Drill chatter

[Black_Moons]

Hi, im wondering why I sometimes get chatter while drilling with my tailstock in my 12x36 lath?
Usally just using my large (and cheap/uneven) silver and deming drill bits (5/8 through 1") into aluminum. Feed and speed doesnt seem to help much on some bits/holes. I did notice my tailstock ram is slightly loose and can be moved side to side a little, bit tightening the ram lock slightly did'nt really help the chatter.

[loose nut]

I usually slow the rpm's right down until the lips of the bit are into the metal then speed up to the proper rpm's. this helps will drill chattering. Don't forget that drills even good ones aren't always straight and the tailstock can be off a bit, these will cause the drill to jump around, slowing down the speed, at first, helps.

[beanbag]

mount an indicator to the headstock and indicate the drill to see if it is actually centered and parallel to the rotation axis

[Peter N]

1. Use a spotting drill (NOT a centre drill) to get a nice centred pilot hole.

2. Slow the speed down.

3. If enlarging an existing drilled hole, and if the above fails to help, get a small square of cloth - old denim is good - fold it over once or twice and place it over the end of the drill. It will push through as you enter the hole and will stop the chatter.

4. And finally, don't worry about the chatter if you're going to bore or ream it afterwards.

Peter

[Black_Moons]

Good trick with the cloth. it was enlargeing a hole too iirc.
I think its partialy my crappy drills fault... and not worrying about chatter is good advice since I was boring it afterwards... I guess chatter doesnt really damage anything it just sounds horrable.

[Evan]

Drill chatter is caused by the bit unwinding under load which causes it to dig in as it becomes slightly longer as it unwinds the helix. The drill bit is a helical spring. When it lets go it becomes shorter which then releases the cutting edge from the cut until it catches again.

It isn't rpm dependent. The best cure for it is a properly sharpened drill bit with a keen cutting edge and the proper cutting lube. That reduces the tendency to unwind in the cut.

[hitnmiss]

My big drill bits squeal like crazy, no matter what rpm or feed I try.

They seem to cut fine with little visible chatter... I think big bits squeal like crazy

[Evan]

It's very dependent on quality. Years ago I bought a set of Sheffield Steel bits and they don't chatter or squeal in any cut. I'm glad I bought them when I did because the equivalent bits if you can even buy them now are ten times the price.

[psomero]

are you trying to drill a hole in one shot?

i was taught to always peck drill and while the drill is out of the hole, knock the chips off and give it a good shot of lube...

[Doc Nickel]

It's been my experience that, in many cases, chatter is caused by insufficient feed.

It's quite common- the tool starts to chatter, so you slow the feed (especially if it's a manual feed like a drill press quill or tailstock feed) in order to try to get it to stop chattering.

As Evan notes, it's a case of the bit digging, releasing, and digging in again. But if the bit is taking a proper-depth cut, it shouldn't be able to 'spring out'.

So first make sure your spindle speed is more or less correct, then check the condition of the tool (grind/sharpen as necessary) and then try pushing a little harder on the feed.

I won't say it's a cure, or that it's appropriate in all cases, but it works for me five times out of six, especially in aluminum.

Doc.

[Oldbrock]

pilot drill

you could predrill with a drill the size of the web. Removes the chisel point force required. Peter

[darryl]

One other point about sharpening is getting the lips the same length. I know this falls under 'proper sharpening', but it's at least as important as getting the cutting edges sharp and ground to the correct angles. One of the best things to learn is how to sharpen bits correctly.

[airsmith282]

when drilling aluim i take the feed in slow and rpm 550 on bits under 5/8 and ything over 5/8 slow down to 330 and still take it slow on the feed and you should also be fine aluim is nasty to drill at times even with sharp drills...

turnning on the other hand let the speed to max and take realy light passes and man what a nice fininsh it gives to on aluim ..



on steel i always drill usualy 330 and take the feed slow and use cutting fluid alot works really slick..

[GadgetBuilder]

Drill bits often have excessive relief, especially larger drill bits. Excessive relief allows the bit to take a larger cut than it can handle so it elongates as Evan described. I bought an inexpensive set of S&D bits which chattered terribly until I reduced their relief to about 7 degrees by using the Honedrill to add a facet.

http://www.gadgetbuilder.com/DrillSharp.html#HoneDrill

Smaller relief reduced chatter considerably but there is another chatter mechanism: if one lip catches then it moves the bit sideways causing the other lip to catch - and back and forth it goes, chattering like mad. What helps here is adding a secondary point angle (SPA); the angled tip on the lip greatly reduces the tendency to dig in, improves finish of the hole and increases drill life.

The combination of reduced relief plus SPA won't eliminate all chatter but can be a big help.

John

[Paul Alciatore]

A lot of good suggestions here. To sum up the ones I would use:

Properly sharpened drill: both even flutes and dead sharp edges. After sharpening on the wheel, use a hand stone to touch it up.

Use coolant or oil

Drilling a pilot hole about the web size is good for a hole that size. It makes the main drill go in a lot easier.

Reduce the clearance angle. This will limit the tendency to dig in. (It will take a smaller bite so it will wind up less.)

Use a moderate but constant feed. Not too slow: not to fast either.

I don't know about the speed thing. I suspect it is less of a factor than the above, but experiment is you want. I would start at the recommended speed for the material and diameter or up to 50% less: definitely not more.