Today I learnt two things that suck. (updated with PRV)

[Toni Ciuraneta]

Hi guys. As mentioned I learned two things that suck, one in the good (and literal) sense, and the other on the bad sense.
I am playing with my new cnc machine and I want to make a sign for my sister. Firts I tried with chipboard but soon I saw that the inner layers or wooddust were not as fine as the surface so I decided to try MDF.
So I started the sign anew in MDF, and after 45 or 50 minutes of milling (unantended) as I was on the garage, I heard a thud sound so went there stopped the machine and I found that my dustbin had collapsed.
Reason: MDF sometimes delaminates smal parts that clogged my cnc dust shoe and the power of my vacuum cleaner has been powerful enough to empty the air of the dustbin and the atmospheric pressure made it collapse. So my vacuum SUCKS! really well.

The other one is MDF, which I am finding that if that is going to be a recurrent problem MDF is not good for certain milling projects, So MDF SUCKS! in the bad meaning.
Question: Is there any way of making a DIY safety valve so this doesn't happen again? I am thinking about making a hole on the lid and puting a rubber disc attached from one side with a bolt and nut covering it from the inside of the lid, so that if the negative pressure increases due to clogging it will give in preventing this happening again, but I'm no so sure if it will work.
Any other sugesttions?
Here you can see the collapsed dustbin.

And here the MDF shavings that clogged the dustshoe. There were many more than shown here.

And if the final finish is going to be like this, MDF really sucks. I hope that with the finishing passes it will be ok as this is the roughing one.
Otherwise I'll have to find a different material.

 

[Ryan Mooney]

Wow, that's exciting!

I hadn't thought of this before but apparently others have.

If you search for "dust collector PRV" you get some nice results like:

How to make an 'Auto Resetting' pressure relief valve for Cyclones

How to make an 'Auto Resetting' pressure relief valve for Cyclones

www.festoolownersgroup.com

Printables

www.printables.com

Or this really simple idea which is just a jar lid held in place by a magnet

 

[Toni Ciuraneta]

Thanks Ryan. The last link takes me to youtube, not to the video. But I get the idea. I think I,ll go for it.

 

[Ryan Mooney]

Woops bad copypasta on my part - link should be fixed.

 

[Leo Voisine]

I can only talk about the MDF on a CNC as I don't know about the PRV

MDF sucks -- BUT -- there are good things that can be done with MDF. The cut surfaces absorb paint, Shellac, Lacquer like a sponge. Once it it sealed really well it can be sanded but not a great finish. There are some compounds that can be applied and sanded smooth - like body filler.

 

[Darren Wright]

I’d probably put a PRV on the output hose of the cyclone on a wye. You don’t want it on the bin, if it is it and it opens up, it may suck the dust into the vacuum from the bin.

 

[Ted Calver]

Pressure relief valve talked about in this YouTube video. Shows a commercial product from a french company that looks nice.

 

[Ryan Mooney]

Pressure relief valve talked about in this YouTube video. Shows a commercial product from a french company that looks nice.

"But with this metal drum there is obviously no chance.." now there's some famous last words right there.

You don’t want it on the bin, if it is it and it opens up, it may suck the dust into the vacuum from the bin.

Good call, have to look at the airflow ofc, but wouldn't want it where it'd stir the dust back up.

 

[Toni Ciuraneta]

Thanks a lot guys.
I just took advantage of having a small cnc machine and came up with this valve. Nothing fancy just two typical pieces, a ballpen spring and a thin bolt and nut. The top piece glued to the lid by capilarity with acetone.
The spring works perfectly. And although if it opens it may cause the vacuum suck some dust as Darren mentions at least it will prevent the bin collapsing. Later on I will either either make one for the pipe and condemn this one.

Here you see it installed.

Darren: I guess that if it has to put in the pipe it should be placed before the cyclone right?, I mean Dust origin-pipe-PRV-cyclone-pipe-vacuum.

 

[Darren Wright]

Darren: I guess that if it has to put in the pipe it should be placed before the cyclone right?, I mean Dust origin-pipe-PRV-cyclone-pipe-vacuum.

It technically should work on either side of the cyclone, but having it on the bin lid will act like a leak in the lid and cause air to pull up through the bottom of your cyclone and dust going in will go to the vacuum.

Having it on the input side of the cyclone still allows for a clog at some point up after the PRV. Having it prior to the vacuum would be the least risk of a clog.

BTW, that is a great looking solution. May have to do one of those when I get my cnc going again.

 

[Toni Ciuraneta]

Thanks Darren. Making it was rather quick; I had it drawn, milled and installed in about one and a half hours. The most consuming time task was finding the long bolt and the spring in all the bits bits and pieces that are on my "just in case" box. .

Later I pretend to make another one on a 50mm diameter "T" pipe joint and mount it prior to the vacuum as you suggest.