can someone help me calculate feed rate please :)

[GER8LE]

hi im new here and have had my cnc machine for about 2 years now and am trying to fine tune production if someone could help please.

ok im cutting mdf (medium density fibreboard) and im using a 3mm bit with 2 flutes

the spindle is water cooled and and the rpm is 2500

max cutting depth im doing is 8mm

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i snap bits now and then, apart from that it works ok.

also my workshop gets quite cold, maybe 3c at its worst, can this affect the snapping of bits, should i warm the cutting bits up before cutting

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[Jim Dawson]

2500 RPM is a bit slow for a 3mm bit in MDF, about 10 times that would be better. Try about half of your current feed speed and see what happens. I don't think the shop temperature will have any effect on the tool bit, it will warm up very quickly when cutting. When making a full width cut, in this case 3mm, I normally limit the DOC to 2x the cutter diameter.

[GER8LE]

2500 RPM is a bit slow for a 3mm bit in MDF, about 10 times that would be better. Try about half of your current feed speed and see what happens. I don't think the shop temperature will have any effect on the tool bit, it will warm up very quickly when cutting. When making a full width cut, in this case 3mm, I normally limit the DOC to 2x the cutter diameter.

thanxforreplying,i would like to increase the speed if possible.could you recomend a spindle as im using a 1500watt watercooled from ebay for the cheap chinese cnc 6040

[GER8LE]

sorry i got it wrong im using a 24000rpm spindle this one here
1.5KW 80MM WATER COOLED CNC SPINDLE MOTOR ER11&1.5KW VFD INVERTER DRIVE 220V | eBay

[Jim Dawson]

Ahhh, 24,000 is good. Again, I would reduce the DoC and make one or two extra passes. I think that will help with tool breakage. Another thing comes to mind, is your tool really sharp? A dull tool bit is much more likely to break due to the increased cutting forces. A dull tool will still cut, but the feed rate has to be reduced which of course increases tool wear. There comes a point that you just have to install a new tool bit.

[GER8LE]

i admit i am using cheap bits, maybe thats the problem but i did buy a much more expensive bit and that broke just as quickly. some of the cheap bits cut just fine.
altering the gcode to do more passes will double the cut time and also be a lot of hassle. is there a way to calculate the correct max speed at a depth of 8mm

[Jim Dawson]

You might find this helpful http://www.shopbottools.com/ShopBotD...sandSpeeds.pdf

The feed also depends on how stiff your machine is. The lighter the machine, the more vibration there will be at the tool bit, and thus more prone to breaking small tool bits.

[GER8LE]

thanx will analyze this when sober lol

[cncjack01]

Cutting refers to the cutting speed of V C, f (feed or feed rate V f), a p. The cutting depth of the three, also known as cutting the three elements.
1, cutting speed VC refers to the cutting edge of the selected point relative to the workpiece to be machined surface in the main movement side cutting dosage
The instantaneous velocity unit is M/min.
2, feed f in the main movement of every turn or every stroke (or unit time), the tool and workpiece along the direction of feed movement relative displacement, unit mm/s.
3, the cutting depth (cutting depth) AP surface to be machined and the machined surface of the vertical distance between the units mm.

hope can help you .
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[GER8LE]

ok i found some usefull info for calculating speed through wood/plastic

bit diameter devided by 0.02 then multiply by the amount of flutes then multiply that by the rpm.
so i have a 3mm bit with 2 flutes running at 24000rpm so

3 x 0.02 = 0.6
0.6 x 2 flutes = 0.12
0.12 x 24000rpm = 2880

so my travel speed should be set at 2880mm per minute? is this correct

[ger21]

I'd keep the rpm down around 18,000.
At 18,000, you can cut MDF at up near 7500mm/min with that tool.

However, the rigidity of your machine will have something to do with that.
I'd start at 18,000 rpm, 4000mm/min, with a maximum depth of cut of 3mm (diameter).
Then play around with lower spindle speeds at the same feedrate. You may be able to go down to 15,000.

If you decrease the feedrate below 4000, decrease the rpm proportionally.

[GER8LE]

I'd keep the rpm down around 18,000.
At 18,000, you can cut MDF at up near 7500mm/min with that tool.

However, the rigidity of your machine will have something to do with that.
I'd start at 18,000 rpm, 4000mm/min, with a maximum depth of cut of 3mm (diameter).
Then play around with lower spindle speeds at the same feedrate. You may be able to go down to 15,000.

If you decrease the feedrate below 4000, decrease the rpm proportionally.

thanx for the help,you have given me much to go on

[A_Camera]

hi im new here and have had my cnc machine for about 2 years now and am trying to fine tune production if someone could help please.

ok im cutting mdf (medium density fibreboard) and im using a 3mm bit with 2 flutes

I am using this online calculator. Works fine.

FSWizard - Advanced Online CNC Speed and Feed Calculator

[Purwa]

i;m using a simple way to get feedrate depend on the rpm ,how many flute and how many cutting per flute,
for example using 3 mm finishing 4 flute and Rpm is 5000, and each flute will be cut 0.04 mm
the count is 0.04 x 4 x 5000 = 800 mm/minute
and cutting per flute can be higher depends on the materials
CMIIW

[jocobs]

Thank you ,that's a good idea .