Howdy everyone, I have a brass cover plate for taps in a shower install. The rough-in of the valves was not placed properly and as such I need to make the holes in this plate larger.
I have included a front and back photo. The plate is 1/8" thick.
How would you suggest I set up for cutting the holes to 1 1/2" each?
I was thinking I might try to remove the back raised covers first. They look spot welded to the plate. A plumbing torch should take them off.
I have been using my 5 pro for lots of wood projects, but have not attempted brass yet.
What size and style of end mill, feed, and step rates would you suggest?
I only get one chance at this. Will run a test cut in wood first.
Thank you in advance for your suggestions and help.
The exact type of brass is incredibly important in my brass milling experience. Some will cut like garbage regardless of your tooling and cutting recipe.
If you are just increasing the hole diameter I would honestly recommend going out and grabbing a nice hole saw. It’ll be much more controllable and I’d guess the chance of success would be much higher.
I needed to move forward on this so I asked Claude. This is what I was given as a response:
The Setup
Fixturing is the most critical part with brass. The plate needs to be rock solid — any movement will ruin the cut and potentially grab. Options:
Double-sided tape + clamps — carpet tape on the bottom, with edge clamps as insurance. The tape alone is often enough for a thin plate if the surface is clean and flat.
Sacrificial MDF spoilboard — screw or tape the brass plate to a piece of MDF that you then clamp to the wasteboard. This protects the wasteboard and gives you a stable flat reference.
Avoid putting clamps anywhere near the tool path obviously.
Zeroing — you’ll need to find the centre of each existing hole precisely. A few approaches:
Use a pointy V-bit or a centre-finding probe to locate the hole centre visually/mechanically before switching to your milling bit
Or measure the hole positions carefully from a reference edge and set your WCS accordingly
Tooling
For brass on the Shapeoko, you want single-flute or 2-flute uncoated carbide — not the 3-flute bits you’d use for wood. Brass grabs with too many flutes.
1/8" or 3/16" flat end mill, 2-flute, uncoated carbide — good control on a circle this size
At 1/8" thick you’re looking at roughly 8–12 passes to get through. Go shallow — brass work-hardens if you dwell or push too hard.
Use cutting fluid — even WD-40 works, or a dedicated cutting oil. Apply between passes. This is important — dry cutting brass will dull your bit fast and risk grabbing.
CAM Setup
In Carbide Create or whatever you’re using:
Draw a 1.500" circle centred exactly on your existing hole position
Set it as a pocket or contour (inside) operation — contour is cleaner for a through-hole
Use climb milling direction if your CAM supports it — reduces chatter on brass
Add a small finishing pass (0.005" radial stock to leave, then a final full-depth pass) for a clean edge
Wood Test Notes
When you do the wood test, verify:
The circle comes out true (measure with calipers)
The centre is where you expect it
Your fixturing holds perfectly
Then transfer directly to brass with the slower feeds above. You’ve got this — the Shapeoko Pro handles brass well when you respect the feeds.
