I have a lot of shelves to cut out of 3/4 cabinet grade plywood. Currently all I have are a couple of 1/4" End Mill Bits from IDC Woodcraft. Standard feed and speed is 70in /min at 19,000 with .25 Stepdown.
Question, Can I run this full depth at a slower feedrate? If Every part has to make 3 passes to cut all the way through it will take a long time to complete the job.
Other ideas out there…roughing bit?
Appreciate any guidance!
My guy tells me if you try to speed things up by cutting more aggressively, your project will end up taking longer due to broken bits and re-running parts.
That is what I was afraid of
I think your best strategy to find optimal feeds and speeds is to first find a slow speed that produces very high quality. Then increase in 10% increments until a negative effect happens, then back of 10-20%. This strategy really only works when you have dozens of the same part to cut. Ideally on small parts that you dont mind scrapping.
If you have IDC roughing cutter I think you can cut full depth of plywood at those feeds and speeds. Maybe try it in 2 cuts as a first test. Just listen to the sound and see what kind of chips you get. When I say sound - you listen for vibration & spindle laboring to pull through the cut. You can move the feed & speed override controls to dial in a good sound. Once done look at burrs left behind look at the cutter to see if it like it is buffing the cutting edge. Look at the chips too. If they look powdery then increase feed until the spindle sound like it is laboring or starts to shutter or vibrate to much. After you run a few parts you will find that happy middle were it gets done faster or up until your quality starts to fall off.
For cutting plywood (through cuts), you should use a compression bit. Since you are cutting a large volume, you should get a larger diameter bit. IDC’s 1/2" diameter compression bit is $65 (only $20 more than their 1/4"). You will be able to significantly increase your pass depth and feed rate.
Rule of thumb is half the width of the bit for depth of cut. Full depth is possible but your cut quality will suffer. I would think you should be able to cut at 200 ipm at 1/8" pass and the right spindle rpm.
Using IDC’s chip load calculator you can run 300 ipm at 20k for spindle and you are still running a conservative chip load of 0.00750 on a two flute .25" end mill. 70 ipm at 19k is way too slow. My math could be off so double check for yourself, but that is about 25-30% faster than running a single pass at 70 ipm.
A lot would depend on the power of your spindle and the quality of the cutter.
Plywood can be quiet abrasive on cutters and it is often easy to get burning and scortching.
Another thing to consider is to if the cutter is fully engaged or part side loaded.
I think 3/4" full depth is slightly ambitious
Another thing to consider is using a table saw. I only use the CNC to cut plywood when I need dados or need to cut irregular shapes. For plain cuts, it’s so much quicker on the table saw, and the cuts are much cleaner.
I just did this on 12mm baltic birch. I used a 1/4 compression bit at 18000/100 two passes. Everything looked great. I think I could push it a little faster but probably not much past 150IPM.
On ply a chip load of 0.007-.0010 seems to be pretty good for me. I make sure I am always using longer z ramps. 18k on the spindle might be a touch high for optimal chip load, but do your own math.