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

[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.

[Davek0974]

I had thought of that but seems a possible method may be to fit the rails as-is and then fit a stretcher bar under the slats to force the beams out a little, 3mm should be easy.

Could even use the middle slat support possibly, not got that far yet though.

[Davek0974]

Got the Y axis motion fitted and the gantry supports tacked up.






Even without the beam fitted the side supports are very rigid, most encouraging.

[Davek0974]

Reclaiming some motion distance....


After building the base frame and motion, I decided to build a new floating head using Hiwin and a single carriage - pretty much a standard design. However, this moved my torch 30mm closer to the front of the table than I had planned which left very little over-travel on a full 1250mm sheet - not good.

The first pic is a cross-section of the average torch mount with the Hiwin at the bottom and the circle being the torch clamp.




Now, as I am using wide/stable Hiwin rail, could this idea work?? It regains a valuable 30mm of spare travel on the Y axis.