Feeds & speeds

[BoomerangInfo]

I'm back again. I'm suffering information overload, and can't sort the wheat from the chaff.

I'm trying to setup the parameters of my bits in the tool database in Aspire. I've been trying to figure out the pass depth, feed rate and plunge rate for the bits I've bought.

Pass depth, from what I've seen, has the rule of thumb of 1/2 the cutting diameter. Does that sound right? If I'm using 3 - 6mm cutters, that seems like there will be a lot of passes required for anything significant. I'm trying to make a pen blank mould for a start with a 16mm, round bottom channel. The default 3mm endmill in Aspire has a pass depth of 9mm, which can't be right?!

Feed rate is the biggest headache (and seems to be a black art), as everything I can find seems to have Chip Load as the critical factor, with RPM x #flutes x Chip Load giving the recommended feed rate. But none of the places I've bought the bits from have chip load for the bits listed. Isn't chip load, which from what I gather is the amount of material removed by each flute, a physical measurement for each specific bit? All of the 'charts' I've looked at vary wildly with values from 0.01 to 0.0002, which is a factor of 50 difference. Also a lot of the sites only give figures for machining metals.

Given I'll be doing mainly wood, and maybe some plastics, can someone give me a starting point by suggesting what the correct values might be for my 6mm, 4-flute carbide Endmill might be?

Thanks. Russell.

[BoomerangInfo]

Been doing some more reading, still no clearer, although I find a recommendation of tool diameter/200, which for a 6mm endmill gives 0.03. This would give 2640mm/min at 22,000 RPM.

Looking at my Walter6545 manual, it suggests 3000mm/min is the max speed the table can hold, but there is also a section which says the flexible coupling max speed is 1500 mm/min.

So, does any of that looks right, and if so, what's the limiting factor on the feed rate? Also, if the table feed rate is lower than the calculated bit feed rate, who wins?

I'm happy to just try stuff out, as long as I'm not risking either breaking the bit/motors/couplers from going too fast, or burning out the cutting edges from going too slow.

Russell.

[Ch4iS]

There's also the stepper motors and what speed they are capable of while cutting, spindle power, and quality of cut.

Step-over I run at about 40%, for starters just start slow @ ~1000mm/min, 2mm DOC with some soft wood and see how it performs.

The speed limit listed on ebay is probably due to a limitation of the drivers.

[kamel]

hi
how about cnc machine and wood turning?

[Ger21]

Given I'll be doing mainly wood, and maybe some plastics, can someone give me a starting point by suggesting what the correct values might be for my 6mm, 4-flute carbide Endmill might be?

Thanks. Russell.

You really shouldn't be using 4 flute tools in wood, for two reasons.
1) They're designed for metal, so they don;t have optimal geometry for wood.
2) You just won't be able to cut fast enough

2 flutes are standard for wood, and for plastics, try to find some 1 flute "O" flute bits.
Even 2 flute bits will melt most plastics, even at high feedrates. "O" flute bits help to clear the chips, and greatly reduce melting. Ebay is a good inexpensive source for these.


When cutting wood, you should have no problems cutting 1diameter deep per pass.

As for feedrates, You can cut about 3M/min at 10-12,000 rpm, and up to 12M min at 18,000 rpm. These are ballpark figures that I use, and can be influenced by machine rigidity. If rigidity is an issue, try taking shallower passes.

With a 2 flute bit in plastics, try lowering the above rpm's by 30% for a 2 flute bit.

[BoomerangInfo]

You really shouldn't be using 4 flute tools in wood, for two reasons.
1) They're designed for metal, so they don't have optimal geometry for wood.
2) You just won't be able to cut fast enough


Really? I thought the 4-flutes were what someone recommended when I started, but I could be wrong. I have some 2-flutes as well, but only in Ballnose.

My biggest concern after reading the CNC manual is that it says the flexible couplers that the machine came with may break at feed rates > 1,500 mm/min. Does that sound right?

Russell.

[snowyskiesau]

The couplings do have a rating (in newton metres) but don't know how that relates to speed. Change of direction perhaps?

[Perfect Pens]

Hi Russell,

Ger is on the money, 2 flutes is what you should be using on most timbers. I have been having the very same issue lately trying to get the feed and speeds as well as the correct cutter selection just right. I think you need to start hear though and then experiment. Here is a calculator that was posted on one of the other forms I frequent, it may be of help to you.

MAPAL Milling Calculator (http://www.mapal.us/calculators/milling/CalculatorMilling.htm)

Cheers
Tony.

[BoomerangInfo]

Hi Russell,

Ger is on the money, 2 flutes is what you should be using on most timbers. I have been having the very same issue lately trying to get the feed and speeds as well as the correct cutter selection just right. I think you need to start hear though and then experiment. Here is a calculator that was posted on one of the other forms I frequent, it may be of help to you.

MAPAL Milling Calculator (http://www.mapal.us/calculators/milling/CalculatorMilling.htm)

Cheers
Tony.

Thanks Tony. I looked at that calculator a couple times, but it always seemed to need a figure i couldn't find, such as chip load, or SFM.

So, this is HSS, not carbide, but is the the general purpose one I should be looking at? HSS Two Flute End Mill 6mm - Straight Shank | eBay (http://www.ebay.com.au/itm/HSS-Two-Flute-End-Mill-6mm-Straight-Shank-/250826529096?pt=LH_DefaultDomain_15&hash=item3a666d1948#ht_2206wt_1180)

[Ger21]

HSS won't last long in wood at all. These are single flute.
5x 6mm Carbide CNC Router Bits Single Flute Tools 25mm | eBay (http://www.ebay.com.au/itm/5x-6mm-Carbide-CNC-Router-Bits-Single-Flute-Tools-25mm-/140548881261?pt=UK_Home_Garden_PowerTools_SM&hash=item20b95dbb6d)

Didn't see any 6mm on your Ebay, but found some on US Ebay:
5 pcs double flute spiral CNC router bits 6mm 22mm | eBay (http://www.ebay.com/itm/5-pcs-double-flute-spiral-CNC-router-bits-6mm-22mm-/170764230313?pt=LH_DefaultDomain_0&hash=item27c2575ea9)

[Ger21]

HSS is generally not a good choice for wood, as it just doesn't last long. Something like this is better.
5 pcs double flute spiral CNC router bits 6mm 22mm | eBay (http://www.ebay.com/itm/5-pcs-double-flute-spiral-CNC-router-bits-6mm-22mm-/170764230313?pt=LH_DefaultDomain_0&hash=item27c2575ea9)

[SawDustSniffer]

So, this is HSS, not carbide, but is the the general purpose one I should be looking at? HSS Two Flute End Mill 6mm - Straight Shank | eBay (http://www.ebay.com.au/itm/HSS-Two-Flute-End-Mill-6mm-Straight-Shank-/250826529096?pt=LH_DefaultDomain_15&hash=item3a666d1948#ht_2206wt_1180)

for your 3d stuff you might need a "ball end mill" , it wont leave steps for you to clean up:2tsup:

[Perfect Pens]

Russell,

Both HSS & Solid Carbide are suitable for timbers and other materials. HSS generally has a better sharper edge than Carbide when new, and if looked after. However Carbide will hold its edge for longer.
The cutting edge is what will generally cause heat as it cuts and travels through the material so the more cutting edges the more heat, the less cutting edges the less heat.
If you look at most router bits for timber they will generally have either One or two cutting edges. I am no expert and still trying to get my head around this as well, but I have found that in some materials standard carbide router bits work better than some of the Solid Carbide cutters be it end or ball nose cutters:2tsup: I have been using cheap Solid Carbide Cutters (not HSS) similar to the ones in your link that I brought in from OS in various sizes, however I am still having some issues with burning etc in certain materials and in some cases breaking bits also.
I think it takes a lot of trial and error to get it right but some of these tables give us a starting point.

Cheers
Tony.

Cheers
Tony.

[BoomerangInfo]

OK, sounds good.

Speaking of breaking bits, so far I've only tried with the 6mm cutter. I'm now at the stage where one of my paths is a very narrow circle in a piece of wood, so I'll have to do a tool change in the middle of the job.

How do you make sure that the steppers don't move out of alignment while changing bits? Do the motors have enough holding torque that they wont move while you make the change, or do you somehow have to try and realign with your home position again once you've changed bits? I don't think I could eyeball a home position reset with enough accuracy so it didn't mis-align with the already cut parts.

Russell.

[Perfect Pens]

Russell,

Once the motors are powered up they should basically hold position. If you are cutting and need to make a tool change both the X and the Y should return to the 0,0 between one tool change to the other. However you may need to reset Z as the tool change will more than likely adjust the height from 0 in the Z depending on how far into or out of the collett you position the cutting bit.
I have a few different small zeroing tools I use for this process.:2tsup:

Cheers
Tony.

[SawDustSniffer]

set the z tool hight buy using the "the peace of paper method " , lay a peace of paper on part of the job that will remain when you start , lower the z axis until it just gips the paper( zero the z axis) , when you change your bit you can do it again

an electric z height setter is best but , a peace of paper works :2tsup:
the ball screws will act like worm drives, where its near on imposable to get the ball screw to turn by pushing on the spindle

[seafurymike]

Here is a chart that I got from NMIT where i do fitting and turning.
Use this as a general setup and tune the cutter to the material being cut.

http://www.woodworkforums.com/f65/milling-feed-rates-126119/#post1228064

/M

[BoomerangInfo]

Here is a chart that I got from NMIT where i do fitting and turning.
Use this as a general setup and tune the cutter to the material being cut.

http://www.woodworkforums.com/f65/milling-feed-rates-126119/#post1228064

/M

Maybe I'm misreading, but that chart maxes at 4000 RPM, and only references metals?

[seafurymike]

The idea is to say pick aluminium and use this as a reference for wood.
Try it on the material you have for the cutter size you want to use.

Its a place to start, then you would tailor the speed up and down and maybe by the time you finish you can make your own chart up which is specific for wood.

No one i know of has anything specific for wood, so this was a means to give you a place to start

[BoomerangInfo]

The idea is to say pick aluminium and use this as a reference for wood.
Try it on the material you have for the cutter size you want to use.

Its a place to start, then you would tailor the speed up and down and maybe by the time you finish you can make your own chart up which is specific for wood.

No one i know of has anything specific for wood, so this was a means to give you a place to start

OK thanks, I'll see if I can make heads or tails out of it.

[SawDustSniffer]

OK thanks, I'll see if I can make heads or tails out of it.

yer its the real fine bits that need the high speed

bit like pen polishing to roughing out 2 foot round bowls :2tsup:

a double cut steel with tungsten tip router bit is designed for 20,000+ , a 10mm mill bit isnt, if the cut is burnished the rev's are too high/ feed rate too slow , ripping up grain the rev's are too slow / feed rate too high !!!!or blunt !!! , bit / speed / material , there is too many variables like knots

brake a bit , well thats just operator error :~ broke a 2mm ball nose tonight :~ no rev's air cut , into the base aluminium , " PING" :no: machines fault i say :no: it is , the machine dosnt have limit switches:2tsup: yet :2tsup: yer yer , 500 mm depth is my fault ??? 50 mm ??? my first berry it into the table and move x back and forth to bore , at least the bit wasn't spinning just a scratch

[Master Splinter]

Details here, including chip loads for different materials:

Calculating Feeds and Speeds - CNC Router Shop (http://www.cncroutershop.com/technical-info/calculating-feeds-and-speeds)

http://www.cncroutershop.com/media/uploads/pages/files/2009/06/02/CNCRoutershop_cutterguide.pdf

[Ger21]

No one i know of has anything specific for wood, so this was a means to give you a place to start

You'll probably need to convert the chiploads into mm's, but if you find an Onsrud tool that's similar to what you have, they'll have a feed and speed for it.
Chiploads | Feeds and Speeds | Metal | Plastic | Composite | | LMT Onsrud (http://www.onsrud.com/xdoc/FeedSpeeds)