[keithmcelhinney]

I was reading a post on CNC Cookbook about chip thinning and speeds and feeds and now that I have most of my toolpaths worked out I want to optimize my speeds and feeds. Link is here:

CNC Feeds and Speeds Cookbook and Tutorial

Being a beginner I always thought going slower meant longer toollife and better finish. This article really showed me what a beginner mistake that is. So now I want to make my cuts a lot more aggressive, lower my cut time, improve my finish and save my tools! I am buying the calculator when I get home from work tonight but still a little hesitant about being so aggressive and have some questions.

First: I hear about tool pullout and with the PDB do I have to worry about this and how do I avoid it.

Second: When calculating the cut, is it better to go slow and deep, shallow and fast, etc. Do you optimize on MRR or deflection or ? I have some deep cuts (2.25 inches) so I have to use a long tool so I know I have to go pretty shallow on those. I do almost all slotting.

I am using Lakeshore Carbide 3fl endmills (lakeshore). I did order some HSS ones and then plugged them into the calculator and on long cutters it REALLY reduced my MRR. So I am back to the carbide for those. I may use the HSS ones for short stickout cuts when my carbide ones die, but for now all my endmills are carbide.

I know some of this is going to be "Try this and keep turning it up until you are using almost full power on the spindle", but the article made me wonder if that is what I should be doing. I could be running at full power but have massive deflection. Any help would be appreciated.

-Keith

[SCzEngrgGroup]

Keith,

Since you are using my PDB, I will guarantee you will NEVER experience pull-out, so don't waste time worrying about that.

Optimal feeds and speeds are as much as function of the machine as the tool, so no calculator can give you the best number all the time. This is especially true with larger tools, which generate higher forces, and require more power and/or torque. For those, there is no option but to use the calculator to give you a starting point, then do some simple test cuts to see what your machine is actually capable of.

For calculators, I much prefer HSMAdvisor to GWizard. Once you get your machines HP and torque limits properly dialed in, I find it gives excellent results that, in most cases, I can just run with. For larger tools, take what it calculates as a guide, then do a few simple test cuts starting with the feedrate reduced by about 30%, then work your way up until you find your machines limit. Once you've done this a few times, you'll come up with a range of feeds and speeds you can use for a wide range of conditions, and you won't need the tool very much any more. It's an excellent tool, and well worth the modest cost. Best of all, it doesn't require an Internet connection to run, and doesn't force you to do frequent cumbersome and time-consuming Adobe updates. I gave up on GWizard when it seemed like every time I wanted to use it, I first had to download one or more updates.

Regards,
Ray L.

[keithmcelhinney]

Hey HSMAdvisor is cheaper so I am all for it! Is there any way to grab your torque limits/etc?

[SCzEngrgGroup]

Hey HSMAdvisor is cheaper so I am all for it! Is there any way to grab your torque limits/etc?

I didn't do anything elaborate. I use the machine model for the Tormach, and set the HP limit to about 1.2HP. You still have to TEST on any cuts that get close to the machine capabilities. This is a non-issue for tools under about 1/2", where the tool will break before you hit the machine limits. Also, if you're not using constant engagement toolpaths, you'll have to set your limits a lot lower, to accommodate the power/torque peaks that WILL occur during plunges, inside corners, etc.

Regards,
Ray L.

[zero_divide]

I would like to add to what Ray said.
Whenever conditions are not ideal. IE you are using longer endmill, of you do not have enough power, always reduce the depth of cut first.

On my calculator you can use performance slider (in advancd settings tab) to forse HSMAdvisor suggest shallower depths of cut than normal. It is especially designed for not ideal conditions.

Also always try to use shortest tool possible and again whenever in doubt reduce your DOC first.

[kvom]

I've been using GWizard for over 4 years, and since then have broken no tools because of excessive F&S. All my tool breakage has been a result of brain farts.

I am a hobby machinist making 1-off parts (see my locomotive thread for examples) and tend to use conservative settings. If I were doing production I'd start with the recommended values and experiment to get the greatest MRR I could without the machine or the tool complaining. I believe larger DOC and smaller engagement will extend tool life for a given MRR. However, I'm not often able to use that strategy. I almost always use ramping even with center-cutting endmills.