MK2: moving gantry router for metal cutting - comments sought!

[paulus.v]

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 with Routercnc's gantry , 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.


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

[Voicecoil]

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!.

[silopolis]

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!.

Seems like a very interesting alternative to asphalt mats, thanks!

Envoyé de mon ONEPLUS A5010 en utilisant Tapatalk

[Voicecoil]

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.

[magicniner]

This aluminium foam looks so sexy.. But how is it produced? How complicated/expensive? I couldn't find an answer yet.

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.

[silopolis]

Hi Paul,

I have not designed anything yet as I still struggle to decide which design route to take.

We're all there at some point(s)

For the frame, filling it with sand (after moving/assembling) looks like a good idea.

Indeed, found an interesting thesis on the matter tending to confirm this.

The gantry needs to remain lightweight. What could be used to fill the RHS to add damping, stiffness without adding to much weight?

In the end, for this size of machine, the weight vs dynamics can be managed with appropriate motion component choices.

This aluminium foam looks so sexy.. But how is it produced? How complicated/expensive? I couldn't find an answer yet.


And here's an article about it: Vibration Damping Analysis of Lightweight Structures in Machine Tools

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...

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.

Wow, never heard of this! Veeeery interesting. You just added another option to investigate to my list.

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.

There are other damping techniques/materials but do we have access to them? http://www.aspe.net/publications/Ann...IS/BAMBERG.PDF

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.
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.

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.

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.

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...

Other usual suspects are epoxy concrete/granite casting, and of course, solid granite stone. These are my second and third options.
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!)

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

I won't even look for pricing infos just to not feel the pain!


Hope it helps

Cheers
Jérémie

Envoyé de mon ONEPLUS A5010 en utilisant Tapatalk

[driftspin]

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 with Routercnc's gantry , 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.


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

Hi Paul,

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.








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[m_c]

Hi Paul,

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....

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.

Off course that's a very general observation, as strength will depend on the exact profile/loading/application.

[AndyGuid]

. . . . . 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!)

Thanks for that link, I spent most of Sunday watching that guy's videos!!!

[paulus.v]

Thank you all for your input!

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!.

Tecsound looks promising. Not sure how different could be compared with the ISODAMP C-1002 mentioned in the MIT paper. A friend is soundproofing cars for 'dB drag racing' with StP. Not sure how good it is at vibration damping but I'll test it.
I don't think the PU foam has any damping characteristics. If you knock it the sound is very well propagated.

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.

I see a few books cited on wiki about ally foam manufacturing. I need to get my hands on one of these books.
Here's an experiment but the result doesn't look that great. https://www.youtube.com/watch?v=8FHTK2LZNTY

In the end, for this size of machine, the weight vs dynamics can be managed with appropriate motion component choices.

Exactly here's my problem. I need a lightweight machine, and being light allows me to use steppers and the price difference to servo I can use to improve damping and stiffness without adding to much weight.

Wow, never heard of this! Veeeery interesting. You just added another option to investigate to my list.

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.
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.

I doubt the expansion agent will work with foam concrete as it will tend to put pressure on the air bubbles in the concrete not against the walls of the mold. This chart shows that the shrinkage increases as concrete density lowers.

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.

i have checked the deflection only with online calculators, two for each and they gave similar values. But now I tried a lot more calculators fot the RHS and the values were different... from 0.007 to 0.11

Could any engineer here help me with a proper calculation?

Other usual suspects are epoxy concrete/granite casting, and of course, solid granite stone. These are my second and third options.
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!)

Interesting granite build.
The epoxy-granite is another story. There's the famous thread on cnczone with almost 5000 replies. But as far as I understand it, the most difficult part is the vibration for compacting. Vibrators are not cheap and not that easy to build and for good results they need to be tuned to the right frequency using inverters...

But a epoxy-granite cnc wouldn't be lightweight so it is out of the question for this build.

I won't even look for pricing infos just to not feel the pain!

They say 5-6 times the price of roller rails. But the price of their rails not the hiwin ones... And requires a dedicated oil pump.

Hi Paul,

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.

I'm not sure anymore about the hollow section stiffness... If the calculation was wrong and stiffness is not a problem I'll probably take the steel/epoxy route with some sort of vibration damping inside them.