die grinder for cutting slots ?

Im making up some engine bearer plates for my project car from 3mm steel and realised I dont have anything that will cut decent slots in them for the engine mounts to drop through.  Would it be best to buy a die grinder for this job and if so would my 2.5hp compressor be enough to run an air one or better to go for electric ?. .

Although my main compressor is a nice umpti unit, it runs out of puff when using my windy grinder. I bought the grinder due to its diminutive dimensions, I wanted it to work in a cluttered area, fortunately the material to be cut gave up without a fight, completing the job without winding it too often.
The other thought is convenience. I have a retractable air line, which is very handy, however I’ve got a number of mains extension cables, in addition to my retractable unit. The airline & all the pig tails run to 15mt; five are an absolute pain due to then acting as if they were still attached to the pig. I have up to 60mt of very well behaved cable.
Read into that what you will.
M

I have a 24 ltr, 8Bar compressor, which runs out when using a die grinder. Die grinders use about 3.5 - 4.5 cubic ltrs of air per minute, so it shows why the compressor runs a lot. When I bought this compressor, it came with the advice not to use it with an extension lead, only to plug it straight into the mains socket, and use a long enough hose, due to possible power drop. I recently bought a Parkside electric die grinder, at £19.99 it's worth having. It is larger than an air powered tool, but it has the advantage of not having the hose behind it, the cable is more flexible.

Die grinders can be savage brutes!, generally I prefer air die grinders as they're much more compact and spin much faster 20,000 RPM+
I'ts bloody hard to explain, but a strong, yet light hand is required to control them though the proper selection of burr size to do the job helps, too many people use to big a burr for the job at hand. The correct shaped burr also helps. Shit goes everywhere and its sometimes bloody sharp, eye protection is essential! You will be picking little bits out of yourself no matter how much protection you use as they find themselves working their way in.
I'm making it sound worse then it really is, but be prepared!
A good selection of burrs is required and good burrs aren't cheap. different burs are required for alloy than steel.
Alloy are what is known as single cut those for steel are double cut, what that means is the single cut cutting head has deeper but less cutting flutes, this is to prevent the softer alloy material from clogging up the burr.

Single cut for alloy
 

Double cut for steel
 

Some of the typical shapes and their uses
   

 

There are so many shapes it impossible to list them all

As for air consumption rates, well if your compressor has trouble keeping up, just stop take a breather and let it catch up! It will give you a chance to clean away swarf, and to see how you're doing.
 

i guess it depends on the size of the slots, if they are for 8mm bolts upwards, then i would drill two holes and use a jigsaw and file to finish.

A die grinder can be quite hard to control.

If you’re working with 3mm mild steel you might consider a pneumatic shear or nibbler, I don’t know how air hungry either is, as I use manual versions of both.
I’ve promised myself one or the other if I return to a sheet metal project. Arthritic hands find difficulty in the “squeeze” these days, having to shake one’s hand to restore circulation, in the way one has to shake another member to rid the last drip.
Oh poor prostate!
M

Pharg55 wrote:

I have a 24 ltr, 8Bar compressor, which runs out when using a die grinder. Die grinders use about 3.5 - 4.5 cubic ltrs of air per minute, so it shows why the compressor runs a lot. When I bought this compressor, it came with the advice not to use it with an extension lead, only to plug it straight into the mains socket, and use a long enough hose, due to possible power drop. I recently bought a Parkside electric die grinder, at £19.99 it's worth having. It is larger than an air powered tool, but it has the advantage of not having the hose behind it, the cable is more flexible.
I bought one of those Parkside die grinders four  or five years ago, I  used it for a huge amount of work with burrs for shaping aluminium and also stainless steel. It eventually gave up the ghost and I bought a Dremel. Although the Dremel is a great tool to own and would cut those slots in the engine mounts very easily another Parkside die grinder is on my shopping list the next time I see one. One point to remember is that air compressors often come with a very small diameter hose, I upgraded mine to 3/8" and 1/2" and the difference with air hungry tools is very apparent

 

Hi, that's exactly what I would do. G.

My Dremel is on its last legs i fear. I had to take it apart and bridge a wire that had burned out a couple of years ago after using it (perhaps unwisely) to cut through an exhaust bracket on my 115 where there wasnt room to swing an angle grinder. It held up pretty well since then but the other week it struggled with ginding away some small swaged joints on 'sealed for life' steel ARB bushes on my daily.  It sounds different and is noticeably down on power. Ive probably used it too often for jobs where I should really have used a die grinder.

Used to be able to buy flexible drives that fit in a drill chuck for using small tools for grinding etc. G.

You wouldn’t want to let one of those loose to flail about with a new carbide cutter in the chuck.
You would be safer with a taipan by the tail.
M

That's true, so switch the drill off before you put the flexible drive unit down.
Safety first yes?