First time build - Steel Frame CNC Router

**Clive S** · 03-03-2016

Originally Posted by examorph

Been a nightmare finding a local supplier that does box section without a 7.5mtr minimum order charge, but got one eventually who can do me some off cuts at a 3mm wall for a good deal.

Will the 3mm wall thickness box section be OK for the bed support beams and horizontal supports shown below in green? Will it also be OK to weld?
Attachment 17786

The main problem apart from resonance with 3mm box is that it is not quite thick enough to tap 4mm or 5mm would be a better option. If it is just for the green bits then it is probably OK

**Boyan Silyavski** · 03-03-2016

3mm is ok, if size is 80x80 or 100x100. I wouldn't use it for smaller than that.

No problem with tapping and screwing 3mm, just have to be careful and drill holes using a guide so they are true 90degree square to profile.

**Clive S** · 03-03-2016

No problem with tapping and screwing 3mm, just have to be careful and drill holes using a guide so they are true 90degree square to profile

6mm bolt in 3mm I beg to differ its right on the edge and suppose he wants to tap 8mm

**Davek0974** · 03-03-2016

Yep, I would not tap past 3 or 4mm into a 3mm beam, just not enough thread engagement.

**examorph** · 04-03-2016

Thanks guys, to confirm, it's just the green bits in the last post its being used for (2x bed supports and some braces).
Only place it needs to be tapped is on the bed supports, so that I can bolt down the ply wood bed onto there. Any options for this with the 3mm box section? Maybe drill through and use a nut/bolt setup?

**Clive S** · 04-03-2016

Originally Posted by examorph

Thanks guys, to confirm, it's just the green bits in the last post its being used for (2x bed supports and some braces).
Only place it needs to be tapped is on the bed supports, so that I can bolt down the ply wood bed onto there. Any options for this with the 3mm box section? Maybe drill through and use a nut/bolt setup?

You don't say what size bolts you want to use. If you drill through the box without a spacer in the box you have the chance of squashing the box of course you could use self tappers.

**Davek0974** · 04-03-2016

If the bolts are near the ends of the tubes, get in there first and weld in a reinforcement plate - a lump of 6mm etc welded in from the end would work.

If not then there are very few options really, you could drill a larger hole opposite the bolts so you can pass a socket and nut through to the front but that will only give you strength of the front 3mm section on the bolt, i doubt the hole will make any difference to the beam strength.

**valdis034** · 04-03-2016

And how about using inserts? Then you dont have to worry about wall thickness.

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**njhussey** · 04-03-2016

Or do what EddyCurrent did and glue in a strip of 6mm flat and drill and tap that...

**examorph** · 05-03-2016

Thanks for the advice guys, I ended up changing the arrangement slightly by only making the rear bed support from 3mm box, all other 4 (including front) are 4mm. So there should be enough box section to bolt the bed onto and will leave the back 3mm section as a support.

Spent half the day cutting/grinding more of the box section and the rest of the day, failing at welding

Some horror shows for you below:

1st weld on frame:
Attachment 17844

thinking of cutting this off and starting again. It was over two runs, had let it cool down after doing a bit

Few more welds after this:

Attachment 17838 Attachment 17839 Attachment 17840 Attachment 17841 Attachment 17843

Ended up grinding it down and squaring it up many times before I got anything close to square. Ended up with the below, plan is to do both sides and then join them with the sections in between.

Attachment 17842

Was jumping from one side of the frame to the other when welding and did not go back to weld the opposite face until I could touch it again, hopefully this is ok.
Settings for the mig were 2 Volts and 3 for the speed.

Before I continue welding/assembling tomorrow, could you guys please help me with a few questions:
- Is it OK to go back over welds to fill in the gaps, if any?
- Any recommendations on getting into the tighter angles for welding?
- I ended up running 100mm constant welds down the side of the 100x50 box section, should I be splitting this into two runs. 50mm at a time and wait for cooling before going again?
- From the images shown, does the amount of "overlap" on each side of the weld look like its enough? I was worrying as I only really concentrated on filling the gap and wasnt sure if I needed to drag the weld over each face enough to properly join the two sections.