Chattering when cutting with countersink tool on lathe

Just can't understand why. I have tried this kind of tools ( 3 blades ) with positive or zero rake angle but once the cutting area gets larger ( > 6 mm ), it will chatter. May be it's due to the backlash of the feeding screw of the tail stock but how come no such problem has been encountered when drilling even if the diameter of the hole is much bigger ( 13 mm  ? The lathe is an Emco Compact 8.

I assume your countersink tool is sharp. I have an old countersink with more than 3 cutting edges and it works better than the 3 bladed ones I have on my old Compact 8. I use a diamond hone to sharpen the cutting edges between grinding.

Thor

Countersink chattering is a perennial problem especially on light machines, try slowing rpm right down.

Tony

Years ago I made my own csk tool which works OK. Chuck short length of Silver Steel in 3 jaw and swivel topslde over to 45° and turn taper on SS bar. Mount bar in Toolholder at right angle to lathe bed and fit milling chuck on headstock to take an endmill and using the point as a guide, mill away almost half the diameter, leaving a small allowance for sharpening. Alternatively, use the mill if you have one. Harden and temper to light straw colour. Works well for me.

I think the countersink bits least likely to chatter are the ones that are solid with a hole drilled through them, I don't know if they have a specific name. I have had chatter problems with all other types of countersink bits. The solution to chattering with other styles is to slow the rpm and go in hard with the bit. This is easy with a back-geared lathe but may be a bit more problematic with electronic speed control. Can you stiffen the tailstock barrel by lightly clamping it?

Have you got a long overhang from the tailstock? Countersinking bits are usually shorter than drills and the resulting long overhang from the tailstock may contribute to the chattering. The somewhat flexible drills may have a different resonant frequency to the extended tailstock barrel and a short stubby countersink bit setup. If you have the tailstock barrel nearly at full extension to use the countersink bit can you interpose a morse taper extension and see if that changes the resonance enough to stop the chattering?

Martin C

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Best regards,

Swarf, Mostly!

I was taught as an apprentice that when you get chatter drilling or countersinking to put a small square of emery cloth under the drill/countersink point and pull down hard, breaks through emery cloth and starts cutting properly.

David

Multi-flute countersinks are a problem on smaller machines. The problem is the backing off behind the cutting edge is too great. Allowing the edge to rub on the work. Putting a piece of Emery Cloth on the countersink is increasing the contact area behind the cutting edge. However I have found that this does tend to blunt the tools quicker.

I use a single cutting edge countersink made by Magfor, these seldom give trouble. RPM is usually the root cause of chatter with this type of countersink.

Regards

Gray,

"Typo error"

Edited By Graham Meek on 11/07/2022 12:03:18

You take a small piece of rag and fold it over two or three times and use that instead of emery cloth and it sometimes helps with chattery drills like that.

Edited By Hopper on 11/07/2022 12:28:18

On a lightweight machine I'd be inclined to turn the top slide around to the required angle to cut a deeper csk rather use a cutter, I use 3 flute cutters from RGD but mainly on the mill, they are fine if the speed is kept down. I use plenty of lubricant/coolant, CT90.

definitely a single point cutter of some sort, be it a lathe tool or single hole countersink (deburrer) but also as said before drop the rpm.

So this is what I think is happening.

Many countersinks are not symetrical in form as far as how they cut. For example the single hole type is ground to be excentric so that there is a small clearence in front of the cutting edge without which it would not cut. The 3 'flute' types again are unlikely to be concentric between the cutting edges and the shank. None of this matters when coutersinking on a drill press where the work is allowed to float. In that circumstance the cutting edge is supported by the opposite side of the cutter and the workpiece usually describes a small circular dance on the drill table to follow the excentricty.

On a lathe the situation is different in as far as the work is constrained and unless the cut is heavy and the tailstock is particularly sloppy the cutting edge does gain any support from the opposite side. As the width of the cut gets bigger chatter will ensue unless on large rigid machines.

If a large slot drill is ground so as to have the required 45 degree angle with the cutting edges concentric with the shank then it will not chatter.

regards Martin

Both tools are best one I’ve ever had:

The other tool is for setting lathe tool height and is perfect.

Geoff - Workshop 25°, outside 30°+

Chatter is common with countersinks, you might try simply leaving the lathe switched off and turn the chuck using the key while keeping the bit tight against the work with the tailstock screw. That is about as slow as it is possible to go.

Hi Y C Lui,

Being mean (dead tight) I would not buy a countersink, I ground a short 1/2" drill bit to 90 ͦ point. Seems to work fine with no chatter.

Hope this helps.

Peter.