View Full Version : Basic machining question

rp designs
03-03-2011, 12:14 AM
Ok forgive the basic question. I haven't done a whole lot of chamfering other than breaking edges to de-burr parts. I can't really find any real good sources for information with regards to these cutters. I guess I will list my specific questions in hopes of getting specific answers for the more experienced, wiser members here.

1. With regards to speed and feeds I have been using the largest diameter to calculate the speed; however, I tend to second guess the speeds because of the decreasing diameter of the cutting edge. What do you typically use to determine chip load? I have not been able to find any manufacturers data on feeds and speeds and have been adapting end mill data as a starting point.

2. For depth of cut how aggressive can you go? I have been basically doing very small 0.5mm 45 degree chamfers so one pass is no problem, but is there a rule of thumb for a maximum depth of pass (conservative) using a 3HP CNC?

3. For larger chamfers the indexable cutters seem like a good option, but what are their limitations compared to the standard carbide end mills?

Most of my work is in Aluminum, but there will be occasional work in steel.
Thanks for your help!

03-03-2011, 12:58 AM
the thing to understand is why there is a cutting speed. temps where the molecule of cutter meet the molecule work are high (coolant stops heat build up, not this localized high temp) and are mostly are a result of the speed of tool relative to work - the surface speed/cutting speed in feet per minute.

All the recommended cutting speed is, is that point of the graph of cutting speed vs tool wear where the slope changes....going above it wears the tool out faster than the material removal rate gained by the increase. Tool life drops off above that number but there's no problem going slower than that number (except you're not maximizing production)

So. knowing that, its intuitive that you take the largest diameter where the cutting is happening as the driver of cutting speed - to maximize tool life vs removal rate you want the fast part of the tool under the recommended SFM number

thats the general theory, but a small cutter in AL in 3 hp mill can be run quite fast!

rp designs
03-03-2011, 09:03 PM
Thanks MC Guyver, Anyone else?

03-03-2011, 09:31 PM
Several issues affect cutter life, sfm being only one. Rigidity in the setup and depth of cut combine to make life difficult for the cutter, and I for one think it's likely that large and fast temperature swings might occur when there's chattering going on, or other deviations from smooth cutting. Inconsistencies in the material would be a factor. Sfm is probably the first thing to make settings for, but then you'd likely want to experiment depending on the material and the surface finish you're getting on it, plus the angles on the particular cutter in use.

I don't mind turning slower than the recommended maximum sfm, but sometimes the results aren't as good. Add coolant into the mix and the different models of machine, and it really becomes an issue of 'what works for you'.

03-03-2011, 09:42 PM
Something to consider: Hammering, Without a helix angle to the cutting tool, Side milling where you have a large cutting edge engaged with the work at once becomes diffacult, starts shaking the machine and is very loud and bad for the tool.