Countersink bits

Good morning,

When using HSS "rose" style countersink bits to countersink and chamfer holes in mild steel, how do I prevent them chattering? It occurs with both machine and hand operations.

It doesn't happen all the time, but when it does, it's impossible to correct.

I guess speed and lubrication might be the main considerations.

Try putting a small piece of thin cotton fabric between the cutter and the work.

MichaelG.

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P.S. 1, 2 or 3 flute cutters are usually less troublesome 

Edited By Michael Gilligan on 27/02/2021 11:30:15

I think I read somewhere that rose bits were really woodworkers' tools.

Single cutting edge countersink bits, of which there are several patterns, cut mild steel without chattering.

Rod

Thank you Michael. Now you mention it, I remember one of the guys at work using a piece of spent emery cloth.

Rod. I did try the "snail" type bits, and they worked realy well, but they didn't appear to be very hard. Probably meant for woodwork. I'll do a search and see if I can find them in HSS.

In my experience, Chamfering tools chatter unless the speed is kept low, and fed very gently.

The 1/2 " one is better than the 3/4" when they are used in the 3 MT Tailstock..

Howard

Hi Bo'sun

I have experienced the same but found low speed (200) and lube with 1 good hit does the job and leaves a smooth finish if countersinking, for de-burring of small holes I use the same cutter but held in a chuck and operated by hand.

Emgee

After years getting oval, off centre or chattered countersinks with these type of cutters, I now get pretty well 100% success with the following 'rules'

1. Work firmly clamped down

2. Slow speed

3. (Probably the key one) be decisive! By this I mean, decide on your depth of countersink, set your stop on the drill press or equivalent on lathe/mill, then 'drill' in ONE FIRM motion to full depth. It always seemed to be the intermittent and 'bit less / or a tiny bit more' approach that causes issues.

regards. Mike

While we are on the topic of countersink bits does anyone have any recommendations for good value/performance?

I always found the cheap ones are shockingly bad and the good ones are shockingly expensive.

You can make your own single point from silver steel hardened of course, just make sure you back off to give clearance.

Or if you have access to a tool grinder do the same from HSS.

Emgee

The range of Sherwood single-flute csks from Zoro are excellent in performance and value.

Alpen three-flute csks give very good performance as well though are a little pricier.

Machine countersinking shouldn't cause chattering as long as you keep the speed and downfeed pressure low, and have good stiffness in the set-up. I tend to use Vactra no.2 as a lubricant, when I do use a lubricant.

Edited By Bill Phinn on 27/02/2021 12:46:23

I use the through hole ones in various sizes as I have zero success with any that have more than one cutting edge, and speed is definitely a factor.

Since I switched to using spotting drills instead of centre drills, I have found that they also make excellent countersink bits with no chatter at all.

Phil

There are *asymmetrical* countersinks where 3 segments with cutting edges are at different angles to each other.

This design is implemmented explicitly to reduce / prevent chatter.

Martin

The RDG 3 flute ones are good. I've got a few, 25mm is the largest, they need to be run slowly with lots of cutting oil, I use CT90.

Dad had one he made when he was an apprentice which had just one 'tooth' at a different angle from the others. It was a delight to use. I think one of my brothers had it when we sorted out Dad's workshop.

George B.