Science/Engineering/Technical forums

Hi,

I just bought some nominal 5mm ID ferrite to go around a 4.8mm cable. But the ferrite appears to be right at the end of its tolerance around 4.7mm. Cable doesn't fit.

I've drilled ceramic tiles with a 'conventional' HSS drill set I have (slowly working up in size, and dabbing water into the hole, fast drill speed, slow advance), so am going to attempt to open these up that last few fractions of a mm.

Any advice before attempting this?

Chris,

The only drill of choice is a diamond and drill fast speed but very slowly penetrating. It is possible to get a diamond coated straight shank drill.

Yes, that's right. There are two ways of going about it: either drill the piece entirely under water, or stop frequently and add water. The second approach is more effective as it creates an abrasive slurry that does the actual cutting. You really need to keep the drill bit cool though, otherwise you lose the diamond bits.

http://www.eternaltools.com/

I've found the diamond hole saws about a zillion times better than the diamond coated rods with flat ends - that middle doesn't cut well. I always use a pretty slow speed - easy to burn the diamonds off. I often make a little dam around where I want my hole of modeling clay to hold the water, which seems to work the best on this hard/brittle stuff compared to other cutting/coolant fluids - you retain the abrasive slurry at the cut the best that way. I set the drill press for a couple hundred rpm tops, put a constant but low down force on the quill (eg tie a weight to the handle, or just the weight of my arm), and wait. I do this the same for glass, quartz, alumina (the last being the hardest) but I suspect this would be the plan for ferrites as well. Waxing a piece of glass or similar to the backside before starting helps with chipping as the drill gets through (and you don't lose your water/slurry until it doesn't matter anymore).

Thank's, guys, I'll bear this in mind. Not sure it seems such a good idea any more if I have to go to the expense of getting a diamond drill (I don't have any) - so maybe I'll just buy ferrites with bigger IDs!!

If there's a Harbor Freight where you live, they're not expensive at all. I got an entire kit of hole saws for about $40 there. A little blister pack of small ones was less than $10. Way cheaper than a machine tool supplier...

Doug Coulter wrote:If there's a Harbor Freight where you live,...

Closest one is prob about 3,000 miles west of here!

This is the UK... you'd be shocked at how little hardware is readily available here for a hobbyist.