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Ask HN: Small-batch builds of smaller phyiscal objects
27 points by huhtenberg 9 months ago | hide | past | favorite | 66 comments
I am prototyping a certain accessory for my BBQ grill. Stainless steel hardware piece, not very complicated, but made out of several parts. Got the CAD drawings and now trying to understand how to fabricate it. Most likely will need to do several revisions to fine-tune things, so there's that too.

I'd guess there's gotta be some services (in China?) that got this need covered. Anyone has any experience with this sort of thing? Any tried and tested companies?

Thanks!




I've done a bunch of builds like that before.

Typically, machine shops specialize in some form of manufacturing type (milling / lathing metal, for example) or specific niche (metal stamping). If your parts require different manufacturing processes, you may potentially need multiple shops to get that done.

I found that Chinese machine shops are going to be both cheaper (about 8x in my experience) and faster lead time than North American shops. The exception will be that if you need something highly specialized (e.g. super tight tolerances), you may find it easier to get it done locally. I'll assume you'll be going with a Chinese place below. For finding Chinese places, I use Alibaba with MOQ set to 1.

Machine shops are always trying to expand and get bigger contracts with bigger customers. They dislike low order quantities and low volumes, and I found that I need to continuously cycle machine shops every couple of years as they move to larger customers. The other thing is that with manufacturing, there's a setup cost (flat cost per batch) plus a per-part cost. At single and low double-digit volumes, setup cost is going to be a lot. Make your part easy to manufacture - easy to clamp, made from readily available stock, use more readily available machining (e.g. 3 axis and not 5 axis, straight lines doable with a manual mill vs CNC), reduce manufacturing steps.

I found that cheaper machine shops (say, 2x cheaper than others) will tend to have a lower ability to understand what I'm trying to get done (will take a lot more & simpler communication) as well as a higher probability of the part being out of spec.

The more proficient you are at knowing what you want (obsessively defined specs and tolerances on everything you can think of) will get you much cheaper results. The less you spec out, the more they need to think about your design and your needs, and that's quite expensive from their side. My process is to have a drawing PDF that I send to 10 manufacturers for quotes, get 5 quotes back and select from those.


Thanks, this is helpful.

Say, if I have a part like [1], what's the best way to get it done? I'm now leaning towards laser cutting the flat bottom (the geometry allows for that) and then welding the top "clutch" after getting it lathed. Is there a better/cleaner/cheaper way to do it? The part should be metal.

[1] https://i.imgur.com/1oqjQ7r.png


Laser / water / plasma / EDM cutting the bottom sounds quite reasonable.

I'm trying to figure out what the application is here. It looks like you want to attach something to a shaft, and trying to use a collet with a set screw. Why not put the set screw in your bottom part? Or perhaps use a shaft key? What kind of forces and what kind of load is this thing taking?

But if I had to answer your direct question: spec some screw holes, welding has downsides for what I think the application is (cost, axis alignment).


The shaft is a part of the existing rotisserie device. The shaft has a square cross-section and it can accept various mountable attachments, e.g. [1] and [2]. They all use collets, so I'm just following their design here.

Force-wise - about a pound of load per "arm", give or take, not much really.

Re: screw holes - noted, thanks.

[1] https://www.amazon.com/GRILLJOB-Stainless-Rotisserie-1-Pair-...

[2] https://www.amazon.com/-/en/25437-R%C3%B6sle-High-Quality-Ba...


In that case, if you make your mounting part a square or rectangular block instead of a cylinder, this way you can avoid the use of a lathe. Or if you spec the outside diameter of your cylinder to be some common size (+/- some loose tolerance), then that would avoid machining the outside (as there's cylindrical metal slock).

I also realized that my original suggestion of "set screw on the bottom part" is also probably hard to manufacture.


Noted. Thanks again.


If you send any sort of marketable product to China, expect that it can and will be duplicated and sold in competition with you.

China sells tons of products they cloned from something pre-existing. I know because I own some of it and I've seen lots of western companies making use of it too. Here are a couple of examples of products from Amazon that existed long before China started producing clones.

https://www.amazon.com/BIG-RED-TAM82012-Hydraulic-Carrying/d...

https://www.amazon.com/BILT-HARD-Vertical-4-Stroke-Compliant...

All that being said, my best advice is to refine your design locally first, before farming out mass prooduction. Lots of local machine shops can fabricate simple custom metal parts --- they exist just for this purpose.


Thanks for the reply and I hear you, but I am not trying to make a commercial product, just something for my own use. It'd be also fairly hard to understand what the thing is for without the context, so I am not worried about it being cloned or the idea stolen. I do care about prototyping it as cheaply as possible. I can also wait.

The cost angle rules out local machine shops as they are (really) expensive. Hence the quest for the online services.


Prototype and cheap are usually mutually exclusive.

In other words, cheap typically means automated mass production.

https://www.onlinemetals.com/en/waterjet-big-blue-saw


If it's just something for your own use, you should tell us in detail what exactly you're trying to do, with pictures, and we'll tell you how to do it cheaply and effectively.

Otherwise you're literally just fucking around with your design software for your own personal fun, with (clearly) zero idea of how physical objects are actually made.


Love you too.


You're looking for a "job shop". There are small machine shops all over the world that can do this for you, but don't expect to get mass production prices... it's going to cost A LOT. You're paying for someone to figure out how to make it, set up any jigs, cut materials, etc.

I suggest you google "machine shop online"


Aye, thanks. Will have a look.


My dad has a small machine shop that specializes in producing single run parts like this. Generally speaking you'd be able to find small shops like this around the country, but machinists aren't great at advertising or having websites so you'd probably have to use something like the Yellow Pages or local business listing to find one.

https://oneoffparts.com/


Generally what does this cost - whats the ballpark?


You'd pay an hourly rate for the machines used, so its going to vary based on the complexity of the part (eg mill time is less than lathe time). I think the average rate for my dad's shop is ~$150/hr.


If it's all sheet metal-esque pieces, where you could suffice with just laser cut features and/or simple bends.. then you should take a look at OSH Cut.

They have a fairly powerful platform -- instant quoting from uploaded design files, 2D/3D views, DFM feedback, good turnaround times, etc -- and the pricing isn't half bad for prototyping... but might not be as good for large-scale runs compared to bigger shops where you can nail down volume pricing discounts.


OSH Cut noted, thanks. Do you know what's their pricing level is like? For a couple of laser-cut steel pieces, about palm-sized each.


I do this sort of thing, but more on the woodworking side of things. I'd look into your local maker spaces. They are filled with one to three person companies doing lots of projects just like this. I'd recommend have prototypes made using a laser cutter and then final parts machined later.

Another option is to just learn to do it your self. Many of the maker spaces will have have classes on metalworking, welding, aluminum cutting, CNCs, laser cutters. I also TA as a 2.5 day weekend workshop on the central coast that will teach you to woodworking and welding.

Let me know if you have any other questions.


I have local maker spaces on the ToDo list. One of them has a sheet metal laser cutter, the rest specialize more in woodworking. Worth a talk regardless, thanks for the nudge.


Sheet metal/waterjet cutting: https://sendcutsend.com/

chineese sheetmetal/cnc milling/3d printing (including metal): https://www.pcbway.com/

But if you can find a local fabricator that is probably best as they can help you understand if you design is manufacturable as is or if there are some simple tweaks that would make it cheaper/easier.


It is practical to iterate in other materials. Cardboard would be the simplest to get started on physical form.

Galvanized steel flashings from Home Depot etc. can be hand formed with tin snips, a hammer, and a block of wood. Or you could buy a cheap brake from Harbor Freight, Amazon, etc. Same with a drill press.

Doing it yourself will speed up development and eliminate most if not all of the need for CAD drawings.

Not to mention it will avoid the mental overhead that your question embodies.

Or not, good luck.


Thanks for the reply. I don't mind the mental overhead. Already learned few things, including laser cutting options and steel varieties :)

I have, basically, the design of the whole thing figured out. I can 3D print it from resin, but that's pointless as it's a load-bearing gadget that needs to withstand high temps. Just need to fabricate it.

Got most of that figured out as well, pretty much all parts can be laser-cut from a sheet metal, then welded together. One bit I don't know is how to make something like this - https://i.imgur.com/RsambTE.png - 15mm long, 7mm in diameter. If you have any ideas, I'm all ears.


Any competent machinist can make that.

So I guess your local machine shop is another option.

Which reminds me that your local welder can build you a custom grill.


My dad was a welder at a machine shop for a long time. Can confirm.

Whether they will is the real question. A lot of shops in my area had some rules around sizes and quantities.


Hmm - could you substitute off-the-shelf gears in your design?

https://uk.rs-online.com/web/p/spur-gears/8787897


Can't, need a slotted hole for the whole thing to work.


There are companies that will 3d print that in sintered metal for not obscene prices. Consider the replacement cost of the BBQ against some custom pieces you design and have manufactured.


Wire EDM? But tbh I'd consider rethinking your design, as custom gears are generally a bad idea for several reasons and there are typically better alternatives.


EDM would be quite expensive, wouldn't it? The issue is that I need a slotted hole in the gear, so no stock gears work.


Probably don't want to use galvanized steel on anything you'll be heating in a BBQ.


Noted.


Galvanized steel will release toxic zinc vapors starting around 400F. You hear this a lot when it comes to welding, but cooking with galvanized is bad as well.


https://www.emachineshop.com/

It’s been a bit over a decade but I used this to make small runs of metal parts for a store I worked at. Their basic CAD is good for simply parts and you can easily adjust settings to find the price vs material/finish goals you’re after.


where are you located. i both do this kind of work and know a fair number of small fabrication shops in the bay area.

all you need to do is look for 'machinist' or 'tool and die' or 'metal fabricator' and make sure its a place that takes on small random work and not some high margin specialized manufacturer. probably call them and get used to rude dismissmals.

show up and shop and ask for the guy in charge. for this kind of work its often done under the table, so offer to pay cash. its very likely that the floor manager or a senior fabricator is going to do this in their spare time and not even put it on the books.

you're gonna pay too much. probably a couple to a few hundred depending on complexity.

you also sometimes ask a metal supplier. they have relationships with these kind of people. they often aren't that friendly though


Plenty of comments already cover a lot of this. I'll throw my two recommendations here as well:

- OSHCut for sheet metal cutting and bending.

- 3DHubs (very very recently became Protolabs Network) for aluminum machined parts.

In general, the task you're now on could be considered "design for manufacture" - you have the basic concept, but now need to figure out how to go from general design to manufactured product.

Design for manufacture includes keeping in mind the process/technology that will be used to produce the part: - you can do some amazing things with laser cut and bent metal, but you're limited to a single thickness per component; - lathes are extremely precise and great for making round/concentric items, but the part is limited to rotational symmetry (barring fancy machines and/or moving the part to a mill for further work); - mills are great for all sorts of things but really shine in "2.5d" work - where you have different profiles milled down to different depths, but from a single direction. Mills also can't handle overhangs (without a 5-axis, multiple setups or very special tooling) or features in different directions without multiple setups (which add time/complexity/cost/risk of misalignment of features).

For one-off or small run products, you can get away with being very inefficient in the process - starting with a piece of stock and milling 90% of it away for instance.

For the one part I saw you post a picture of, that could be done through either SLS or similar metal 3D printing (as someone else said), or one of the "official" ways to make a gear is to cut it with a custom single tooth cutter - where you run a special cutter along the length of the gear, rotate the gear one tooth, and repeat, cutting away the space between the teeth each time. Clickspring on Youtube has a bunch of videos covering the topic. I don't know who could do that as a service though.

If you post more pictures / sketches of the project, people here might be able to give better guidance for specific parts and operations.


Thanks, this is very helpful. You are correct that I'm in the "design for manufacture" phase... and it's somewhat overwhelming.

With regards to the specifics, here's one of the parts - https://i.imgur.com/1oqjQ7r.png - basically a flat (bottom) piece that can be laser-cut and a cylindrical clutch-like bit with a cutout for a "flat-leaf" bolt. The idea is to pass a rotating axis through the central hole and to affix the part to it to have it rotate with the axis. Needs to be all metal as it's a high-temp (BBQ) setup.


Still not sure the general layout of this - is the end goal to have some form of rotisserie that has multiple rods, each of which rotates about their own axis in addition to the primary axis, so that the food is cooked more evenly? If so, be careful about your gear ratios - you don't want the rotations to match up every time, otherwise you won't actually gain anything from the secondary rotation axis (the same side of the food will be rotated down closest to the flame on every rotation). I'd have to do the math / play with it, but off the top of my head I'm thinking as long as the gears aren't the exact same number of teeth you'd had full secondary rotation after [larger number of teeth] rotations.

That being said - to make that part, if concentricity isn't _critical_, you could easily split that into two sections. As you said, the bottom flat section would be laser cut (/water jet) out of sheet material; you could add some mounting holes around the central axis, then threaded holes in the rod mounting boss (or through holes for very long bolts and nuts, but that's better for prototyping with limited tapping/etc. capabilities).


> Is the end goal to have some form of rotisserie that has multiple rods, each of which rotates about their own axis in addition to the primary axis, so that the food is cooked more evenly?

That's exactly it. Well-deduced. Secondary rods are just skewers.

> If so, be careful about your gear ratios.

Yep, got that covered. The gear ratio is 16/11.


In that case, you might want to look at a mechanism called a "planetary gear set" for inspiration - I don't know if it's common for the rotation of the "planet" gears to be harnessed to drive something other than a synchronized output shaft, but it's still the same basic mechanism.


Planetary gears need a stator. It can be done, i.e. have the gear box attach to the side of the barbeque, but that'd be way more expensive to fabricate and it will be BBQ-specific. Here however - one inner gear, one spur gear and a rotating shaft and that's it. Stupid simple and it works.


And one final message for now...

First, once you get several projects under your belt, you should start integrating "design for manufacture" into your main design process - that way you don't waste time designing some custom part, then searching for that specific item / someone to make it, when with some minor adjustments and off the shelf part would be _significantly_ cheaper and readily available.

Second, for designing with available parts, I love McMaster-Carr - they have great specs and drawings for just about everything, and 3D models you can import into most CAD software for most parts as well. They are more expensive than other sources for most individual parts, but the confidence you have with ordering from them is great, and for one-offs and prototyping they're invaluable.


> ...or one of the "official" ways to make a gear is to cut it with a custom single tooth cutter ... I don't know who could do that as a service though.

Any local machine shop?

I remember watching a video a while ago where they were talking about how it's better/cheaper/easier to buy a part out of a catalog than custom machine whatever you are needing because chances are really, really high you don't actually need a custom part. IIRC they were talking about bearings but I'd imagine gears would be the same.


Ah, caught one of my unspoken assumptions when talking about suppliers - I try to avoid operations that are very custom / very different from their normal operations.

In this case, yes, any local machine shop could theoretically get or make the gear cutters, get a piece of the stock the correct diameter (/turn down from larger), mount it in a mill with the stock in a rotary fixture of some sort, then cut the teeth. Again, Clickspring has a bunch of videos on the process, including different ways to make the cutter. All that being said, you'd have to be on very good terms with your local machine shop folks, or be willing to pay for all of that new tooling and setup stuff, to get any random shop to make the part.

Going with someone like SDPSI might be better for this specific part, as it's in the realm of what they do.

Could also look at starting with "timing pulley stock" - it's basically the part that was shown elsewhere, but without the internal keyway cut. https://www.torontogear.com/bar-stock/ - starting with _that_ - yes, any local machine shop should be able to cut it to length, mount it in a mill and mill out the slot (with a small enough endmill).

One more recommendation here, based on what Uncle said about buying stock - and this is a part of design for manufacture in general - is to design around standard parts. Look at SDPSI/Toronto Gear for common gear specs (IIRC "module" is the main property defining a gear and how they will mesh with other gears - so stick with one module size), pick one and change your design to use those off the shelf parts.


Last year, I backed a really interesting project on Kickstarter called Powercore. The simplest idea is that you take a cheap 3D printer (like a refurbished Ender 3), swap out the print head module for an EDM module that can disintegrate metal the way a CNC machine mills wood.

https://www.rackrobo.io/

They appear to be between versions right now, but to their credit, they are the only KS project I've ever backed that has shipped a high quality product on time and on budget. I anticipate big things from this team.


If you're near a university, check if they have a machine shop that accepts external jobs. They're used to one-off manufacturing for student projects or research lab tooling.


I used to use SunPe: https://sunpe.com

They were relatively cheap and fast (I haven’t done any prototyping in five years though)


Were they OK with (very) small batches back when you used them?


Yep I last used them for a single unit prototype made up of 20 unique CNCed aluminum parts.


There's a Youtube channel I watch, a machining/welding shop in Australia that makes and repairs parts for construction equipment. What amazes me is the work he gets because fabricating a new part, or substantially replacing much of an old worn part, can be like 1/2 the OEM price of a replacement part.

https://www.youtube.com/@CuttingEdgeEngineering


We've used SunPe before.

https://www.sunpe.com/

They have about a 10% full-rejection rate; so order at least 10% more than you need

Also sometimes they just mess up and get the part out of spec. Then just complain and they'll make it right

After getting more funding we switched to US based rapid proto shops that charge 3-4x, but have a better experience.

(DISCLAIMER: I only spoke to the ME guys talking about SunPe. I never used them myself)


Clough42 (YouTube machining mainly, plus CAD, 3D printing, electronics) recently said he hasn't really used sheet metal tools since discovering sendcutsend.com (I haven't used them, don't think he has any affiliation/sponsorship either).

For machined/moulded parts there's shapeways.com (I haven't used them beyond quoting).

I'm sure there's plenty of alternatives for both too, if you search 'x vs' or whatever.


A cheaper alternative to SendCutSend is Fabworks: https://www.fabworks.com/

They do stainless from .048" to .120" thick: https://www.fabworks.com/resources/materials/stainless-steel


Hadn't heard of Fabworks until today. Testing out a quote on some parts I was looking at getting from OSH Cut, they're actually much better on pricing _and_ have more capabilities. (!)

Have you used them a lot? Curious what your experience with them is if you're willing to share.


I’ve not personally used them, but the company was founded and is ran by the mentors of a high school robotics team. I volunteer with the program, so I’m familiar with the team.

I have made several quotes for different personal projects, but those projects have all been tabled for the moment.

Here’s the announcement post on the main social forum for the robotics program: https://www.chiefdelphi.com/t/introducing-fabworks-fast-affo...


You can try Ponoko or Shapeways - both are online services for prototyping / 3d printing

https://www.ponoko.com/ https://www.shapeways.com/


There's good advice in this thread but also you can call around to small product design/mechanical engineering shops and find out who they use for prototyping.

Otherwise yeah find a local machinist and if you're only doing a single one-off it shouldn't be too spendy.


Shapeways metal prining? Can do steel. Kinda expensive but also not when you think about it.

https://www.shapeways.com/business/metal-3d-printing


https://www.protolabs.com/ does this all day every day, but your iterations for fine-tuning you should probably try to do by finding a local 3d printer.


https://www.pcbway.com/rapid-prototyping/manufacture/


Does the initial prototype have to be made of metal? Can you work out the initial kinks with something 3D printed before moving to a expensive and laborious material?


I did that exactly. Got it done in resin. Worked on the first iteration oddly enough :)


Find a local machine shop or two and ask them to machine them.

An expensive machining job that finds problems early will save lots of money.


Where I live in Canada here it's like a mini-china when it comes to shops and manufacturing. You can speak to someone that speaks English and won't steal your product. As well as USD is worth more than CAD, you will get a decent deal. I know of one shop that does custom fabrication that I've done IT work for: https://www.acmetalfabricating.com/


Xometry will fabricate pretty much anything from anything and it's easy to use - but not cheap.


Sent them a quote request this morning, it'd be interesting to see what they say.




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