90 degree Jig.

[Mick B]

I intend making a jig to help me weld pieces at exactly 90 degrees. I know you can buy such a thing and it is much better that anything I can make, but there's no fun in that plus this will cost me nothing except electricity, gas and wire.

Basically it involves a piece of 200 X 200 X 5 mm flat with 2 pieces of 50 X 5 mm X 140 mm long welded as shown below. When finished you simply place 2 pieces of (say) 35 mm X 35 mm RHS against the sides and clamp in position knowing they will be exactly 90 degrees.

My question is mainly to do with the bottom drawing ............. should I grind the edges off at 45 degrees for added penetration, and to help weld the internal corner I thought I could cut a groove to allow the weld to get in without building up too much. RHS would sit in there no problems because the external corners are radiused, but some material are a sharp 90 degrees, and any weld would prevent it sitting in the jig properly.

 

[cumbriasteve]

If it's only a jig then it won't be under any significant stress so I would have thought light tacks on the outside would be ample and also avoid introducing distortion.

 

[Kent]

Get it lasercut and folded for you in as thick as they can handle

 

[Welderpaul]

I wouldn't weld it. It will pull all over the place.

If you need it to be really accurate even small welds may cause it to pull.

I made one years ago, just use the piece of square plate with the corner chopped off, then bolt two short pieces of box section to each side. You can nip the bolts up and tap then precisely square before final tightening.

 

[harryb94]

What you could do with is a jig to hold it square whilst you weld it
What about slitting the plate and Bending it up to form the sides and then welding up the slit? Could keep it squarer?

 

[Mick B]

I ended up welding pieces of 5mm together and it is now ready for use. I did have to make a very slight adjustment to get it perfectly square after checking it all. It was out about .006 " after checking it with some feeler gauges between the square and the sides and I was able to hit it with a flap disc and get it spot on.


Below shows how I made sure the sides didn't move after tacking and before welding it up properly. Just tacked a spare piece on as a brace.

Below shows how I made a series of long tacks while it was still braced.
The other 4 little beads are just so the jig sits nice and flat and doesn't wobble as I didn't grind the welds down flat.

Below shows how I ground into the internal corner and filled the gap with some long tacks.

 

[Kent]

I fear it wont remain square that long
Things like this need over engineering
Heat and odd bumps are the issues

 

[Mick B]

I hope you are wrong .
If need be I can always ask Santa for one of those whiz bang adjustable ones with the copper screws.

 

[Kent]

You can make your own anythings been at it myself ten mins ago but its best too seek all advice first listen and think
No doubt these will work for a while just keep checking them before use