Need good cut-off disks

[DeadlyAura]

Today I bought a 30,000RPM variable speed Black and Decker dremel. It was 34.99 at Home Depot and is fine for what I need it for. However, the cutoff disks it came with wear out down to nothing 1/3 of the way through the 80mm holes I am trying to cut out.

It is taking me 3 or more disks per 80mm hole and is a waste of my time. A few of the disks have actually exploded while I was using them. I just need a disk that will last me a while and be able to cut through aluminum. Its not heavy by any means, but I am running out of disks now and I need to get these cut out before my new PSU gets here tomorrow.

By the way, 30,000 RPM is fast as hell. Medium speed is fast enough for me.

 

[SarverSystems]

Wrong tool for the job.

Cut-off wheels are straight, not round. That's why you can't cut a round hole very well.

I would use either a drill with 80mm holesaw, or use a jigsaw. Nibblers are a good alternative as well.

Also, if you have the B&D RTX, if it came with the guideplate thing (looks kinda like a funnel), go buy a rotary cutter (it looks like a drill bit) and use that to cut your circles.

Here's a pic of my tools I used to cut 4 80mm holes in acrylic:

I used the same technic to cut 4 80mm holes in this Shuttle:

 

[Diablo2K]

I can cut some really nice 80mm fan holes useing a Dremel and a cutoff wheel, if you take your time it can be done well. They sell reinforced cutoff wheels, they last alot longer and are less likely to explode on you. however I used the normal wheels when I did my last case, it had 6 fan holes I had to cut out in Steel, I used about 1 wheel per hole. Dont rush, pay attention to the RPMs and keep them up, if the RPMs start dropping to much you are going to fast.

 

[Doberman]

If you're using the smaller cutoff wheels (which I assume you are since you metion them exploding) you might wana try what I do. I double them up. Put two on the shaft. It really helps reinforce against breakage. With more practice it'll happen less as well. You cannot shift the angle of the tool when you've got the discs very deep into a cut or they'll bind & shatter.

To cut a round hole with a Dremel & cutoff wheels, you need to make VERY shallow passes. Don't try to cut all the way through at once. Go all the way around your entire hole just barely cutting a groove. Continue on like this until you're all the way through.

Use very little to no pressure from your hands to make cuts. Let the weight of the tool be all the pressure. If you force it down into the work you'll eat up discs at a much higher rate. And you're alot more likely to bind & break them.

FWIW, ServerSystems tip is the way I usually do it now. I've got the router attachement for my Dremel and just use a rotary cutting bit from my RotoZip (do they make these same bits specifically for the Dremel?) in there. Actually, most of the time I just use my RotoZip itself, but it's basically the same thing. MUCH easier than using cutoff wheels.

 

[Susquehannock]

>>>>>>>
By the way, 30,000 RPM is fast as hell. Medium speed is fast enough for me.

You really should try keep the speed up. Since the Dremel has no torque to speak of you have to
rely on high RPM's to do the work.

If your cutting disks are breaking that easily you likely aren't using the reinforced type.
They look like this :

When used properly you should not have trouble with them breaking. If you do you need to stop
trying to use the sides of the wheel. Despite what some may believe they are NOT made for lateral
cutting. Straight lines only.

Wrong tool for the job.

Cut-off wheels are straight, not round. That's why you can't cut a round hole very well.

< snip >

^^^ - agreed. The thing to do is cut a hexagon or octagon and round it out with a stone
or cutter bit to make the circle.

A reinforced disk will last through four or five 80mm holes that way. Does for me anyway.
This is how much 20ga steel I can cut with only 7 reinforced disks.

 

[bartsimsonii]

Get the diamond ones. they're worth it, they cut through steel like butter.

 

[Susquehannock]

Get the diamond ones. they're worth it, they cut through steel like butter.

Are you talking about these?

Those diamond coated disks are made more for cutting tile & stone if I remember correctly.

The reason I ask is because I would not recommend those for metal personally. They do not
last very long, certainly not enough to warrant their price. Once the diamond abrasive wears
off what you have left is a useless metal disk.

Better to buy a 25-pack of the reinforced disks for $7.

 

[DeadlyAura]

I wasn't cutting circles technically speaking. Because there were fan mounts already there, I was just cutting out the perforated metal that was blocking air flow. So, I really probably cut about 50 straight lines per hole. Thoses disks suck though. They were about 1in in diameter and wore out pretty damn quick.

I started out with 36 of them... I think I have 10 left.

I spent more time replacing disks than actually cutting. But I got the job done. I didn't have time to run to Home Depot today to get the reinforced ones, but I will next time I need disks.

I need to get some other attachments for it as well. The dremel is nice, but the accessories it came with suck...

I'll get more as I need them, but first is the reinforced disks.

 

[Susquehannock]

You are going to pay about $1 a disk at Home Depot. You can get them MUCH cheaper here*. - 25-pack = $7

That is where I got my last set & so far they seem to act exactly the same as the Dremel branded disks, but at a much lower cost.

There are some good guides lynked at the top of that page too = "Instructional Projects". Though I do not agree with the circle cutting guide. Much better to cut in straight lines IMO. But at least that guide tells you to hold the disk at a sharp angle to the work while cutting a circle. Better than some other guides I've seen.

 

[Doberman]

I wasn't cutting circles technically speaking. Because there were fan mounts already there, I was just cutting out the perforated metal that was blocking air flow. So, I really probably cut about 50 straight lines per hole. Thoses disks suck though. They were about 1in in diameter and wore out pretty damn quick.

I started out with 36 of them... I think I have 10 left.

Those disks most definately DON'T suck. It's novice operator error. We all go through it.

As I said, double them up to help prevent breakage (as long as the cut allows it - which most do), keep the tool at the exact same angle at all times so as not to bind the wheels, and use little to no pressure other than the weight of the tool. (These last two tips apply to ANY cutoff wheel you use.) I find when following these tips I get more than double the life of a single small one and more than double a reinforced wheel as well.

 

[Arcygenical]

I once went throuhg 20 disks doing a side panel. Wondering what went wrong, I googled dremel tips. Turned out I was using "more than the weight of the tool" to do the job, something that was totally detrimental to the overall job. A 1/2 as wide mirror of the panel, cut into the top of the case, used... 3 cutoff wheels. Problem solved.

 

[Susquehannock]

Agreed ... you do not want to apply too much pressure when using a Dremel since it relys on RPM's & has little torque to speak of.

To be honest, I don't think doubling up the disks is a good idea. If you are breaking reinforced wheels that often you need to change your technique. Plus when you double up the disks you are removing twice as much material. Given the limited power of the Dremel that is not exactly a good idea. But hey .... do whatever it takes to get the job done.

 

[Diablo2K]

I sure wish I had pics of the circles I cut with the Dremel useing the Cut off wheels, this stuff about cutting polygons and then grinding it out to a circle is just making more work than what is necessary.
If you take it slow, and dont let the disk go thru the metal any further than necesary you can make really good round holes!! The first fan hole I did I actually was surprised myself how little "grinding" needed to be done, all I had to grind away was the sharp edge. I think what you all are doing wrong is that your allowing the cutting disk to go to far thru the metal your cutting, dont cut with the forward edge, cut with the bottom, if the metal is 1mm thick then there should only be about .5 mm of disk going all the way thru the metal. If you have 1/4 of the disk sticking out the bottom of the metal your doing it wrong, you cant make tuns that way, that is why you can only cut straight lines.

 

[Susquehannock]

< snip >
I think what you all are doing wrong is that your allowing the cutting disk to go to far thru the metal your cutting, dont cut with the forward edge, cut with the bottom, if the metal is 1mm thick then there should only be about .5 mm of disk going all the way thru the metal. If you have 1/4 of the disk sticking out the bottom of the metal your doing it wrong, you cant make tuns that way, that is why you can only cut straight lines.

Well ... not all of us. Actually, I am a retired machinist, & have worked as sheet metal mechanic, so I have a lot of experience with this sort of stuff.

You are absolutely right about using the bottom edge of the disk - and not going all the way through with the 1st cut. Best to lightly draw a line with the disk 1st, then make successively deeper cuts. Like you said Diablo, much easier to retain your straight line that way.

Have to say I disagree with you about making turns with a disk. That wears down the sides, and also requires you to remove more material. Both of which will wear out the disks faster. Plus it puts lateral force on the disk which is not a good idea.

To be honest I have cut circles several ways, including making a circle. And I am quite sure that cutting straight lines creates less wear & takes less time than trying to make a circle. But hey, if you prefer to do it that way, and it works for you, that is all that really matters in the end.