[perlmonkey]

Hello everyone.
I work in industrial robotics and have an old robot that was to be scrapped stored in my basement. I'm building a frame for it to sit in out of square tubing, and the robot itself will sit on a 1/2" steel plate. I bought a 3' x 3' plate from the local recycle center and it looks like one side was cut with some kind of saw which is pretty straight, but the other side looks like it was cut with a torch - real scraggly looking, high-to-low spots are maybe 1/8" deep.
All I need to do is clean up those two edges and wondering the best way to go about it. I'm more into lathes and mills these days and am a noob when it comes to dealing with something like this so I'm looking for a little advice before I go at it with an angle grinder (which I think is the best way).

Should I just use a regular thick grinding wheel from the hardware store, or a flap disc with coarse grit, or is there a better way?
Any help is appreciated.

[weldin mike 27]

Hey there,

I searched a bit on you tube for a video explain good heavy grinding technique but i couldnt really find one, How ever theres is lots of videos on angle grinding in general so you may want to check it out.

As for your current question, its easy to show hard to explain in writing. The main thing is that you dont just use the leading edge of the wheel in a back and forth motion as this will only follow the high and low spots instead of eliminating them. This is a good initial way to knock down any really high spots but if it is reasonably flat there is a particular method that i would use to end up with a nice flat edge.


Here goes... The grinder is held at 90 degrees to the length of the plate with the underside of the wheel resting on the surface to be ground, The wheel is held flat on the job so that there is multiple contact points.

It jumps around a bit but it results is a flat surface that also indicates high spots by taking material off them and not any adjacent low spots. Kind of like the milling cutter would do. I tried to take a pic but it was to big to up load.

I hope you catch my drift, If you do start with the grinding wheel and when its flat swap to the flap wheel to smooth off.

If your plate is standing on its edge just use the weight of the grinder, if its flat on a bench you will have to concentrate on holding the grinder straight up and down.

Let us know how it goes.
Mick

[perlmonkey]

Hi Mike.
Thanks for the reply. Yeah, I spent a lot of time on youtube and google, but found nothing really specific to what I'm trying to do. I know these angle grinders can be dangerous... up to this point I've only used it to clean up welds & spatter. Was looking for someone else's opinion before I do something wrong and end up with a face full of abrasive shards.

My plate is standing on edge, so hold the angle grinder perpendicular to the work, parallel to the ground and hold on tight. I think I see what you're saying. BTW, is it safer to use an abrasive grinding wheel or better to use a stone? Not sure the hardware store has stone anyway, but curious.

Anyway, I'll have to give it a try tomorrow - kids are taking naps and the sun won't be around much longer! Good time to go buy a face shield.

Thanks again!

[weldin mike 27]

Hey,

No worries. I dont think there are too many stones out there any more, not for hand held grinders. Some special "cup" wheels are out there. Its seems you have the idea, Wheel flat on the job, parallel to the ground. If you would like to PM me your email address, ill send you all the pics i took. I will also try and make a quick video for you tube.

Good to hear about the face shield, also wear safety glasses. Remember to take it slow and dont put too much force on the machine, that may cause it to run away from you.
This method can take a bit of time but it is a handy technique.

Mick

[weldin mike 27]

Hey there,

Ps You can use the front corner of the wheel to grind off any really high spots before you start the method i said. but still work with grinder at 90° to plate. ie along the cut flutes rather than across them.

Mick

[weldin mike 27]

Hey again.

Heres a video i made, the camerawork is dodgy but you get the idea.

http://www.youtube.com/watch?v=liSsHNRxeU8&feature=plcp Part 1

http://www.youtube.com/watch?v=BzZtn8ey ... ata_player Part 2


Mick

[perlmonkey]

Hey, Thanks for uploading those videos to youtube. I did exactly that and I'm about half way through the job and it looks good already - almost down to a flat surface. It's a little more work than I anticipated, being that it is three feet long, but I'm almost there.
I drew out a guide line on the top of the plate to follow and my cut is pretty straight, but not perfect - a little wavy. Any tips on how to get a straight edge before I remove too much material?

[weldin mike 27]

Hey,

My pleasure, im always ready to help if some one is ready to learn. The easy way to do what you are asking is to "pad up" the low spots. That means if you have an exceptionally low spot, instead of grinding for ever and eventually making your part to small, you weld some beads in the low areas to add metal. This will enable you to smooth every out by Adding(+) metal with the welder to the low spots and subtracting(-) metal from the high spots with the grinder. The idea is to add enough weld that you are able to shape it back to the dimentions of the original plate with the grider. Hope this is not to confusing.

Mick.

[perlmonkey]

Sheesh. Thanks. I need get get my mindset out of metal removal only and realize that I can add material now that I have a MIG. Thanks for waking my brain!

So, I got it looking pretty good. Down to the level I need, pretty flat and square. Now I have to remove all the surface rust from the face (front and back) prior to prime/paint. I just tried smearing a liberal amount of naval jelly on the front surface with a chip brush, scrubbing it in as best I could. Says to let it sit for up to 10 minutes. At 10 minutes I went and checked - scrubbed it with a brush and wasn't down to bare steel so I let it sit for 10 more. No luck.
Some rust came up in a few spots where I accidentally scratched the surface with the angle grinder... so I assume that it just isn't penetrating enough.

What do you recommend? Wire wheel first, then naval jelly to get the divits that the wire wont reach? or maybe just a rust deactivator? I don't really care if the surface is rough - I just need to paint over it and bolt the robot down.
Thanks in advance.

edit...
Maybe it is part mill scale too? Looks like there's a spotty black section in the middle, but 90% of the surface is rust.

[Otto Nobedder]

A rust converter primer, like ZEP RustArrestor, will do the job. It converts iron oxide to iron phoshate, neutralizing it, and serves as an excellent primer for any paint (though a light scuff with some 240-grit before paint helps assure adhesion). Used full-strength, it's a fairly high-build primer with good self-leveling properties, for a good finish.

Steve S

[weldin mike 27]

Hey, I hope all the info helped you out. As for your surface preparation, i havent got much experience in that area, but ottos' advice seems right on the money, The only other thing i can think of is a wire cup brush for your grinder. What is your robot going to do? We have 3 welding robots where i work, they work great sometimes and sometimes they make a total dogs breakfast out of it. They are awesome to watch though. Id like to see photos of yours, No photos of mine cause we're a military contractor.

Mick

[perlmonkey]

Thanks again everyone for the advice. Plate has pretty clean edges now and I am in between coats right now with Rustoleum "rusty surface" primer. I looked for ZEP, but they didn't have it at the hardware store. Unfortunately the paint is the same color as the rust so i'll have to hit it with a few coats of white afterwards.
Thanks again.

[weldin mike 27]

Hey,

Pleasure .

Mick

[perlmonkey]

Hey Mick.
It will be a pick and place robot for mounting electronics to PC boards. I haven't done anything with welding robots, (I'm a software engineer for semiconductor robotics) but I could see how things could get goofed up if you're not watching it run and something goes wrong.

[weldin mike 27]

Hey, thats right. I dont work the robots but i sometimes have to fix their welds. Can be a little challenging but i spose their good bad ratio is not too bad considering they lay down about 200 metres of weld per job.

Mick