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Newbie CNC project, cutting narrow pieces from glued boards. Help/advice please!

809 Views 5 Replies 6 Participants Last post by  PhilBa
Hey everyone!
I’m used to doing laser cutting projects, but I’ve been wanting to get more into CNC so I can cut out larger items with thicker material.


I’m needing to cut out several, large, custom art/photo wood frames. I’ve done my best to scour the internet to figure out how I should approach this, but I still need answers to questions that my Google searches have been failing me on. Since everything is so expensive right now, I’m just wanting to make sure I’m on a relatively clear path of knowing how to correctly do this before I screw up a million times wasting money.


Project: I am needing to cut several tall and narrow pieces (pieces of an all-together large outline with a 0.5” line stroke. Gluing together after cutting out separately) out of wood- both pieces that are straight, as well as a bit curved. Each piece is approximately 0.5” wide and 17” tall.
I am planning on cutting out several of these pieces on a 24”x48” panel.


I need the pieces to be at least 0.75” thick and relatively smooth without tons of money, so I’m staying away from plywood and was thinking of gluing four 6” x 1” pine boards together to create the 24”x48” panel. The wood is going to be painted in acrylic, so I’m not bothering with buying fancy pretty wood. I was planning on buying a 1/4” compression bit to cut it (?)



My questions:

1. Do you think it’s feasible to cut out these thin shapes out of a panel made of glued 1” pine boards? What is the chance of them snapping? If not good, which kind of wood boards would be better, or am I stuck with plywood or mdf?
2. To prevent snapping on items this thin, how far apart should I place the tabs?
3. If these tall and narrow pieces are 0.5” wide, is that too thin? Do I need to make them 0.75” or 1”?
4. Would a 1/4” compression bit be appropriate for this?
5. Are the normal small knots in pine going to be an issue?
6. I’m trying to fit as many pieces as possible on the panel. I currently have my pieces spaced 2” apart from each other. If the 1/4” bit is appropriate, is that enough material to leave in-between?
7. This isn’t specific for this project, but I’ve been wanting to know this for a different project idea and I cannot for the life of me find the answer on Google. I’m used to taking kerf into consideration with the laser cutter. There is always lost material from the laser that has to be accounted if you want to snugly fit together items. Is the same with CNC? I wouldn’t think so, as the bit cuts around the outside of the shape/vector, instead of on the middle center of the line like the laser. But, I couldn’t verify that anywhere online.


I appreciate your help!
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Depth of cut is typically about 3/4" on a 1/4" compression bit so that limits how thick you can cut. Pine is very soft and doesn't machine cleanly like hardwoods. Poplar or similar wood will machine cleaner but you'll have to check on the cost. Got any photos you can share? That will help get better responses.

And welcome to the forum!
G’day Melia,
Welcome to the forum.

Thank you for joining us, .
You will find many on the forum, from hobbyists
to professional with similar interest in the router and its uses.
Take the time to learn how the forum works and ask any questions you want.
Welcome to the forum Melia.
Straight sticks? Do you have a table saw?
On a CNC, holding the parts down is step 1. How would you hold the glued up panel down while the strips are being cut from it? I'll also recommend poplar rather than pine/fir. Knots in pine will indeed make thin strips weak/break at the knot. To keep the strips from moving after being cut around they should have tabs between them and the surrounding wood. In hardwoods like poplar I don't bother with a compression bit. A simple upcut spiral bit will cut clean with the grain and at most leave a few fibers to sand off as it runs across the end grain. In 3/4' wood you could use a 3/16" upcut spiral bit for a smaller kerf between parts.
4D
1. Do you think it’s feasible to cut out these thin shapes out of a panel made of glued 1” pine boards? What is the chance of them snapping? If not good, which kind of wood boards would be better, or am I stuck with plywood or mdf?
Yes, possible but it isn't clear to me why you need to glue up a panel if you are gluing the pieces together later but then I'm pretty sure I don't have enough info to visualize the project. If it is to minimize waste, I'd suggest you not bother and cut the parts out of the unglued boards. Make multiple runs to cut them all out.
2. To prevent snapping on items this thin, how far apart should I place the tabs?
As long as you can hold down your work piece, 1/2" wide pieces should not be a problem. Pine, ply or mdf won't have a lot of flex so tabs every 6 to 9 inches should be fine. Personally, I'd use a down cut spiral. It may even pack the sawdust in enough to allow you to avoid tabs. Be careful when taking the cut piece out. Use a knife or small saw rather than snapping them.
3. If these tall and narrow pieces are 0.5” wide, is that too thin? Do I need to make them 0.75” or 1”?
Probably OK.
4. Would a 1/4” compression bit be appropriate for this?
It would be ok. But, your depth of cut depends a lot on the size of your bit and how rigid your CNC machine is. If it's a typical hobbyist machine, I'd probably use 1/2 the bit diameter for your cut depth and make multiple passes. If it's more of an industrial machine, you could probably use the full diameter for your cut depth - probably will still need to make multiple passes.
5. Are the normal small knots in pine going to be an issue?
Definitely an issue, especially for narrow pieces. Maybe you should use MDF.
6. I’m trying to fit as many pieces as possible on the panel. I currently have my pieces spaced 2” apart from each other. If the 1/4” bit is appropriate, is that enough material to leave in-between?
See my above answers. You can probably space them 1" apart or even less. Think of your resulting cut panel in terms of it's structure. Make sure nothing is "flapping in the breeze".
7. This isn’t specific for this project, but I’ve been wanting to know this for a different project idea and I cannot for the life of me find the answer on Google. I’m used to taking kerf into consideration with the laser cutter. There is always lost material from the laser that has to be accounted if you want to snugly fit together items. Is the same with CNC? I wouldn’t think so, as the bit cuts around the outside of the shape/vector, instead of on the middle center of the line like the laser. But, I couldn’t verify that anywhere online.
Depending on you CAD/CAM software, you can usually create a tool path to cut to the outside of the vector (perimeter) of an object. You can also direct it to cut inside the vector or on the vector. For a laser, you are usually cutting on your vector. You do need to worry about kerf when spacing multiple parts on a piece of material - they need to be at least your tool (ie bit) diameter apart. A good CAD/CAM will tell/show you when there is overlap.
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