Wobblycogs CNC Mk1

Quote:

---

Originally Posted by Wobblycogs

I'm seriously tempted to swap out the extrusion for some box section aluminium with a good thick wall. I can't help feeling that three pieces of box arranged as I currently have the extrusion would be equally strong. I'd almost certainly then fill the middle one with kiln dried sand to damp vibrations. The problem then moves to joining the box section to the gantry sides but that feels like a fairly easy problem - I feel version 6 coming on...

---

Then again.... if going for box section, why not go directly to Steel for it's greater rigidity ?

Btw, for me it all started about four months ago.... I was simply sitting thinking that it would be quite nice to be able to see the cut taking place on the router table, like one can see when making hand held router cuts.... And I started thinking "upside-down" router tables, and then there was simply no turning back...

That one single thought started my downfall ;-)

Funny you should say that as I was just looking at steel prices. I'm favouring aluminium because it's flatter and I may at some point move over to profiled rails. I saw a discussion on self levelling epoxy earlier today which I've put to one side for later (got to get some work done today), that could be a solution.

Quote:

---

Btw, for me it all started about four months ago....

---

Oh you should think yourself lucky I reckon it start about 12 years ago for me. I've just kept putting it off and putting it off till I have a good workshop etc etc. I've still not got a good workshop space but I'm going to do it anyway. I have to admit though that I respect you for giving it a go in the space you have available, that's what I call real dedication.

Some bits turned up today...... :glee:

Attachment 7418

I haven't tried this but I've been thinking about it. The supported rail (at least the stuff I got from chai) has a series of machine screws(red) that bolt the rail to the support from below. Maybe these could be replaced with slight longer ones(blue) and bolt through the extrusion, support and into the rail.
Attachment 7419

Oooh steel, the build begins today :yahoo:. I'm hoping that's not all mine, I've already got more angle brackets than I know what to do with! Good to see it supporting it's own weight on what it probably about a 3m over hang though, I think this frame might just be strong enough :-). Cheers for to the update.

That's a cunning idea with the bolts asbo (and I like the drawing). Some careful planning would be required to get the bolts in as well as a long socket wrench and some careful hole cutting on the opposite side of the extrusion where it looks fairly weak already.

Quote:

---

Originally Posted by Wobblycogs

Oooh steel, the build begins today :yahoo:. I'm hoping that's not all mine, I've already got more angle brackets than I know what to do with! Good to see it supporting it's own weight on what it probably about a 3m over hang though, I think this frame might just be strong enough :-). Cheers for to the update.

---

No yours is only the bundle on the left, in fact there are 2 lengths missing (20x20) which should be here tomorrow.

Will start the cutting tomorrow morning :)

Quote:

---

Originally Posted by Wobblycogs

Now here's where I'm going a little off-piste with the gantry

---

It's very similar to this one:

Quote:

---

Originally Posted by Wobblycogs

One thing that is starting to concern me a little is cutting all this aluminium. I have a good selection of wood working tools but not much in the way of metal working tools. Do you think it would be possible to hand route 20mm aluminium? From what I've read slower bit rotation is better, the slowest my router will go is 10,000rpm which seems to be slower than most so I think I'm in with a shot but some advice would be much appreciated. Cheers :-)

---

You could try using a carbide cutter, since 6mm is good at 13000rpm and 8mm is good at 9700rpm. Probably best to try 6mm as there's then more margin for error on the feedrate.

Quote:

---

Originally Posted by Wobblycogs

Has anyone managed to find a good solution to this?

---

Yeah...don't use extrusion, or add a 10mm plate. The plate is a good idea anyway to reduce local deformation (spread the load).

Quote:

---

Originally Posted by Wobblycogs

I'm so tempted to just give up and use profiled rails but the extra cost is off putting to say the least.

---

Linear guides are much stronger than round rails and just generally better - you wouldn't regret it. However I'm confident that with your current design you could cut aluminium quite well, so it's not a necessity.

Quote:

---

Originally Posted by WandrinAndy

Then again.... if going for box section, why not go directly to Steel for it's greater rigidity ?

---

Problem is the accuracy of steel box section compared to aluminium box, or extrusion. If just using round rails you'll probably get away with it, but it would be hard to mount linear guides on steel box section without entertaining self levelling epoxy.
(Oh just noticed Wobbly said that in the next post!)

Quote:

---

Originally Posted by Wobblycogs

Good to see it supporting it's own weight on what it probably about a 3m over hang though, I think this frame might just be strong enough :-)

---

It doesn't really tell you anything. With a CNC machine we're not worried about the material failing/passing it's elastic limit, we're instead concerned about making sure it doesn't deflect by a few tens of micrometers. In the image that will probably be bending at least a milimeter.

Quote:

---

Originally Posted by Jonathan

It doesn't really tell you anything. With a CNC machine we're not worried about the material failing/passing it's elastic limit, we're instead concerned about making sure it doesn't deflect by a few tens of micrometers. In the image that will probably be bending at least a milimeter.

---

I didn't stop to measure as it was raining ;)

Been busy this morning...

Attachment 7426

Last weekend, in the pouring rain, I collected the steel for the base from Neil who very kindly sourced it for me and cut it all to length.
Attachment 7490
It was all covered in a good coating of oil which has been doing it's best to get every where this week so I turned it in to a somewhat cleaner pile of steel by rubbing it down with a degreaser.
Attachment 7491
After spending an hour or so cleaning it I decided to get a couple of rust spots off with a wire wheel which is when I discovered that I'd actually only managed to get a light surface layer of oil off, there's a much heavier oil still on the steel. My question therefore is this: how clean do I need to get the steel in order to paint it?
Attachment 7492
The image above shows a very clean piece at the bottom and a pieces that have just been degreased above. I'm sure the bottom piece is clean enough for paint but are the other pieces? If I've got to get all the oil off what is the quickest method as wire wheeling it all will take ages.

Some good news though. I've tested a couple of the long rail pieces of steel with a reference straight edge and they are fairly close to straight <0.5mm in 600mm.

Cheers :-D