Looking for feedback on an idea

[levelzero]

I'm planning to build a small cnc router for 90% aluminum cutting. I've seen the plans for the skate bearing and although functional I'm concerned about the lack of contact area as I'm looking to build a fairly rigid set up.

This is what I'm thinking of doing instead but I'd like some feedback from others with some experience.

[ewest]

Hey!

You should definitely build a CNC router. It's an awesome project. I did, and I love my machine. However, I don't think you should use skate bearings except for foam work. Plus, if the shaft thing isn't supported, and you put any kind of load on it, it's going to deflect a LOT, and to get the rigidity you would need out of this setup, you'd have to pre-load it quite a bit, which just makes matters worse. If you're routing aluminum, you need rigidity. Some will claim otherwise, so I should probably say "If you want to route aluminum well and have a good finish and acceptable feed rates, you need rigidity." Don't forget to use actual aluminum ROUTER bits. Anything else will immediately gall up and ruin everything.

I can't recommend anything except decent linear bearings. I used THK, but they're expensive. The now out-of-business PracticalCNC used Hiwin bearings, which I'm sure are much cheaper. You can also use the round profile recirculating ball bearing linear rail - the kind that go on over a supported shaft. Mcmaster sells them. They're pretty user friendly and not that expensive. Get something like that, and some nice lead screws with wear compensating nuts, build a decent steel frame, BOLT IT, don't weld it, hook up some oversized steppers and go to town.

Good luck!

[levelzero]

Thanks for the feed back.

The main reason I want to build a router is to take over doing bunch of small aluminium stuff that is currently being done on my mill. Surface finish and tolerances are fairly loose but I obviously would like the router to be as good as my budget will allow.

I have looked into linear rails as well as the recirculated ball bearing blocks. Linear rails are outside the budget for the first build, and the ball bearing blocks have a few drawbacks like not being able to support the rail in the middle and they look like they would get contaminated with metal shaving easily, especially seeing as I plan to run flood coolant. I really like the idea of components that I can remake myself when they wear out, it helps prevent down time as well as making it easier to improve them as time goes on.

I'm going to be making the body out of aluminium with steel for the motion components (lead screws/rails ect). It will be bolted together and should be fairly ridged but worse case down the road I can remake some of the structural components out of steel.

[ewest]

The round shaft bearing system has a supported shaft.


They're not cheap though - In fact, they're not much cheaper than linear rail. Don't rule that stuff out. The THK blocks for a 15 mm unit are $70 each, and 640 mm of rail is $107. So its not super cheap, but still...

What about track rollers? Track runs around $20 a foot for nice ground stuff. Rollers aren't' super cheap, but way better than skate board stuff..

So what's your working envelope that you need, and whats the budget?

If I were in a pinch, I'd do what the EZ router guys did, except I'd use a steel I-beam on its side with V groove rollers, or even better, if you have access to a lathe, turn four rollers that space correctly to ride the edges of an I-beam, drill them all the way through, bore the ends for some ball bearings, and drill out two plates that mount on the ends of the rollers. Use cheap thrust bearings if you want, and through-bolt the whole thing. Basically, box in an I-beam. I don't think it's that bad an option if you've got time but not money. In case I described this badly, I can draw a picture.

Also, if you use the aluminum router bits, you can pretty much dry cut. Some guys use Dove bar soap. I just brush on a tiny bit of alumi-tap for my own peace of mind.

Again though, whats your envelope, whats your budget (please don't say as little as possible)

Regards,

Andy

[levelzero]

I'm looking for roughly a 24x12 cutting area. My budget is whatever it costs without being frivolous, but obviously the cheaper it is to build the sooner I'll be done. I'm hoping to bring it all in under $2500 considering I'll be machining most of the components in house. One of the biggest cost so far is going to be the metal as I'm using a combination of 1.00" and 0.50" aluminium plate.

For cutting I actually plan to use carbide end mills, if those don't have the results I'm expecting then I'll try specialized router bits. I've crunched the numbers and a 0.25 carbide 3 flute end mill will be right in the happy zone of a router for rpm and hp, and I don't expect to have any problems reaching the desired cutting speeds. For the cuts I am planning I don't need a lot of horsepower, I need rpm which I why I decided to build a router.

That rail is actually pretty cool and will lend itself well to my design. I don't want to use skate stuff, but at the same time quality bearings are fairly cheap and would make maintainence/repairs easy which is why I am looking into solutions I can produce in house. Every time something on one of my current machines breaks I end up losing 1-2 days of productivity and paying through the nose to have the parts sent overnight to me. The goal of this router is to take over the jobs that are simple 2D shapes in 0.125" aluminium. This will not only increase throughput but also reduce wear on my cnc mill. It also means if/when the mill is down for repairs I'm not dead in the water.

In the picture I posted the tube would be precision ground drill rod with aluminium/derlin rollers. The bearings would be sealed ball bearings. The contact area of the rollers should help distribute the load and allow me to add more rollers as needed.

[multiplex]

check out vxb bearings for supported rails like that in alot of different sizes. for the size table you are talking they should be somewhat affordable.

with your requirements of cutting aluminum, i think it makes sense to build the machine correctly the first time.

2500 sounds like a decent budget, depending on how much of that goes to aluminum

[svenakela]

There are wheels already with the design you have in the first post, I think Isel sells them.
A friend to me made a small groove directly in the bearing outer ring in the lathe. Works really well.

[cadcamdave]

Just to throw in my 2 cents, I agree with "ewest" in that you really should try to get a good solide rail and bearing system. Skate wheels are toys and perform as such.
If you plan to build a frame out of extruded aluminum such as 80/20 or ITEM, consider the rail and bearing system they sell... it is expensive, but you can integrate the slides directly into the framework if you watch what you're doing and save some bucks.
Maybe even search Ebay for slides and rails, sometimes they can be had for a bargain.