Second CNC table build, here we go again....

[Davek0974]

Got the metal cut today...

Ends squared up and deburred, also cut,drilled and tapped the mount plates for the motion frame and the insert plates for the cross-beams. All ready for a welding session now.

I'm fitting castors and screw-down feet so I can move it about and level it up when assembled.

While I'm gathering info, extraction....

On my little table I built an air-box that sits along the front of the table between the now unused water tray and the slats...


In the front i cut a slot with an area bigger than the pipe cross-section and also slightly tapered towards the middle in an effort to even out the air flow. It works well as long as the unused parts of the table are covered - i get no muck in the shop at all.

It's connected to this radial blower...



I know I can get more out of it by dumping the corrugated pipe and fitting solid duct but it's not going to do a table with an area four times as big.

I don't have any spare power capacity so simply sticking a big-ass blower in there won't do it, need to get smart here. I could maybe run two of these blowers, they are pretty cheap to buy and with external motors they are immune to metallic hot muck.

I had thought about a zoned system - a four zone would work ok with the same blower. Question is, how would I do it???

Any smart ideas on extract??

Don't want water - its only half as effective and makes the machinery in the shop rust.

[Davek0974]

Welded the end plates into the cross-beams...



The leg joint plates onto the main beams...



And the foot plates onto the legs...



Fairly confident in the welds, did a quick destruction test on scrap first, nice and hot concentrating on the thicker parts and washing into the 2mm tube. Joints are ground flush now. Casters will be added soon, to the side of the feet, the feet can be screwed down to lift it off the wheels.

[Davek0974]

Got two welded side frames - standing side by side, there is no visible warp, I'm pretty chuffed with that as it was a concern. I levelled the frames between the bench and sawhorse using a spirit level wedged them up, shimmed the bolting points between frame and top beams then tacked the outer and inner faces, seam welded the lower and upper faces fully, then seam welded the outer face, inner face is left tacked as there is a cross-bream to go in.




Its a bit bigger than my existing one Looks good though.



Upon assembly i realised i could not weld in the lower cross-beams as planned, I'm not really up to vertical mig yet, cannot get it on the bench, and the underside welds could not be done at all. Answer - make some more bolt fitments out of 10x50mm bar, weld them on and bolt the lower cross-beams in, this will make disassembly easy too.

[Robin Hewitt]

Good welding, you deserve to succeed

[D.C.]

how to weld the closer plates in - only way i can think is to heavily bevel the plates then insert and fill bevel with weld tying into the tube sides?

If you are trying to weld thin steel and thick steel together you need to run the weld pool down the thick piece of metal and then quickly move across to the thin metal, back to the thick metal, down a bit across just enough, back again to the thick piece, down again etc etc

If you try running a bead equally down the joint, the thin metal will blow out or the thick metal will not get proper penetration.

A CNC machine is never going to generate enough force to cause a properly formed weld to fail, it will probably never get above 1% of the failure point. But if you decide to do nice 'stack of pennies' welds that would make an instructor happy you will be introducing a lot of heat into your frame that will cause stress and distortion over time.

Clamp it, tac it, clean it, back weld an inch at a time and drink lots tea so the heat doesn't build up.

This is an awesome video for demonstrating welding heat distortion, well worth 10 minutes.

[Davek0974]

Amazing, thanks.

Is it the same for Mig though which is a lot faster, I guess it would be???
I would love to be able to Tig like that ;)

[Davek0974]

If you are trying to weld thin steel and thick steel together you need to run the weld pool down the thick piece of metal and then quickly move across to the thin metal, back to the thick metal, down a bit across just enough, back again to the thick piece, down again etc etc

Exactly how i do it, always bias towards the thicker part and set power for the upper end of the thinner part.

I had to cut a 10mm plate off the end of a 50x50x2mm tube yesterday as i welded it on 90deg out and i was impressed with the penetration i was getting, took some cutting to split the joint.

[Davek0974]

Had a quick mess about with the Tig, i was semi impressed but seems a lot hotter, probably moving too slow?


I'll stick with the Mig


Got the lower cross-beams fitted, then after a few tests it seems that a good way to fix my spacer/support strip was to use good ole pop-rivets, worked nicely. Also managed to get one of the racks fitted.

[Davek0974]

Ok, linear rail came today

Using a taught line to check my beams, I have a slight bow in both sides, as you look at the table they would bow towards each other at the centre, the amount is about 1 to 1.5mm on each side so thats pretty bad and would give me a 3mm variation from centre of motion to either end.

Question is - how best to tackle this????

[Clive S]

Ok, linear rail came today

Using a taught line to check my beams, I have a slight bow in both sides, as you look at the table they would bow towards each other at the centre, the amount is about 1 to 1.5mm on each side so thats pretty bad and would give me a 3mm variation from centre of motion to either end.

Question is - how best to tackle this????

You can always use the epoxy method that is quite often used on here.