Toroid Cracking for Gaps

In the "sci.electronics.design" context, you are probably talking about a magnetic toroid, core for a transformer or inductor.

Toroids are self-shielding, and cutting a gap will ruin that; why not use C and I sections to make your inductor, instead? Winding is easier if it's NOT a toroid.

Tape-wound toroid cores: don't cut all the way through. Powdered iron toroids: use a jeweler's saw. Ferrite toroids: abrasive cutoff saws (you might need to make a wide kerf and rejoin the halves to get back down to that small gap).

Exactly my thoughts. I always considered the tile cutting tools to be a ploy used by the tile layers union to keep home owners from attempting DIY. I found the way around the union was a wet saw (diamond blades are cheap).

Yep. I have two sizes of wet saws, plus a hand-held Makita (actually has a drip bottle as well).

...Jim Thompson

No. Ferrite is like glass (no cleavage planes), and powdered iron is like iron filings embedded in glue.

What do you have, and what are you trying to do with it? i.e., What's the goal?

Thanks, Rich

I have a ferrite toroid ID 30mm ID 20mm Height 7.43mm Magnetics Inc. material F

Idc = 1.2A Iac ~0.1App f=800khz L = 400uH

The toroid needs a gap. Between 0.1mm to 0.2mm

It's for a smps.

In this case, I think the ferrite volume is less than powdered iron volume.

D from BC myrealaddress(at)comic(dot)com British Columbia Canada

When ferrite tooids are shipped in bulk, the cracked ones tend to come 'free', if you can match up the bits.

I haven't seen recommendations for adhesive in this thread. Cyano-based adhesives will tend to degrade catastrophically with heat. Epoxy takes longer to break up, but is probably the best bet for the

Source a pot core experimenter's kit.

Thks all for replies..

Here's what I did:

Step 1 Scoring Scored ferrite toroid by 0.3mm depth with a thin abrasive disk on a dremel. (I just can't say 'rotary tool'.)

Step 2 Braking Taped up toroid and clamped in vice. Couldn't find hammer so used screwdriver handle to 'whack' the toroid. Toroid broke at scored points. Yah Some tiny lost shrapnel :(

Step 4 Glueing Couldn't find the fkn super glue..

Used Permatex threadlocker (anaerobic adhesive). Mixed in some glass microspheres. Adjusted gap by using digital calipers as a clamp. Covered gap with glue gun glue (Ha! Hot melt glue to cure an anaerobic glue.) Placed glue on room heater for overnight cure.

Note: Anaerobic adhesives for threadlocking have different cure rates depending on the material.

Next step: Winding without the glued core snapping.. :(

D from BC myrealaddress(at)comic(dot)com British Columbia Canada

idea 1: use "rope" instead of solid. - less stress.

idea 2: hold the core in vise-grips (or generic locking pliers) such that the force keeps the parts together.

are you going to pot it when done?

Such "adhesives" are meant for high pressure mating surfaces such as the faces of a thread against another. They do not work for simple surface to surface attachment at all.

I still would have dremeld the whole thing in half, then lapped the faces for an exact re-mating. You only lose about 0.5% of the media. You can stop the separation by winding a band of tape around the circumference.

Ahh... Of course.. Multifilar wire and litz wire wind very easily.

Thanks D from BC myrealaddress(at)comic(dot)com British Columbia Canada

I pulled off the hot melt glue the next day. (Glue gun glue has very low adhesion to ferrite.) I tried flexing the toroid. Sticks!

I've heard anaerobic adhesives don't cure in the tube due to a special air permeable plastic. Dunno if that's true.. I think it could be the air in the tube that prevents cure.

I think it's all about air starving the adhesive. That's why I covered the gap with glue gun glue. Also, the glass microspheres will help choke off air in the gap but that was just to get my gap size.

It was quicker to whack the toroid. Machining takes time. Also, I don't think I have good tools to do 90 degree flat surfacing.

D from BC myrealaddress(at)comic(dot)com British Columbia Canada

No..I don't trust the reliability of the glue + ferrite bond. So no potting..yet. Maybe later...if I get into a heat dissipation problem.

For now, the toroid is just for bench testing to educate myself in magnetics design.

D from BC myrealaddress(at)comic(dot)com British Columbia Canada