Teardrops n Tiny Travel Trailers

hi,

I have a minor countersinking problem. I'm using a proper ali counter sink drill bit, in 3mm ali.

http://i135.photobucket.com/albums/q135/muggnz/rusty/countersinkingburrs.jpg

I cannot get the edge of the hole as smooth as I'd like by drilling. No matter how slow I drill, using light pressure & a slow speed drill. There always seems to be some rough edges.

The slowest speed of my drill press is 625 rpm.

I know I can sand them off, however that leaves other marks I'd rather avoid.

Is there an easy way of counter sinking, without creating this problem?

thanks
david

you are galling the material with the chips and the buildup on the CS. use some lube (wax, oil, soap, WD40 etc.) on both the material and the CS. don't keep the bit cutting continuously. drill a little and extract the bit a to clear the chips and repeat. keep the cutting edges of the CS clean AND SHARP and don't use a lot of pressure, just enough to make it cut and no more. slow rotation is correct.

that little lip on the surface tells me your bit is getting dull (or never was sharp to begin with) and/or you're cranking on the handle too hard.. since you say you're using light pressure and drilling with slow rotation my bet is your bit is dull (cheap hardware store countersink?)

You can use a handheld chamfer/debur tool and clean that up in about 0.5 seconds per hole without sanding.

Cost for one over here is less than $2.00 or so.

in our shop we use anodized 1/8" x 1" aluminum bar stock for hanger cleats on file drawers. these are screwed into rebates on the front and back or the sides of the drawer box. ours is a very high end shop and these have to look real good. because they are anodized aluminum we cant file or debur the holes after, they have to be clean right off the drill press. this is the CS we use. they are designed for drilling CS holes for rivits on aircraft and work real good.. still need lube though. HSS and sharp enough to cut flesh..

http://www.aircraft-tool.com/shop/detai ... %2f2X3%2f8

here's a deburring tool like NathanL mentioned. this one has a selection of replaceable cutters to choose from of different shapes and sizes (comes with two). you can also get the $2.00 kind but you have to sharpen them when dull.. and they are only one shape per tool. this one is $10.00

http://www.aircraft-tool.com/shop/detai ... T_ID=SVBHD

625 rpm isn't slow; that's yer basic problem. Aluminum that thin is difficult to hold stable unless you have a pilot on the countersink

Ageless wrote:625 rpm isn't slow; that's yer basic problem.

I prefer single flute countersinks.

I wouldn't turn much over 150RPM.

A "light feed" is part of the problem; slow feeds will cause a countersink to want to chatter.

If the above parameters are adhered to and the finish is still galled, then there is a lack of lubrication. Motor oil will work pretty well for lubrication.

In many instances we'll use 30 weight non-detergent motor oil for many "manual" countersinking and tapping applications.

chorizon wrote:

Ageless wrote:625 rpm isn't slow; that's yer basic problem.

I prefer single flute countersinks.

I wouldn't turn much over 150RPM.

A "light feed" is part of the problem; slow feeds will cause a countersink to want to chatter.

If the above parameters are adhered to and the finish is still galled, then there is a lack of lubrication. Motor oil will work pretty well for lubrication.

In many instances we'll use 30 weight non-detergent motor oil for many "manual" countersinking and tapping applications.

if you're in a metal fab/machine shop you're likely using a HSS or carbide CS so a more aggressive feed will be fine but most people just have cheap carbon steel CSs and an aggressive feed will just kill it.

we do woodwork and can't afford to risk using oil as a lube so we use liquid soap.. that way we can just rinse the finished piece off under the tap and not worry about oil contaminating the shop or the tools. it actually works pretty well.

I don't know if this is the style of single flute CS you're talking about but they work good. we use this style for lexan, plexiglass and other plastics.

http://www.aircraft-tool.com/shop/detai ... T_ID=ZFC02

afreegreek wrote:I don't know if this is the style of single flute CS you're talking about but they work good. we use this style for lexan, plexiglass and other plastics.

http://www.aircraft-tool.com/shop/detai ... T_ID=ZFC02

Those work even better than single flute c'sinks on non-ferrous metal. They are an excellent choice on aluminum.

I'm using a bit with one cutting edge. Is this a single flute? It was brand new about 25 holes ago, costing $40. However maybe I've blunted the cutting edge with the faster speeds I've been using. Sounds like I need a new slower drill press.

I tried with kerosine lubricant on the bit earlier today. ( A local recommended it over lunch ). It made a little difference on the 2 holes tried, by reducing the burr by about 50%.

I have been drilling pilot holes of around 4mm. With the countersinked hole being around 10mm.

neither of the 2 local hardware stores I discussed this problem with have mentioned hand held chamfer/debur tool. They were small to medium sized. I'm hoping to get to a larger store tomorrow.

david

Muggnz wrote:I'm using a bit with one cutting edge. Is this a single flute? It was brand new about 25 holes ago, costing $40. However maybe I've blunted the cutting edge with the faster speeds I've been using. Sounds like I need a new slower drill press.

I tried with kerosine lubricant on the bit earlier today. ( A local recommended it over lunch ). It made a little difference on the 2 holes tried, by reducing the burr by about 50%.

I have been drilling pilot holes of around 4mm. With the countersinked hole being around 10mm.

neither of the 2 local hardware stores I discussed this problem with have mentioned hand held chamfer/debur tool. They were small to medium sized. I'm hoping to get to a larger store tomorrow.

david

yes, one cutting edge is "single flute" and Kerosene can be used as a lubricant in certain cases. the old timers used it with oil stones to sharpen plane blades and chisels as it won't make mess on wood like oil does but on a drill press?? not sure. it doesn't matter what the CS cost, it matters what material it's made of. carbon steel will dull extremely fast in a drill press on metal due to heat, it's more for wood and plastics. High speed steel is what you need for metal. if you can find one, a three jaw brace and some elbow grease will work to finish off the holes with the CS you have or even a 3/8" cordless/plug in drill. or you could take your material to a metal fab shop and get it done for a case of beer..or you can just but a new one at the link I gave before. it will work really well and it's just postage plus the cost of the bit. about $15.00

I have an old 16 speed Harbor Freight floor model drill press in my garage that I use for metal work. It may as well be a one speed machine as I almost always use it at the lowest speed which is 200 rpm. I have used this drill press with 1, 3 and 5 flute countersinks on aluminum, steel, copper and brass. If the aluminum is clamped firmly to the table or in a vise bolted to the table, the countersink bit is clean and sharp, and I apply good firm pressure, and I lift the bit out occasionally, kind of a pumping motion, I get good clean countersinks. If there is vibration or light pressure is applied chatter will occur leaving a scalloped appearance. If I fail to apply and release pressure by "pumping" the drill press to help clear chips, or if the bit is dull I get galling.

For aluminum the attached chart recommends a 5 flute countersink bit at 250 rpms with firm pressure. That's very close to what seems to work for me.

http://www.ibiblio.org/twa/info/drillSpeedChart.pdf

Larwyn wrote:For aluminum the attached chart recommends a 5 flute countersink bit at 250 rpms with firm pressure. That's very close to what seems to work for me.

http://www.ibiblio.org/twa/info/drillSpeedChart.pdf

That's a great PDF, thanks

I bought a 5 flute bit today. And some CRC spray drill oil lubricant. At 625 rpm. This combo worked better. With only a very small lip, which was the same size all around the counter sink and no sharp bits. I was somewhat suprised to see that it didn't seem to matter how much pressure or the method of applying it. As for me this didn't make any noticeable difference to the end results.

At the weekend I'm going to try with different ( soap based ) lubricants, in the hope that they'll work. As they'll be easier to clean up before applying sealers.

I'm also going to pay more attention to clamping the ali.

And see if I can find a Shear Cutting bit.

david

yesterday I showed some of my later attempts at countersinking, to a friend. Which whilst I new were better than the earlier failures. I still thought that they still weren't very good. It turns out that he ( a few years ago ) trained as a machinist. He told me that my latest attempts were as good as I needed.

So this morning I started countersinking the holes for my trim, with a 5 flute bit. All counterinking holes were pre-drilled with a 3.5mm pilot hole. What I found was :
- soap as a lubricant didn't work very well for me
- applying cutting pressure & easing off helped
- too much drilling oil ( spray ) made the bit chatter, produce a very rough cut which I couldn't fix & occasionally produce a hexagonal hole
- to little drilling oil & the drilling was very hard
- just the right amount of oil & I got a good clean & quieter cut. Unfortunately this didn't happen as often as I'd hoped for
- spraying the oil directly onto the bit and/or the ali created to much oil on the cut for the first hole
- spraying the oil directly onto the bit only lasted 4 holes, before needing repeating
- even the moderate pressure I was applying, caused the end of the bed furthermost from the pillar of my drill press to sink a couple of mm. A block of wood fixed this.
- countersinking to around 20% of the hole size. AND dipping a finger on the oil & wiping the finger over the cut gave a reliable & mostly repeatable burr free cut. H&S comment - I did not place my finger under the bit, I pulled the ali out of the way before applying oil
- using a 13mm drill bit with my hands, I was able to de-burr what little burrs I created. A larger bit would've been easier to use.
- black sealant hides a few features.

david

Muggnz wrote:yesterday I showed some of my later attempts at countersinking, to a friend. Which whilst I new were better than the earlier failures. I still thought that they still weren't very good. It turns out that he ( a few years ago ) trained as a machinist. He told me that my latest attempts were as good as I needed.

So this morning I started countersinking the holes for my trim, with a 5 flute bit. All counterinking holes were pre-drilled with a 3.5mm pilot hole. What I found was :
- soap as a lubricant didn't work very well for me
- applying cutting pressure & easing off helped
- too much drilling oil ( spray ) made the bit chatter, produce a very rough cut which I couldn't fix & occasionally produce a hexagonal hole
- to little drilling oil & the drilling was very hard
- just the right amount of oil & I got a good clean & quieter cut. Unfortunately this didn't happen as often as I'd hoped for
- spraying the oil directly onto the bit and/or the ali created to much oil on the cut for the first hole
- spraying the oil directly onto the bit only lasted 4 holes, before needing repeating
- even the moderate pressure I was applying, caused the end of the bed furthermost from the pillar of my drill press to sink a couple of mm. A block of wood fixed this.
- countersinking to around 20% of the hole size. AND dipping a finger on the oil & wiping the finger over the cut gave a reliable & mostly repeatable burr free cut. H&S comment - I did not place my finger under the bit, I pulled the ali out of the way before applying oil
- using a 13mm drill bit with my hands, I was able to de-burr what little burrs I created. A larger bit would've been easier to use.
- black sealant hides a few features.

david

ya, the soap isn't the best option but in the case of our shop where the main thing is high end wood work it's the safest option. cutting oil has a way of traveling around the shop and contaminating the wood. it's just too much risk for us to take. that's the reason the CS I linked to is the one that works the best for us because it has a rake to the cutting edge (like a drill bit) and cuts the material rather than scraping it off. the only time it causes a problem is when the material isn't clamped well as the CS will actually dig in and lift the material.. good to hear you got something that works to your satisfaction.. I know what it's like to get results you're not happy with..