I'm making a bell for my friend whose retired from the Coast Guard. He's in good health but he's getting up there so I want to get it done. I'm using plans linked by HT1 in Zapins' bell thread. It's the 200mm bell. Using those specs I drew the bell profile in my CNC design program (Vectric Vcarve) and cut profiles for the inner and outer forms. I cut the profiles out of 1/4" dibond which is a plastic core sheet product coated on both sides with 4mil aluminum. I cut two pieces for each profile mirrored to each other with the edges at 5 degrees so that when I screw them together it makes the profile 1/2" thick with a defined central "cutting" edge. The profiles were cut to accommodate a 3/4" pivot shaft. I cut 2 sets of profiles for each of the inner and outer forms: one set of internal sweep forms and one set of external sweep forms because I'm not sure whether I'm going to produce each of my patterns by additive sweeping or subtractive. Maybe a combination of both. I'm not even sure yet if I'm going to sweep right into the petrobond or make hydrocal master patterns. I'm leaning towards making masters. I'm not even sure yet if I'm going to make the profile pivot on bearings or turn the pattern an a turntable, but I decided to get moving anyway. The picture is of the external sweep for the outer profile. Comments appreciated. Pete
Ive so wanted to Try some sweeps in Petrobond... Every time I get started I get overwhelmed with the Process. best of luck and record everything even failures V/r HT1
Nice! This is exactly what I started making but haven't finished yet. What are you going to make it out of? Wax? What will you use for the inner core.
Holy cats I just had a brainstorm. My drill press! This isn't mine in the picture but mine is identical including the table. I just dont have a pic of mine handy. This just made the process a hell of a lot less complicated. I may have to turn the end of the pivot shaft down to fit in the chuck but it's a ready made fixture with all the features! Zapins- I'm going to start with the drag mold by just taking a beach bucket of rammed petrobond and paring it down to size with the external sweep. Then I'll ram the cope solid and dig it out with the internal sweep. I'll most likely do a trial pour in aluminum. Another option is to use the sweeps to make patterns. For the exterior form I could form an undersized shape in hydrocal, let it harden, and gradually build it up with hydrocal while sweeping before it sets up till I get to the shape. Pete
Pete, The thickness is going to end up around 1/2? I’ve never looked into bel making too much. I do have this 16” bell hanging from the front of my cottage. The bottom flange is about 1/8 thick.
I thought you were going for cast iron. If you're going for Bell bronze thicker is better. I think they also used to call this canon bronze. My bell has a very high ding. I think a thicker bell will just give a deeper dong. Just keep in mind that there is a lot of stresses within a complete shape. Are you planning on making this from aluminum bronze? If so, I would probably try to stay around 8% to 10% aluminum with copper by weight.
Specs can be downloaded here: http://everyspec.com/DoD/DoD-SPECS/DOD-B-24673_23252/ It calls for C87200 which is silicon bronze. Everdur. Coincidentally I have more than enough for the job. Hopefully it will end up in the correct tone range as-cast. My petrobond issues seem to be resolved since its getting warmer out and I've also completed mods to my muller by adding torch holders. This not only works, it works well. I also have my pyrometer functioning correctly. So there's no reason for further delay. The mounting bracket and clapper will be neat little projects themselves.
the tone is effected more by shape and thickness then by the alloy. if any of you remember the Video of the bell I made, it was 60-40 yellow brass from scrap and It did not sound different than the SB original it was patterned off of V/r HT1
3/4" shaft end turned to 5/8" to fit in the chuck and flats milled on the shaft for attachment tabs. This one is for the outer surface which will be the cope. I'll be going directly into the petrobond but will have rammed it hard so I'll either ram in a conical pattern of some type or dig out a starter hole by hand and use the sweep to finish. I'm thinking of just cleaning out my little shopvac and using that to evacuate the sand as I go instead of trying to continually scoop or dump. I'm still trying to work out a registration strategy. I'm thinking of drilling a centered hole in the common moldboard like a matchplate which has been previously fitted to the cope and drag edges with dowels and then align that to the drill spindle and then clamp it down before commencing. At this point I intend to gate into the drag so I will have rammed my sprue pin into the cope before starting the sweep. I'm thinking that after I have bottomed out with the sweep I should penetrate through the cope for venting and possibly for use as a riser. Opinions? Pete
That will be a pretty slick way to make cylindrical molds. If you can get that to work, it should be very versatile in that you could sweep out any profile with the same set up and technique. Do you have enough quill stroke for the whole profile?....or will you have to reposition the table? Any time I've ever used a sweep to place/displace material, it seemed to cut ok but will tend to cut rough with an occasional gouge from material balling up ahead of it. To get a decent finish seems to require a very low angle of attack, like you're troweling cement.......like when I was applying the moldable ceramic fiber on my low mass furnace build...... http://forums.thehomefoundry.org/in...w-mass-electric-furnace.607/page-3#post-13564 .......but depending on how the molding sand behaves, maybe you can cut effectively with the sweep and polish the mold surface by hand if needed? Best, Kelly
Yes this is the question of the hour. The sweep will certainly displace the sand, but how abrupt will the scraping action be and how smooth will it leave the surface. As you pointed out the character of the sand and the cutting edge will tell the story. At the very least even with rough or gouged surfaces I hope to at least cast an aluminum pattern that can then be cleaned up to a usable form. This has the potential to be a bit of a rabbit hole. The direct cutting into the molding sand is the first attempt. It would be great to be one-and-done. Making patterns by building up positives and corresponding negatives out of plaster to yield mold forms is another possibility for these sweeps and possibly what Zapins was alluding to, and what you were demonstrating in your link above (at least the building and smoothing part). So we shall see. As to the quill stroke, no it's at least an inch short. My table raises and lowers on the pole with a typical (but clever) rack and pinion setup. When the squeeze lever is released it frees up the sleeve to allow the table to raise but also allows the whole mechanism to pivot. The rack is long enough so that there is enough excess to allow it to be clamped to the post without damaging or bending it, eliminating any pivoting, and still give me the additional vertical travel. Pete
Petee, your first sweep looks like the correct orientation, but the one on the drill press is reversed. In the Complete Handbook, Ammen shows the spindle mounted on the bottom board and the exterior shape swept from molding sand above the drag. Then the cope is rammed on that shape and then lifted. cutting the sprue might need to be done at this stage. The interior sweep is then mounted and oriented to the original spindle and the interior shape is swept. Since only the thickness of the bell is removed at this stage there is minimal cleanup to remove at the drag parting line. Done this way there is no rollover, but some internal supports might be needed. Neat project.
Thanks for pointing me to Ammen's book. I actually have it but hadn't consulted it. That's why I'm here! I looked at his diagram and will try that method. I had thought of a similar method (pretty close) except instead of building the form up, starting with a solid block of rammed petrobond and then shaving it down as I lower the quill. My main concern with doing this is that the cut form wouldn't be strong enough to tolerate ramming the cope. I would have had even less confidence in a built-up form squeezed in place by hand, but I'll give it a try. I'll take an experts advice. Since the sweeps will be used more for smoothing than for hogging it may improve some of the concerns Kelly and I were discussing as well. It will give me a better opportunity to smooth the form before ramming the cope too. It will certainly resolve the registration issue. I think the drill press set-up will allow me to forgo the through shaft. Pete
It's still awful cold here- for the purposes of my sand anyway- and I'm not sure if my sand will degrade between the time I make the molds and the time I actually get to pour so I've decided to wait for warmer weather for that part of the project. But there's a bunch more to do so I've moved on to another part of the project, the clapper. Seems pretty simple, right? How the hell do you make that? How do you mold it? How do you make a pattern to specs that won't break? Well, I have some time, some machine tools, and some scrap aluminum, so let's have at it. So here's the clapper project. I decided to make it in 3 pieces. Bulb, tapered shaft, and upper hook. I chose that order of operations for several reasons. In no particular order of importance: I didn't have a single piece of stock big enough to turn the whole clapper at one time. You cant have a single part that's too long sticking out of the chuck and expect to have the needed rigidity to take heavy cuts with any kind of accuracy. You always need to maintain a reference for measurement and you always need something to hang onto. The flat surfaces of the hook and lanyard hole have to be parallel to each other. The process I've chosen requires that those parts remain cylindrical until after all components are assembled. The diameters of those cylinders represent the final width of those respective features. They will be milled flat to their proper thickness as a final machining operation after assembly. Once they're flat I will use a circle template to finish the diameters with a file. The holes will be drilled and final shaping of the S after the part is cast. More on that later. The bulb portion which I made first is shown in several phases. I turned it out of an ingot I had made by filling a dog food can with aluminum sometime in the past. I have a few of those laying around. It was about 4" long and 3" in diameter. Once I faced it off I center drilled it on both ends to fit the live center of the tailstock so it could be reasonably repositioned if I had to flip it. The part required alot of material removal. The whole part took about 4 hours. That file I used is excellent for aluminum removal. You use it on the spinning part just as you ordinarily would, taking the obvious precautions. The wooden handle is a must. No bare-doggin it unless you want it embedded in your wrist. Of course I used the lathe tooling to get it to the basic rough shape and then finished it with the file. The bulb is 2" (50mm) at max diameter. I drilled and tapped the center on both ends. The upper hook portion (cylinder at this point) came from a piece of scrap mold gating which was basically a cube. I knocked the square edges down with the bandsaw and some filing as best I could before mounting in the lathe. I was basically turning a cube into a cylinder on the lathe which is awfully hard on the machine as well as the tool, so I took it easy. I got it eventually. I really need to cast more turning stock! I drilled and tapped both ends. The tapered shaft was pretty straightforward. I turned it out of a sprue from a previous casting. I left it cylindrical a few thousandths larger than final max diameter, assembled all three components, and then cut the taper to ensure all of the parts would transition seamlessly. It was really the moment of truth and its success was going to be dependent on how well all of my threading and centers were going to align. Everything went together well and the assembly spun true. The alignment was good but my technical skills were not. You'll see a groove in that shaft about half way across its length. I had started to cut the taper and hadn't tightened my tool sufficiently. Fortunately I caught it when I did and the error wasn't catastrophic. I can fill it with JB Weld and sand it smooth. The taper wasn't exactly perfect either but no ones going to put a micrometer on it. I still hit within a few thousandths of the required diameters even though the taper isn't 100% correct. The measurements are a bit of a bastard on this project. Even though they're all metric they're basically all imperial measurements converted to millimeters. I didn't take any liberties though and I did all of the conversions to imperial with an online tool as I went along. I spent a lot of time with the drawing to figure out the needed dimensions of the components as I went, but I got it. The most critical is the 114mm from the hanging surface of the hook to the bulb diameter, and I'm within 1/2mm of it so I'm pretty happy with it. Incidentally that height gauge in the background of one of the pictures is a super handy tool. It allowed me to mark and retain my references. It's usually used with a granite surface plate (which I have but chose not to use (my back said "no")) but my table saw was close enough. Those more experienced at this may roll their eyes at this whole project and have an easier or faster way to do it but I've tried and learned a few things so far and I think the part will perform well as a sand casting pattern. Plus I get to play with my toys. I'll be doing the milling today.
I milled the flats yesterday. It went well. Work holding remains a bit of a dark art but I eventually got it. Once the flats were done I covered the surfaces with Dykem and scribed my centers with the height guage, lightly centerpunched with a scriber, and swung the diameters with a pair of dividers. I sawed and filed to the line. I only cut and filed the upper S hook portion leaving the circular end on. I left the lower end as-is and will most likely cast it that way so I can us that end for my ingate. I just filed the inner faces a bit for draft. I'll drill and tap holes at the centerpunched points on the flats so I can use screws to withdraw the pattern from the sand. I plan to put a blind riser between the runner and ingate for the benefit of the bulb but I may end up having to attach the riser directly to the bulb. At it's thinnest points the pattern is 9mm so I don't think the bronze will have any trouble filling the length of the casting. I'm hoping to not have to put the finished casting back on the lathe to clean it up but I'm leaving the circular ends on just in case. Pete
Just noticed the note at the bottom of that page Matt posted. It says to make the clapper not less the 3% of the mass of the bell. So if it turns out thicker due to limited bell making skills, can't you just upsize the hell out of the donger dong?
