Grinding out a small crack for welding with Dremel

[pgrbffParticipant @pgrbff]

I need to buy a grinding stone for my dremel to grind a V in a crack in a cast iron plate. Is aluminium oxide going to work? Will it last long? Is there something better I can use?

[pgrbffParticipant @pgrbff]

[mechman48Participant @mechman48]

I reckon you should use a carbide burr much better metal removal rate.

George.

[Jeff DaymanParticipant @jeffdayman43397]

I'd suggest a 4 1/2" angle grinder with a cutoff disk of 80 or so grit. You may be a long long time and go through many expensive Dremel grindstones doing the vee out with a Dremel.

"don't bring a knife to a gun fight" as they say in the movies.

[OldironParticipant @oldiron]

You can get carbide burrs for the Dremel. A much better way to do it. An angle grinder is a quicker and dirtier way to go.

regards

[Michael GilliganParticipant @michaelgilligan61133]

Sorry to nit-pick … but surely the choice between Dremel and 4 1/2” angle grinder depends upon the physical size of the job.

The title mentions “a small crack” and the text mentions “a cast iron plate”

… any advance on a 6mm long crack in a 50mm square plate, 4mm thick

MichaelG.

[mechman48Participant @mechman48]

For that size… carbide burr !

George.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by mechman48 on 12/02/2021 18:13:36:

For that size… carbide burr !

George.

.

I agree, George … my point being that we don’t know what the OP meant by small.

MichaelG.

[Grizzly bearParticipant @grizzlybear]

9 inch 230 mm dia. if its a dinner plate.

I blame the lockdown.

Regards, Bear..

[Grindstone CowboyParticipant @grindstonecowboy]

Carbide burr gets my vote – not so much because of removal rates, but anything abrasive may (will?) leave contamination embedded in the metal. May or may not be important depending on what you plan to do after forming your V…

Rob

[Dave HalfordParticipant @davehalford22513]

A 2.5mm welding stick needs a 2.5mm vee or you only weld or braze the surface.

[Pete WhiteParticipant @petewhite15172]

My input at post no 11 to try to solve this, small or big, problem, lol.

Cast iron and plate sort of tells me its an angle grinder job without much doubt, could be wrong often am, as the wife she will confrim that for sure, again without much doubt !

I go with The Bear, on both of his points. lol

Pete

Edited By Pete White on 13/02/2021 08:56:29

[pgrbffParticipant @pgrbff]

It's approximately 2" long in a 1/2" thick plate. Some of it is in a corner, that's why I wasn't going to go for the angle grinder option, difficult to get in there and do a tidy job. Really just wanted to know what material was best to grind cast iron. I tried one "pink" grindstone, it was from a cheap multitool and it really isn't lasting very long.

Edited By pgrbff on 13/02/2021 11:45:22

Edited By pgrbff on 13/02/2021 11:46:12

[pgrbffParticipant @pgrbff]

And I couldn't find a carbide burrs on the Dremel website suitable for metal. Any pointers for choosing one that will do the job? You see lots for sale on eBay but I have no idea of quality.

[Dave HalfordParticipant @davehalford22513]

Might be better to use the dremel cut off disc's at an angle to the cut then snap a chuck out with a screwdriver blade. Don't push the dremel, be a shame to cook it.

Dont forget some cast iron welding sticks cannot be machined easily.

Edited By Dave Halford on 13/02/2021 12:00:42

[noel shelleyParticipant @noelshelley55608]

The OP has not stated that he intends to weld this, but it's a fair assumption. I would think that a dremel will struggle to do the job. A 4.5" grinder or an air driven die grinder might be better. The success of a burr will depend on the hardness of the iron, and a disc or wheel will soon shatter or wear very quickly if allowed to bounce on the work. To weld or braze, a slow heat up and a long cooling will aid the chances of success. If welding try to buy a rod for cast iron, it will be high nickle and not cheap. Good luck Noel.

[JasonBModerator @jasonb]

Posted by pgrbff on 13/02/2021 11:51:35:

And I couldn't find a carbide burrs on the Dremel website suitable for metal. Any pointers for choosing one that will do the job? You see lots for sale on eBay but I have no idea of quality.

Keep loading more items onto this Dremel page and you will get to the carbide burrs, or just enter "carbide" in the search

Edited By JasonB on 13/02/2021 12:20:20

[pgrbffParticipant @pgrbff]

Posted by JasonB on 13/02/2021 12:19:22:

Posted by pgrbff on 13/02/2021 11:51:35:

And I couldn't find a carbide burrs on the Dremel website suitable for metal. Any pointers for choosing one that will do the job? You see lots for sale on eBay but I have no idea of quality.

Keep loading more items onto this Dremel page and you will get to the carbide burrs, or just enter "carbide" in the search

Edited By JasonB on 13/02/2021 12:20:20

Thanks. Not sure where I was looking. I thought I'd gone through them all.

Ah, I was looking at the grinding category only.

 

Edited By pgrbff on 13/02/2021 12:28:51

[pgrbffParticipant @pgrbff]

Posted by noel shelley on 13/02/2021 12:10:05:

The OP has not stated that he intends to weld this, but it's a fair assumption. I would think that a dremel will struggle to do the job. A 4.5" grinder or an air driven die grinder might be better. The success of a burr will depend on the hardness of the iron, and a disc or wheel will soon shatter or wear very quickly if allowed to bounce on the work. To weld or braze, a slow heat up and a long cooling will aid the chances of success. If welding try to buy a rod for cast iron, it will be high nickle and not cheap. Good luck Noel.

If I can find someone to do it I hope to have it brazed rather than welded. I have used cast iron electrodes myself with an inverter but the result wasn't very tidy, even if it is still holding up several years later.

[pgrbffParticipant @pgrbff]

Posted by Dave Halford on 13/02/2021 11:58:53:

Might be better to use the dremel cut off disc's at an angle to the cut then snap a chuck out with a screwdriver blade. Don't push the dremel, be a shame to cook it.

Dont forget some cast iron welding sticks cannot be machined easily.

Edited By Dave Halford on 13/02/2021 12:00:42

Can't get into the corner with a disc.

Edited By pgrbff on 13/02/2021 12:36:05

[Nick WheelerParticipant @nickwheeler]

Veeing that out with a Dremel will take about as long as ordering a proper die-grinder and burrs, then waiting at home for it to be delivered. The cost is likely to be similar.

Dremels are like the tools from salesmen at shows; the well thought out spiel makes you think it's worth having, but experience proves otherwise.

[mechman48Participant @mechman48]

'If I can find someone to do it I hope to have it brazed rather than welded'

Try getting in touch with 'Doubleboost' he has brazed CI before with his TIG set, shown on one of his videos.

George.

[Michael GilliganParticipant @michaelgilligan61133]

Well-said, Nicholas

MichaelG.

[Nicholas FarrParticipant @nicholasfarr14254]

Hi pgrbff, if it were mine, I would cut along where I've drawn the yellow line first, with a thin in a 4-1/2" angle grinder, aiming aim the best I could judge, to the bottom of the crack and then along the red line as best I could. Don't worry about trying to get into that little corner and you can build the shape back up with weld or brazing.

Regards Nick.

P.S. You can always tidy the V up and take any dirty bits out with a small stone or burr in your Dremel.

Edited By Nicholas Farr on 13/02/2021 15:47:37

[Dave HalfordParticipant @davehalford22513]

Posted by Nicholas Farr on 13/02/2021 15:43:10:

Hi pgrbff, if it were mine, I would cut along where I've drawn the yellow line first, with a thin in a 4-1/2" angle grinder, aiming aim the best I could judge, to the bottom of the crack and then along the red line as best I could. Don't worry about trying to get into that little corner and you can build the shape back up with weld or brazing.

Regards Nick.

P.S. You can always tidy the V up and take any dirty bits out with a small stone or burr in your Dremel.

Edited By Nicholas Farr on 13/02/2021 15:47:37

As Nick says above and use these and clamp it to something so it can't move. Nickel is not a hard metal so will machine with HSS, note it says for hot and cold welding and they are being sold by a proper welding supply company.

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