Dust tent a static issue?

[MooreBroCo]

We have one of the 5-axis machines and have a job coming up machining syntactic foam which is about as nasty as it gets from a dust stand point. We are planning on tenting off the machine with plastic sheeting to keep the dust fully contained but it occurs to me that we could be creating a massive static problem.

Does anyone else have experience with dust enclosures creating static issues?

We are even considering putting up a layer of chicken wire under the plastic sheeting and grounding it. Seems a little excessive to be building a faraday cage but is it necessary?

Are we over thinking this or is this something we need to be really careful with?

Oliver

[Kyle Stapleton]

Look up "static free plastic sheeting" lot of stuff put there.

[MooreBroCo]

Check. Just order a roll. Thanks

[donek]

How about a mist lubricator. I'm not sure how sensitive your material or other projects would be to moisture, but water and moisture would be the best way to contain the problem. Most machinist use a flood lubrication system to carry chips away. You could also take that approach.

[MooreBroCo]

I talked to a friend who had just finished a job machining syntactic foam and he had some horror stories. I guess the dust clogged up the linear bearings on his machine enough to blow the ends off and chewed through bits. So our original plan of plan of tenting off the whole machine and letting the dust fly inside the tent seems less ideal. Our current thinking is to put some curtains on the side of the machine but to leave the top open so we can get in with the vacuum and try to vac as we go. We are going to put a large plate on the table first to try to keep the dust out of the x axis bearings then be aggressive with both the dust collector and the vacuum as we work. We shall see.

[Brady Watson]

For that machine one of those fabric garages would be ideal for controlling dust floating throughout the shop. Filtered out in/out should be pretty easy with a box fan and furnace filters. You could probably get all you need at a big box store and auto parts store. You want one big enough where you can move around. Is this what you meant by 'tent' ?

In terms of the machine itself - there is no worry about the V-roller bearings. They are made to plow through metal, plastic and wood chips day in and day out. Visit BWC and view their demo videos. You should wipe the rails with a clean dry cloth to keep residue from building up from the rollers. A lightly dampened rag with WD40 will act as a solvent. Follow it up with a dry rag so it doesn't become an attractant.

The real place where the foam will 'gum up the works' is going to be the rack & pinion drive system. My recommendation would be to avoid using heavy grease, but apply a lighter coat (I like Cyclo brand) spray grease - and wipe off the excess. Foam for some reason has a high affinity for gear racks. It gets smushed into the rack gear and pinion teeth & needs to be raked out after each job. This is par for the course when machining foam. A clean machine is a happy one...so make it part of your routine to clean.

Safety glasses are a MUST with that stuff...it is just nasty & WILL SHOOT YOU RIGHT IN THE EYES if you move the material after machining! I know this from 1st hand experience at a Naval base machining model hulls. Right in my eyes. It was awesome...just like sand.

Static is WICKED - ground the machine, and yourself or you WILL get zapped pretty good. A ground clip to your wrist will usually be enough. Be touching one of the X rails with your left, while shopvac'ing with the right...or the static will go through you...or your ground strap.

-B

[MooreBroCo]

How about the A and B axis bearings? I'm not sure exactly what they are. Any advice on preventative servicing for them?

What you are describing is basically what we were thinking. Our concern was whether a plastic dust tent was going to create a major static build up problem. Plastic sheeting grinding/spray booths I've worked in have had major static build up on the walls and we are worried that wrapping the machine in a static cocoon could have bad results. We've got a roll of anti-static plastic showing up tomorrow which will hopefully help to mitigate the issue.

The issue with the syntactic is that it is actually made of microscopic glass spheres in an epoxy matrix. So you end up needing pretty good hepa filters to grab the stuff and its about as nasty from a respiratory stand point as I've encountered. We've done some work with it in the past and if you aren't careful the dust makes you feel noticeably shitty and as boat builders we are pretty used to nasty dust. The reading we have done says you are safer to actually contain the dust, let it settle and then vacuum it up with good hepa vac. We will definitely be wearing good respirators. Whether we break out the full faces is another issue. But definitely a good call on the wrist clip.

[Brady Watson]

A & B bearings are sealed and part of each rotary actuator. I wouldn't worry about them.

-B

[MooreBroCo]

A & B bearings are sealed and part of each rotary actuator. I wouldn't worry about them.

-B

Good to know. What about grounding the spindle? Do you think we need to get a grounding wire onto the spindle itself or would grounding the Al extrusion that is the z-axis be adequate? The instructions for grounding a 3-axis machine only have you go to the z-extrusion but the spindle is bolted to that extrusion. Is there enough metal contact in the a and b axis bearings to ground the spindle? Is that something we should worry about?

Thanks for the advice. Hugely helpful

Oliver

[Brady Watson]

If your zero plate is working then you have ground through the spindle.

You don't want to create a ground loop.

-B

[MooreBroCo]

Good call. That makes sense. We will just ground the frame then.

Here is what we have come up with for a dust enclosure. It leaves a little to be desired from a visual stand point but hopefully it will make up for its form shortcomings in function. We have bungee pulling the two flaps around the z-axis and we may need to figure a way to better seal up the gap. The dust collector is getting close to being able to do the full a and b axis range. Plus minus 360 for the A axis make it pretty challenging.

I was definitely a little disturbed by the amount of static shock I was getting when I was pulling apart the special "anti-static" plastic sheeting but hopefully it will live up to its billing.



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