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you could build a trigger shoe for it, like:  Those little set screws will be a pain to add but you could probably get away with an adhesive or friction fit if you machine it with that in mind. Ambrose Burnside fucked around with this message at 16:12 on May 12, 2017 |
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May 12, 2017 15:52
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IDK what machine tools you have access to, but if you don't have a mill or lathe, a "kinda weird" approach I personally might take would be to make the trigger shoe from copper or bronze metal clay. It's a mouldable putty used by artists for both artistic and functional components. You can shape it to conform exactly to the trigger/pull and shape the opposite side with your actual finger for that Custom Fit, let it dry, carefully do any precise material removal (it's drillable and fileable in this state if you have a delicate hand), and then fire it with a kiln (ideal) or hand torch on a firebrick (workable) to burn out the binder and sinter the copper powder together. The final product will shrink something like 5-10% from its pre-firing dimensions, which will slightly undersize it for the trigger, which is fine because you can now use needle files and rifflers to open up the trigger-conforming part just enough to grip the trigger, ideally without any fasteners. ***I have not attempted this specific thing with metal clay, but using metal clay to produce components that are a negative impression of an existing part is a well-known technique for the material, and I've definitely successfully done something a step or two removed where I cast a Customized Tool Comfort Handle from pewter by taking a direct impression of the existing uncomfortable handle in oilsand ******* If you don't care if the final result is real ugly and are fine with a non-metal solution, I do the even lazier version of this all the time with rigid thermoplastic to create bespoke grips for repousse punches. Buy a pound of pellets for $30 or so up here in Canada from a jeweller's supply place, soften the pellets in just-boiled very hot water, fish em out and quickly mould them into a lump of hot putty, jam it onto the handle and shape it how you like, and it'll be hard and hold onto the trigger once it's cool. You can remove it by submerging the part in boiling water and pulling the softened plastic off (it's reusable, which is nice). Ambrose Burnside fucked around with this message at 20:23 on May 13, 2017 |
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May 12, 2017 16:14
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Those are excellent ideas as well, I wasn't familiar with the thermoplastic or the bronze clay. I like the trigger shoe idea also, it seems to dovetail into the idea ReelBigLizard had. I have lathes and mills and such but a putty or clay is enticing.
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May 12, 2017 17:17
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Bear in mind the thermoplastic looks like you gobbed a bunch of bread dough onto whatever, unless you want to machine it prettier in situ (when it's hard you can saw/drill/file/etc it, albeit not well, and the swarf gets contaminated with metal bits and cutting fluids and so on so I don't reuse it), and you might want to paint it a matching colour to be a little more discreet if it's on there in the long term. It's great stuff to have around in general, though, it's one of those things with a million uses you can't guess at until you run into em. Besides bespoke tool grips, it's downright miraculous for fixturing small and delicate or awkward-geometry one-off projects. I made a pewter ring and did a bunch of chasing to the ring after it was bent and welded into a loop, and did it without distorting anything that I didn't intend to distort by packing most of it in thermoplastic and affixing the whole thing to a block of wood in the vise. Rio Grande used to sell generic bags of thermoplastic but don't seem to stock it any more, but the equivalent product seems to be this stuff: https://www.riogrande.com/Product/Jett-Ballistic-Fixturing-Compound/118226 but this will likely do you just fine as well, same deal without a ceramic rigidizer so it's got a little softness when cool, nice for handles: https://www.riogrande.com/Product/Jett-Basic-Fixturing-Compound/118221#ReviewHeader Ambrose Burnside fucked around with this message at 20:39 on May 13, 2017 |
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May 13, 2017 20:30
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got some quality anvil-time in today. Mother's day -and- a friend's birthday: devastatingly covered 
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May 13, 2017 23:21
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Ambrose Burnside posted:Bear in mind the thermoplastic looks like you gobbed a bunch of bread dough onto whatever, unless you want to machine it prettier in situ (when it's hard you can saw/drill/file/etc it, albeit not well, and the swarf gets contaminated with metal bits and cutting fluids and so on so I don't reuse it), and you might want to paint it a matching colour to be a little more discreet if it's on there in the long term. This is really great info, thanks. I'm going to order both. Now that the great air soft cocking crisis is solved, I'm moving on to figuring out how to make spur gears without spending a million dollars. I have an electric scooter with a roughly 105mm diameter main gear that was originally made out of a sintered metal. The guy I bought the scooter off of (not working) mentioned that his kid was playing tokyo drift with it. Of course the sintered gear exploded and the Israeli company that makes the scooter will only sell the entire rear end for $800 + s/h. I've tried to reverse engineer it using Fusion 360 and the closest I came wasn't that close. The original gears are helical cut to reduce ringing I'm guessing, but I ain't even gonna try to reproduce that and just go with a straight spur gear. The measurements I got off the gear are: 82 teeth 105mm in diameter (tooth to tooth) 20mm thick Tooth diameter at root ~2.5mm The gear in question:  Mockup aligned with gear:  Fusion 360's gear plugin seems pretty unintuitive. After screwing with it this is the closest I got (which aint very close):  My thoughts are: 1. Keep screwing with fusion 360 and 3d print a gear and cast that from aluminum 2. Screw that and mod my spindexer with a stepper motor and arduino and cut one from a cast iron gear blank (and then machine all that weird poo poo inside) 3. Find a commercially available gear very similar, bore it out till it's a wedding band, turn off the bad teeth and press fit the wedding band gear teeth ring on 4. ??? edit: it bears mentioning that the mating gear is a 15 tooth gear that's also torn up and will need replaced Pimblor fucked around with this message at 01:17 on May 14, 2017 |
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May 14, 2017 01:14
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Pimblor posted:This is really great info, thanks. I'm going to order both. You get me a cad file and I can probably wire one out for you.
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May 14, 2017 01:26
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A Proper Uppercut posted:You get me a cad file and I can probably wire one out for you. Ok good to know, I didn't realize you could edm a gear. I'll keep loving with cad until I have something reasonable. I may drop back to openscad and the gear libraries cause I've made herring bone gears with that with way less effort than the spur gear plugin in fusion.
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May 14, 2017 02:32
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Or just measure the distance between the two shaft centers, pick two gears off Mcmaster that have their pitch diameters add up to the right amount (make sure they have the same pressure angle and diametrical pitch), download the CAD models, and make any modifications you need to. You're not going to be able to wire a herringbone gear.
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May 14, 2017 02:54
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Ambrose Burnside posted:got some quality anvil-time in today. Mother's day -and- a friend's birthday: devastatingly covered go to hell for making me so jealous of how nice those are  (nicely done!!!)
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May 14, 2017 02:55
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Karia posted:Or just measure the distance between the two shaft centers, pick two gears off Mcmaster that have their pitch diameters add up to the right amount (make sure they have the same pressure angle and diametrical pitch), download the CAD models, and make any modifications you need to. You're not going to be able to wire a herringbone gear. The original gear isnt a herringbone gear, it's a helical gear. Irregardless its completely unobtanium, nobody makes it off the shelf. I don't care if it's a helical gear or a straight cut spur gear. At the speeds it's designed for if it rings a little bit at 8 mph who cares.
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May 14, 2017 04:04
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Pimblor posted:The original gear isnt a herringbone gear, it's a helical gear. Irregardless its completely unobtanium, nobody makes it off the shelf. I don't care if it's a helical gear or a straight cut spur gear. At the speeds it's designed for if it rings a little bit at 8 mph who cares. Herringbone was in response to your comment about openscad, sorry if I misinterpreted. I did overestimate McMaster's selection (and assumed they would have anything in metric.) Hell, I can't even find any working combos on SDP-SI, so doing the CAD yourself is going to be necessary in the end. Guess I should check my suggestions before posting them. However, since you seem to be having difficulties, I'll offer this, and I apologize in advance if this is patronizing. I just don't know how much you know about gears. You'll have better luck focusing on the pitch diameter rather than the OD of the gear. That's the diameter at which the gears actually contact, and is the essential thing to have match. You gave an OD of 105mm and 82 teeth, but the pitch diameter's going to be a couple millimeters in from there, likely at 102.5mm because that gives a diametral pitch (the ratio of pitch diameter to number of teeth) of 1.25mm, and I find it very hard to believe that the designers are using a non-standard pitch. It's not impossible, but unlikely. The diametral pitch has to be the same for both gears, so for the 15mm gear it's probably got a pitch diameter of 18.75mm. I googled and found this plugin. The only variables you really have diametral pitch (which they're calling module, and using the reciprocal for diametral pitch for some stupid reason. Just put 1.25 in module and you should be fine) and number of teeth, which you already know. Pressure angle I'd suggest 20 degrees, which will give higher strength for the teeth at the cost of more load on the bearing versus the more common 14.5 degrees. Since the teeth sheared before, I'd say play safe even if it lowers bearing life. Clearance you'll have to play with until it works. In short, given the plugin I linked: Pressure Angle: 20 degrees Number of teeth: 82 Module: 1.25 mm Again, sorry for the unprompted gear lecture. Largely was bored and felt like writing about gears. Gears are cool.
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May 14, 2017 05:36
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Karia posted:
They are pretty cool. I've had to learn a bit about them as we have a fair amount of people who come in with blown up gears that need to be recreated. Once it kinda clicks how it works it's really cool.
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May 14, 2017 13:06
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Karia posted:
No that's great info, sorry if I came off as brusque. I'm definitely not an engineer by trade and can be pretty thick headed. I tried looking through a few explanations of spur gears and kept getting lost in the terminology so that certainly was helpful. That plugin you found for fusion created a gear that looks an awful lot closer to what the busted gear looks like.
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May 14, 2017 13:18
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I recommend measuring what you have and buying close enough replacements. SDP does have CAD that I've used to wire out spur gears with success but you may find helical replacements here: https://shop.sdp-si.com/catalog/?cid=p335 And bore to your shafts.
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May 14, 2017 14:50
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One last thing: definitely still measure the distance between shaft centers, as accurately as you can. That distance needs to be equal to the average of the pitch diameters of the gears. If it's not 121.25mm then the numbers I gave you are wrong.
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May 14, 2017 16:41
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How well do wire edm cut spur gears work compared to hobbed / etc? I keep having delusions of making car gearsets
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May 14, 2017 20:30
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mekilljoydammit posted:How well do wire edm cut spur gears work compared to hobbed / etc? I keep having delusions of making car gearsets For one-offs, they're ok, the finish isn't great, it's slow, and suffers from hydrogen embrittlement though. For production, hobbing is the way to go. These days, lots of gears are sintered powdered metal. sharkytm fucked around with this message at 22:09 on May 14, 2017 |
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May 14, 2017 22:05
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If you're not hand-filing your replacement gear, tooth by agonizing tooth, I don't even want to talk to you 
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May 15, 2017 01:34
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sharkytm posted:For one-offs, they're ok, the finish isn't great, it's slow, and suffers from hydrogen embrittlement though. For production, hobbing is the way to go. These days, lots of gears are sintered powdered metal. The finish is as good as you want it. We cut prototype gears for Ford transmissions that we do a couple skim passes on and they look good. But yea, you're right, it's definitely better for one off or short run production. A few years ago we cut maybe 1000 prototype gears before they finally made a powdered metal mold.
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May 15, 2017 01:58
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Ambrose Burnside posted:If you're not hand-filing your replacement gear, tooth by agonizing tooth, I don't even want to talk to you that's taking it too far even for me but if you wanna try it with a manual horizontal mill and index head lets talk
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May 15, 2017 02:11
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While milling machines fetch a bit of coin in Australia, I've seen large lathes go somewhat cheaply. I'd bet this 3 metre lathe sells for under $2k - https://www.lloydsonline.com.au/LotDetails.aspx?kw=lathe&smode=0&lid=1056160 - are these things cans of worms you don't want to open though? I saw a newer large on go for $3k a month or so ago. New it was $25k.
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May 15, 2017 13:00
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Mudfly posted:While milling machines fetch a bit of coin in Australia, I've seen large lathes go somewhat cheaply. I'd bet this 3 metre lathe sells for under $2k - https://www.lloydsonline.com.au/LotDetails.aspx?kw=lathe&smode=0&lid=1056160 - are these things cans of worms you don't want to open though? I saw a newer large on go for $3k a month or so ago. New it was $25k. The primary question is do you even have enough power at the pole to run it, the next question is how quickly it'll drive you to poverty tooling it up.
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May 15, 2017 13:24
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sharkytm posted:For one-offs, they're ok, the finish isn't great, it's slow, and suffers from hydrogen embrittlement though. For production, hobbing is the way to go. These days, lots of gears are sintered powdered metal. I'm not as up on some of the details for this part of things - why hydrogen embrittlement with EDM? Specifically what I'm thinking of (and should not be thinking of because it's crazy, but you know) are pretty highly loaded gears - last I poked my machine design texts, automotive transmission gears are kind of unusual in terms of loading per tooth area, and racing transmissions moreso. So if EDM would be ruining the metallurgy of something like 9310, that's a non-starter.
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May 15, 2017 13:48
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Ambrose Burnside posted:Bear in mind the thermoplastic looks like you gobbed a bunch of bread dough onto whatever, unless you want to machine it prettier in situ (when it's hard you can saw/drill/file/etc it, albeit not well, and the swarf gets contaminated with metal bits and cutting fluids and so on so I don't reuse it), and you might want to paint it a matching colour to be a little more discreet if it's on there in the long term. I just bought J. Random Thermo Plastic off of amazon before I saw your supplier post and you're right I made an ugly potato but it's way better than the original cocking lever.  This really is great stuff so thanks for the recommendation.
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May 15, 2017 13:58
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^^^^^ Hahaha I love that mekilljoydammit posted:I'm not as up on some of the details for this part of things - why hydrogen embrittlement with EDM? As I said before, we did a butt load of prototype gears for Ford, out of 4142, I would think if that was an issue (I've been doing g this a long time and I haven't heard of it being an issie, but that doesn't necessarily mean anything) they wouldn't be wiring them. Never mind all the mission critical aerospace stuff we do. Gonna be honest, I don't know what hydrogen embrittlement is, unless it's just what it says on the tin. A Proper Uppercut fucked around with this message at 14:28 on May 15, 2017 |
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May 15, 2017 14:22
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A Proper Uppercut posted:Gonna be honest, I don't know what hydrogen embrittlement is, unless it's just what it says on the tin. You run the risk of hydrogen embrittlement anytime water is electrolyzed such as in electroplating. The hydrogen molecules are small enough that they dissolve into the grain structure of the steel. If it's below 40 Hrc, no big deal. (I think that's the SAE threshold) However if it's above that hardness those little molecules slowly migrate into the grain boundaries where they create tiny little cracks that spread into big cracks. The way to prevent it is to bake the parts at 375f for 4-23 hours. (See the SAE spec if it's critical) You've got 4 hours from hydrogen generation till it needs to be in the oven. Aerospace runs into this a lot as they have very hard parts that need special coatings.
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May 15, 2017 14:40
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Hydrogen embrittlement is caused by hydrogen getting into the surface layer of metal because it's being turned into a plasma by the ED part of EDM. It can cause the metal to be very brittle, leading to excessive wear and cratering of the loaded surfaces. Feel free to read on practical machinist about it, that's where my info came from. I have no experience in it, but was researching some very small gear prototypes that EDM would be ideal for (post heat treating, small quantities, and helical teeth). The project didn't end up going forward, but I did a bunch of research about it.
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May 15, 2017 14:41
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I guess that makes sense. All the parts I'm thinking of, ie the gears, aerospace, were either just 4142ph which is like 30rc, and the aerospace stuff is generally some exotic alloy thats not necessarily hard, but holds up under heat usually. I've never had a job come through here where they require the parts to be in an oven within 4 hours. Interesting stuff!
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May 15, 2017 14:56
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Hydrogen embrittlement isn't quite as well understood as those guys put it, though the mechanisms described are both common hypotheses (at least, this is my short few years' experience: Grain boundaries are almost certainly the diffusion path for hydrogen, but the exact mechanism for severely reducing the elasticity once the hydrogen is in the boundaries is less clear). ~40 HRC is the typical threshold for susceptibility, but HE can be a problem below that, too in certain alloys/applications. Most of the gears used in aerospace engines are case hardened by carburization or nitriding, which can give them surface hardness of up to ~60 HRC. Many also get plated with silver so there's a compliant layer for wear resistance. It's really interesting technology and actually a centerpiece of next-gen passenger aircraft engine design.
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May 15, 2017 15:09
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Cool info, thanks! Another option I've done is replace gears with chain drive. Two sprockets and some chain will get you going if you have room.
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May 15, 2017 17:15
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Pimblor posted:I just bought J. Random Thermo Plastic off of amazon before I saw your supplier post and you're right I made an ugly potato but it's way better than the original cocking lever. lmao it really is the most hideous-ergonomic solution conceivable, ain't it
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May 15, 2017 18:37
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Huh, speak of the devil. Just got an order for like 50 more prototype gears.
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May 16, 2017 12:39
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Anybody have any experience with the delightful task of stripping titanium oxide from flame-anodized parts? I'm doing some hot-forging work on 6mm CP2 stock and it takes too many heats to get an attractive anodization effect, the oxide ends up dark and matte. My preventative options- fluxing the stock for all hotwork or working in an argon atmosphere/vacuum- aren't viable. As I understand it, I can bead-blast or abrasive-tumble the parts (not ideal for batches of small, fiddly parts with really weird geometries) or pickle them in, christ almighty, hydrofluoric acid, or maybe a merely-very-strong conventional acid if i have patience. so, basically, do all my options here suck tremendously or am I missing something? [edit: preventative stuff is -probably- not viable, I haven't tried much there so I shouldn't rule anything out. Fluxing might actually be fine, it's just going to be extremely messy and would probably add a fair bit of time per part, which I'm trying to avoid.] double-edit:  When forging titanium, care should be taken to prevent contact with steel scale. A thermal type reaction can occur and seriously damage a forging die. Apparently the titanium reduces iron oxide in an exothermic reaction set off by pressure and high temperature. Ambrose Burnside fucked around with this message at 22:28 on May 16, 2017 |
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May 16, 2017 20:12
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Anybody ever use a Mcdonald rolling mill/have opinions on how they stack up to similar-calibre power hammers or fly presses?
Ambrose Burnside fucked around with this message at 01:42 on May 17, 2017 |
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May 16, 2017 20:36
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The gears we're making have pinions pressed into them. So, here's pinions
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May 17, 2017 18:25
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What's a good way to accurately and consistently secure small dies to a larger ram? I'm starting to put together a guillotine tool for small die-forging operations on that CP2 titanium I keep mentioning, for hot and maybe even cold work if I can get away with it, and because I have access to sinker EDM I think it makes sense to cut em with turned brass electrodes and use a nice hotwork-appropriate tool steel. Butttt those alloys are way too expensive to make the entire tool out of, seeing as how a typical guillotine upper tool is .5"x1.5"6+" all told, so interchangeable die faces it is. I'm just having trouble thinking up a low-profile way to hold the dies in position in the ram in a way that doesn't risk being damaged over time, like any tapped holes in the column might through deformation. Maybe some sort of clip attached to the die that holds onto a milled groove in the ram, or a socket/tang + set screw arrangement? I don't know if there's an approximate industry standard here. Ambrose Burnside fucked around with this message at 21:05 on May 18, 2017 |
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May 18, 2017 17:06
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Domed dowel pins and magnets?
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May 18, 2017 23:07
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I can't quite picture how that would work- do you mean a detent-kinda setup with magnetic reinforcement, or vertical dowel pins that butt up against the magnets? Ambrose Burnside fucked around with this message at 21:52 on May 23, 2017 |
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May 23, 2017 21:39
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I meant to use the dowel pins for alignment and magnets for retention. I don't know the sizes involved, but it made sense to me. 
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May 24, 2017 14:34
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