Thoughts about the Othermill?
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ajfisher
May 6, 2013, 8:05:46 PM5/6/13
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Hi all,
I've been thinking about building (/buying) a really small CNC mill over the last few months and then this popped up in my twitters yesterday:
"The Othermill is a portable, computer controlled, 3-axis mill that is specifically designed for use at home or in a small workspace. Our objective is to build a mill that is compact, clean, and quiet enough for use at home, yet is precise enough for high level electrical and mechanical prototyping work. The Othermill will be at home on your desk, in your workshop, or on your kitchen table."
The project is kind of interesting and the size is more or less what I was after (really to mill small custom prototype components, PCB etc so doesn't need to be massive).
Not ever having purchased or bought a mill before I thought I'd get a view on what people think about their approach, possible gotchas etc?
Cheers
Andrew
James Denier
May 6, 2013, 8:17:53 PM5/6/13
to connected-commu...@googlegroups.com
I was looking at this one just this morning.
To my completely inexperienced eye it looks great but I wonder about the price point. Seems a bit on the costly side.
Still, custom shaped, custom etched PCBs would be awesome.
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John Spencer
May 6, 2013, 9:53:57 PM5/6/13
to connected-commu...@googlegroups.com, James Denier
This is an interesting little machine, and I've actually already gone
through and ordered a tinyg controller to have a look at.
My main question is the price point. For that kind of money you can get
an chinese 3040 router.
Of course, I've never seen them side-by-side, so comparisons are difficult.
John
On 7/05/2013 10:17 AM, James Denier wrote:
>
> I was looking at this one just this morning.
>
> To my completely inexperienced eye it looks great but I wonder about
> the price point. Seems a bit on the costly side.
>
> Still, custom shaped, custom etched PCBs would be awesome.
>
> On 07/05/2013 10:05 AM, "ajfisher" <ajfis...@gmail.com
> <mailto:connected-community-hackerspace%2Bunsu...@googlegroups.com>.
> <mailto:connected-commu...@googlegroups.com>.
through and ordered a tinyg controller to have a look at.
My main question is the price point. For that kind of money you can get
an chinese 3040 router.
Of course, I've never seen them side-by-side, so comparisons are difficult.
John
On 7/05/2013 10:17 AM, James Denier wrote:
>
> I was looking at this one just this morning.
>
> To my completely inexperienced eye it looks great but I wonder about
> the price point. Seems a bit on the costly side.
>
> Still, custom shaped, custom etched PCBs would be awesome.
>
> On 07/05/2013 10:05 AM, "ajfisher" <ajfis...@gmail.com
> <mailto:connected-commu...@googlegroups.com>.
Clifford Heath
May 6, 2013, 10:00:41 PM5/6/13
to connected-commu...@googlegroups.com
Nowhere in the Kickstarter page does it mention rigidity of the frame.
Frame rigidity is the primary factor that determines the quality of the cut.
Milling machines produce & require huge forces with minimum displacements.
This rectangular frame will have a large number of largely undamped
oscillation modes across a wide range of frequencies. Use of anything
other than tiny cutter diameters and/or slow cutting speeds will produce
forces that are easily sufficient to excite these modes, and that will cause
the cutter to judder and cut circles like a Spirograph.
Based on the authors not mentioning this possibility, I'd have to assume
they're rank amateurs and the results will show that.
Clifford Heath.
Frame rigidity is the primary factor that determines the quality of the cut.
Milling machines produce & require huge forces with minimum displacements.
This rectangular frame will have a large number of largely undamped
oscillation modes across a wide range of frequencies. Use of anything
other than tiny cutter diameters and/or slow cutting speeds will produce
forces that are easily sufficient to excite these modes, and that will cause
the cutter to judder and cut circles like a Spirograph.
Based on the authors not mentioning this possibility, I'd have to assume
they're rank amateurs and the results will show that.
Clifford Heath.
Luke Weston
May 7, 2013, 1:36:37 AM5/7/13
to connected-commu...@googlegroups.com
It looks like they're trying to copy the "box" design of some MakerBot products, which is notoriously noisy.
And OtherCAM ONLY runs on OSX !? A user-friendly toolchain, preferably open source, or at the very least low-cost and compatible with all major OS families, will be the dealbreaker here I think.
You really want to be able to take DXF files, and/or allow the user to CAD up their own DXF files, and send them to the machine with minimal stuffing around and a relatively low barrier to entry.
They've kind of partially got the right idea... and then they're like, oh, we'll make it only run on OSX.
And for milling PCBs, I'd really prefer something that can parse industry-standard gerbers. Deciding that the user is locked in to one particular CAD software choice such as Eagle is not the ideal way to go.
"Still, custom shaped, custom etched PCBs would be awesome."
Personally, I'd rather just send the Gerbers off to a professional board photolithography contractor and wait a couple of weeks.
They claim the design rule limits for this machine are 10 thou / 10 thou (trace/space), which is substantially coarser than the industry-standard design rules (Usually something like 6/6 nowadays for cheap 2-layer boards) that you just assume that every board fab everywhere can make, even the really cheap ones.
The trouble with PCB CNC machines is that in almost all cases you can't take existing gerber files for a design and send them to the mill, because the design assumptions and design rules you're used to are just not manufacturable. For example, you're limited to 10 thou trace/space, you need quite large vias, you can't put vias under the components, you need to bring the via out to a relatively large pad out in the open and drill it and solder a bit of wire through it. And putting the components on the board and using the board can be substantially harder with no soldermask and no silkscreen.
Something like a TQFP chip with 0.5mm pin pitch has a gap between the adjacent pins of about 10-12 thou. (Depends on the manufacturer's specified tolerance for the pin width.) So, if the machine ends up not delivering the claimed 10/10 capability, even if it slips above that a little bit, then designing a board that accepts something like an ATmega2560, for example, and milling it on the machine is just impossible, it will struggle to deliver those pads in a usable way.
So you end up having to design the board twice - design the board once for CNC milling, if it is even practical to get the results you want at all, and then you have to go back and design the board again to get the final result you want with a more compact board, which is the version you're sending to the factory.
And OtherCAM ONLY runs on OSX !? A user-friendly toolchain, preferably open source, or at the very least low-cost and compatible with all major OS families, will be the dealbreaker here I think.
You really want to be able to take DXF files, and/or allow the user to CAD up their own DXF files, and send them to the machine with minimal stuffing around and a relatively low barrier to entry.
They've kind of partially got the right idea... and then they're like, oh, we'll make it only run on OSX.
And for milling PCBs, I'd really prefer something that can parse industry-standard gerbers. Deciding that the user is locked in to one particular CAD software choice such as Eagle is not the ideal way to go.
"Still, custom shaped, custom etched PCBs would be awesome."
Personally, I'd rather just send the Gerbers off to a professional board photolithography contractor and wait a couple of weeks.
They claim the design rule limits for this machine are 10 thou / 10 thou (trace/space), which is substantially coarser than the industry-standard design rules (Usually something like 6/6 nowadays for cheap 2-layer boards) that you just assume that every board fab everywhere can make, even the really cheap ones.
The trouble with PCB CNC machines is that in almost all cases you can't take existing gerber files for a design and send them to the mill, because the design assumptions and design rules you're used to are just not manufacturable. For example, you're limited to 10 thou trace/space, you need quite large vias, you can't put vias under the components, you need to bring the via out to a relatively large pad out in the open and drill it and solder a bit of wire through it. And putting the components on the board and using the board can be substantially harder with no soldermask and no silkscreen.
Something like a TQFP chip with 0.5mm pin pitch has a gap between the adjacent pins of about 10-12 thou. (Depends on the manufacturer's specified tolerance for the pin width.) So, if the machine ends up not delivering the claimed 10/10 capability, even if it slips above that a little bit, then designing a board that accepts something like an ATmega2560, for example, and milling it on the machine is just impossible, it will struggle to deliver those pads in a usable way.
So you end up having to design the board twice - design the board once for CNC milling, if it is even practical to get the results you want at all, and then you have to go back and design the board again to get the final result you want with a more compact board, which is the version you're sending to the factory.
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