Initial design advise wanted

[routercnc]

Hi driftspin

Noise reduction is related to how heavy the walls are. Look up 'mass law sound reduction' for more info.

There are some basic calculations on this site:
http://www.engineeringtoolbox.com/so...ls-d_1409.html

Let's say with the cnc machine running noise levels inside the workshop are 90dB. If the surrounding urban noise levels near the workshop are 50dB (with the machine off) then you need to achieve 40dB reduction.

With concrete at 2300kg/m3 and 0.2m thick this gives surface mass of 460 kg/m2. This gives an average noise reduction of 52dB, which would be enough.

With wood at 400kg/m2 and 0.044m thick this gives surface mass of 17.6 kg/m2. This gives and average noise reduction 28dB, which is not enough on its own.

Assuming you are stuck with wood, this can be improved by adding another wall with an air gap in between. Using the air gap you get more noise reduction than if you just stuck the walls back-to-back with each other - but they must not touch each otherwise the vibration will pass easily from one to the other and the benefit is lost. So mount them on separate vertical studs. The larger the air gap the better the performance, but workshop space is lost.

Finally you can add absorption material in-between the walls which takes out the high frequencies (it does nothing for mid to low frequencies which is why you need the double wall first). This can be anything fluffy, so rock wool is fine.

Make sure you seal any gaps otherwise lots of the noise benefit is lost. Make sure the roof, door and window specs are considered as well (plus floor if it is just suspended wood).

[driftspin]

Thank you routercnc.

This is what makes this site so great for me.

You guys give excellent advice.
Backed with theory explained in a simple way.

So is the number 90db a real world guess? I have no clue on this...

It might be a deal breaker btw....


I guess high freuquent sounds s the ones that are most annoying.

Your example says 20cm concrete as the ideal solution.. i think i agree, but can't do that though...



so rockwool air gap sounds like the way to go... i will look in to this.






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[mekanik]

Have a look @ this
http://www.fermacell.co.uk/en/docs/f..._082014__s.pdf
It gives construction methods for various grades of soundproof stud partition wall. nice stuff to work with(nothing like standard plasterboard)
and you can get it in one man boards(1200 x 1200)
Regards
Mike

[Boyan Silyavski]

I have tried to soundproof my garage. Almost wasted effort. I used 30db or sth sound isolation material on garage door inside. Nahhh.

The best soundproofing material is Asphalt sheet heat glued to whatever door you have . Noise will not come from walls. It will come through windows or through doors. Basically you need all outside possible vibrating surfaces to be hard dampened, not just covered with sth. Of course depends where you live though. I live in extremely quiet neighbourhood where people pay big $$ to come for 10 day at sea and quiet, so my challenges are bigger than yours. I simply can not work at night, but daytime you can not hear it from neighbours.

[driftspin]

Mike, thanks for the farmacell link.
I can get their product here locally too.

Boyan sorry to hear you feel like you failed to soundproof your shop.

Sounds like soundproofing aint that easy.

What i read about the farmacell panels sounds promissing though.


Maybe build a free standing 2.5 x2.5 x 4 meter box with a solid wooden door ( it will be the weakest point) and make a the pc station outside.
Or make 2 compartiments having 2 doors between machine and inside of the shed.



I feel like when the machine is working in a (smaller and insulated) closed box, temperatures might rise quickly since most electrical energy used by the machine will be turned efficiently in to heat.

So soundproofed ventilation is the next requirement.











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[driftspin]

Ok... so i am in a bit of a struggle... i am not sure about my gantry beam.. i have not found a way to calculate deflection for the beam.. Iam not a strucural engineer ☺

So my beam is 940mm wide between the rail blocks. It is a 120h x80w x4t mm profile.

The maximum z extension is about 25cm on the tip of the tool.
Planned working extension maybe 15cm


The tool is extended about 15 cm.

Can sb point me to a tool to guestimate deflection based on real world cutting forces?

Is read on this forum cutting forces in any given direction do not exceed 400Newton? In soft metals.


I need this info to guestimate the total weight of the gantry and continue on to electronics selection...


Any help is welcome here.

Bert.

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[Boyan Silyavski]

cnc machine stiffness calculator

for soft metals 120x80 x4 is not rigid enough . Weld 2x / 1 thin side and one wide side 10mm steel plate/ and you will have reaper

[driftspin]

Ok sb is good with excel... wow.
This is exactly what i needed


Boyan.. thanks for the link.

Hmm deflextion is within 0.01 mm not sure cutting what material.

Will have a better look tomorrow.

I think i better step up to a bigger size gantry beam maybe 120x120x10, there will be more meat to mill flat also.

BTW i cant weld more than 4mm.
Oh... endcaps ... hmmm well...
Need to figure out that one

I will bolt the gantry beam to the bearingblock mounts i guess then.



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[Boyan Silyavski]

If its to cut wood and occasionally aluminum its perfectly fine.

But apart from deflection, there is ringing, vibration, when cutting metal. Ideally when an engineer is designing a machine he will know frequency of the tool - material and space bearings of Z and all other parts so it does not synchronize so all starts ringing like a bell. And i suspect use much more weight than needed just to be sure .


I remember what Dean said about one commercial machine , an expensive one, that if you hit it with a hummer it would "thump" not ring. So thats also important especially with metal machining.


In a DIY situation after designing a couple of machines as light as possible and as rigid as possible / blamed to be OTT even / i believe using 10mm plate as an additional steel bracing here and there we could imitate at least 5-8 times heavier machine properties.


For example my machine /1300x2600x200/ weighs 700kg all included and is at least as strong as 4 ton commercial one, if not more. You could lift it and hold it from one side, other side in air and deflection will be less than 0.05mm if not less than 0.01/


So remember the magic word- " bracing" with thick 10mm steel in all possible directions to imitate solid shape properties and at the same time keep things light. If you are making a machine to work aluminum. For wood your problem always will be not this but the spindle KW and how fast the machine could move.

[driftspin]

Ok.. so i did some calculations.

Based on my original design the total moving gantry weight is +/- 65kg

~32kg z
~65kg z+y


Aditional bracing would add some 35kg.

Can this still be run on twin nema 23 / 3.1 nm gearing 1:2/ 1610 screws (y)

These numbers are a bit overwhelming to be honest. ..




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