Supported slots for OSH Park? How to create a slot/gap?

I just need to create a spark gap/hole/slot. It is not round. It is a meandering shape. See lime green line.
OSH Park says that they support KiCad slots, but I can’t find directions on how to create it. I tried creating it using the edge cut function. It closes fine, but the OSH Park rendering still shows it filled in on the board. I can find hints that it needs to be in the drill file, but, again, no direct instructions on how to do that. Another hint was that some slots could be found in the mounting holes library. I did not see what I thought was the correct item.

Thanks for your help!

Hmm, I did a search and OSH Park Docs ~ Submitting Orders ~ Slots says:

These slots are represented on your Drill file, rather than an outline.

So that’s from the OSH’s mouth; not like the Chinese fabs who usually use edge cuts.

I too would ike to know how it’s done only out of busy curiosity as they are too expensive for me due to shipping. Maybe a more caffeinated forumer knows.

Following retiredfelines link to Oshpark, they say the slot use G85 for creating slots. And there are several links on this forum connecting G85 with Oshpark.

Apparently Oshpark / KiCad assumes this feature is mostly used for pads with oval holes, and pads are inside footprints in KiCad. Also note that Ospark has some extra rules concerning slots:

For now, supported slots must meet the following criteria

  • Defined fully within your board area
  • Must not cut through another slot or drill hit
  • Non-plated slots must not cut through copper
  • Plated slots must have a valid annular ring, as well as have copper beneath the entire slot.

Or you just use their:

Legacy Slot Callouts

Slots generated on the Board Outline using the older documentation have not changed, and will work exactly as they have previously. The support status of these features is as follows:

  • Non-Plated slots with a width of 0.1” defined on the Board Outline were previously supported, and remain supported.

Thanks for your help. As for expensive shipping, I take it that you are speaking of the Asian manufacturers, as OSH Park’s flat $5/square inch rate includes free shipping anywhere in the world… Unless their international shipping policy has changed. For me, OSH Park is often the better deal - I am in the USA.

Free actually means it’s factored into the price. For a full 100x100 mm board that would be just under 16 sq in. → $80.

Thanks for the G85 tip, Paul. I will check out the links.

Well, I think I could sort out how to build a footprint for the slot, using the pad tools, but it does seem a bit convoluted.

So, how does one select this option. It is not happening automatically, as you can see that the slot is still included in the OSH Park rendering.
Great stuff, folks. Thanks.

Yes, that is true. A single Asian 100mm board usually ends up being about $28 dollars, total, for me. So, I can get say 6 inches, from OSP Park, for that amount. I have had little sleep, so I may not be calculating that correctly. Interestingly, delivery time is about the same, for standard/cheapest/DHL shipping.

The information in the links is what I found before. I looked through it, again. However, I am not seeing what I think are specific directions on using either the drill layer method, or the legacy function. I will send OSH Park a note.

Here’s what G85 does: Support excellon slot command G85 · Issue #3 · mcous/gerber-parser · GitHub Essentially drill a row of round holes with diameter = width of slot, then repeat with different spacing until a smooth side is obtained.

How to specify this in KiCad I have no idea.

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I found instruction that seem to work… The single line method…

  1. Draw a line on the edge cut layer down the center of the line that you wish to be your slot. The line may meander, as you like.
  2. Edit the width of this line to be the width that you desire for your slot.

That’s all there is to it. The slot will now appear in the OSH Park order review renderings.
I do not know, if this is the most current means of creating a slot at OSH Park with KiCad, but it does seem to be working.

Thanks to everyone, for your help and pointing me to this method.


Yep, that is a good way.
Sometimes I add a specific feature on a specific layer, and provide instructions for that layer on at least two other layers that I know they will see and read.
That is how I do 2mm wide tab routes for tooling strips. I put tab route on MECH6 as 2mm wide lines, and then write on top overlay, board outline and top layer “TAB ROUTE MECH6”

And, yes, G85 also useful
In Altium there is this dialog in the NC Drill Setup
But G85 here will only apply to elongated (slot) pads / holes

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