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Guncraft
04-24-2016, 01:34 PM
How does a guy go about calculating chip load at a given SFPM and feed rate? I have an Acurite DRO on my mill that displays "feed rate" - I can not find in the manual what the unit of measurement for this is though. Feet per minute???

What I am looking to do is to do a better job of getting the most out of the cutters without going to slow and rubbing, or going way to fast.

Thank you!

Andy

Mcgyver
04-24-2016, 01:35 PM
feedrate is usually stated in inches per minute

tmarks11
04-24-2016, 03:07 PM
How does a guy go about calculating chip load at a given SFPM and feed rate? I have an Acurite DRO on my mill that displays "feed rate" - I can not find in the manual what the unit of measurement for this is though. Feet per minute???

Feed rate is in inches per minute.

Here are the calculations:

rpm = sfm*4/D (where D= cutter diameter)

FR = rpm * CL * N (where N = number of cutting edges and CL = chip load per tooth, typically 0.001-0.004").

Chip Load is the entering argument in the calculation to get feed rate, and is generally provided by the manufacturer's data, and is tabled based upon material and cutter diameter and cutter type.

Harvey Tools has a great chart that shows this.... note that this is for carbide tooling (I don't think Harvey sells HSS):

http://www.harveytool.com/cms/GeneralMachiningGuidelines_17.aspx

or... you can use a calculator like HSM Advisor or G-Wizard and it will calculate this for you.

Andre3127
04-25-2016, 11:03 PM
I dont mean to rock the boat, but I think on a manual machine it really doesn't matter. As long as you're making a chip, it's not squeaking and the tool isn't obviously stressed or breaking you're going to be okay. On a CNC where feedrate is controlled it might be advantageous but on a manual, just make some chips.

Sent from my XT1053 using Tapatalk

Black_Moons
04-26-2016, 01:08 AM
I dont mean to rock the boat, but I think on a manual machine it really doesn't matter. As long as you're making a chip, it's not squeaking and the tool isn't obviously stressed or breaking you're going to be okay. On a CNC where feedrate is controlled it might be advantageous but on a manual, just make some chips.

Sent from my XT1053 using Tapatalk

The type of machine you are using does not change the physics at play. you NEED to know about feed rates and chip load or your doing your tools (and time) a horrible disservice.

Its very easy to control feed rate on a manual mill, even if you don't have power feed. You just count the handwheel revolutions per 6 seconds. at 0.1" per revolution, you know that say, 10 revolutions over 6 seconds = 1 inch per 6 seconds = 10IPM.

Too fast? try 5 revolutions per 6 seconds (or one~ per second), about 5IPM.

With manual mills, sure you might not get +-10% accuracy, but you really don't need 10% accuracy when setting feed rate. What you need is to get it in the ballpark. 10IPM might be fast enough to snap a cutter while 5IPM does just fine.

Its very easy for a human to get +50% -30% or so accuracy for feed rate just turning the handles.

For a human to just guess at chip load/etc, he might be +500% -90% wrong easily. More then enough to break a tool or wear it out very prematurely, and make a job take WAYYY longer then it should.

You can't just tell when a tool is stressed by guessing. Its much easier to do the math and have a good starting point that is in the ballpark.

Andre3127
04-26-2016, 01:28 AM
I agree that you need to have a good idea of the physics involved, but in the hobby mindset (this is a hobby forum after all) you can pretty easily tell if your chip load is too light or too heavy - and adjust accordingly. Seeing, hearing, and feeling the cut isn't guessing.

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Black_Moons
04-26-2016, 04:28 AM
I agree that you need to have a good idea of the physics involved, but in the hobby mindset (this is a hobby forum after all) you can pretty easily tell if your chip load is too light or too heavy - and adjust accordingly. Seeing, hearing, and feeling the cut isn't guessing.

Sent from my XT1053 using Tapatalk

I think many people have no clue what too light or heavy of a chip load looks like. I know my dad sure never did as it would take him 5 minutes to drill through 3/16" steel with a 1/4" drill. He assumed that little powder shavings coming out of the hole meant it was working..

Doing the math and running it according to the math will teach you what the correct sized chips look like, and eventually you can start doing it by 'gut', but most likely all your 'gut' is really doing is interpolating/extrapolating from settings you remember using in the past and using them as a starting point.

"Well I used 500rpm for 1/2" and 5IPM before, so I guess I'll try 300 RPMish for 3/4".. Uhhh, About 5IPM still I think. Oh wait this is aluminum not steel. Double that, make it 600rpm and 10IPM"