I’d like to ask the community for some advice on how to cutout thin letters. As I’ve researched the topic, it seems most CNC work is done with thick letters. When I attempted to cutout thin letters, I was met with a string of failures.
Here are the common failure modes
Lignin shears when routing tip of letters.
Lignin shears during handling and cleanup.
Here are issues I noticed that could contribute to failure
Material was slightly bowed with ~5mil gap between table and material. Caused vibration with down cut bit. I’ll fix this in the next iteration, but I’m listing it for full disclosure.
Material was very flimsy and left ripples in cut.
For work holding, I have alignment pins for flipping, and I apply pressure at the edges of the wood. Contours then use tabs to hold the letters in place.
Here’s my current flow (with 8mm poplar)
Cut alignment holes on backside with 1/8 downcut
Flip material over
Pocket out holes and potential loose material with 1/8 downcut
Contour with 1/8 downcut using 3mm stepdown (using tabs in easily removable places)
Cut tabs with dremel and remove fuzzies
There are a few things to try that I already see:
Use plywood to improve strength of material. It’ll be a fixed thickness, but that’s probably okay.
Improve work holding
2a. Double sided tape would help, but it is a pain to clean up. I highly suspect more damage will be done removing the tape than will be prevented.
2b. Vacuum work holding seems the most promising, but I know this is a deep rabbit hole. I am interested in this topic as it would produce a very efficient workflow.
Use a compression bit. It won’t solve the vibrations due to wood rigidity and lateral forces, but it should help eliminate vertical vibrations and help prevent lignin shearing.
For the compression bit, I have concerns about implementation. To create crisp letters, I’m using 1/8" end mills, but the 1/8" compression bit requires 1/4" DOC to down cut the top fibers. I worry I’d likely snap that $60 bit due to lack of rigidity despite having the Pro.
All that being said, I wonder if I’m trying to fit a square peg in a round hole. I suspect most of the thin letter designs I see out there are all cut on laser cutters.
It’s a baby gift for a friend so that’s the aesthetic for which she asked. I think going to a steep V endmill would drastically change that aesthetic. The thickness to width ratio is already very high so using a V endmill would make them look chunky.
Are you taking about thin/thick as in the Z direction? Or thin/thick as in width of the letters? How thin are we talking about? Do you want to keep the letters, or remove the letter and keep the field?
Here’s a picture of the final product that’s been glued back together. It broke in two places, and require significant processing after the fact. I don’t mind doing the work for a one off, but it’s not a reliable process. Thickness doesn’t matter too much, but you see some pretty wicked moment arms that the cutter is pushing against
Unfortunately the wood grain, going in the X direction in your picture, makes your narrow sections in the Y direction very weak.
Some possible suggestions:
I would personally still try double sided tape, but maybe tape your workpiece to card stock, then then hold the cardstock down with clamps / small bits of tape.
If you were just going to glue this onto another panel and that panel fits on your CNC, then you can do this: cut the mirror/reverse of “Sophia” and leave some backing material. Glue that onto your panel, then face off the backing material. This wouldn’t be as much help though if you were gluing this to a door or wall (can still sand through the backing material in that case).
@markg90 , stop trying to do the whole thing at once. Figure out how to cut each letter as an individual piece and “assemble” them at finishing time.
You can use the blue tape and super glue method to hold the raw wood piece and the cut out letter. Since these are fairly delicate, careful removal of the blue tape is necessary.
Having said that, create a vacuum fixture of a size as close to the largest letter. Perhaps standardize the raw wood piece so the vacuum fixture will be standard sized. Vacuum isn’t a “deep rabbit hole”, its just another tool.
I don’t run production, but I cut this out for my wife in a couple attempts using 1\2" baltic birch plywood…
I think I eventually clamped the stock down, left an onion skin, and then ran the board through a drum sander to separate the cutouts from the stock (sand the onion skin away) - worth a try to see if the technique can be duplicated/repeated. Do you know anyone with a drum sander? What did you cut on your Shapeoko/ Nomad today? - #35 by RoughDraft40
I had considered doing a facing operation while mounted to a fixture. I didn’t try this on my first attempt because I wasn’t sure if it’d create more problems than it solved. I really only need to change my order of operations a little to achieve this. I could contour partially into the material, then flip and surface. I think I’ll try to do this next.
I’m not opposed to cutting individual letters, but for script type fonts I don’t think it’s an option. Repairing any damage seems like the same level of effort as assembling them at finish time.
I’m aware of the blue tape method, and just kind of lump it in with double sided tape. I suppose in this instance it would work better as it’s much easier to remove than double sided tape. I’ll give this technique a try as well.
As far as the vacuum fixture, it’s a deep hole in terms of how complex you want to get. I know a lot of people use shop vacuums to pull vacuum through mdf. Would a 1cfm vacuum pump work with this method, or does mdf require more cfm? I’ve been thinking of getting a pump for workholding on more than just the cnc. In particular I’ve been looking at Rockler’s pump.
I think this would be a good solution, but I don’t know at what point I’ll have access to a drum sander. I’ll certainly keep this in mind if an opportunity arises.
