Build Suggestions w/ Welder, Router?

[pippin88]

pippin
Had a look at BST Automation. The li express site says genuine Hiwin rails and bearings but thier own site seems to indicate a no brand version.
What have you bought, genuine or copy. If the copy how good are they and can they be had in various preloads.

I will never deal through Ali as i have been ripped off and ALi only protect the buyer

I had a very good transaction with Fred from BST Automation. Others on CNCZone have also reported good experiences. My rails definitely look genuine. They sell both Hiwin and a different generic brand (different shape etc).

I got mine in medium preload (ZA I think) and I got high rather than standard precision. Meant I had to wait a few more days for them to get them from the Hiwin factory

[pippin88]

Thanks very much for all the insightful replies.



Fantastic, I've been looking, and there really are quite a few options. I'm looking at something like this for the long axis: SBR16 Linear Rail Support Aluminm Assembles 2pcs L1500MM 4pcs SBR16UU | eBay

The question is, what diameter should I shoot for on the supported rail? The gantry might end up being 50 lbs (1/4" steel side plates, two supported rails, their crossmember, and rack/pinion).




Are you saying you would use tubing as the gantry crossmembers? I was looking at a design where they bolted in the linear rod (unsupported) as gantry members, which seems quite efficient, especially if used in conjunction with at least one supported rail. CNC Engraving Machine CNC Frame CNC DIY 3040 Aluminum Alloy Ball Screw | eBay




All very good suggestions. It may end up that I HAVE to design my own Z carriage, just because I'm thinking about using linear rails on either SIDE of the spindle, as well as two behind, as it is traditionally. From the standpoint of Z-axis deflection on harder materials (aluminum), that would seem to make more sense to me, especially if I just bolt them in (as above).

But, if I find one for cheap, I'll settle. Just have to find some machines in the local scrap yards.



You think profile rails are better than supported rods? Just asking, because I have no idea. All the nice machines I've ever seen use rods, from what I remember.

Out of curiosity, would that 15mm rail support a 5' long steel gantry? I see they make wider ones, but I can't find many for sale.

I'd suggest a few months of reading and looking at these forums. This stuff has been covered many times. Unsupported rails are best thought of as soggy noodles, because they are about as useful for CNC machines. Supported round rails can be adequate but allow rotation around their axis and have a lot of flex. Profile (square) rails are vastly superior and are now available new and second hand for reasonable prices.
All that said, people have been building MDF based machines with skate bearings on angle iron for years and produced a working machine. They however almost always build a second then third machine, and certainly won't handle metals.

I'm now building my third machine and doing it properly this time. Like many others, I thought I could do it cheap, 'didn't need a machine that cut fast' (hint, cutting speeds are dictated largely by the material, rather than your budget). And now I have thousands sunk in to stuff that is useless. (Admittedly profile rails have gotten a lot cheaper since I started my CNC journey)

[wizard]

Thanks very much for all the insightful replies.



Fantastic, I've been looking, and there really are quite a few options. I'm looking at something like this for the long axis:

I think a key point here is that the more you expect out of a machine the more robustly it must be manufactured. For the basic materials it doesn't really cost a lot to add in structural robustness.

The question is, what diameter should I shoot for on the supported rail? The gantry might end up being 50 lbs (1/4" steel side plates, two supported rails, their crossmember, and rack/pinion).

I'm beginning to wonder if we are not on the same wave length here with respect to "supported Rails". These rails still have to be bolted to a frame. That is what a box beam would be for on a gantry.

Also 1/4" steel plates for the gantry vertical supports are barely acceptable. Again your best money would go into a box section.

Are you saying you would use tubing as the gantry crossmembers?

Yes! It is the least difficult way to build a gantry, especially if you get a beam that is relatively straight and flat to begin with. Further I'd make a good portion of the machine out of either square or rectangular tubing.

I was looking at a design where they bolted in the linear rod (unsupported) as gantry members, which seems quite efficient, especially if used in conjunction with at least one supported rail.

At least they where honest and called it an engraving machine! That machine would be next to useless if you wanted to drive a 2 HP router to full capacity. If you are looking to build a machine to push Dremel sized tooling around, doing CNC engraving, you might get away such a design. Try to do something more involved with larger cutters and up you are basically screwed.

All very good suggestions. It may end up that I HAVE to design my own Z carriage, just because I'm thinking about using linear rails on either SIDE of the spindle, as well as two behind, as it is traditionally. From the standpoint of Z-axis deflection on harder materials (aluminum), that would seem to make more sense to me, especially if I just bolt them in (as above).

If I understand this correctly you are implying using four linear rails for one axis. If so that is a very bad idea. Most home builds don't have access to the precision equipment required to pull that off. Further select the right two rails and you will have a very nice axis with plenty of strength.

But, if I find one for cheap, I'll settle. Just have to find some machines in the local scrap yards.

Auctions are good sources if the commonly is going out of business. However watch out for companies holding auctions for machinery removed from on going operations as often that stuff is shot to hell. Much can be had in E-Bay with respect to used linear motion equipment as some guys have ongoing business salvaging tooling from factories.

You think profile rails are better than supported rods? Just asking, because I have no idea. All the nice machines I've ever seen use rods, from what I remember.

Profile rails are far better than supported rods from the mechanical rigidty standpoint. The gotcha is that to take full advantage of that mechanical rigidity you need to have a well constructed machine. This means a stiff frame and a build that keeps the axis normal to each other. I see little point in putting profile rails on a machine built out of wood, but that is me.

Out of curiosity, would that 15mm rail support a 5' long steel gantry? I see they make wider ones, but I can't find many for sale.

Sure. In all things machine tool there are trade offs. For a specific rail it is best to consult the manufactures web site for the mechanical specifics including load handling capability. You can buy some rather massive linear rail systems that can handle tons of loading, you don't need that.

In any event a couple of points:

1. Just because somebody builds a machine one way doesn't imply it is right for you and your needs!
2. Once you have a desire to machine metals, even just Aluminum, you need to beef up the machine significantly to get good results.
3. When I say machine aluminum, I mean just that, I don't mean engraving or other operations that just skim the aluminum. Rather I mean machining the aluminum in such a way that you use a good fraction of your spindles horsepower capability.