Tapping 6-32 in aluminum

Oh, those! I have the 60V 100A AODE model. The voltage is pretty close but the current actually resolves to 0.2A (9 bits?) despite the appearance that it reads to 10mA. It fakes the difference by "dithering", or injecting random noise to make the display bounce around.

"USes DSP to increase ADC resolution ..." But not ADC accuracy.

It's still useful, just not to monitor trickle charging or equalizing. I put Andersons on the 33V, 3A meter for that.

-jsw

Perzactly. AAMOF, I have a better rapport with machines than I do with people. They talk back a lot less and I can read them a whole lot easier.

LOL!

You didn't finish the whole saying. Its:

-- You just can't fix stupid because it ain't broken ! --

6-32 is an abomination. If you are ever going to break a tap, it'll probably be a 6-32. The 32-pitch thread is too coarse for the skinny diameter. The standard should have been 6-40.

If you insist on tapping aluminum, use plenty of lube. A lube that works really well in aluminum is ... Goo Gone! Orange Goop works quite well also. Both have high content of d-limonene. Use HSS taps rather than the sharper and cheaper but much more brittle carbon steel taps found at hardware stores.

Get under sized taps and work up. The undersized ones are standard when you buy them - and don't bite as much out of the hole.

Mart> >

I agree -- and I am very happy to see you Don!

i

Martin Eastburn fired this volley in news:Bq0Xw.247130$ snipped-for-privacy@fx30.iad:

Or, here's another unique idea: Learn to use a tap!

Lloyd

I go the other way with aluminum -- I use forming taps, not cutting taps, and lubricate with soft wax made for the purpose. One drills the hole somewhat larger than for cutting taps. Forming taps have more meat in them, so are harder to break. Works very well.

Joe Gwinn

I ended up doing the same with screws -- drilled a 1/8" hole and threaded the screws right in. Worked like a charm.

i

But, a heatsink might require a very flat top surface; a forming tap will raise the surface slightly as it deforms the material, so it might not be suitable for this particular application (unless a second operation follows, to flatten the mating surface you've just disturbed).

"Good machining practice dictates that a countersink be provided at the top of the tapped hole. Countersinking is recommended before tapping to create a good starting thread."

Easier said than done, though.

-jsw

let's just burn that straw man right now.. Debur or countersink / chamfer the top of the hole and any possible "distortion" of the extruded aluminum heat sink will be totally dealt with. You are disturbing a few tens of thousandths of an inch of extruded aluminum inside a drilled hole - it is not going to cause any flatness problems beyond POSSIBLY raising a tiny ring at the top of the hole.

easier said than done? How? Hit the top of the hole with a countersink, or a drill a few sizes bigger than the hole if you can't afford (or can't find ) a countersink. Best done in the drill press, but for crying out loud it's "just" aluminum - you can do it with the drill bit in your bare hand if you have to.

My Clausing 8525 mill lacks a DRO to easily repeat a pattern so countersinking after drilling is a tool change at each location that loses precise depth on blind holes, since the chuck jaws move down as they tighten. I don't have countersinks with shanks as long as drills, to cut before hitting the depth stop, and there isn't enough quill travel to allow hand countersinking or clearance to swap chucks and arbors.

Maybe I should buy a set of intermediate length center drills to use as countersinks and spotting bits. I have only the long ones. Burrs on steel deflected larger drill bits.

I do swap the drill, countersink and tap on through holes. Hand-tightening the chuck is enough to start a tap straight by pulling on the drive belt.

-jsw

My first model Clausing 8525 is limited by its low spindle to table height and B&S7 collets. It's very nice for milling small parts in a home shop but the working envelope is smaller than a mill-drill's.

I could do that on a Bridgeport if I could fit one in my basement.

-jsw

A Swiss engineer at Mitre bought an ER collet adapter for this, which is quite similar to the old Clausing. There was maybe 50mm max clearance between the collet and vise.

After he left I inherited it for my model shop, put the useless ER collets away and bought the R8 set it was meant for. Other than the poor fit and quality of some small parts and 8 TPI leadscrews it was a pretty decent small knee mill, more rigid than mine.

-jsw

Have you ever gotten a Microstop countersinking cage? The shaft is spring loaded in the cage, with provisions to set the depth by 0.001" intervals, and a nice bearing between the shaft and the cage. You can find a lot of them on eBay by searching just on "Microstop". Here is an example:

ebay # 361220396427

or:

I prefer the auction number search, personally. Less to cut-and-paste. :-)

Anyway, the countersinks screw into the shaft, and come with various size pilots. (Hmm ... this one says bronze bearings, but the ones which I have feel like ball bearings. :-)

Anyway -- it looks like at least one of those countersinks will fit your tap hole for the 6-32.

So -- drill and tap first, then come back with this in the drill press chuck, use the pilot to align it, and countersink to the depth which you preset.

There are some with a smaller footpiece if you need to get close to flanges on the heat sink.

These are normally used for countersinking sheet metal for aircraft use to accept countersunk rivets, but work nicely for many other things. The #30 pilot is pretty close to the tap drill size for a

6-32. It should work with roll tapped aluminum in 6-32 as well.

The piloted MicroStop countersinks are less likely to deflect, even if you are using a hand-held drill motor instead of a drill press.

Ever look into the drill/tap bits? Useless for blind holes, but nice for through holes -- especially if you have a tapping head for your drill press. I've even used some down in the 4-40 size range. Cutting lube for aluminum was WD-40, though others would work well too. It just happens to be one of the few things which WD-40 works well for, unlike the things they *claim* it to be good for. :-)

Enjoy, DoN.

(snipped)

4564

A mystery of many years solved. I used to find those little countersunk bi ts for the microstop in your link laying around on the work tables in the U SAir hangar in Charlotte. I've got lots of them in my junkbox. I was an R& E, not a sheetmetal mech., and never knew what kind of tool they were used in. I imagine if I'd have looked up at the noise from the workstands next t o the ships, I'd have seen one being used.