Printable View
I watched a training session the other day and now I'm a little confused.
I'm trying to set up my tool database with my tools. I have the chip loads recommended for those tools, but this training said I should run the RPMs at the highest speed I have (18,000)and adjust the feeds. If I take a 1/4" end mill, (2 flute) at
18,000 rpms and 3ips the chip load is .005. Any thoughts?
Most of my plywood cutting is done at 14K RPM feeding at 7IPS. I use a 1/4" compression bit to cut all my plywood parts. The best thing to do is experiment with your machine. It took me awhile to dial in good speeds and feeds for MY machine. Each machine will be a little different. For solid wood I will adjust my feed rate but keep my RPM's fairly consistent at 14K. Alder I cut faster than hickory. Listen to your machine while it's cutting. If you're getting a lot of screaming, the bit is hungry. Either faster feed or slower RPM. The speed you can cut is determined by your hold down capability and what the bit you're using can handle. I could cut at 10-12IPS with a 3/8" bit, but since I live at 2500' altitude I don't have the vacuum hold down capability that someone at sea level would have.
Thanks Don, I'll just have to experiment. I actually asked specifically about speed and he said your machine has it's most power at max RPMs.
Mike,
I'm guessing you're using a router instead of a spindle. A spindle has a wider power range and can develop a lot of power at low RPM's. A spindle gives a bit more freedom in regard to RPM selection, is quieter, and can last a lot longer but they are a lot more expensive.
I would like other members to give me their opinion on this... it's related to the current topic and I was never quite sure (being a relatively new CNC user as well).
I always thought that a procedure for setting feed and speed where the final goal is to run the tool at the highest possible speed is based on the assumption that the CNC owner uses it for production work, therefore attaining minimum machining time is important... Slower speeds (reducing RPM and reducing feed rate) can also give proper results.
Since machining time is not so important for me, I don't feel obligated to run my tools very fast - also because I have a router and not a spindle, running at lower RPM increases my router's life.
Am I in the right direction here ?
There is no shame in running your machine below maximum speed. Maximum speed also means the machine is exerting maximum stress on every component so deflection is also at maximum. The slower everything runs, the lower the stress. And counter to the prevailing wisdom of using the largest possible end mill, I go the other way and use the smallest possible since smaller diameter end mills require less force to move than larger ones. The lower the forces on the end mill, material and machine, the lower the deflection and hold down requirements. I'm not a production shop either so time isn't a factor. To me, it's far better to have better cut quality and precision.
As for the router? I always run my hand routers (and table version) at maximum RPM so they don't bog down. You can try your router at various speeds and see what it can handle. I suggest testing in scrap as you're likely to break bits and damage material if the router stops turning.
Thanks for the reply, but I am using a spindle. It is maxed out at 18,000 rpms. This training said as you lower the RPMs, you actually decrease the effective power of the spindle. It can be very confusing when Shopbt has a feeds and speeds chart for starting points that are nowhere near 18000 RPMs and 3 or 4 ips.
Speeds and feeds are not set in stone and many have different approaches to dialing them in. This is where you get varying starting RPMs and feed rates when you look at different charts. They are written by different machinists and their preferences. Remember that these are all just suggestions and that ultimately your final cut result and the look of your chip is the ultimate test.
When you run the tool at maximum RPM you are requiring that the tool run at production speeds to accomplish the proper chipload. This is not always the correct approach if proper feeds cannot be attained to reach the desired chipload.
The difference in power on the curve for the spindle is negligible between its operating RPMs (operating speeds being between 9k and 18k RPMs).
I will provide below a number of resources on feeds and speeds, dialing them in and learning more about chiploads. I will leave one more tip in that you can adjust the speeds on the fly by holding SHIFT and then pressing the > or < key on the keyboard.
Feeds and Speeds
Here is the best info we have here in support. This is one of the hardest things for people to get right as it is a learned skill to come up with and adjust feeds/speeds. There is no set in stone number for any project:
The info I am providing is on feeds/speeds and calculating them using chipload. I am including some document links and want to throw in a couple of reminders that chip-load values are key, so finding you bits chipload from the manufacturer and then finding the federate plus 12k-18k rpm that gets you the chipload:
A good place to start -http://www.woodguide.org/files/2014/...bit_basics.pdf
A good reminder to use chipload calculations -http://www.talkshopbot.com/forum/sho...-find-the-data
And an extra reminder that chiploads are based on a 1x full depth cut. 1x full depth is the diameter of the bit. So a ¼” bit has a 1x full depth of cut of ¼”.
http://www.shopbottools.com/mSupport/tutorials.htm See feeds and speeds category
Feeds/Speeds
https://www.youtube.com/watch?v=glfoB7THcqs Tips for Cutting Aluminum
https://www.youtube.com/watch?v=p-lj5q7xy1Y Cutting Acrylic
https://www.youtube.com/watch?v=a2DwsC2iDNY l Tool Database and Bit Selection
https://www.youtube.com/watch?v=XteEyLYvtXA Plywood
https://www.youtube.com/watch?v=1p9vpZpMhNU Plastics
https://www.youtube.com/watch?v=zzzIpC39WUg (for milling but the techniques are very similar)
Documents:
https://www.dropbox.com/s/s62flixoq3...harts.pdf?dl=0
https://www.dropbox.com/s/bwl3opve8b...20Ref.pdf?dl=0
https://www.dropbox.com/s/rm4vsfny3k...stics.pdf?dl=0
https://www.dropbox.com/s/umrdtr6o3r...minum.pdf?dl=0