Thread: Milling feed rates

For starters how many different feed rates does your mill have.

Have you considered just winging it.

If it sounds good looks good just use it.

Feed rate will depend on cutter size material and ridgidity.

If its that older mill that your talking about it will probably have a limited range,more than likely in inches or feet per min.

The bigger the cutter the slower the feed and visa versa generally.

Consider it a bit like the lathe,I wouldnt lose to much sleep trying to calculate the (correct) feed rate,the one that gives the best result for the job at hand will be good.

If you do go down the track of trying to find the (correct) feed rate you will have to take into account the number of cutting edges and the chipload per tooth.

If you are using the horizontal or Vertical spindle will have an effect also on the feed rate.

If you do go down the (correct book formula route) have a great time with the Calcs and reading,then cross your fingers and hope that the (correct) feed rate is available on your Mill.

Not sure whether you are talking about using Indexable Insert Cutters or HSS Cutters, but for Inserts you need to check out the manufacturers recommendations for your Grade of Insert. I use Mitsubishi VP15TF and Mitsubishi publishes recommended feeds and speeds in charts for their inserts.

For example VP15TF is good for 100-200m/min cutting speed in Steel, Stainless Steel and Cast Iron, 50-110m/min in Hardened Materials and 20-40m/min in Titanium and Heat Resistant Alloys.

Feed rates are 0.1-0.4mm/tooth in Steel and Stainless Steel and 01.-0.3mm/tooth in Cast Iron.

Using these two numbers for your material, plus the spindle speed, you can plug them into the second formula on this page to give you your table feed rate.
MITSUBISHI MATERIALS CORPORATION###Formulas for Milling

I also use the second formula on this page to check that I am not overloading my machine. I dont know how accurate it is so I stay well away from 1.5kw as the required power figure!
MITSUBISHI MATERIALS CORPORATION###Formulas for Drilling

If you're looking for a program to provide this information, check out GWizard.
I've been part of the beta testing for a while and for a newbie like me, it's pretty handy.

It's not too expensive but I don't like that it's a subscription rather than an outright purchase plus the fact that the software 'phones home' when used and must be able to contact the host server at least once every 2 weeks.

If you do decide to go with the gwiz and pay ,you can tell me your cutting parameters and ill take your money.

Its got 12 feeds between .47 inch per minute and 15.4 inches per minute. I was after a simple formula for calculating feed speed based on tool size and work piece material. I have found some forumulas online but they all reference a 'feed per tooth' value that I didnt know how to calculate. Last night though I found a chart that lists reccommended feed per tooth for a variety of materials, cutter diameters and cutter types. Up until now I have been winging it and so far havent had good results. Turns out I have been erring way to much on the side of caution. I have been doing test cuts at about 1 or 2 inches per minute, when the formula said 6 would be more appropriate. So I ramped it up and got a much better cut and finish.

I also did some long cuts with my slitting saw and it was great. Went through 6mm mild steel like a hot knife through butter. Got pretty warm though...might have to make fixing the flood coolant system on my mill a priority.

FPT is just what it says it is. (say 0.003")
Count the number of teeth on you cutter. (say 20)
Take the RPM. (say 500)
500 x 20 x 0.003=30inch per minute(these numbers are to demonstrate the math, I doubt there is a cutter with 20 teeth that you would spin at 500rpm)
Even when you have your number its really just a guide. How deep is the cut? How hard do you want to push your cutters?

Stuart

p.s. As you've found out, with milling going slower isn't always the answer. Especially if you are down milling.

Thanks Stuart, thats brilliant. Just what I was after. I have written that formula down on the chart I have printed and will be able to calc approx feed speed easily now. From there I would feel much more comfortable experimenting with different feeds.

Re chip colour, am I right in saying that blue chips are bad (too much heat)? What about when the chips are coming off a tan colour...is that still too hot? Im talking about mild steel.

Glad to help Brendan.
Assuming HSS cutters. Blues about as hard as I would go(others may disagree). HSS should handle it. If the surface finish is ok then go with it.
Some say it's better to take a shallower cut and keep the feed the same. When down milling the cutter rubs before it starts to cut, the slower you go the more it rubs. Rubbing doesn't do much good for cutters or surface finish.
Stuart

Yeah, HSS cutters. I have heaps of HSS end mills that I bought from the US which are sized between 1/2 inch and 2 inches (prob 20 in total?). I have been using them for various things and some of them seem to be brand new, so I dont really want to ruin them. The other day when I was starting to get worried about going to hard I made the cut shallower but kept the feed the same. It seemed to work well.

Brendan,

I knew I had scanned this from school (TAFE).
This chart should help you start the job at close to the correct speeds and feeds. We use it all the time and was made by someone within TAFE for the students.

It says for turning and drilling, but applies equally for milling.

To use it, start at the right/bottom box and choose:
1. your material (turning tab)
2. Follow the red line up and left until you get to the diameter of your material
** In this case replace this with the cutter diameter.
3. Follow the horizontal line to the RPM required
** This will be spindle speed in your case

Hope this helps you

/Michael

Thanks Mike, thats great.

Brendan

I wouldnt be getting blue chips with hss, are you using coolant? Shouldnt even really be getting tan chips with hss, but with carbide blue chips are alright even slight sparks are alright. But with hss if you are getting blue chips your cutter wont last long at all

Blue chips make me nervous so I back off as soon as they appear. I wasnt sure about tan chips though, should I back off if im getting those with HSS cutters?

What type of Cutters are you using.(shape/profile)
If you havent got a coolant system with pump I would at least be using a plastic bottle.
If the Cutters are HSS normally the swarf will be the same colour as the material your cutting,there shouldnt be any discolouration.