Fixture ideas needed

brianweldor · Feb 13, 2016

I make a lot of aluminum post caps that fit over square wooden posts. They typically fit a 6" or 8" square post, and are made up from 4 separate parts, one for each side. Right now I just clamp to a simple square fixture, tack up (Tig), and then struggle like hell to get the weldment off of the fixture because the shrinkage from the tacks sucks it tight to the fixture.
I'd like some kind of collapsible fixture that would hold my dimension for clamping and tacking, but then get out of the way so I can easily remove the weldment. Any ideas? I was thinking some kind of central cam that would press outward against the parts, but could then rotate and release the pressure for removal. The travel shouldn't need to be more than .030" or so.

Heavey Metal · Feb 13, 2016

Fixture on the outside and upside down

Tack on the inside.

billzweig · Feb 13, 2016

I am not sure about the shape of your post caps, but maybe those could be made by forming. I did this in a number of projects, one in fact as a conical caps for a 4x4 posts.
Some decades ago I made a series of copper lanterns that had two caps, both pressed. The formers were machined from aluminum and steel and the metal pressed into polyurethane rubber for the shallower caps and lead block for the deeper. I was mostly working in copper , but the wood posts caps were 5000 series aluminum.
The former shown in the photo is resting on the polyurethane rubber used for moulding.

gbent · Feb 13, 2016

Take your existing fixture. Cut it corner to corner and remove and discard a slice of material, say 1/2" thick. Replace the material and you have a 3 piece removable fixture.

brianweldor · Feb 13, 2016

Heavey Metal said:
Fixture on the outside and upside down

Tack on the inside.

I've tried that, but the tacks can interfere with the fit on the post

brianweldor · Feb 13, 2016

billzweig said:
I am not sure about the shape of your post caps, but maybe those could be made by forming. I did this in a number of projects, one in fact as a conical caps for a 4x4 posts.
Some decades ago I made a series of copper lanterns that had two caps, both pressed. The formers were machined from aluminum and steel and the metal pressed into polyurethane rubber for the shallower caps and lead block for the deeper. I was mostly working in copper , but the wood posts caps were 5000 series aluminum.
The former shown in the photo is resting on the polyurethane rubber used for moulding.

Yes, very similar caps, but much taller/deeper pyramids with .100" 3003 aluminum, and sometimes more complex shapes which would be impossible to form/draw. Tooling cost on the runs I do ( 10-50) would be prohibitive. What thickness aluminum did you use to form with??

brianweldor · Feb 13, 2016

gbent said:
Take your existing fixture. Cut it corner to corner and remove and discard a slice of material, say 1/2" thick. Replace the material and you have a 3 piece removable fixture.

I like it. But how to make it easily repeatable?

billzweig · Feb 13, 2016

brianweldor said:
Yes, very similar caps, but much taller/deeper pyramids with .100" 3003 aluminum, and sometimes more complex shapes which would be impossible to form/draw. Tooling cost on the runs I do ( 10-50) would be prohibitive. What thickness aluminum did you use to form with??

For the 4x4 posts caps I was using something like 18 gauge, shallow pyramid with sides, very similar to the former for the copper dome shown in the photo. Not impossible to form bigger/deeper/thicker parts, but indeed would require a large press and steel dies. But the part takes only seconds to press and the investment might pay back even after 100 pieces.

Sea Farmer · Feb 14, 2016

Can you redo your existing fixture using compression springs to squeeze inwards and pop the parts off?

Heavey Metal · Feb 14, 2016

brianweldor said:
I've tried that, but the tacks can interfere with the fit on the post

Cut windows in the fixture

Tack from the outside

gbent · Feb 14, 2016

brianweldor said:
I like it. But how to make it easily repeatable?

Two pins on one side, two holes in the other. U slots in the filler plate.

One of the pins needs to be diamond shaped or one of the holes needs to be oval. This allows for center to center variation without compromising the alignment.

brianweldor · Feb 16, 2016

gbent said:
Two pins on one side, two holes in the other. U slots in the filler plate.

One of the pins needs to be diamond shaped or one of the holes needs to be oval. This allows for center to center variation without compromising the alignment.

I'm not visualizing what you are describing.

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Fixture ideas needed

brianweldor

Cast Iron

Heavey Metal

Banned

billzweig

Stainless

gbent

Diamond

brianweldor

Cast Iron

brianweldor

Cast Iron

brianweldor

Cast Iron

billzweig

Stainless

Sea Farmer

Diamond

Heavey Metal

Banned

gbent

Diamond

brianweldor

Cast Iron

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