Welding legs onto BIG longitudinal beams

[Red_boards]

I'm building an extended Z-axis. Accordingly I have these monster 300 x 95 longitudinal beams. While the 100+kg weight of each doesn't scare me too much (except when they start to tip over!), I'm concerned about fixing the legs adequately. The problem is the the flanges of the beams are about 15mm thick (1/2") and I'm worried about getting the weld to penetrate deep enough with a small 140A inverter and 6013 rods.

1. Is my only solution to pre-build the leg structure and then have someone with a big welding machine come and attach the legs to the beams?

2. Any suggestions on different strategies for fixing the rails on? I anticipate that drilling these beastly beams might just take tooo long.

[Gerald D]

The strength of those welds is not important, IF you are using the diagonal bracing to the bottom ends of the legs.

[KenC]

If you still worry, sizedown your material thickness.

[Surfcnc]

Red

Preheat the steel with a map gas burner - they are cheap, very useful for many other jobs and really really hot.

Regards
Ross

[Mountaincraft]

Red

Preheat the steel with a map gas burner - they are cheap, very useful for many other jobs and really really hot.

Regards
Ross

Hey that's a great tip! I have several of those laying around..
Thanks!

I was wondering if I should pay to have my stuff welded, seeing as I only have a weld pak 100 mig (Well I do have a stinger if a certain neighbor would ever return it)... So, between beveling the attachment surfaces and heating it, I'll probably be okay then... seeing as I live in snow country, and plan on using some of that 'snowed in' time to work on this thing, the heating idea is that much more relevant..

I had never even heard of or thought of that, but it makes a ton of sense...
Thanks again for the tip,
Mark

[Leko]

Weld on a thinner plate and bolt them together.

[Red_boards]

Thanks for the tip Ross, never knew about pre-heating.
Thanks for the reassurance, Gerald. It just worried me that the weld might let go with all the movement of the cars on the table if the weld didn't penetrate deep enough (I guess the big chunk of steel simply conducts heat away too quickly for the weld to penetrate? Hence the value of pre-heating the area). By the way, my longitudinal bracing is as in the plans, but I'm planning for the ends of the table to have 2 horizontal box beams with diagonal supports between them and bolting to the legs, rather than follow th plans exactly.

Leco, bolting is an option. I'll be drilling some holes in the beams this weekend, so will know what I'm in for drilling 1/2" steel. If it's crazy, then I may have to follow Ken's option.

[Gerald D]

Red, a quick test will tell you if you are getting penetration - take some scrap and check.

Anyway, multiple pass welding will always work - lay 3 beads with a thinner rod rather than trying to do one fat one. Grind the surfaces clean first.

[Red_boards]

Weld on a thinner plate and bolt them together.

This ended up a good route. Turns out it's not so bad drilling 15mm steel, so the legs now bolt to the beams.