Failing to cut through / tabs - idea for "saving" the project?

So I’ve been experimenting heavily on a little project that involves multiple tool changes, etc. I’m facing a thicker piece down to the 7mm target for the item I want to cut out. Between variance in my material, possible unevenness in the board between my piece and the waste board (I’m not ready to mar up the pretty waste board I paid so much to have shipped :slight_smile: ) and my own possibly lousy measuring, I keep hosing the final cut. We’re talking fractions of a millimeter here between clean and screwed, of course, so I might have all kinds of calibration issues I’ve not yet perfected.

I’m either off a hair too much and cutting the object loose before the tabs can be formed (and it can be flung out if I don’t stop things fast enough), or I’m conservative and end up with tabs on top of a ragged or paper-thin final layer. I’d rather end on the conservative side, of course, if there is hope for rescue.

So it dawned on me tonight a way I could possibly deal with this. Does this sound reasonable or insane?

If I end with tabs but an incomplete full cut, my thought was to go back into Fusion 360 CAM, declare the stock maybe 0.5 mm thicker, increase my tab thickness for safety and, without resetting the zero point in Chilipepper, simply post-process just that job and run it. My theory is it will retrace accurately, hop high over the existing tabs and cut deeper into the waste board to release the death grip on my piece. It will involve sitting through some air cutting before the final layer, but so be it. I guess I could adjust depths to make it a single or other tweaks… but I’d take slower over messing up the work yet again.

Crazy? Good idea? Or is there an easier way short of getting it all 100% precise the first time? I still need to hunt down the main source of my initial mistake… but this almost seems like a safety approach, albeit more work.


  • Aaron

That ought to work as long as you haven’t touched your machine, and can use its 0 point as a reference for the new file.

Another option is to face down a piece of, say, 1/4" MDF that’s bigger than your stock, so that you’re starting point is flush.

I don’t know the specifics of your project, but have you considered using carpet tape to hold the material to the wasteboard? This way you can definitely set the depth “a little too deep” and not have to worry about the piece being flung out. If you use a faced intermediate wasteboard as I mentioned above, you should be able to pull this off pretty easily.


Thanks for the reply. Yes, this is predicated on immediately performing this without moving the machine and letting the 0,0 location I set at my starting corner remain valid. I can even do a tool change if needed and use my touch plate again, I suspect, as long as the x and y remain associated with the start of the overall job.

I actually started to do this before I wrote about, but I hadn’t done a tool change and I sent the updated re-run I describe configured to use the smaller end mill I had in the spindle. The problem I spotted was the smaller end mill was shorter and the collet was going to hit the higher part of the stock outside of the pocket before it could complete the re-run. I ended up stopping it and decided I’d need to make the tool change next time back to the original wider end mill that did the original contour cut in the second to last step. Again, I’ve got my touch plate for reasonable accuracy on setting the z axis here.

I wish I could figure a way to stop chilipepper while retaining the 0,0 point. If a ton of gcode is in the pipe, I seem to be able to stop it, but not flush it without a Ctrl-x that also screws my machine’s sense of 0,0. Would seem you could rescue yourself from a lot of issues if you could start over with the origin accurate.

Could you elaborate on the MDF idea? I’m not sure completely followed what you were describing in relation to this situation. Sounds intriguing. And I’ve read about carpet tape but have been meaning to ask if it has to be isolated under the object being cut out, or if I can use it across the whole work piece and just cut through it cleanly during the process. I picture it gumming up, pulling or otherwise screwing with the end mill and causing havoc if it can’t cut it like butter.


  • aaron

maybe i don’t fully understand your question, but i think you’re being too cautious

I ALWAYS set stock thickness 1mm thicker than it really is, so I always cut clean through, despite small variances. That is what a wasteboard is for!
Secondly, make your tabs about 75% of total material thickness. This way you always have a clean reference edge topside, and your object should never come loose before tabs can be cut.

Afterwards, sand down the tabs with a dremel or belt sander

easy peasy lemon squeezy

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I suspect you are right about my caution. Being the geek that I am, I think I tend toward trying to reach high tolerances and precision rather than, as you described, just giving myself plenty of margin and letting it make good use of the waste board. I have an unreasonable sense of that being “cheating” and need to remind myself this isn’t a $50k milling machine and highly precise source material. :slight_smile:

Good advice I will follow.

  • Aaron

funny how so unbelievably many people don’t want to damage their wasteboard. It’s a WASTEboard. :joy: Ok, except if yours is aluminium or so…
Note that I don’t consider the standard MDF bottompiece the wasteboard. In fact I screw a thin MDF board on top of that which I consider my wasteboard. I make sure it is not larger than the actual cutting area. This way you can plane it whenever you need to, and replace it when it’s really unrecoverable.

btw cheating isn’t cheating when it gives you better results imo, then I just call it doing yourself a favor. :slight_smile:

I have scrap pieces of thin plywood that I always stick under my pieces. They are easy to replace and with several different widths it’s easy to have the right size. Maybe not as easy as screwing down to MDF but I don’t loose any z travel and I don’t have to mill them down when they wear out, and I would wear them out quickly.

Another great way to cut tabs is a scroll saw. I know it’s another piece of equipment but I use mine all the time. I got lucky too, though, only paid $50 for it on Craigslist. It’s an old Delta so it’s way better than units that cost a couple hundred bucks right now. I know because I tried replacing it about 1 1/2 yrs ago with a Porter Cable and that thing was joke and I took it back while the old Delta just keeps going.

The MDF Idea I mentioned, which has been echoed a couple of times by others, is simply to use another sheet of MDF on top of your wasteboard as a sort of “wasteboard wasteboard.” This way you can use a facing bit (really just a 3/4" or 1" slot cutting router bit) to keep that second board flat relative to the machine’s travel.

While in philosophy I agree with @anon68752607 that the wasteboard is there to be wasted, The Inventables one with pre-drilled holes cut to the right size for the machine is very expensive to buy and ship, so replacing it is a last resort. That said, it took me almost a year of use to get to the point where I’m thinking of replacing mine. I just took a facing bit to it which ought to give me a few more months of use out of it, but it will need to be replaced at some point.

Regarding the carpet tape:
I’ve done a lot of experimenting with tapes and adhesives. I really didn’t like using tabs on my shapes, because for a long time we couldn’t adjust them (now we can though and I may have to revisit my mentality) and it would invariably place tabs in the most awkward places.
I started using carpet tape because it’s the strongest, flattest tape that’s easily accessible and easy to work with.
I’ve also used standard permanent double sided scotch tape and that works ok too, depending on the mass of what you’re cutting out.
It’s true that either way you’ll get some residue when the bit cuts through the tape. I have to clean my bit with goo-gone or WD40 whenever I cut through some tape. And, the adhesive bonds with the sawdust to make a bit of a mess on the part you’re cutting out. But it’s only dust, and the closer you come to that onion-skin “just-barely-cut-through” bottom layer, the less of that you’ll see.
For placement, Again it depends on your part and the wood you’re using. Thicker, denser woods require more tape, while less dense woods like pine, balsa or basswood hardly need any. But you do want to make sure that there’s tape under the part you’re cutting. Especially in skinny or delicate areas that stick out from the body of the part. A best practice is to just cover the whole bottom of the material in tape.
Then, I just use a drywall joint knife to wedge between the part and the wasteboard to pry the part free.

The MDF Idea I mentioned, which has been echoed a couple of times by others, is simply to use another sheet of MDF on top of your wasteboard as a sort of “wasteboard wasteboard.” This way you can use a facing bit (really just a 3/4" or 1" slot cutting router bit) to keep that second board flat relative to the machine’s travel.

Oh, yes. Sorry. I am doing that extensively. I’ve used other MDF as well as some birch ply I had. In fact, I created a job in Fusion 360 that drilled all the holes to match the underlying Inventables waste board holes so I can screw my clamps right through. Works well.

But you do want to make sure that there’s tape under the part you’re cutting.

Definitely recognize it needs to be under the shape that is about to be cut free. My question, rather, was whether it can be under vastly more than that section so when the cutter goes through to the waste board it cuts through tape as well. I’d like to just liberally tape down the item, then cut a shape out through the wood AND the underlying tape without risk of the tape wrapping/binding or otherwise jerking the cut piece off the board via the end mill.

That make more sense?

Thanks for all of your great info!

  • Aaron

I’ve cut through carpet tape with no problems of it wrapping or pulling into the bit, however like I said the adhesive does create a paste of the sawdust.

I’ve recently learned of a new method of taping I’m keen to try, which is to use masking tape on both waste board and work material, and superglue the tape together. That way when you go to remove it you only have the adhesive from the tape to deal with. And because it’s paper tape it shouldn’t gum up the sawdust as much. I heard of this from a luthier who uses it to route guitar neck and body templates, so I imagine it would work perfectly for our needs also.