# How NOT to break small milling cutters.



## John S (Nov 27, 2011)

Bit of background first.

Making a raft of HTD 5M series pulleys, mill a stick out on the 4th axis CNC in two sizes 40 teeth and 20 teeth for 2:1 reductions for the CNC conversions.







These are dead easy to do, get the OD from tables or off the HPC web site and for the 5M series you need a 1/8" ball nose cutter plunged in to a depth of 2.16mm - job done.

Now the tricky bit, ball nose cutters are a ***** to traverse with because as the radius gets to centre there isn't much clearance and right on centre that part of the cutter isn't rotating, so feeds have to be very conservative.

The only cutters I had on stock were long reach two flute Chinese cutters and the chances of breaking one of these with 20mm of flute length will either be high or very boring if done in 17,457 passes [ approx ]

So brilliant brainwave, not seen this posted before but it's that simple it must have been done before.
Took a piece of 10mm steel and cut and faced it both ends equal to 5mm less than the length of the cutter, centre driled it and drilled one end 1/4" to a depth just over the shank length and the other end was drilled 1/8" to match the cutter. Slot cut in the side with a hacksaw and the cutter inserted so that it stuck proud by 5mm.

This way only 5mm of the cutter is unsupported.













Started off doing it in two passes but them swapped to full depth with no problems.

End results.






John S.


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## woodchip85 (Nov 28, 2011)

Karma point to you, the nuber or small ballnose cutters that I "insert expletives" snap due to being over length. This will be used next time.


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## chuckallen (Nov 28, 2011)

This may be simple, but it's brilliant! I've got about a pound of .030 - .125 end mills than are nothing more than shanks. Wish I'd figured this out earlier myself.
chuck


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## peatoluser (Nov 28, 2011)

now THAT really is a top tip. simple and brilliant. :bow:

definately filing this one away for future use. 

thanks for posting it

peter


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## BillTodd (Nov 29, 2011)

Nice one John 

I'm sure you also know of tipping the head at an angle to lift the slow cutting centre 'point' away from the work.

Bill


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## CMS (Nov 29, 2011)

Now this is some good stuff!!!


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## Gedeon Spilett (Nov 29, 2011)

Hi

That is clever and so useful, a first class tip, thanks


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## ttrikalin (Nov 30, 2011)

karma for you!


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## Simon0362 (Dec 1, 2011)

Excellent idea - but does anyone have any advice about what to do with the broken tips around ~5-10mm long which I have been religiously keeping in case I could reuse them. A holder needs to be concentric and able to hold the cutter by the 2/4 remaining flutes.

Lets hear those ideas please......


Simon


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