Countersinking aluminum chassis - best method?

[amplifiednation]

I've been experimenting with different countersinks, trying to find a good clean way to countersink screws in aluminum chassis', and also aluminum trim.

I recently got a three flute bit from McMaster and thought it was going to make flawless circles, but it's not working up to my expectations. It cuts right into the metal, but doesn't leave a perfect circle. I've been reading that the single flute bits can cut cleaner, but I don't want to buy another $15 drill bit if I don't have to.

Any advice on the best countersinks for aluminum and also the best lubricant to use when performing these tasks? I think my 3-in-1 oil is too thin.

I have a good Delta drill press, there is no reason why I shouldn't be getting better results.

[Cliff Schecht]

Have you tried countersinks like this?
http://www.amazon.com/DEWALT-DW2538-Cou ... 313&sr=1-5

I don't know how big they make these though..

[amplifiednation]

Yes, I looked at those. I think they are mainly for wood. I think the problem is either the speed or the lubrication.

thats what she said

[Prairie Dawg]

I would try and obtain a microstop countersink like those used in the aviation industry. They have replaceable bits and you can select among a number of options. I've also used the bits for turning out staked primer pockets in military brass back before I figured out that amps were more fun than guns.

Aircraft Spruce has them.

http://www.aircraftspruce.com/menus/to/ ... sinks.html

[ToneMerc]

Taylor if you have some Type F automatic transmission fluid handy, try using that as a cutting lube.

TM

[Tubetronix]

I think what you have going on is chatter. The cutter falls into a repeating pattern of digging in and releasing when the chips break off. Try running the speed up or way down, and slow down your feed rate. Multi-fluted cutters seem to do this more readily, so maybe a single-fluted cutter would be worth a shot too. You should be able to pick one up at the local Lowe Depo for not too much. Most woodworking cutters will easily handle aluminum.

[amplifiednation]

Here's a picture of the bit I've been using. It is an aircraft countersink. I have drill press set at it's lowest speed of 620RPM.

Tubetronix, I think you are correct on the 'chatter'. I thought i could reduce this with more oil but it doesn't seem to be working. I've tried slowing my feed rate down, and the vibration increases!

Do you think increasing the speed would help?

Thanks TM, I do not have that handy, but could pick some up.

I have a cheap Ryobi wood countersink, and it produces the best results so far, but the flutes get clogged up and then it won't cut at all...so that's why I thought a real metalworking countersink would be the answer.

[diagrammatiks]

I grabbed one of the integrated drill bit/countersinks from mcmaster.

It works pretty great.

almost perfect holes and I drill by hand.

[v846]

I picked these countersinks up at home depot a few years ago, work pretty good with a hand drill but as Tubetronix mentioned gotta watch the speed.I don't remember the brand ,the only marking are made in Germany.

[Structo]

I've used one like this for quite a while.

I think it's made for wood but seems to work fine on aluminum.

But if I was after professional results then I would probably look to the aircraft type.

[img:272:210]http://www.aircraftspruce.com/catalog/g ... -01863.jpg[/img]

[John_P_WI]

At my last job we had a complete machine shop with CNC vertical mills, knee mills and all kinds of crazy stuff with Lista cabinets full of tooling in our engineering lab. I always used zero flute countersinks with excellent results in aluminum and other soft metals.

Something similar to these, but not this brand:

http://www.amazon.com/Champion-CSK-SET- ... B001TREYFK

John

[Luthierwnc]

I use one that looks like John P Wi's set. Fluted ones always chatter.

Part of getting these cuts right is getting the size of the through hole right first. Notice the cutter doesn't start until slightly up from the point. You need to have enough clearance for the cutter to cleanly hit the vertical side of the hole. If not, you end up rubbing metal on metal until the steel wins and starts cutting. By then its hot and has probably drifted.

FWIW, I seldom use oil when cutting aluminum. Grind the drill bits so they don't have an aggressive rake. They work better when you are slightly scraping rather than digging. Less chance of grabbing the piece too. That hole-though countersink usually cuts a one-piece waste strand very cleanly without slinging grease around the shop. Low speed. sh

[Cantplay]

The rake angle of the edge needs to be less. It should scrape, not hook.

It should be pushing the work away, not grabbing it.

This means either straight fluted, or slight left hand flute, not rh flute.

This is the same reason your drills grab the work as it breaks through the back side. You have to change the angle.

I'll take some tool pictures Monday when I'm back in the shop.

John

[M Fowler]

I have a set like what v846 posted that works great and I also have some of the kind Structo posted.

Sometimes I get lazy and just gently use a larger drill bit to make the countersink. Just don't get carried away.

Mark

[sixstringer]

I use the same type bit at Strutco and Mark, I did some tests with aluminum and found that what Tubetronix said is correct, any chatter will cause a faceted bevel, clamping the material to be drilled down firmly and using a drill press eliminates the problem.