1.5m by 1.5m cnc at rigidity

[__Britt]

Stick a scope on that and you'd have a blaster Han Solo wouldn't mind having at his side!

[wizard]

How would you surface the beams after welding so they will be in the same plane before connecting the rails ?
I guess that need to be done only after the weld

There is an endless number of ways to design and build a gantry beam. The vast majority of them can benefit from a machine shop. The problem with machine shops is the cost which is why everyone explores work arounds. Part of the cost comes from the need for a large mill to handle a large frame or gantry beam, a 1.5 meter working area implies a killing machine with almost 2 meters of travel.

On beam thickness: If this was an MDF only machine you could get by with relatively thin wall thicknesses in the beam. However you need to consider screw holding capability so you will want a wall thickness of at least 1.5 times the screw diameter for the selected rails. This is if you choose rails with through hole mounting. The alternative is to buy rails with threaded mounting holes and put the clearance holes in the beam. Depending upon you expectations for MDF you could get by with a beam wall thickness of 2 to 3 millimeters with the taped rails.

I’m not suggesting that you do this as it would be a compromise in my opinion and would not be suitable at all for you Metal machining goals. In freedom unit terms I’d would want at least an 8 inch square beam of half inch wall thickness. That is off the cuff with no engineering calculations done. If you have specific performance goals you need to do the calculations to design a beam to exceed your maximum allowable conditions.

Even more importantly there are design considerations that make it a mistake in my opinion to expect much more than extremely occasional use in metal ( aluminum only really).

For one; any amount of metal machining beyond the trivial really needs flood coolant this alone impacts the machines design.

Second; a moving table design, with about the same investment in materials and time, will leave you with a stiffer more accurate machine. The materials cost might balloon over a moving gantry a bit but you must realize the need to a heavier and flatter table to support the metal work.

Third; people have already touched upon the spindle issue but the cost of a proper metal machining spindle that can also handle high speed routing really inflated the machines cost. This especially if you are considering an HSK, 30 or 40 taper spindle.

Fourth; the size of the Z axis can become an issue in sizing the gantry beam. If you end up with a couple of hundred pounds in the Z axis you impact your potential performance with low cost components.

Fifth; on a router, cutting wood, you vacuum up dust. When cutting metal you create swarf so chip handling can be very different especially if coolant is involved. The two do not mix well and you would want a dry machine to cut wood. There are approaches for dry machining metals but the reality is you are better off with a coolant / lube so anything CNC wise I would expect the use of coolant.

Sixth; chip containment is a big problem with machining metals. I run a manual Bridgeport at work and frankly clean up is always a chore. A CNC is often worse due to the machine techniques chosen. Flood coolant might help to contain the flying metal or just make the mess worse. So even without flood coolant a machine enclosure is of big benefit for metal machining.

In any event it is hard to judge ones expectations and actual usage patterns on this forum. As such some of the above might not apply. However do consider if any might be a problem for you. I really believe it is best to express caution when people indicate a desire to machine metals on a low end router. It might be possible to one degree or another or might not work at all. Frankly what might be possible in one persons eye might be a joke in another’s. As such you really need to get a handle on your expectations because it might not be possible for a router to meet those expectations.

[__Britt]

However you need to consider screw holding capability so you will want a wall thickness of at least 1.5 times the screw diameter for the selected rails.

How about using rivet nuts? I'm assuming of course that he can order them & the requisite tool without paying an excessive amount in shipping?

[wizard]

My dad is a civil engineer; and I’ve visited some of the projects he’s worked on. Several of them have been re-builds after fires; it’s quite eye-opening to look up at steel I-beams that are 10, perhaps 12 inches wide, and see them drooping down like cooked pasta.

Bent steel or punctured steel is always impressive to see. Locally a guy driving a largish crane had that crane get loose while drinking under and underpass. That crane punched right through the massive welder iBeam. Shocking really to see the mess.

Sorry - that’s what I meant about doing in a fireplace - just the small connectors with welded-on bolt flanges. I suppose it’s not really necessary; but would be an optional step.

I have stress relieved weldments in an out door grill with the aid of a vacuum cleaner blower. At least I hope that I did. The parts got to a very bright red doing so. This is possible but I’m not sure I would call it scientific.

I’m operating under the presumption that he doesn’t have access to a machine shop (he can’t get aluminum profiles in his area?!?); but I still don’t know roughly where he is, so...

One little question that seemingly is hard to get answers too on these forums. Location helps a lot because of all the regular readers here. Often somebody locally can chime in with a pointer to the right business to solve the materials problem.

If he was someplace with more industrial resources, my thinking would be different... probably think about getting the profiles ground after milling, if there’s room in the budget for that.

That 3M adhesive is definitely interesting... although I think I’d still clean the area with acetone or isopropyl alcohol before using it. Hmm....

The biggest problem with large frame machines is that they require work on large machines with large hourly rates. Around here it is very possible to find retired machinists with Bridgeport’s in their garages. The problem is a Bridgeport is a bit useless when you start to consider machine components for large router frames. It would not be impossible to find machining costs equal the cost of the metal in the frame of a lot more.

[__Britt]

This is possible but I’m not sure I would call it scientific.

"The difference between screwing around and science is writing it down." - Adam Savage.

The problem is a Bridgeport is a bit useless when you start to consider machine components for large router frames.

I've never used this method (er, not yet - I've got plans, er, schemes, um... crazy notions? for doing a big DIY machine... some day); but I've read about it being used:

Take a reasonably stiff backing rod of some sort, attach a pair of posts to each end, and string a thin steel wire between the posts. Put this steel wire under significant tension - it's now assumed a catenary curve towards the center of the earth; and it's deflection is described by an equation (I'd have to look it up to get the exact equation, but it's parameters include the strength of the local gravitational pull, the value of the Young's modulus for the wire, and the wire's cross-sectional area, IIRC). Perpendicular to the gravitational pull, it will be very close to a straight line.

Get a micrometer head (readily available on eBay; also Shars does sell them - it doesn't need to be super-precise, just repeatable). Make a slider plate that will run along the machined surface that you are going to be measuring; and mount the micrometer head in it, with the spindle of the micrometer head pointing away from the surface.

Attach an electrical wire to the taut steel wire; run that to a one side of a battery. Run another wire from the spindle of the micrometer (mounting it on the slider plate so that the wire is brushing it should work, but make sure you get good electrical contact with the spindle) to a one side of a LED; and run the other side thru an appropriate resistor (so you don't fry the LED with too much current) to the other side of the battery. Touch the spindle to the steel wire; the LED should light up; if it doesn't, first flip the battery around, and if that doesn't work, check your wiring.

OK - now you can set up the wire & tensioning rig parallel to your machined surface, slide the micrometer head/slider block along it, and determine how far away the spot that the head is currently at from the wire by turning the micrometer head until it just barely touches the steel wire and the LED lights up.

Now, if you have two machined sections of the gantry beam, and need to get them to be co-planar, you can use this rig to adjust both of them so that the distance from the surface to the wire is the same for the entire length of the wire. I think that another method would need to be applied to get the two beam sections to be rotationally co-planar, though - perhaps a test indicator mounted on a flat block (123 block? surface gauge?) and swept across the surfaces, with the flat block resting on one surface and the probe of the indicator on the other one; adjust the beam sections until there is no movement of the indicator when it's swept.

The point of all this is to allow you to use a smaller milling machine (like a Bridgeport) to make a larger machine.

[peteeng]

Hi Britt - I think these days you can get a laser system that is better and easier then that process. Peter

https://pinpointlaser.com/applicatio...nery-leveling/

[Gerry_H]

Hi
i have seen some DIY machines made from 4020 (100*50mm) modular aluminium profile gantry showing amazing accuracy
would you say it is much stiffer then 80*80mm steel?

maybe filling the profile with sand and epoxy or concrete will help?
cause i dont have access to any profiles thicker then 4 mm and 100*100 also they are very expencive...

For my DIY router, I made the gantry using a LVL (laminated veneer lumber) scaffold plank. It's 42mm thick, 230mm wide.
It's rigid by itself but even more so with the SBR16 supported rails bolted on.

[peteeng]

Hi Rocket - Here's a quick paper on gantry design. If you drop the "steel" from the wish list you will have a chance. From analysing several machines you will need a gantry of at least 200x200x12mm to cut aluminium at 1.5m plus wide. If you drop steel and because of your budget you could make the machine from plywood. People will look down on that but it is doable and there are many examples here of excellent timber machines. If you make a good timber machine you can use that to make good aluminium parts and then make a better machine. Then use that to make better parts for your steel machine. This is how we progress. The first machine you make will have lots of niggles and you will want to get into machine two asap. So don't get too hung up on machine No1 just get into it and once your through that learning curve you will do machine 2 and then maybe No3. See attached for gantry sizing... Peter