90 Degree outside corner clean-up

[Toscane]

Well, I wasn't posting so much lately but I have a pretty good excuse. I was working on my thesis and I've passed with a full score after 4 months of hard work. I have to thank you all for your help, especially the Pack Rat, his advices were dead on. Anyway...

I'm working on a different project now and time is not an issue so I'm trying to do my best however I need help from you folks on a specific matter.

What I'm doing is joining 3.0 mm sheet metal and creating a box section, 90 degree outside fillet welds, all around.

I am aiming for a seamless look and considering clear lacquer on roughly polished steel (wirecup). I might let it rust too but that's another topic, coming in a couple of months.

I have a die grinder and an angle grinder.

Today, I tried to clean one of the edges and disappointed by the result horribly. I was going to have a sharp edge, 90 degree, clean-cut but ended with this terrible bevel.

I used grinding stones, carbide burrs (hate em!), grit papers on foam backing but can't achieve what I want. It's impossible to have a sharp, clean edge with these tools. So I searched the web and MWUK (hmm...) and found this thing called "belt sander".

I think it might work for me but I don't know if it's the right tool. It's expensive as heck so I can't risk going to the 'trial'n error' route. Could you please give me some insight about this tool?

Here is what I'm doing, please check out the pictures. I'm sorry for the quality but capturing the beveled edge is almost impossible with the camera. There is one photo before welding and leveling then the todays result.

One of the pictures has what I want marked with a, erm, tick (?) and it shows how it is now, marked with X.

 

[shenion]

What about using a flat file?

A disc or belt sander would work.

 

[Toscane]

Flat file as in a regular hand tool, bastard file? Or is it a power tool?

If it's the hand tool, I don't think I can use it for the whole thing; it's so big for that. It's 55x40x170 cm and has over 45 edges that needs to be corrected. Power tool is a must, unfortunately.

I tried disc sanding with my angle grinder but it's hard to keep a consistent level, some sections go deeper than others and result is a little wavy. I keep trying and trying for leveling it flat but this process eats through a lot of metal.

I'm having doubts about this belt sander tool because everywhere, even on the manufacturers website, they say it's used for wood work.

I'm considering this B&D tool, it's the least expensive one but even the product pictures are showing it being used on wood.

 

[shenion]

You can get belts for steel or have them made.

I'd look at a large disc sander with a good table.

 

[Toscane]

I made myself a welding table and it's pretty sturdy, I just shoot the pictures inside the house, I'm not working on the ground. I clamp the piece on my welding table and it's not moving at all, pretty solid.

So, I need a larger diameter angle grinder huh? Can I use bigger discs with my angle grinder instead of buying a bigger machine?

EDIT: I currently have 115mm angle grinder. It's 4 inch in States I suppose, or 4.5.

 

[shenion]

No, a disk sander not an angle grinder. Here's one with a belt sander.

No comment on brand/model, just one that came up on google.

 

[fluxcored]

Interesting problem ... sharp edges you say.

I'll probably cut the weld down with the grinder until it's slightly proud of the surface using many passes with very light cuts. You'll have to work carefully and not put any pressure on the grinder to cut too deep, just many frequent passes over the seam.

Then I'll use a bastard file on it to file it flush to the surface with final finishing off with a belt sander. More and more these days I reach for a file or the hacksaw.

This is going to be a lengthy process which ever way you look at it. It'll go faster if you braze instead of weld, even more so if you fold your box section reducing the number of seams you have to weld.

I have got the same B+D belt sander. You have to babysit it through any sanding operation. I must say though that I do use mine mostly for metalworking and it fairs OK if you are patient and regularly give it a period to cool off. OK for light DIY use, not so good for production or prolonged use.
Stay away from it if you're a serious metalworker.

 

[astro_al]

Do you have acces to a milling machine?

Al

 

[Archie]

I find you can get pretty good results on 90º joints with a light tickle of a flap disc.

Also, and it's a bit tricky to tell from the pics, but it looks like you've set the join up so that you're welding into the corner. You could try setting it up so that you're doing more of a butt joint. That way you'd already have the sharp edge formed by the edge of one sheet.

 

[GrahamGKD]

Toscane,
Would it help to clamp a piece of scrap angle or similar to the outside of the corner and flush with the one side and then use that as a guide to stop your angle grinder disk eating the corner away. You would have to clamp first to the one side and then to the other but I would have thought that would leave you a pretty square edge? Is that approach feasible? Hopefully you can understand what I'm on about - otherwise I'll try and figure how to post a drawing on here?
Graham.

 

[piman]

Hello Toscane,

I have to agree with Archie, that is the only practical way of getting a sharp corner. Forget all the abrasive, etc ideas as you will have to reduce the thickness of your stock by about 50% to get a sharp edge and keep the section square.

The other alternative is to run a couple of low current passes to build up the edge but that is not easy and is more time consuming both in welding and dressing than Archie's suggestion.

Alec

 

[Sam]

What I'm doing is joining 3.0 mm sheet metal and creating a box section, 90 degree outside fillet welds, all around.

I am aiming for a seamless look and considering clear lacquer on roughly polished steel (wirecup). I might let it rust too but that's another topic, coming in a couple of months.

I have a die grinder and an angle grinder.

Today, I tried to clean one of the edges and disappointed by the result horribly. I was going to have a sharp edge, 90 degree, clean-cut but ended with this terrible bevel.

I used grinding stones, carbide burrs (hate em!), grit papers on foam backing but can't achieve what I want. It's impossible to have a sharp, clean edge with these tools. So I searched the web and MWUK (hmm...) and found this thing called "belt sander".

I think it might work for me but I don't know if it's the right tool. It's expensive as heck so I can't risk going to the 'trial'n error' route. Could you please give me some insight about this tool?

.

You will have to build the weld up above the sheet face then using a 4 or 4 1/2 grinder with fibre disc (not a flap disc same material tho)60 grit and backing pad I find also using an old disc behind the new fibre disc helps. When buffing take care in keeping the disc square to the sheet face, only practice will prevail then finish off with a sander if it has to be painted.

 

[Tim53]

Sharp edges

Toscane,

I attach some photos of one of a pair of ashpans I made out of 2mm steel. I set up the pieces with perfect edges using magnetic clamps, as in your photo of the tack up stage, and corner welded. Clean up was with very light passes with grinding wheel in angle grinder followed by 60 grit flap disk. Use a very light touch and adopt a comfortable position and it is easy to achieve a near perfect finish (as Archie also has suggested).

Tim53

 

[Sam]

You may find if not carefull using a flap disc there is more chance of causing a dwell in the sheet than with using a fibre disc.

 

[Hitch]

Archie has told you the best way to go about it.


Then use fibre discs with a backing pad rather than a flap disc. They are a lot less likely to dig in. When you hold it, you need to keep it quite shallow and pressure on the back of the disc, so you dont pull metal from the sharp corner.

 

[Toscane]

Thank you very much for the responses folks! I've tried everything you guys said and unfortunately, I made a mistake at the very beginning while designing and cutting the material.

Archie, you are correct brother. Healthiest way to obtain sharp edges is using the flush corner joint method, period.

However, I've cut the pieces already for a full-open corner joint and flush corner assembly ruins the design and more importantly, I've tack welded everything!!! Yes, stupidity.... I have to cut almost half of the materials to different sizes because I have too many 90 turns on this box section.

I'm going to finish this project with the rounded edges, unfortunately.

If I sand down to make a sharp corner, I have to shave almost more than one third of the material and that is unacceptable.

I made a drawing to explain it but it's not accurate. In reality, I have to shave way more than that because weld digs into the corners of the sheet metal and sits lower.

I've also tried filling the corner weld by welding on top of it 2 more times but got frustrated and just let that go... Besides, it takes hell of a long time this way and I melt electrodes like ice on a stove.

I should have asked BEFORE...

I am going to finish this one as soon as possible and start a new one, from scratch, so I can have sharp corners by flush joints.

Also the plan of buying a new power tool is currently on hold. I don't need a new power tool, I need to think, ask and research more...

Thank you very much, again, for all the help guys! I do appreciate it! :thumbsup:

 

[piman]

Hello Toscane,

are you intending to paint this item or leave it natural.

The reason I ask is that there may be a way to salvage it by lead loading the edges if you are going to paint it. This is the application of plumbers solder (60% lead\40%tin) which can be shaped with wood or cloth while still semi molten. It has been used for years to shape car bodies before the popularity of plastic filler.

Alec

 

[piman]

Hello Toscane,

I have just re read your original post and see that you want to leave it steel colour, so lead loading won't work.

Alec