Hello! It’s been awhile since I’ve asked for help here, as I have had a great experience overall with my CNC. I usually stick to hardwoods, but have recently needed to use 1/4" for some projects and the only stuff I could find thin enough was various types of plywood.
I bought some maple ply from Lowes and it’s proven to be awful. It chips and breaks with almost every project I try and cut. I’m using a v-bit and cutting fairly shallow lettering and designs, with oramask… but it’s just not working well. Any suggestions? Is there a big difference in quality, say if I buy from the local vendor I get quality hardwoods from vs a home improvement store?
Hello jmiller, getting straight to your question…YES…buy from your local vendor! I brought many project panels from Home Depot, I have came up short with some crappy 1/4" panels that did not CNC well! The only one that did not chip or break away was the baltic birch panel. The $23 price tag for a 2’x4’ panel adds up quick though. My local hardwood vendor here in Texas has 5’x5’ baltic birch panels for $33 (1/8") and $37 (1/4"). I have them cut them in half, which makes each 5’x2.5’ panel equals to $18.50. Now I know it’s not a big difference in cost, but with today’s wood prices a win is a win. PLUS! way better quality for CNC millwork. Hope this helps
“plywood” can range from awful to decent quality, indeed.
If you cannot source quality plywood (it’s hit and miss…), to mitigate the problem you can try and favor downcut tools (for cuts that do not go all the way through), and compression endmills for through-cuts.
There is such a thing as a downcut vbit (search for the Groovee Jenny…), and compression endmills are great for cutouts
That’s good to know, I will certainly try that. Another question for you regarding baltic birch, I plan to paint the carved areas, which will be cut with oramask, but I know birch tends to bleed. Is there a way around this? I don’t have any experience with baltic birch ply.
I watched a few (wink, wink), maybe a thousand youtube videos where they sealed the wood after CNC milling, but before painting. This has worked for me, minimum bleeding, but I am working to perfect it. I seal mine with shellac, but it is subjective- some use sanding sealer, some use polyurethane- you get where I’m going, whatever floats you boat, yet stops the color bleed.
This works real good. You should read about shellac. This is 2 pound shellac. I cut it in half with denatured alcohol. With 8 coats and sanding, I can make MDF as smooth as a baby’s behind.
Ive had this issue as well plywood can be a nightmare with chipping and splintering. My most recent project was a small teasure type chest i cut using 4mm birch plywood. I got some down sprial 1.5mm bits via Amazon and that helped with the chipping a little bit. Then i got thinking. I tend not to stain wood as i like the natural look, so before i cut the second box i coated the sheet with varathane indoor water based poly. (Home depot at arounf 24 bucks a gallon) Just used a sponge roller and applyed a rather thick coat. That product dries in 2 hours. Sanded lightly with 220 to remove the bubbles applyed a second the same way, then knocked the bubbles down with a brush. Sanded a second time just to smooth it out, then went to cutting. The parts turned out beautiful. I only had some splintering when i assembled the parts and that was very minimal. Mostly due to the rou ded corners in the pockets where pieces had to slide in
Here a link for the bits https://a.co/d/aj2ZDcm
Cutting speed 40 inch a min
Depth .050 per pass
Spindle speed 18000
40 inchs a min seems ro be the sweet spot for these bits i broke 1 at 60 and another at 50
Here is a project I made thanks to the great advice about getting good quality plywood! This was rotary cut, which I hadn’t heard of before. It made a lot more mess in my enclosure. And, had a fuzzy kind of MDF feel when carved. But it painted well!
They rotate a log and continuously shave off a full continuous sheet. I hadn’t heard of this before and the guy at my local supplier gave me a pretty unhelpful explanation, so I had to google it. The cut areas don’t really display grain and look a bit like MDF, unlike the surface. It cut beautifully though!
Thanks for the info. My twisted mind had somehow read this as “I used a rotary cut technique to make this piece”, so I wondered if there was a new CNC technique out there that I was unaware of
Haha! Nope. But I’m sure you would be way ahead of me if there was
My local wood shop has a bunch of varying types of plywood on hand, but the only maple said “rotary” one and it was confused.
But the quality compared to home improvement store was a billion times better. I cut a project 3 times and failed miserably before hopping here to ask about it. This place is the best!
I’ve never seen a video of making plywood any other way than with a “rotary cut.” The better plywood is made of better logs with more and thinner layers. Look up “baltic birch” plywood for better quality plywood, but there are others these days.
Probably the lesser quality stuff is also rotary cut as well — as @CrookedWoodTex noted, it’s the typical way to make plywood, and it’s rather exceptional to find flat-sawn plywood, and usually that is put forward as a mark of quality, since the wood isn’t distorted by being flattened out, but one is necessarily limited in the size of available wood.
