geekhack
geekhack Projects => Making Stuff Together! => Topic started by: Vidhur100 on Mon, 18 May 2020, 16:23:33
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I am currently working on designing a keyboard. I am looking to see how I can get it milled. It is designed for a 3 axis CNC and I need 1-3 boards milled. Any recommendations as to how I can get this done. (I have found a cheap way to get my PCB so all I need a CNC service)
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Is your design optimized for manufacture? (e.g. avoid undercuts, radius your internal corners to the largest you can, avoid very thin walls, avoid tapers in the Z-axis, minimize the number of setups, etc.) Otherwise it's down to finding a machine shop that will do it at the right price.
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Cheap is relative, but it's pretty hard to get into the range of what most consider cheap at those low production numbers. If a good suggestion comes up I'll be happy tbh.
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Is your design optimized for manufacture? (e.g. avoid undercuts, radius your internal corners to the largest you can, avoid very thin walls, avoid tapers in the Z-axis, minimize the number of setups, etc.) Otherwise it's down to finding a machine shop that will do it at the right price.
Hi, is there any documents for these optimizations? (if there are any images accompany these optimizations, that would be very helpful)
I can do some basic modelings but I'm clueless about these optimizations, I'm greatly appreciate if you can give me some pointers.
Thank you!
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There's this guide here, though the writing isn't terribly beginner friendly.
https://www.3dhubs.com/knowledge-base/how-design-parts-cnc-machining/
Anyways, a general guide - a lot of this comes from my experience. The best way to get a feel for this is to do some machining yourself - you'll quickly learn what's easy to make and what's not, and you can learn all of this on a manual mill.
As a general guide, the simpler, and smaller your part, and the less-exotic materials you use, the cheaper your part will be. Parts that are easier to make are cheaper to make.
CNC machining costs come from:
- Material cost
- Labor costts
- Machining time
Material cost is impacted by:
- The cost of your material. Aluminum, and most common plastics (POM, polycarbonate, etc.) are pretty cheap. Brass is somewhat more expensive. Titanium is $$$. Some exotic plastics (e.g. PEEK) are $$$
- The size of your material you're starting off with. In CNC machining everything is machined down from billet blocks of material, and the smaller the billet that your part has to be made from, the lower your material cost. Be aware of commonly available material stock sizes - in the US I generally browse McMaster-Carr to check this. Say you have two case designs - one that's 11.5" long by 5.5" deep, and another that's 12.5" long by 6.5" deep. In the US material generally costs in 6" increments in length and width, so the first one can be made from a 12x6" stock, while the second probably has to start from 18x12" stock since that's the next available size up, so even though the second one is only about 25% larger, you're paying for 3x the material.
Labor cost is impacted by:
- The location of your shop - e.g. Chinese labor rates are generally cheaper than US or German ones, so Chinese shops are often cheaper (though you should account for shipping costs, which may raise prices back up)
- The amount of time it takes to program the CNC and run CAM software to process all the toolpaths, etc. This only has to get done once no matter how many parts you make, which is why CNCed parts are cheaper if you order more than 1 - the cost of programming gets spread out over many parts. Generally, the simpler your part, the less time is spent programming.
- The number of setups - this is the number of times you have to take the part out of the CNC's vise and reposition it (flipping or rotating it, usually) to make your part. The endmill or drill on a 3-axis CNC can only come in from one direction, and if you have say, countersinks or blind holes or other features coming in from multiple directions, then the part has to get taken out of the vise, repositioned, and placed back in. This is done manually, and often requires the machine to get re-zeroed, which adds quite a bit of cost and labor. Try to minimize the number of setups necessary to make your part.
For example, this part (a block with a hole in it) only requires one setup to make - the drill comes in from only one direction, so it's doable on a single setup.
[attachimg=1]
This part (a block with two blind holes coming in from two different directions) requires two separate setups. First, you drill the hole on one side, and then you have to take the part out and flip it so that the CNC machine can drill the other hole.
[attachimg=2]
You might be able to modify your design, and instead of having two blind holes, just have one through hole, which can cut your setup back down to one since you can drill from just one side now and have it drill all the way through.
[attachimg=3]
5-axis CNC machines can often reduce setups (e.g. for the part with two blind-holes above, a 5-axis can do in a single setup because it can rotate the part itself), but time on a 5-axis machine costs a lot more than time on a 3-axis machine. Generally, you should design your part to minimize the number of setups.
Machining time directly affects cost, since it costs time and electricity to run a CNC machine (and the machine shop might have other, more profitable jobs that they could be running instead). Machining time is impacted by:
- How much material has to get removed
- How difficult the material is to machine - some materials (e.g. aluminum, brass, POM) are easy to machine, and you can cut faster and therefore run your machine faster. Other materials (e.g. stainless steel, titanium) are hard to machine, and requires you to cut slowly and carefully with your endmill, and takes a lot longer to machine (harder materials also wear out tools faster and cause more tool breakage, and often require fancier tools like diamond-coated carbide endmills, versus a cheap uncoated steel endmill for machining POM, which again, add to cost)
- As a general rule - you need to radius your internal corners in the X-Y plane, and use the largest radius your design allows for. The larger the radius, the larger diameter endmill can be used to cut, and larger diameter endmills are stronger, less-prone to breaking, and can cut faster, and you run your machine faster.
- Generally, flat planar surfaces machine a lot faster than surfaces with fancy curves in the Z-axis or tapers (other than 45 degrees, and sometimes 60 degrees) in the Z-axis. Otherwise you need to do 3D-profiling with a ball endmill (https://www.youtube.com/watch?v=CIH3Oahi5zA&t=39s) and run that ball-endmill up and down your part many, many times, which is much slower than just running a regular flat endmill to make a flat surface. 45 degree beveled tools are generally available, so 45-degree tapers or chamfers are generally less of an issue.
- If you have deep pockets, very deep holes, or very thin walls, you have to run the machine slower to avoid either breaking the tool or breaking the part you're trying to machine, so avoid those. Stick to the recommended maximum depth-to-width ratios in the guide.
- Number of tool changes - every time you have to switch tools (because your design has a lot of different-sized holes that require different-sized drill bits to make, for example) adds machining time.
Other costs:
- Tooling - if your part has funky geometries that makes it difficult to hold in a standard vise (e.g. your part has no two sides that are parallel), the machine shop has to make specialized tools to hold the part, which will cost you more money. This is another fixed cost.
- Turnaround time - if you need your part quickly it will cost you a lot more money - 2-3 weeks is the standard turnaround time in the US. Going faster often requires paying expediting fees to your machine shop.
- Tolerances - this shouldn't impact keyboards since keyboard cases generally don't need tight tolerances, but if you need very tight tolerances (less than .005" or 0.1mm) you generally have to pay more, as the machines have to be run much more carefully, and there may be more parts that have to be rejected and remade.
- General ease of manufacture - if you have say, very deep holes, or very thin walls (easy to break and result in ruined parts) your parts will cost more, as the machine shop will have to spend more time making the part, or has to make extra parts to compensate for ones that may be broken or out of tolerance.
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Great infos shared here, thank you !
Did you had any experience with 3DHubs for CNC service?
And if yes what are their general CNC and finishes (anodizing, powerder cot, ...) quality ?
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I have not previously used 3DHubs - I've gone through SuNPe for work-related stuff in the past with pretty good results.
I'm a mechanical engineer by day (though currently unemployed) - if anyone wants a manufacturability/optimization review of their case design I'm glad to help out.
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Thank you very much for the information about SuNPe, I will have a look !
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Great infos shared here, thank you !
Did you had any experience with 3DHubs for CNC service?
And if yes what are their general CNC and finishes (anodizing, powerder cot, ...) quality ?
3D hubs is ok for prototypes but they (like Xometry and a bunch of others) are just a middleman for other factories. I would feel comfortable doing a fit and finish test through them but not production runs. You are rolling the dice every time on who's making it.
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I have not previously used 3DHubs - I've gone through SuNPe for work-related stuff in the past with pretty good results.
I'm a mechanical engineer by day (though currently unemployed) - if anyone wants a manufacturability/optimization review of their case design I'm glad to help out.
I have a good album of complaints from my project with SuNPe.
https://imgur.com/a/MQWHw3q
They really mucked up the tolerances needed for my project, anodization was bad, even covered up with paint or marker in some parts, and overall turned a project with flaws into something much worse than it should have been.
I would not wish my experience with SuNPe upon my worst enemies.
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Good to know about their anodization issues - they apparently outsource their anodizing according to their website, but that does look pretty bad.
I've only gotten non-anodized parts through them for work (mostly in aluminum 6061), though we were a sizable customer of theirs (we ordered somewhere around $20,000-$40,000/month of parts through them) so we likely got better QC and customer service to keep our business. Though they had their fair share of minor mistakes (forgetting to tap holes, etc.)
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Wow, the amount of issue you had !
Some of the marks you can see, notably around holes and mx swithes cutouts in your plates, are most probably due to the fixture for the anodization process. These are hard to overcome by anodizers unless they use titanium screws in your threads to fix the board; I heard this is not a very common way to attach objets to anodize, probably because of screws cost and additional labor.
But the dirtiness and uneven anodizing job ...
You can see the fingers of the guy who manipulated the piece...
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By the way, I'm also in the process of selecting a CNC service company for my own keyboard project for 3 units.
I will be happy to share my experience with you guys.
Already finished a keyboard around 1 year ago and used Weerg for the CNC and anodizing job.
The tolerances and quality of CNC job was great, the anodizing job (was silver, difficult to do right) was soso (but far from what Krelbit experienced) and they have limited colors (black or silver).
So for the CNC work I definitely recommend, for the anodizer maybe find another place.
Most of these companies seems to provide anodizing to customer that don't look too hard for cosmetic issues, and mostly for part protection.
Recently had a look at 3DHubs and Xometry US, they unfortunately don't accept orders from individuals, so is Xometry in the US.
But Xometry Europe does and I will probably use their service in the near future ;)
I will keep you posted.
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Is there any other alternatives to Sunpe? outside of USA and europe.
I am from Singapore and CNC prototyping in my country is bloody expensive.
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Is there any other alternatives to Sunpe? outside of USA and europe.
I am from Singapore and CNC prototyping in my country is bloody expensive.
It's bloody expensive every where,might be cheaper for you to pick up a 3 axis desktop cnc off Amazon/Ebay/Aliexpress and use it to teach your self what you need to know to get the design right.
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Also if you have a nearby makerspace they often will have a manual mill if not a full CNC. Great to learn machining on.
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Is there any other alternatives to Sunpe? outside of USA and europe.
I am from Singapore and CNC prototyping in my country is bloody expensive.
There's a lot of Chinese rapid prototyping services (Star Rapid, etc.), though I have only used SuNPe in the past.