What size does my aluminium extrusions need to be for a CNC router?

[abdullahseba]

Hi
I've no idea how strong extruded aluminium is and I want to make an accurate CNC router.
What size do I need? 20x20 50x50?
The work area is about 50x50CM and I want it to route in metal.
I was looking at these:
D01-5 - 20x20 Base 20 Extrusion - Base 20 Aluminium Extrusions - Kanya Aluminium Extrusions - Mechanical
MA1-1 - Heavy duty extrusion 50x50 - Base 50 Aluminium Extrusions - Kanya Aluminium Extrusions - Mechanical
Also would it be strong enough to make a small CNC lathe?
I'm having the same problem with choosing the bearings HIWIN HGW TYPE Moore-international.co.uk are they strong enough for a lathe tool holder and what rail size?
Any advice would be appreciated.
Thanks in advance.

[Falcon69]

Although Extruded Aluminum plays a big part (or steel) in accuracy in a CNC Router, it's the Linear Rails and the Rack&Pinion that provide the most accuracy. Some will even use High Precision Ball-screws instead of Rack&Pinion for shorter runs (Rack & Pinion is best for a very long table, as the ball-screws will whip on long runs). Most people will use the Rack&Pinion for the Y-Axis and X-Axis, and a Ball-screw for the Z-Axis.

The cheaper method, and less accurate because of backlash and movement of the bearings, would be to use the cheap eBay linear rails and lead-screws.  Some use skate bearings as well, but on the CNCRouterParts.com machines, they are pretty good, especially for a hobbyist machine.

For Aluminum Extrusion, 8020.net has some decent extrusion, and they will even cut and drill them for you. But in my opinion, I think the Bosch Aluminum Extrusion is better.

The HiWin Bearings are more then strong enough I would think for what you're looking for. Just get them with the bearing pre-loaded. They aren't the best, but are a great choice for price and use for a hobbyist machine.

To route in metal.....If you're talking steel, you would need to make the gantry and table one piece, and then make the table move.  If cutting steel, that gantry will vibrate and chatter all over the place.

You can get more information on this stuff over at the forums on CNCZone.com

[Koen]

You can get more information on this stuff over at the forums on CNCZone.com

While reading your post and before reaching the last line, I thought to myself : damn, this reads like a CNCZone post. This forum is terrible. Plenty of talking, plenty of CAD, plenty of dreams, few works in progress, very few successes and even fewer people who've really dealt with machining.

abdullahseba, if you know nothing but a few physics basics, start with a cheap steel rigid and heavy frame, chinese prismatic linear rails and chinese ballscrews. It's the safest bet. In the end, they'll cost the same price as V-Groove bearings, aluminium extrusions, rack+pinions, timing belts and other "cheap" hacks. And yes, chinese eBay stuff will be good enough. If you were chasing 0.01mm accuracy, you wouldn't be asking on forums.

Another advantage of going for the above solution is resale. You'd easily recover the cost of ballscrews and prismatic rails by selling them on eBay if your project went south or when your new found experience pushes you to build another machine. Harder with other strange "non-industrial" systems.

As you are in the UK, Hepco Motion might be worth a call too.

[Falcon69]

WoW! Koen.

That was pretty harsh towards me. I was just trying to be helpful.

abdullahseba,

CNCzone, may not be the best place, but they are more knowledgeable about this stuff then what you'll find on this 'electronics' forum and they do have a VERY large following compared to other CNC forums. There, like all forums, are the good and the bad. If you do a search, you'll see on that site many pros and cons to every DIY CNC machine design listed there.  Plenty of projects to get ideas from, and unlike Koen says, many of them are built and in working condition.

There is nothing wrong with Aluminum Extrusion built machines for hobby use. But if you are seeking accuracy's better then 0.01mm, then you will need to step up on the cost and the build.  High Precision Ball-screws for example (not Chinese ones) are no joke, You could be talking several thousand dollars for even a small 500mm precision ball-screw.

Building the machine out of steel is tough. Mostly because it's tough to control the warping that happens from the welding process. Aluminum Extrusion is simple, simply cut the parts square, and bolt them up.

[Koen]

Yeah no, it's not about you, it's about what you repeat from CNCZone. Chinese ballscrews will cost him 40usd for 500mm and be miles ahead of whatever hack CNCZone could have imagined.

Yes welding and warping is an issue but nobody recommended that. Steel frames can be assembled with bolts and nuts, like aluminium extrusions would. Steel simply is much cheaper, much heavier, available locally and less prone to dents.

[Falcon69]

Chinese ball-screws aren't even close to the quality of SFK, NSK, Thomson Linear. But they are better then Belt driven (belts stretch) and lead screws (bad backlash).  That's what I was trying to get at. And those 3 I mentioned are not even the best ball-screws you can get. 

Most of the people on CNCzone are just people who build the machines for hobby use. Most of the 'good' machines on there are seeing accuracy's of 0.005 inches.  That's just barely 0.1mm, and for most people, that is pretty good.

I don't know what you refer to as hack. Everyone building these machines have their own way of doing it, which I have explained. Obviously you have had a bad experience with that site and have some bad mojo about it.

Steel is much better, but it requires alot more work to assemble it than extrusion does. I'm in the process of 'still' designing my CNC, although, it will have a steel Base and Gantry, for the table it will be using Aluminum Extrusion for two reasons......

Aluminum extrusion I think is more flat, and 2..
If I accidentally route through the spoilboard, I'll hit the aluminum extrusion and will be able to replace that piece pretty easily.

[Koen]

Once again, nobody said chinese ballscrews are better than top-of-the-line major brands ballscrews. Of course they aren't. They are a safe and cheap bet to move a linear device. The hacks I refer to are rack and pinions or belt-driven axis and so on which should, respectively, be constrained to large woodworking routers and light-assembly machines. Sadly on CNCZone and the likes, they are regularly introduced as a solution for "milling" machines because on paper, it appears to be cheaper to buy a large belt and two pulleys. In the end, the price is the same as an eBay ballscrew which, however worse than a THK certified screw, will still be miles ahead in accuracy, resistance, force, easiness of installation, easiness of maintenance and resale value.

There's a misunderstanding here somewhere. I didn't mention the 0.01mm accuracy to say he needed it or that prismatic rails and ballscrews would provide it for him.

For example, you "think aluminium extrusions are flatter than steel" but if you can't measure it, if you don't have the tools to measure it, if you won't have it measured at some point and if you didn't order grounded extrusions then it was of no importance to you.
In the same vein, if abdullahseba is unsure about his requirements (which obviously aren't 0.01mm accuracy or else he wouldn't be asking here, that was my point), I suggest he starts small and safe with reliable, trusted, industry-used, relatively cheap, easy to buy and easy to resale equipment rather than take on the perilous task of once again reinventing the rack/pinion or timing belt linear motion.

[Falcon69]

I Agree, Timing Belt is bad idea, and I guess could be considered a 'hack' But it works, not well, but it works.  Other then small machines like 3d printers or laser cutters, I would never use a timing belt for anything like a router or spindle because the lateral forces would just bee too much for a belt.

He did mention he wanted an accurate machine, so I threw the options out there, but he also mentioned using aluminum extrusion. Yes, getting ground steel channel/square/rectangle would be much more flat/accurate than extrusion, but that can be very expensive to machine, even for short lengths.

Ultimately, when I have my machine built, I will have the base made from steel, taken down to a local machine shop who has a large enough machine, and have the whole surface ground flat, then apply the aluminum extrusion.  Any other discrepancies in flatness from the aluminum extrusion (if any) will be taken out by surfacing the spoilboard.  Yes, my machine will just be for wood/plastics/aluminum/brass, etc. No steel milling. Part of the reason for using aluminum extrusion for the top of my machine, other then the two points i mentioned already, is that they can provide quick easy channels for using holdowns for the piece to be milled. (my machine I'm also designing for vacuum hold down as well, just need to come up with the money for the high volume pump needed).

Rack and Pinion is not more accurate than precision ground ball-screws, I agree, however, for a large machine (like a 10 or 12 foot), then I think Rack and Pinion is the way to go for a machine that would mostly be used for routing wood, plastic, brass, aluminum, etc. If milling steel, then you may want to step up to a ball screw and get a larger diameter for the long length to help reduce the 'whip' the ball-screw may have. Another advantage to using rack&pinion is that they can be used for fast jogging/routing without much backlash in them (if any if adjusted correctly).

[Koen]

In an ideal world, having it grounded and milling the spoilboard would work perfectly. Realistically, you'll still spend ages with a test indicator and a grounded test ruler adding shims left and right. Good luck ! After this project, you'll look back feeling you've learned a lot and, most probably, will use the first one to build the next.

[abdullahseba]

Although Extruded Aluminum plays a big part (or steel) in accuracy in a CNC Router, it's the Linear Rails and the Rack&Pinion that provide the most accuracy. Some will even use High Precision Ball-screws instead of Rack&Pinion for shorter runs (Rack & Pinion is best for a very long table, as the ball-screws will whip on long runs). Most people will use the Rack&Pinion for the Y-Axis and X-Axis, and a Ball-screw for the Z-Axis.

The cheaper method, and less accurate because of backlash and movement of the bearings, would be to use the cheap eBay linear rails and lead-screws.  Some use skate bearings as well, but on the CNCRouterParts.com machines, they are pretty good, especially for a hobbyist machine.

For Aluminum Extrusion, 8020.net has some decent extrusion, and they will even cut and drill them for you. But in my opinion, I think the Bosch Aluminum Extrusion is better.

The HiWin Bearings are more then strong enough I would think for what you're looking for. Just get them with the bearing pre-loaded. They aren't the best, but are a great choice for price and use for a hobbyist machine.

To route in metal.....If you're talking steel, you would need to make the gantry and table one piece, and then make the table move.  If cutting steel, that gantry will vibrate and chatter all over the place.

You can get more information on this stuff over at the forums on CNCZone.com

Thanks for you reply it and Keon's helped me a lot . But what Keon says about CNCZone is true. I asked the same question over there and a few other's and ether got no reply or a useless reply . I think I will make it from cheap Chinese parts to get an idea of what is involved than by proper parts.

[abdullahseba]

You can get more information on this stuff over at the forums on CNCZone.com

While reading your post and before reaching the last line, I thought to myself : damn, this reads like a CNCZone post. This forum is terrible. Plenty of talking, plenty of CAD, plenty of dreams, few works in progress, very few successes and even fewer people who've really dealt with machining.

abdullahseba, if you know nothing but a few physics basics, start with a cheap steel rigid and heavy frame, chinese prismatic linear rails and chinese ballscrews. It's the safest bet. In the end, they'll cost the same price as V-Groove bearings, aluminium extrusions, rack+pinions, timing belts and other "cheap" hacks. And yes, chinese eBay stuff will be good enough. If you were chasing 0.01mm accuracy, you wouldn't be asking on forums.

Another advantage of going for the above solution is resale. You'd easily recover the cost of ballscrews and prismatic rails by selling them on eBay if your project went south or when your new found experience pushes you to build another machine. Harder with other strange "non-industrial" systems.

As you are in the UK, Hepco Motion might be worth a call too.

Thanks too for your reply too. The EEVBLOG forum has always been far more helpful than CNCZone.  I did have a look at Hepco Motion but I cant find out how you buy from them or any distributors. Do you know how you can get hold of there stuff?

[Koen]

No, we had a machine with Hepco linear bearings and I simply remembered they were based in the UK. As you were looking at buying new Hiwin's, Hepco might be interesting.

Used linear bearings prices have gone through the roof these past years but still, have a look on eBay Germany for used THK HSR. It's a safe bet once again which you'll have an easy time selling for the price you paid.
If new HiWin's are too expensive, if used THK's are nowhere to be found, ask your chinese ballscrew seller for prismatic rails and bearings. It usually isn't in their catalog, you'll have to contact them.

Most important thing in machining is to remember your machine is only as strong as its weakest link. This also means you won't have the use nor the need for the best motors, bearings, screws if your frame is weak.

[Koen]

Another important thing to consider is what you expect of it and how it relates to the spindle and the machine dynamics. Engraving or routing wood calls for a fast spindle and fast dynamics with, for example, a light but sturdy moving gantry. Remember triangles are the base of every light but rigid frames. On the other hand, milling steel calls for a slow spindle and slow dynamics with, for example, a moving table and a heavy fixed gantry.

Anyway, it's a fascinating experience and there's loads to learn. When you need an idea, a solution, a quick glance at what others do, have a look at what the best brands produce rather than what forums sell you.

[sistema]

Ultimately, when I have my machine built, I will have the base made from steel, taken down to a local machine shop who has a large enough machine, and have the whole surface ground flat, then apply the aluminum extrusion.  Any other discrepancies in flatness from the aluminum extrusion (if any) will be taken out by surfacing the spoilboard.  Yes, my machine will just be for wood/plastics/aluminum/brass, etc. No steel milling. Part of the reason for using aluminum extrusion for the top of my machine, other then the two points i mentioned already, is that they can provide quick easy channels for using foldowns for the piece to be milled. (my machine I'm also designing for vacuum hold down as well, just need to come up with the money for the high volume pump needed https://www.ams.ie/Sheet_metal_fabrication.cfm).