Tapping a hole in aluminum?

Not really.

This tap & drill chart online-

that the standard drill size for 3/8-24 is a #Q drill bit

which this drill chart online-

is .332" inch. Note that it also indicates that a #Q drill is 8.4328 mm diameter, so an

8mm hole is -probably- too small to attempt with a cheap tap.

Sure, in a lathe. Possibly close enough, in a milling machine with a coax indicator. Not freehand.

For regular-length taps, I like the Hertel spiral-point taps at Enco. A

3/8"-24 is about $7.50. They have a better cutting edge than the usual China generic straight flute taps, but 8mm is still quite a bit undersized of a hole.

If you can find a thin-shank tap you could tap most of the 64mm length. A regular 3/8" tap won't go that deep though. You cannot tap in from both ends, because the threads won't match up in the middle.

You can try to search eBay for 3/8-24 pulley taps, there's some for $10. You can grind the shank diameters down on a bench grinder. Also note that many pulley taps are usually plug or bottoming taps, and you may need to start the threads with a regular-taper tap.

If the threads must be straight, you'll need a machine-guide to do that,,, a tapping press, a drill press, a mill or a lathe.

tap finish doesn't matter much really, at least for hand tapping

Im not sure of the question, but it sounds like you want a lathe here.

In taps, the "H" number is the measure of looseness, or oversize of the tapped threads. Increasing numbers mean increasing looseness. I would suggest H1 if you can find one, but H2 & H3 are the more common fit sizes (common zinc-plated hardware store bolts are probably H3-H4 fit).

Can anyone specify a 3/8-24 tap that might work without enlarging the hole?

The 3/8-24 H1 Hertel spiral point tap is back ordered.

Okay, thanks.

Description: Hand Sets - Taps Thread Size: 3/8-24 Ground Thread Limit: H1 Finish/Coating: Bright Material: HSS Overall Length:

2-15/16 Number of Flutes: 4

Is that likely to work as any other hand tool? Thanks.

No. But enlarging the hole is not that big a deal. You are not enlarging the hole by a lot. So even done free hand, the hole will be very close to centered. And if you get the hole a bit bigger, it should not be a problem. The ratio of the threaded length to the diameter is large, so you will have plenty of strength. I would probably use a H3 tap. A H1 would give you slightly more strength , but with the ratio of the length to diameter much greater than one, you do not need the strength.

Dan

Handbook says that for a class 3 thread, your minor diameter should be .330 - .337 , so no, I wouldn't attempt tapping it without enlarging it.. I would just take the hole out to size with a reamer and tap it. Making sure to put a lead in chamfer on the part so the tap doesn't end up chipping.

Or you could try a drill, drills tend to not make great reamers, but you might get lucky in aluminium.

Firstly: That is a set of three taps--a taper, plug and bottoming tap. Did you want all three? If you don't have any other metalworking/machinist tools or a drill press--you'll probably never use a bottoming tap, for instance.

They are also 4-flutes (3 flutes are stronger) and are straight-flutes (so you have to reverse to break up chips).

If you only wanted one tap, then here is a $12.48 Hertel H1 spiral point (spiral-point taps don't require reversing to break up chips, normally)

alternately here is an Interstate brand (imported) H1 spiral-point for $5.71-:

When I checked on eBay, all the pulley taps in 3/8-24 that gave a fit spec were H3. I'd bet somebody makes them in H1 (or you could custom-order one) but you'd pay $50+ for it, maybe $100+.

Thanks for the tip. That is useful also for cramming a rod into an aluminum tube. Infrequently done here, but I need to remember that one.

Plus that much more for tax and shipping, but I did not find it anyplace else. And the local megastore has a relatively very limited selection of tools. I guess the old-fashioned way would be to have some local store special order the thing.

And thanks also for the tip about the type of tap, I was confused about that one.

Yea, I normally go a bit bigger, about .015 - .02 per side, than the OD of the tap.. eg. for a 3/8 tap, I would go with ~ .405-.415 chamfer.

OK but why 2017? It machines OK annealed but might be a bit crumbly at the T4 temper. Also the screw that threads in might end up stripping out the threads as you start and stop. You shouls also consider what happens when the wheel is turning and the motor stops, In a threaded drive like you describe it is likely to unscrew I think.

If you are trying to make a drive to attach a motor, why not press in a socket to the wheel and then either use the hex or the square end to interface with the drill motor. what might work pretty good is a ball end Allen wrench that would tolerate some misalignment.

Roger Shoaf

...

Because that was available to this layman.

The current motor is not really very powerful, but I will keep that in mind.

Yes, for sure. The arbor has a reverse threaded screw. If the arbor is long enough, the screw might solve that problem.

Yup, in another design. At the moment, this ultralight version has the scooter wheel attached directly to the drill arbor with no support on the other side of the hub.

FWIW.

There is some unusual sideways pressure on the DeWalt right angle drill arbor bearing, but that is a big bearing and it is doing well so far. Also, this next one will have the wheel even closer to that bearing.

Regular drills have a small bearing at the arbor, but they include a clutch. This right angle drill has a big bearing at the arbor, but has no clutch. A clutch would be very useful even though it slightly increases the weight. I could use a regular drill and have it sticking out sideways from the wheel without a right angle gear, if the wheel is at least 7 inches diameter. That will require a sturdy attachment to the drill case up forward near the arbor. But they might not be as tolerant to sideways pressure on the chuck.

How about getting a weed whacker and use the flexible drive shaft to drive the wheel. Saw a guy do this on a little scooter, went like a bat out of hell.

Roger Shoaf

If I'm not mistaken... Weed eaters are single speed. They spin very fast with little power. It might require adding a variable speed controller and gearing, and have to be at least 18 V.