CNC Beginner here … a personal project I am working on needs some holes drilled in 7/8 inch plywood. Specifically 77 holes that are mostly 1/2" diameter, and some at 3/4". The tolerances of the hole diameters are not critical. I was initially going to use a spade bit and doing a lot of manual drilling, but realized that maybe my new 5 Pro can do the work for me. I shouldn’t have a problem designing this in Carbide Create, but my concern is the usage of the 5 Pro for hole drilling, the recommended tooling, and the tool paths for the individual holes. I would probably make each row (11 by 7 grid) of holes a separate tool path to make it easier if I break or dull a bit.
I am assuming that I would use either a 1/8 or 1/4 Upcut Milling bit and start at the center of the hole and working outwards with small steps at 1/2 the Milling Bit diameter max for the depth of each cut. I do NOT have Carbide Create Pro, so I can’t use a ramping cut to minimize the stress on the end mill.
So …
Is this reasonable to do in plywood or should I just hand drill the holes. If reasonable, then
Is an 1/8 inch or 1/4 bit flat endmill best? Or would a ball nose be better.
Do I start at the center of the hole and “spiral” outward? Or is this standard with Carbide Create?
What depth increment should I use? 1/2 the mill diameter or 1/4 the mill diameter?
What is a good step-over to use, or just use the default for the bit.
I want to round-over the holes when completed, but can use a hand-held router for that unless there is an easy way to do that on the machine. I will be manually rounding over the bottom holes regardless.
I very much understand the urge to know everything you can before sending it with a CNC. That said, if you’re waiting for responses, you’ll never get anything done
I’d recommend getting a scrap piece of your plywood and just trying the default values in carbide create. They’re pretty safe and if time isn’t an issue, their conservative speeds don’t hurt much. (If you find yourself doing this a lot, there’s definitely room to speed things up)
For plywood the thing I would care about most is blowing out the surface layers but if you’re rounding over anyway that probably doesn’t matter much. The round will end up removing any frayed edges.
1/8” vs 1/4” I would also assume doesn’t matter a whole lot. 1/4 is probably what I’d go with. Bigger tool removes more material and is stronger so less likely to break (though again I wouldn’t worry too much about breaking tools with default feeds and speeds, regardless of tool size)
It’s probably also better practice to use 1/4” as a lot of wood working tools are sold in that size.
I’d expect 77 holes will not even begin to dull a carbide cutting tool. Though with plywood I suppose the laminate glue might be rough on the tool? I’d likely use a coated version to try and keep the tool from building up any gunk. (This is probably a non issue and I’m just being a little too cautious since I’ve got coated on hand anyway)
Good luck and keep us posted with your results!
P.S. If Will Adams (or anyone else for that matter) disagrees with what I’ve said…assume they are right and I don’t know what I’m talking about
Thanks for the feedback. Was just trying to not re-invent the wheel and was also trying to see if I was not off-base with my expectations. I will now proceed to do some testing and then move on to the real piece.
On plywoods, an upcut is a disaster and the top just chips off randomly in large chunks. For pocketed holes that have a floor, use a downcut. For thru cuts, use a compression and make sure your first depth of cut is below the upcut portion of the endmill.
I will experiment with both 1/4 Downcut and Upcut Mills. I will be putting a piece of MDF under the plywood to give me a cleaner bottom and to eliminate 77 new holes in my spoil board.
On the topic of compression bits … from what I read, a 1/4 bit usually needs to go down at least 1/4 inch to get to the downcut portion of the bit. Maybe I read too much, but isn’t 1/4 quite a bit for either plywood or hardwood? Or is it OK in plywood to take a 1/4 bite.
EDIT: ACK … my bad … my test simulation had two tool paths … the drill one and the pocket one. I didn’t realize both ran after each other and I saw the first plunge go all the way thru … which doesn’t happen with a pocket cut. So, as Will says below there is no problem with a downcut and chip evacuation. Ignore the below paragraph. Don’t see how to do a strikethru in this editor. Apologies.
IGNORE BELOW PARAGRAPH. USER ERROR.
Also, again from what I read, downcut bits have chip clearing problem on holes the diameter of the bit … which is what the first plunge cut will be. For Pocket Cut there is no options like the Drilling Toolpath where one can peck or peck and retract to help with chip clearing. So the first cut will be a through cut of the full diameter of the plywood. I suppose I could define an inner hole that has an initial downcut toolpath that will be only partially through the wood, or even a drilling toolpath with a peck. Then I can define the pocket cut on the initial hole that just cuts over the existing hole (ie, doing nothing new).
In my experience, a downcut, w/ a Sweepy usually clears chips well — so long as it is cutting a pocket, not a slot or a drill operation (though that latter may work okay with full retract).
I do think you’re over thinking it a bit much…I know…I’m prone to it myself.
With a compression bit your first cut doesn’t have to be all the way thru, just past the upcut portion of the endmill. In my experience with the S5Pro and the 65mm VFD spindle will do the 1/4" or so for the first cut just fine. There are compression bits specifically made for non-industrial machines by companies like the “Jenny” with a shorter upcut section.
But if you’re completely covering the bottom with a fresh piece of MDF, a downcut will work well if your material doesn’t bow up on you any.
OK … did a test file/cut … 2 holes with an upcut bit and 2 holes with a downcut bit. With the MDF backer there was no tear-out on the bottom of any of the holes, and the expected tear-out (but not bad) with the upcut bit on the top. Will definitely use the downcut bit as it made perfect holes with hardly any mess. Used 1/4 flat mills.
For pocketed holes that have a floor, use a downcut. For thru cuts, use a compression and make sure your first depth of cut is below the upcut portion of the endmill.