How effective is penetrating oil?

I would like to replace the power cord on a vintage 1940s Hamlton Beach malt mixer, and the only access is from under the base.. The mixer is in mint condition. However, the metal base plate is mounted to the bottom of the cast iron mixeer with four screws through the four rubber feet. The screw heads are approximately 3/16" in diameer and are completely corroded/rusted. The base of the mixer is a commercial model that was probably useed at a soda fountain and was probably subjected to plenty of liquids over the years.
I have tried to gently unscrew all of the screws but they are definitely "frozen" in place. I'm afraid if I apply too much torque that the screws or even the shafts might break off.
I haven'tried using penetrating oil yet, mainly because the screw heads are somewhat recessed into the rubber feet.
I would appreciate any suggestions for removing these screws either with penetrating oil or by some other method. Because they are recessed it would be virually impossible to grasp the screws by any other method I can think of.
All reasonaaable commens welcome.
TIA
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On 9/4/18 10:59 AM, Wayne Boatwright wrote:

Can you insert the screwdriver in the heads then tap on it with a hammer? The vibration should help to break things loose. Try tightening then loosening them repeatedly.
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Dean Hoffman posted for all of us...

That would be my suggestion. For what it's worth a You tube vid compared all of popular ones and found no difference. The oil may also ruin the rubber feet.
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If he's going to get new rubber feet - probably wise - I soak the screws with a chemical rust dissolver before using penetrating oil. Use a shallow tray.
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On Wed 05 Sep 2018 01:22:44p, Vic Smith told us...

Thanks all!
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On Tuesday, September 4, 2018 at 11:59:37 AM UTC-4, Wayne Boatwright wrote:

Sometimes it works, sometimes it doesn't, but it's the first approach. I recommend PB Blaster, IMO it's the best. The good news is that from what you say it sounds like the heads are still in good shape. I'd turn it upside down, spray plenty of PB blaster in there, work the feet around, rotate them, so that hopefully the blaster can work down to the threads. Let is sit overnight.
If that doesn't work, then try to twist them off, which you can probably do if the heads aren't buggered. Then you may have to drill out what's left, unless you can get them out from the other side when it's apart. Another option would be to cut off the rubber feet with a hacksaw so you can get to screw with vice grips. If they are the typical cone shaped, rubber, black feet, you can find them for a couple bucks on Ebay if needed.
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On Tue, 4 Sep 2018 15:59:33 -0000 (UTC), Wayne Boatwright

If you can replace the rubber feet, destroy/remove the old ones - this allows you get penetrating oil where needed and perhaps get vice grips on the screws ?
http://www.leevalley.com/en/hardware/page.aspx?p@043&cat=3,40993,41285
Be careful using any impact driver - in case you crack the cast metal. otherwise impact drivers can work well. John T.
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On Tue 04 Sep 2018 09:37:59a, told us...

Thanks, John. I think the rubber feet are expendable and replacements could be easiiy found, but I'll take another look before I destroy them. I do have an impact driver, but I would be very afraid to use it since the cast iron base and the screws are about 75 years old. Vice grips might just be the best options if I get rid of the rubber feet. I appreciate your suggestions!
Given those options, should any of the screws simply fracture, I think I would opt for mounting the plate using epoxy putting or similar after I've replaced the popwer cord. It's unlikely that I'd ever have to open it up again.
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On Tue, 4 Sep 2018 17:21:35 -0000 (UTC), Wayne Boatwright

Get someKano kroil. By far the best "conventional" penetrating oil. Deep Creep from the Sea Foam folks works pretty good too. Wurth's RostOffExtra is also very effective,
As for tools, a simple cordless impact driver set on low power to start (and possibly working up from there) will GENERALLY coaxr them out without snapping them after applying the penetrant and letting it soak. try a bit aznd if it doesn't work add more penetrant and let it soak another few hours, then trythe impact again. DoNOT try the hammer impact - too high chance of breaking the casting
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On Tue, 4 Sep 2018 17:21:35 -0000 (UTC), Wayne Boatwright

The minute you epoxy it, the switch or some other internal part will go bad. If you do break off a bolt in the cast iron, just drill it out and tap the hole. Cast iron is not all that hard to drill. If you have to, move the hole over a little and drill a new hole in the base plate. Or drill a hole and epoxy a tiny piece of threaded rod in the hole, and put a nut on it to hold the base. The rubber feet can be put next to the nut. Use epoxy on the rubber feet if you must.
One other thought. If you cut off the rubber feet, soak the whole base of it in ATF (automatic tranny fluid). Just put enough ATF into a bowl and let it sit in the ATF for several days. Just use a half inch or so of the ATF. You want the bolts submerged, but not the motor. ATF is a good penetrant.
You could even use one of them pencil flame butane torches to heat the bolts. after the feet are removed. Just heat the bolts, not the whole cast iron frame. Or even apply a 100W electric soldering iron to the bolts and hold it there for awhile.
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On Tue 04 Sep 2018 11:35:20p, told us...

All good points. Thank you!
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On Tue 04 Sep 2018 09:37:59a, told us...

I forgot to thank you for the reference to the bumper feet. One of those sizes would be perfect.
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On 9/4/2018 10:59 AM, Wayne Boatwright wrote:

[snip]

Wayne, if you decide to go the penetrating oil route instead of, or in combination with other suggestions which have been posted, I'd recommend using Kano AeroKroil
<https://carcaretotal.com/best-penetrating-oil/#1_Kano_Aerokroil_Aerosol_Penetrating_Oil
The stuff is amazing. It really works well and is highly rated.
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On Wed 05 Sep 2018 05:51:32a, Unquestionably Confused told us...

Thank you. I'll look for it. Yes, I'd rather try a penetrant first before taking more serious measures.
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