Hand vacuum for potting pickups?

[Steve A.]

I just noticed this in the latest catalog from American Science and Surplus. Is a vacuum of 2" HG sufficient for potting pickups in a crock pot rig?
$22.85 with free shipping through April 3rd.



VACUUM HOME PUMP

NATURE ABHORS A VACUUM
But science teachers can't work without them. Experiment with this good-quality manual vacuum pump made of durable polychloroethylene plastic. Works with a pistol-grip action and pulls up to 2" Hg. Includes a 17" length of clear vinyl, 1/4" ID tubing, and a release valve

Steve Ahola

[Richard]

2" of mercury is not much. I helped a friend make rubber molds, he had a vacuum chamber that would pull down to a near vacuum (nearly 30" of Hg) to get the bubbles out of the liquid rubber. It was essentially a pipe with a plate welded to one end, a lid, an air compressor set to draw air from the chamber, and a couple of valves. 2" is not a lot of vacuum, about 1 psi, compared to 14.7 psi. How many pickups do you want to do? What are you using for a vacuum chamber?

[elipsey]

Here's what I use:





This is a 12V automotive tire pump inside a gasketed plastic food jar, with the outlet hose connected to a tire valve. So, basically, since I couldn't afford a vacuum pump for sucking, I got a tire pump for blowing, and turned the world inside out.

A brass nipple is threaded into the top of the jar, which is connected to a vinyl hose, which is in turn connected to another brass nipple soldered into the top of a ball jar. The ball jar is filled with 70/30 beeswax/parafin. I melt this in hot water with a sealed lid on it, while monitoring the water with a thermometer. When the temperature is right, I unscrew the normal lid, put the pickups in, and thread the vacuum pump lid onto the jar. Then I connect a power drill battery to the jumper wires until the pump guage shows the desired vaccum. It will develope about 10psi of vacuum, which seems to be more then adequate for this purpose.

[Steve A.]

As an HVAC service tech I've worked with refrigeration vacuum pumps that go down to 50 microns but don't know how that translates to inches...

I like the rig that Pete at Vintage Vibe uses: a crockpot with a gasketed clear plastic lid that has a scrader valve to hook up his vacuum pump. He uses a variac to control the temperature.

Steve A.

[Richard]

I like how you out the pump inside the jar to get the suction. Can you see bubbles coming out of the pickups when you used it?

[elipsey]

I like how you out the pump inside the jar to get the suction. Can you see bubbles coming out of the pickups when you used it?

Yep.

[elipsey]

As an HVAC service tech I've worked with refrigeration vacuum pumps that go down to 50 microns but don't know how that translates to inches...

I like the rig that Pete at Vintage Vibe uses: a crockpot with a gasketed clear plastic lid that has a scrader valve to hook up his vacuum pump. He uses a variac to control the temperature.

Steve A.

That sounds pretty pro. I used a ball jar partly because they are intended to stand up to vacuum. I wonder how much vacuum the average crock pot will tolerate before imploding? Apparently that one could take it...

[Richard]

I had to look it up. 50 microns is probably about as pure of a vacuum as you could get outside of a lab. Inches Hg gets higher with more vacuum, measuring what is taken away, microns is what's left.

[kayakerca]

As an HVAC service tech I've worked with refrigeration vacuum pumps that go down to 50 microns but don't know how that translates to inches...

I like the rig that Pete at Vintage Vibe uses: a crockpot with a gasketed clear plastic lid that has a scrader valve to hook up his vacuum pump. He uses a variac to control the temperature.

Steve A.

That sounds pretty much exactly like what I use, including the variac for temperature control. Works great. . .

I have long since reinforced the lid (based on comments by Jason Lollar on his lid implosion experiences with less structurally sound lids).

[J M Fahey]

Loved your vacuum potting ideas

Will try something similar for vacuum impregnating my transformers, so far only drop them in the pot, hanging from wires, until they stop bubbling (~15 minutes) but obviously this is better.
Thanks.

[Lollar Jason]

yes- pump, crock pot, variac, offset vacuum line location in lid, 3/8 to 1/2 inch thick lexan running about 20- 22 inches of vacuum for a short period of time- 10 seconds to 1m30 or so depending on what you want to accomplish. Add to that pre heat your wound pickups so you can be sure your results are consistant. I domnt see much bubble action until the vacuum gets up close to 15 plus

[kayakerca]

yes- pump, crock pot, variac, offset vacuum line location in lid, 3/8 to 1/2 inch thick lexan running about 20- 22 inches of vacuum for a short period of time- 10 seconds to 1m30 or so depending on what you want to accomplish. Add to that pre heat your wound pickups so you can be sure your results are consistant. I domnt see much bubble action until the vacuum gets up close to 15 plus

Forgot about the pre-heat part. I use a pair of shop lamps to warm them up to a point where they take the wax nicely and you have a bit of time after the potting to wipe the pickups down without the instant solidification of the wax when you remove them from the pot.

[Steve A.]

I have long since reinforced the lid (based on comments by Jason Lollar on his lid implosion experiences with less structurally sound lids).

We have TAP Plastics stores where I live and they sell Lexan rounds in various diameters and thicknesses. Pete glued on a thick o-ring to make a tight seal with the crock pot.

Steve A.

[kayakerca]

We have TAP Plastics stores where I live and they sell Lexan rounds in various diameters and thicknesses. Pete glued on a thick o-ring to make a tight seal with the crock pot.

Steve A.

I really like the o-ring idea! A little less clumsy than my rubber gasket setup.