Covering our naughty bits and using lube

[Goemon]

I noticed that a lot of the diy CNC machines here have exposed rails and ball screws etc while decent commercial machines cover them with bellows. What do you guys recommend for a diy build? Are bellows necessary? They seem fairly cheap to leave out if they help.

On using oil or some other lube for the screws and rails etc, high end machines have these auto oilers. How often do you guys lube your CNC machines and is this why you don't use bellows? I.e. Do they make it too arduous to lube your screws if they are covered with bellows?

I am asking because I am considering completely enclosing my rails and screws to protect them from the dust in my work area. If I have to use lube on the screws before every use, this is not practical...

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[dharmic]

Limited experience here. I have one machine with dovetails that are covered and another with linear rails, some of which are covered and others not.

And my experience is: it depends.

If dust is flying, covers are moderately useless unless they're really good. That dust has a habit of getting everywhere. Swarf and coolant, on the other hand: if the bellows are decent and stop most of the liquid then it's all pretty good.

On the other hand, unless you have some kind of automatic oiler system bellows are a PITA to get around to get the lube into or, even then, the dust out of.

If I was doing a lot of timber I'd say leave them open where you can get a rag at them. Same with the lead screws. For metal, bellows for sure.

[ger21]

Our $150K router doesn't use bellows, and if you look at most similar machines, not many do.
I uses to use a big router with bellows, and yes, a lot of dust got behind them.

[wizard]

Lubrication can get complicated! For instance back when i was working on diamond turning machines, running plain linear bearings, each firing of the lube system impacted the lathe a bit. Also the product was extremely small vs the size of the saddles, so we had to implement a cycle where the lathe backed out and ran the saddles of each axis the full stroke of the axis to keep the entire bearing surface wetted.

On machines with linear profile bearings and automatic lube the lube system in my estimation keeps the bearings operable even in dusty environments. Machines with the highest failure rates are those with msnually greased bearings that collect a lot of dust. In a nut shell such bearings can get plugged up if not manually lubricated enough. So from my perspective if the lube isnt done automatically you need good access to the bearings to manually lube them. The qualification here is that it is fairly easy to run grease lines to the bearing blocks thus reducing the acccess problem.

So if you want to cover things up it would make life easier to run grease lines from the bearings to an external manual grease point.

As for things like leadscrew bellows from what ive seen they can do wonders for shorter strokes. The qualification here being a complete seal and reqular maintenance to replace worn bellows. In some cases the bellows on a machine are there not so much to protect the screw as they are to protect the work area from the screw and lube. It is a bit of reverse thinking but a bellows around a leadscrew isnt always there to protect the leadscrew.

As for way covers and various ways to protect linear bearings, the term dust shield is misleading as dust can get everywhere air can go. Where covers offer advantages arecin keeping the larger chips from falling directly on your rails. These larger chips generally arent a problem until the get past the wipers. Depending upon what those chips are they can ruin a linear rail pretty fast. If you are running somthing halfway between dust and chips such as what cast iron produces, you will want to go to extremes to keep that stuff off your rails. So in a sense what you are running on the machine factors into the importance of protecting those rails.

[Goemon]

Our $150K router doesn't use bellows, and if you look at most similar machines, not many do.
I uses to use a big router with bellows, and yes, a lot of dust got behind them.

Are there any better alternatives to bellows?

I am actually less worried about the chips from the aluminum and tooling boards I'll work with. It's the carbon fiber dust in the room from the work I do near the machine. I.e. I won't be cutting cf on the CNC but the dust from it is super fine and gets everywhere. It can easily destroy motors if it gets in them.

Are the lead screws (or ball screws) just exposed on your $150k router?

[ger21]

Are the lead screws (or ball screws) just exposed on your $150k router?

Yes, out in the open, with no covers.
The auto lube system greases the ballscrews and linear bearings every 3 hours of runtime.

[louieatienza]

Are there any better alternatives to bellows?

I am actually less worried about the chips from the aluminum and tooling boards I'll work with. It's the carbon fiber dust in the room from the work I do near the machine. I.e. I won't be cutting cf on the CNC but the dust from it is super fine and gets everywhere. It can easily destroy motors if it gets in them.

Are the lead screws (or ball screws) just exposed on your $150k router?

You can "pressurize" the bellows to keep dust out. It doesn't have to be much really, as long as it's slightly more than outside it - maybe even a bubble pump for an aquarium would suffice. I think CF dust would destroy a motor more because of it's conductivity rather than the dust itself - I can't tell you how much fiberglass, resin, and wood dust was pulled through my routers on my machines. The CF dust will destroy YOU first if you're not careful!

There was a guy here who actually made "sweeps" for their ballscrews out of strip brush material... I keep forgetting who it was, but it seemed to help a lot. The bamboo CNC router build has some great ideas for managing dust with custom bellows.

[Goemon]

Yes, out in the open, with no covers.
The auto lube system greases the ballscrews and linear bearings every 3 hours of runtime.

Every three hours is more regularly than I was expecting but at least it gives me some insight into how easily accessible by lead screws need to be. I'll be manually applying oil at least to start with.

I think that the way to deal with this in the short term is to make sure my enclosure is finished for day 1. I'll figure out how to built covers for the screws (that don't prevent access for oil) later on. Thinking out loud.... bellows could be made to slide open fairly easily....

[CL_MotoTech]

I've never liked the bellows type covers. They seem to accumulate crud at an astonishing rate. Nesting sheet metal type seem the best in my experience, they are compact, and don't collect crud as badly. For my home mill, I've gone to a simple rubber mat type covering. They don't really collect crud, they are easily removed, easily replaced, and they do a fairly good job keeping swarf out of the moving parts. It's important to note that I don't have a one shot oiler on my mill. I generally grease the ways and screws, but I use a very light covering of grease. It took some adjusting to get the covers setup, but ultimately I gained Y travel, and the ways stay cleaner than they ever have before. The only cleaning they really need is after I clean the chips out of the enclosure, and the last ball screw I repacked was perfectly clean when I disassembled it.

[Goemon]

I've never liked the bellows type covers. They seem to accumulate crud at an astonishing rate. Nesting sheet metal type seem the best in my experience, they are compact, and don't collect crud as badly. For my home mill, I've gone to a simple rubber mat type covering. They don't really collect crud, they are easily removed, easily replaced, and they do a fairly good job keeping swarf out of the moving parts. It's important to note that I don't have a one shot oiler on my mill. I generally grease the ways and screws, but I use a very light covering of grease. It took some adjusting to get the covers setup, but ultimately I gained Y travel, and the ways stay cleaner than they ever have before. The only cleaning they really need is after I clean the chips out of the enclosure, and the last ball screw I repacked was perfectly clean when I disassembled it.

I like that idea. I have tons of silicone rubber here. Silicone is perfect for this job as nothing sticks to it. Plus, I have an additive that reduces surface friction so dust won't cling to it. I can paint a brush-on silicone layer over the top of some rigid fiberglass covers. If the silicone covered fiberglass covers are on hinges, it won't restrict access.

[wizard]

Carbon fiber is a lot like castiron "dust" with respect to it being abrasive. So in that respect keeping it of the linear motion components makes lots of sense. The problem is bellows are less than optimal on longer axises. About the only thing left are various forms of covers. Even here traditional covers still allow air born dust to flow into the good places.

One option is the use of flexible stainless steel covers that are magnetically held in place. These sorts of covers are seen on linear actuators with leadscrews or even pnuematic cylinders. On servo driven linear actuators they are common in clean room environments. IAI is one manufacture if you wish to research the idea. Im on my cell phone so no posting pictures or links. There is likely a descriptive name for such covers but im not up to date on the proper name.

The big problem with the magnetically held in place covers is the major engineering required to implement such covers. Each axis would have to be redesigned to work with such covers. However for long strokes they often represent the best possible option for a prettey good seal. In many uses, do realize that these sheilds are actually there to keep stuff in. Stuff being grease, belt dust, oil and whatever else normal operation throws out.

Maybe once my PC comes back from the shop i can post a picture of sldes using these flexible SS covers. This is certainly a case of a picture being worth a thousand words.