Machinable removable bondo

donleybill · Aug 13, 2018

I have 2" X 3" X 28" rough ornate iron casting that needs to be machined around the periphery. The best surface to locate this part for machining is on the ornate side which is anything but flat.
My thought was to spread over the ornate side of the casting with an auto body bondo and parting agent. Once the material cures, it would machined flat and become the primary datum for all other milling operations. After machining, the "autobody bondo" would be come off clean with the help of a parting compound.
A life time ago I used a material called Tooling Stone. I fabricated to a simple drill jig with tooling stone to accurately locate a Cadillac badge onto a hub cap.
This material was easy to apply, didn't srink, machined fairly well and worked with a parting agent.
Today I can't find Tooling Stone and hopefully someone has a better material suggestions than auto bondo. Any suggestions would be appreciated.
This is one of two castings for model engine project.
Bill

Milland · Aug 13, 2018

You could try plaster of paris: Dap #535 4.4LB Plaster Of Paris, 2-Pack - - Amazon.com which is non-shrinking, cheapish, and should wash off if not set for a long period. At worst, coat the part with a release agent meant for fiberglass and the like first, this should aid separation (perhaps too well, test before machining).

metalpyro · Aug 13, 2018

For just two parts, that I assume you will be painting after you complete the machining, you might think about prepping both parts at the same time instead of trying to reuse a single mold. Whatever time you are trying to save, will be negated if you aren't successful in removing the mold from the first part. If the castings are to be coated, you should probably plan on blasting them anyway, so I wouldn't worry much about the mold release issue. Using plaster or bondo, you should be able to remove most of it with some tapping from a small hammer.

thermite · Aug 13, 2018

donleybill said:
I have 2" X 3" X 28" rough ornate iron casting that needs to be machined around the periphery. The best surface to locate this part for machining is on the ornate side which is anything but flat.
My thought was to spread over the ornate side of the casting with an auto body bondo and parting agent. Once the material cures, it would machined flat and become the primary datum for all other milling operations. After machining, the "autobody bondo" would be come off clean with the help of a parting compound.
A life time ago I used a material called Tooling Stone. I fabricated to a simple drill jig with tooling stone to accurately locate a Cadillac badge onto a hub cap.
This material was easy to apply, didn't srink, machined fairly well and worked with a parting agent.
Today I can't find Tooling Stone and hopefully someone has a better material suggestions than auto bondo. Any suggestions would be appreciated.
This is one of two castings for model engine project.
Bill

Gawds sake NOT "Bondo" it actual tries to - wudyah believe "bond"!

Use Plaster of Paris. It comes off lots of easy ways. Heat-shock of dropping the hot castings and plaster into water was the low-effort one.

Residue down in the fine details? No need to chase-up tediously with a sewing-machine needle.

Ignorant household white vinegar and its gone real soon, now. Warm it up, speed it up. Don't breathe the fumes, but dilute Acetic acid is otherwise "food grade".

Your pickles come in vinegar. Well... the shy ones might just hold hands..

Anyway, no disposal issues.

GregSY · Aug 13, 2018

Hey Thermite...if Russia attacked Turkey from the rear, would Greece help?

thermite · Aug 13, 2018

GregSY said:
Hey Thermite...if Russia attacked Turkey from the rear, would Greece help?

Present state of affairs in the government of the RF? The Turks are safe as houses.

Roosha would never reach the point of entry.

Security by obscurity.

All turkey assholes looking much alike, they'd die of exhaustion before ever making it out of their own command bunker.

Read Sorokin. Not entirely futuristic:

Day of the Oprichnik: A Novel: Vladimir Sorokin, Jamey Gambrell: 97837453316: Amazon.com: Books

"Warning" herein. Life has gone as grotesque as fiction:

Day of the Oprichnik - Wikipedia

PS: Assistant Professor of Air Science who had served there pointed out that the Turks had been at war with Russia thirteen times in recorded history, and only lost nine of those wars.

Which a Turk considers rather favourable odds for another go at any time. Worst outcome is the rus go thought them and then have to deal with the Kurds. That should keep them busy the next thousand years.

You'd have to know the Turks. And the Kurds. Or just ask an Armenian. More to it than dried Apricots.

Milland · Aug 13, 2018

thermite said:
More to it than dried Apricots.

Way to date yourself. As for me, I don't give a fig about it, and would be grapeful if you would quit raisin the subject. Doesn't apple-y to our day and time.

Orange you glad I didn't say "banana"?

adh2000 · Aug 13, 2018

Here is a long list of materials for doing what you want to do:

FMSC - Liquid Tooling Materials

Once you get into it you will find there are dozens of options with slightly different characteristics to match every conceivable situation. Too many choices really.

adh2000 · Aug 13, 2018

I've personally used this stuff for what you are talking about:

FMSC - Repro One Fast-Cast Urethane

Worked great. It can be a bit pricey, best to fill in around your work piece with blocks of wood as much as possible, then pour this stuff in around it.

donleybill · Aug 13, 2018

Thank you. I'll look into this product.
Bill

Triaged · Aug 13, 2018

Sounds a bit big for it but it is reusable

CS Alloys - Using Cerro Bend Working Holding

thermite · Aug 13, 2018

Milland said:
Orange you glad I didn't say "banana"?

Given that they are slightly radioactive, yes. Now... about that spider on your sleeve...

Milland · Aug 13, 2018

thermite said:
Given that they are slightly radioactive, yes. Now... about that spider on your sleeve...

Dang! Thanks for letting me know, I just swatted it away.

BTW, nothing wrong with a little radioactivity, living in NH means we can go on radon parties on neighboring states.

thermite · Aug 14, 2018

Milland said:
Dang! Thanks for letting me know, I just swatted it away.

BTW, nothing wrong with a little radioactivity, living in NH means we can go on radon parties on neighboring states.

I recall a classmate ....half a century ago ... as we were all taking a break to head home for the holidays - he to Californicyha - his eyes were lighting up in anticipation of something he described as a "Wesson Oil Party".

Naturally, naif that it was at the time, I just HAD to ask...

I shall be just as happy now to NOT ask what constitutes a radon party, lest they come soliciting my vote and donations for yet-another political figure that believes himself to glow in the dark!

DDoug · Aug 14, 2018

thermite said:
I shall be just as happy now to NOT ask what constitutes a radon party, lest they come soliciting my vote and donations for yet-another political figure that believes himself to glow in the dark!

Sort of like this .....?

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