I’m machining out some small parts on a 4x6x1/4" brass plate. I decided to go with double sized tape fixed to an MDF board for holding the plate in place. Downside is how much it gunks up the workpiece and endmill as soon as it breaks through the adhesive layer on contour cuts. The tape I used is XFasten Double Sided Woodworking Tape, as I read it’s optimal for thickness and hold. Are there any better options for reducing or eliminating the goo? A different double sided tape perhaps, or would I have better luck with the masking tape and super glue method?
I have used superglue and painters tape for a long time. As long as you let the super glue set I have never had anything come loose. I use TiteBond Medium SG and it has never let me down.
The good thing about painters tape is it does not leave goo behind. I have occasionally had some of the tape/SG get on the bit but I just clean it with CMT blade cleaner and it comes right off.
I use double sided tape when turning and as you said it leave things behind and on something as delicate as a thin piece of brass getting it peeled off the spoilboard could bend the brass. Give the painters tape and super glue a try. I use the regular 3M painters tape in 2" strips. The trick is to get the pieces lined up with no overlap and no gap. I run the pieces on the spoilboard and the piece parallel starting at the front of the piece. I then use an S pattern on the base painters tape and press the workpiece down firmly to seat it. Then wait for it to set. You could use accelerator but that is likely wasteful. Just adjust your work flow to place the work piece first then setup the Shapeoko with setting zeros and checking the CC file for one last time. Then you should be ready to go.
Additionally I use bottom of material for about 90% of my jobs. This keeps the spoilboard from being cut up. The second advantage of using bottom of material I dont get an onion skin at the bottom of projects or large gouges on my spoilboard. Material measure is important for any material you will machine.
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You could whatthe guy from Woodsmith shops that did the cnc bootcamp ( I think it was Chris Fitch)did for machining thin brass. He affixed the brass to a sacrificial piece of mdf with hide glue when the machining was done he just put it a bucket of water that dissolved the hide glue and separated the ppiece
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If possible, I trim the tape away from the contour cuts.
I like the hide glue idea. As long as you have enough sacrificial substrate
If you’re doing enough of them, a fixture could work instead of tape.
Bondo or fixture wax could also be a viable alternative.
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You could also try out a little vacuum fixture if you leave an onion skin. It’s less convenient to trim off the excess but it would also have uses beyond just this project.
Personally though, I’d try the wax or hide glue. Double sided tape has worked well enough for me as well but it can be fiddly to get the contour just right.
I’ll be cutting some small brass parts out of 2mm thick brass in the coming week. I’ll be interested to see what you land on 
I remembered it wrong. It is CNC Basecamp (not bootcamp)
Here is a link to the youtube video, using the hide glue.
CNC Basecamp-EP006 Metal Inlays
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