I've been getting a lot of shop time in. Here's some of the castings. About 10 minutes into todays burn, the Aerobed blower started making noise (plastic impeller spun on the shaft). Grabbed the backup Pollonex Whirlpool Spa blower and a router controller, back in business. Took down the 8 foot fluorescent that I had to use a stool to plug in and rarely used it because of that. Replaced it with a 4 foot 5000 lumen LED pull cord. Now I can see down in the moulds. Sweet Made a new pattern yesterday and threw together a 12 x 13 1/2 flask today for a test mould. It pulled well so I went ahead and did a real mould for pouring. That thing is heavy so it'll be a two person lift. If it pours OK, I'll tweak the flask size to cut down the weight.
That would weigh about 110 pounds assuming it is about 12X12X13=about 2000 cu in. One cu inch of sand is about .055 pounds. That is more than I would like to lift off the bench and set down in a gentle fashion onto the floor. Flipping it on the bench is OK. But the lift down... Got a chain fall? I've done that and then moved them to the pour area outside with a two-wheeled hand truck. Hooking the chain fall so that it is hooked a foot or so toward you slides the mold off the bench as you lift and then it is a straight shot to the floor. Works pretty well. I had a chain fall on barn door hardware so I could traverse with the mold. That worked quite well. The best has been the foot-pedal remote-controlled ginned-up power lift on barn door hardware. It's nice to not have to depend on help. Oh yes, I am curious to see the pattern. You are a dog for teasing us with the first post. ;-) Denis
It's a wood copy of the tripod head that was posted in the Will it Cast thread. I didn't even think to get a photo of it. Sorry about that.
Got to pour the tripod head today. The flask wasn't as heavy as I thought, maybe around 80 pounds. I was wondering if shrinkage would be a problem and there was some around each of the tabs. Dimensions: 8 3/4" diameter, 5/8" thick, tabs are 3/4" tapering to 5/8", 1/2" forged eye bolt double nutted, 3/8" bolts.
Bonz, Looks excellent! Nice finish. From all the rumors I've heard (no experience) about aluminum, you seemed to get away with a rather thin runner and sprue base. Well done! This is for a lifting tripod, right? Should be good and strong for that. Denis
Thanks guys. I'll put a 1 ton chain hoist on it. It'll probably never see 1k. The bolts were just what I had on hand, They might get upgraded (need washers and acorn nuts). I have no clue what the load limit would be for it. Maybe some of you engineers could give it a hypothetical rating. I've used that long skinny sprue before. It works like a pouring basin if you keep the runner/gate the same size. Pour fast at first, fill the sprue, keep it full.
No enginerd here, and without knowing the alloy I'd safely wag you are around 35,000 psi. I think you're low at 2000lbs. I bet that thing would handle twice that before breaking.
That sounds good. I had the pattern at 1/2" and didn't like the look of it. Bigger is better in this case. It just has to be stronger than 2 x 4 legs.
That's the plan. Here's one example. They've even scabbed on an extension for more height. I would have never thought 2 x 4's could do that lift.
The 2x’s themselves have impressive strength, for sure. But, the weakest point in your tripod, as I’m sure you know, is the join of raw 2x4’s with the very strong head you cast. If they fail, it will be by splitting beginning with the hole and extending along the grain. That will be due to a combination of straight-down-the-board pressure and racking of the tripod which twists the bolts in their holes. One simple modification that would greatly increase the strength of the head-to-board joint would be inletting thin plywood on each wide face of the 2x for a distance of 8 to 12 inches. In my shop I’d grab a piece of hobby shop Baltic birch plywood around 1/8 to 1/4” thick and just slice off enough 2x to allow the plywood inlay to sit flush with the 2x4 surface. Simply gluing that in with yellow glue or epoxy would reduce the tendency to split and the plywood has better bearing properties as well. I claim no engineering training, but have used this and other methods to improve metal-to-wood joins. I apologize if I’m over-complicating a design that may do the job just fine as is. Denis
That possible failure was my concern too. I did a test fit by inserting a board all the way, drilled, then radius the top just enough to give clearance. I had thought about running a deck screw through the board about an inch below the bolt. The taper on the tabs gives some lateral movement of the legs which I've found is needed when setting the tripod. I'll keep the plywood insert tip in mind if there's a problem. Thanks
.....or possibly could make metal adapters for the end of the 2x4s to interface with the tripod head.? Maybe metal plates or a rectangular box that slips over the end of the 2x4 sort of like those hinged saw horse joints you see in the big box stores. Best, Kelly
I get that simplicity is important. In an otherwise simple radiused 2x4 end a 1/4” carriage bolt placed an inch below the bearing and parallel to the “4” axis would offer a great deal more security than a deck screw for about the same time investment. And, as Kelly suggests, all manner of box/tab and inserted metal slats like those seen in commercial timber construction are possible at ever increasing costs and strengths. Give me a chance and I can make the simplest problem ever more complex... ;-) Denis
Sorry about the after-the-fact armchair stuff, but any thought of making it with sockets to hold the 2x4s instead of just bolts? I too think the bolt hole might be problematic under loads, but that really all depends on what you're using it for. I built a shear leg derrick out of 2x4's originally to lift sections of a quonset structure for assembly and it occasioanlly gets setup for the odd task here and there, so I know how much a 2x4 (or in my case, 2x4s glued and screwed together to make 4x4) can withstand. Few people do any rigging, but it's amazing what can be done with relatively simple machines.
I went through several different design options. I had considered casting sleeves for the 2 x 4's with tabs to pin between pillow blocks. Same sleeve with just cast mating tabs. In the end, the KISS principle won out. What I used to throw a tripod together quickly was just a pipe stuck through the 3 boards with a chain wrapped around. It was cumbersome and awfully wonky. This should be a lot stabler. There is also the option to put a bushing in the boards and run the bolts through them.
This is what I'm going to run with. Up-sized the bolts to 7/16" and used a piece of 3/8" black pipe as a bushing. The bushing will give more surface area to carry the load.
Round two. Increased the diameter 1/2", that will be a full A10. Added a customized top. Made it a match plate. Sliced 1" off the cope and made a bottom board that is attached after moulding the drag. It was threatening rain all day so didn't get to cast it. The sign board letters came today so I fettled the 3/4" and 1" sets. These are flat topped, sweet!
I wish the sign board letters came in 3/8 and 1/4 size. I have not seen them that small. Has anyone. Where did you get yours—-link please? Yoir tripod top is lookin very good! Denis
