Thread: 3 Axis CNC router
You're frame is broadly the same design as mine and even partially built I can tell mine will be strong enough so you shouldn't have any problems.
In terms of strength I'd drop it down to 50x50x4 to save some cost. If you look around here you'll find a spreadsheet that does gantry deflection calculations. The span on the the x-rails (between leg and centre support) is the same sort of problem, if you plug in the details of your steel you'll find that the deflection is tiny (<1um I'd guess) and it'll also be tiny for 50x50x4. If anything that spreadsheet will over estimate too since the ends of the rail will be welded into place.
The only thing I'd say about 50x50x4 is that is doesn't give you a lot of room to mount the rails on. I wish I'd gone for 60x60x4 now but that's the great thing about hindsight.
From someone that has tried to bolt together his machine to someone about to try, don't bother. It's very slow and you don't get any meaningful adjustment at the end. In SketchUp it's really easy to place a bolt hole and give yourself a perfect 1mm of play so you have some adjustment. In real life you won't be able to work to the sort of accuracy necessary unless you have a full on machine shop in which case you'd be better of just buying a CNC. Like you I'm going to bolt the main x-rail on but pretty much everything else will now be welded together (I've got the welder I'm now just waiting for a workshop that has sufficient power). I'm not entirely convinced that bolting on the x-axis rail will help all that much in preventing distortion, I've tried welding some of my 50x50x4 and I couldn't spot any distortion. What bolting will help with is shimming if you find your two rails aren't quite parallel in the z dimension.
I just priced up similar at fhbrundle in birmingham and it came to £350 inc vat and delivery. But bear in mind that I think they only sell in 7.5mtr lengths so I was ordering quite a bit more steel than you have listed.
Steel Sections from stock to meet any fabrication specifications - F H Brundle
Not to sound to nuts, but have you considered filling the beams with some, erm, epoxy...?
You could also save a bit of money by dropping down to 80x40 & 40x40 instead of 100x50 & 50x50, just make sure you can still mount your rails.
Just tried a different basket,
3 lots of 7.5mtr 80x40x3 = £146
1 lots of 7.5mtr 40x40x3 = £30
1 lots of 6.1mtr 60x60x6 angle = £40
1 lots of 6.1mtr 60x6 flat = £21
Total inc & delivery = £282
If you can drop down to 80x40/40x40 and redesign the diagonal bracing so that you use some flat and some equal angle for the bracing you should save a fair bit on what you thought.
Cheers guys, really helpful. I'll have a bit of a rethink! Must cost a bit to fill with epoxy right??
I too will be building a similar style frame to your, with lots of bolting. I think it means not only adjustment, not sure how much, but also allows me to do the welding outside then bring it in to fit together, manoeuvrability I mean. The only difference is I plan on using 90x45 extrusion just where the x rails rest. I think this is an easier method to fix profile rails onto. Not sure if it flatter, but we'll find out when the time comes, but I still do expect to file and sand till its 100% flat. Just don't want problems with the profile rails binding once everything is built.
From what I've read in the past, people use sand for filling in the hollow sections for dampening. Epoxy could be used for levelling out your 100x50mm RHS to provide a flat surface for your rails to rest on. Also could be used on the joints where you bolt the frame together like a thin shims to make sure everything ends up square and parallel. With this method you have to tighten your bolts just enough till the frame is where you want it, let the epoxy dry and harden fully, then tighten the bolts fully.
Cheers all for the heads up on types of cost involved.
Assuming you want to fill 1m of 80x40x3 steel box internal the volume is 0.002849 metres cubed (or about 2.8 litres of space). 6kgs of epoxy/hardener is about 4.5 litres so a 10% mix would get you 16m or a 20% mix would let you fill 8m. The total cost include the aggergates (if you can buy them in small enough quantities) would be about £200.
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Waste of money buying the pumps for something like this, couple of plastic measuring jugs from the supermarket will do the job, west systems is a 5 to 1 ratio & you would need a slow hardener. West systems is a good product but I would imagine a cheaper resin would do just as good a job for this sort of thing. Not sure about the process of filling a machine frame but generally speaking adding something like 403 or 404 fillers will aid. You can find a list of fillers & uses here. I generally use the 403 but that's more specific to work I do & not filling a machine frame.
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