I really like Robart's hinge and have rarely used anything else. Four years ago, I ran some tests on 1/8" Robart hinges with four different types of glue and posted the results on the old RCO forum. These results should still be true today provided Robart hasn't changed their design or materials. Deadeye's post indicates that the hinge is good for only 20 lbs tension; my tests showed much higher allowables so hopefully Robart hasn't changed anything since 2002. Sorry for the long post, but here is the complete story (typical structures engineer speak).

Gary

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March, 2002

Four 1/8” size Robart Hinge Points are tension tested for the following glues. The hinges are from Robart’s package number 308.

* Titebond, Original (from Home Depot, noted as “TB”);
* Super Z RC/56 by J & Z Products (from Cedar Park Hobbies);
* Elmer’s Probond Polyurethane (from Home Depot, noted as “PB”).
* 30 min. Epoxy, Bob Smith Industries (house label from Cedar Park Hobbies);


HINGE PREPARATION

* Each hinge is used stock and not roughened, sanded, or modified.
* The hinge side to be glued was cleaned with denatured alcohol and not touched again after cleaning.
* The hinge lugs were not oiled or treated to prevent glue from binding them up.


TEST SAMPLES

* The hinges are glued into a 1/2" thick balsa block 1.1” apart (ensuring that each is glued to similar wood grain).
* 1/8” holes are hand drilled only to the length of the hinge, and the first 1/8” length of hole is widened to accept the wider boss of the hinge near the pivot lugs.
* The holes are centered and squared by using Robart's drill guide.
* The holes were cleaned with a shot of compressed air.
* Glue is applied to both the hinges and holes, and a toothpick is used to work the glue down into the hole.
* Per Elmer’s instructions, the hole for the Probond sample was slightly moistened with a Q-tip that had most of its cotton removed.
* The hinges are sunk as deep into the block as possible such that the hinge pins are about 1/32” from the surface of the block.
* No attempt was made to clean the glue out of the hinge lugs; excess glue was wiped clean.
* The samples were allowed to cure for 48 to 50 hours before testing.
* The balsa block is of a “medium” grade and was purchased from Lone Star Models in June 2000.


TEST SETUP

* A 1.5” x 1.5” x 1/8” angle iron was horizontally clamped in a bench vice.
* The balsa block sits on the horizontal leg of the iron and the free end of the hinge passes through a 1/2” hole in the iron.
* Large forceps are clamped to the free end of the hinge and a 5 gallon bucket is hung from the forceps. The bucket & forceps weigh 2 lbs 6 oz.
* Pennies are gradually added to the bucket from a supply of 50+ pounds of pennies.


PRE-TEST OBSERVATION

Since no attempt was made to clean the glues out of the hinge lugs, it was noted prior to the test that the RC56 hinge action was stiff while the TB hinge “broke” loose and was much easier to rotate. Both the epoxy and PB hinges “broke” free as well, but were stiffer to rotate then the TB hinge and not as stiff as the RC56 hinge.


RESULTS

The RC/56 hinge pulled out at 38 lb 13 oz (38.8 lb)

* The hinge pulled cleanly out of the block; no large chunks of balsa were removed.
* Almost no glue or balsa was attached to the hinge.
* The hinge lugs and pin were not deformed and the hinge rotated smoothly.


The Titebond hinge pulled out at 46 lb 5 oz (46.3 lb)

* The hinge pulled cleanly out of the block; no large chunks of balsa were removed.
* Some glue and balsa remnants were still attached to about 1/3 of the glue surface.
* The hinge lugs and pin are deformed & stretched; the Titebond glue held almost to the full static strength of the hinge’s plastic.


The Probond hinge broke at 56 lb 3 oz (56.2 lb)

* The glue held to the full static strength of the hinge.
* The hinge lugs broke at the hinge pin; the barbed end of the hinge remained glued in the balsa block.


The 30 min. Epoxy hinge broke at 59 lb 5 oz (59.3 lb)

* This glue also held to the full static strength of the hinge.
* The hinge lugs broke at the hinge pin; the barbed end of the hinge remained glued in the balsa block.
* The 59.3 lb failure load occurred on the second test attempt on the hinge.
* The first test ended at 46.3 lb when the forceps’s grip on the free end stripped the plastic barbs off of the hinge.
* The hinge lugs were deformed after the first attempt, but continued to hold to a failure load of 59.3 lb on the second attempt.