Tapping 6-32 in aluminum

"Lloyd E. Sponenburgh" fired this volley in news:XnsA473D918BCD15lloydspmindspringcom@216.168.4.170:

ps... that's all at the 'imaginary' fit of 100% threadform. It's less in practice.

Lloyd

Have you considered adhesive, even hot melt? Another possibility is drive screws typically used to mount labels on machines.

Self tapping? suggest rollform [no chips/flakes] square or torx drive.

1/8" is the specified hole diameter for roll tapping a 6-32. Admittedly, running a screw in, is not exactly proper thread forming, but in some situations, should work OK, if loads are low and servicing not likely. Just as much a factor I'd think, is the probability that the screw crest will deform due to not being hardened, and I believe this more than the hole size would reduce the strength.

Jon

Lloyd, I used those holes to mount TO-220 voltage regulator chips, not for anything structural. worked great!

Ignoramus32423 fired this volley in news:mP6dnUZlVb1S7L snipped-for-privacy@giganews.com:

They won't hold with temperature swings, Ig! Put a nut and lockwasher on the backside! Go with me on this... I've done many THOUSANDS of semiconductors on heatsinks, and had both many successes, and every sort of failure you could count -- from taking shortcuts. Shortcuts just never work in a temperature-cycling environment.

Lloyd

Because of bigger diameter.

i

How careful you need to be depends on how close to the rating you are operating. TO-220s aren't fussy at a few Watts but need thermal analysis as you approach 20W.

"Belleville washers, or compression washers are generally considered the preferred method of attachment to a heat sink."

-jsw

Hm, this is a good point, I did not think about it.

The story is as follows.

My son and I made a robot for a kids homemade robot competition called "robocross". He won his local competitions and we will be going to the Illinois state competition.

Since the state competition is so important and there is a chance for him to become semi-famous if he wins it, we decided to make another robot.

Here's a picture of it, more or less completed:

I will hopefully add more pictures and documentation soon.

Anyway, if you look at the controller, you see that there is a rechargeable battery attached on the bottom, and a black heatsink attached to the top.

There is a hole in the plastic box where the heatsink attaches, and in that hole, there is three positive voltage regulators. One for 10v to drive the lifting arm, and two 5v regulators to drive tracks. The reason for using different voltages is that 10v is too much for the tracks, the robot becomes not controllable.

The robot itself is intentionally made to work like a skid steer loader like Bobcat T300. (I have a S300 myself).

The competition itself allows only 3 minutes driving time.However, he will spend hours preparing for the competition, and so, the robot needs to be heavy duty enough not to fall apart or burn out during practice.

The regulators are KA7810 3-Terminal 1A 10V Positive Voltage Regulator, and two 1.5A 5V L7805CV Postive Voltage Regulators.

The good news is that, as they run, even after a while, the heatsink is only barely warm. I had an undersized heatsink (a small copper bar inside) before and it would get very hot. But with this aluminum heatsink, everything is nice and cool.

i

A couple of minor points: You can tap aluminum to a higher thread percentage than steel, because it takes so much less force to cut. But there's little advantage to cutting deeper than 70% depth in any material.

And two, if you have any old Tapmagic lying around (we who have it hoard it like it's fine whiskey), don't use it on aluminum unless it's the version that says "aluminum." It will boil and form a foul, black gummy mess as it eats your aluminum for lunch.

Oh, and one more thing: "coarse" is not "course." d8-)

That's cool! (Shades of my old Erector set, but many generations ahead.)

I like it! (What, no paint on the tubafore?)

Great. Good luck to your son.

"Ignoramus32423" wrote in message news:bPydnQ91nfl-Eb snipped-for-privacy@giganews.com...

If you used an LM317 adjustable regulator for the tracks you could tune the voltage for best performance while retaining control, and waste less of the battery's energy as heat. You could put a knob on the voltage adjustment pot so you have a throttle instead of just on/off control.

-jsw

Jim, you are right. I actually have several LM317T regulators. I just wanted to take the easy route. I wish that I could somehow have a ramp-up of speed, though, not go from zero to full throttle in an instant.

i

Oh, and why would LM317 waste less energy as heat?

Ignoramus32423 fired this volley in news:bPydnQ91nfl-Eb snipped-for-privacy@giganews.com:

What you did not say was 1) the raw battery voltage, 2) the current (both peak and average) for the arm 3) the current(ibid) for the tracks.

Like Jim said, at only a few watts, nothing's in particular danger here.

A star washer works ALMOST as well as a Bellville spring, so long as you don't torque it down flat.

Lloyd

Ignoramus32423 fired this volley in news:_pSdnT_To6I_PL snipped-for-privacy@giganews.com:

It would not. It's a linear regulator, also, and disspates exactly whatever is the drop*current across itself.

But it's darned handy for 'tuning' stuff.

There is a way, with an LM317 to get a 'soft start'. National Semi shows a circuit or two that does that.

Having that constant-current output on the reference lead can give you interesting possibilities.

LLoyd

12v nominal

Not sure, not a lot. The arm operates very intermittently.

Not sure what is the current for the 5v tracks, but my best guess is 1.2 amps when driving in a straight line, and about 3A when turning on a dime.

OK, I will add something. I will also add heatsink paste, I will receive it on Tuesday. I could not find my old one.

i

I have a string. How long is it?

Because you could deliver the maximum acceptable voltage to the track motors to move fast. Maybe it's 8 or 10V if you don't start or stop with a jolt that breaks traction.

I'd put the throttle knob or slider under the thumb that holds the box, and have enough resistance in series with the pot that the motors creep at the pot's minimum setting. The switch would start the track barely but visibly moving in the right direction, important when it's not facing away from you, then you throttle up the speed.

-jsw

Are you using spring-loaded momentary toggles on that controller? Seems less than optimal.

To check current draw, throw one of these inline with the power line, using standard USB connectors. They're great little units, and you can't beat the price.

I picked up a couple when they were a buck, with free shipping. One went to my niece, with a power module for her cellphone.