quote:
Originally Posted by paulus.v
Hi Paul,
We're all there at some point(s) [emoji846]Quote:
Originally Posted by paulus.v
Indeed, found an interesting thesis on the matter tending to confirm this.Quote:
Originally Posted by paulus.v
In the end, for this size of machine, the weight vs dynamics can be managed with appropriate motion component choices.Quote:
Originally Posted by paulus.v
Interesting, will surely read the paper, but I doubt this can be DIY, and wonder if companies able to do it can be found easily...Quote:
Originally Posted by paulus.v
Wow, never heard of this! Veeeery interesting. You just added another option to investigate to my list.Quote:
Originally Posted by paulus.v
About shrinking/retraction, I don't think this such an issue, or at least that it can't be solved easily, as this is a construction method used daily in buildings. Quite sure there should be something in Sika or other product range for this problem.
This is actually my champion ATM! I find this Constrained Layer Damping technique very interesting by its use of multiple materials, smart mechanical principle, and affordable materials and build techniques.Quote:
Originally Posted by paulus.v
Visco-elastic mat used in the thesis can be found and is not insanely expensive, and I'm sure can (and most probably will) be replaced by other cheaper and/or more easily available products. I'm currently thinking to asphalt mats...
They also use (IIRC) aluminum oxyde in concrete mix as an expansion agent, which should also be an answer to the previous retraction issue.
Even if I'm a little surprised by your stiffness numbers... Price remains one of the top decision factors, at least because all cents saved in structure will be to increase quality and performance of other components.Quote:
Originally Posted by paulus.v
Other usual suspects are epoxy concrete/granite casting, and of course, solid granite stone. These are my second and third options.Quote:
Originally Posted by paulus.v
You'll find tons to read about the first, and high end machines are also built this way.
About the second, you should be very interested by this build series https://www.youtube.com/playlist?lis...BoMfvQ8Ttsq-57 (as well as by all other videos from this guy!)
I won't even look for pricing infos just to not feel the pain! [emoji6]Quote:
Originally Posted by paulus.v
Hope it helps
Cheers
Jérémie
Envoyé de mon ONEPLUS A5010 en utilisant Tapatalk
Hi Paul,Quote:
Originally Posted by paulus.v
Are you sure about the stiffness you describe above.
As a rule of thump, steel is more rigid by a factor of 3 for a given shape at the same weight.
Box section should be more rigid than tslot profile..
You explain above the tslot alu 13.5kg is more rigid than the steel box at 18kg....
I am not saying you are wrong... it just doesn't sound right.
Please check to make sure.
Also weight is your friend preventing vibrations.
I know it is hard to make the choices.
If you have access to tools and skill to go the steel frame / epoxy route i recommend it.
Grtz Bert.
Verstuurd vanaf mijn SM-A320FL met Tapatalk
Seems like a very interesting alternative to asphalt mats, thanks!Quote:
Originally Posted by Voicecoil
Envoyé de mon ONEPLUS A5010 en utilisant Tapatalk
Tecsound is good stuff, but to get the best of it DO face the side that's not stuck to the extrusion with some metal foil or thin metal sheet, this gives the "constrained layer" effect where bending of the substrate is translated into shearing of the Tecsound which is MUCH more effective than just bending/wobbling it. 100u foil tape seems to work pretty well (I used it with good effect to quieten down my awesome but quite noisy Subaru STi) but if you can find something thicker it would improve further.
Aluminium is stronger/stiffer than steel for a given weight. By volume steel is stronger, but not necessarily stiffer, as Steel generally has more elasticity than aluminium.Quote:
Originally Posted by driftspin
Off course that's a very general observation, as strength will depend on the exact profile/loading/application.
Thanks for that link, I spent most of Sunday watching that guy's videos!!!Quote:
Originally Posted by silopolis