CNC Speed & Feed...

[riche543]

Hey guys , just curious what other CNC users have for there speed & feed rates for cutting Acrilyic/perspex. as most calculators ive found on the net are for Hard Materials ie: metal.. Im cutting ok at 400mm per min at 21000 RPM & a depth of 1.5mm with a millend of 1.59mm. If anyone one does know a good calculator or formula That would be great..

Cheers all....:)

[Westozy]

I have been cutting out panels with a 3mm endmill at 300mm/min at 15,000rpm and this is giving good results. There is no fixed formulae for machinists only guidelines really. Look, Listen, Feel! If it looks good, the motor doesn't sound like it's straining too much and you can feel the cut is smooth then you're on the right track. Be careful with the RPM if the cutter gets too hot it will pick up material as it goes and make bad cuts. If you are going to cut any aluminium, use CRC spray or kerosene as a lube/coolant and use minimal speeds and feeds.

Cheers Gwyn

[flatlandpilot]

1mm deep, 3mm.bit 150mm./min at 15000 rpm works fine for me in acrylic
for PVC I throttle down the rpm, with MDF I can go deeper and faster.

With too much speed the bit can become hot, the acrylic dust than can stick together.
the next pass, the bit will hit than melten down dust, wich sounds horrible.

for speeding up you better use bits with 2 or 4 cuttingsides? instead of the endmill bit with 1 side I use. (sorry for my english)
you can try it by hand, just to get a indication of the force it will have later in the mill with that speed.

The "Endmills for plastic" gave good result for me.
Damencnc (http://www.damencnc.com/damencnc.php?dir=cpt&PHPSESSID=4ab9778e1ff4ab1c01fef73df6336ae2&langId=EN&idType=9&PHPSESSID=4ab9778e1ff4ab1c01fef73df6336ae2)

more info on cutting in plastics:
www.plasticrouting.com/van.asp (http:/www.plasticrouting.com/van.asp)

[riche543]

Thanks for the reply guys, Gwyn at what depth are you cutting per pass?.
Looking at that link there talking bout cutting 300 INCHES? a min at 18000rpm. That seems way to fast ??.
Cheers..

[flatlandpilot]

cutting per pass?.
With more feed and less depth/pass everything is cooler,
with plastics its good to keep the feed high.

300 mm/min a minute looks a lot better :?

for me 150mm/min with a small bit is fast.
(on a small 200x200mm. Sable table)

[Westozy]

Thanks for the reply guys, Gwyn at what depth are you cutting per pass?.
Looking at that link there talking bout cutting 300 INCHES? a min at 18000rpm. That seems way to fast ??.
Cheers..

I usually do 3mm step cuts in acrylic, (3mm x 300mm/min x 3mm cutter = 3x3x3 there's a formula!!!) I have some single flute endmills which clear out the waste really quickly and allows quicker feeds. I am doing plate production stuff and making multiple pieces of the same parts so finding the quickest feeds is a priority! I'll ask Matt to create a CNC forum, there is quite a few of us now!

Regards, Gwyn

[Westozy]

I'll ask Matt to create a CNC forum, there is quite a few of us now!

Regards, Gwyn

Matt, you're a champ! He has created a new CNC forum for us!!!

Cheers, Gwyn

[fweinrebe]

The "Endmills for plastic" gave good result for me.
Damencnc (http://www.damencnc.com/damencnc.php?dir=cpt&PHPSESSID=4ab9778e1ff4ab1c01fef73df6336ae2&langId=EN&idType=9&PHPSESSID=4ab9778e1ff4ab1c01fef73df6336ae2)

more info on cutting in plastics:
www.plasticrouting.com/van.asp (http:/www.plasticrouting.com/van.asp)

Thanks for the very handy link. I've been looking for an info page like this.
I am still aligning my CNC with a black permanent marker and will move to the heavy stuff soon.

[riche543]

Hi guys, I started this topic as i thought my Speeds & Feeds Wernt quite right. so i tried Gwyns numbers there to see how it came out. Funny thing is that at 300mm per min 18000rpm depth of 1.5mm per pass my cuts were worse. Thery wernt smooth. Now running at 300mm/min 22000rpm & getting much smoother edges. I am using a (2 flute endmill 1.59mm) the only thing i can think that is diffrent is the endmill 1flute to 2 flute ???? Dunno , anyways as you said before gwyn There is no real formular for this its just look listen feel

Cheers.
Riche.. Happy CNCing..........:)

[DaveC3]

Check out this web page, it may help you figure where the sweet spot is for you material, speed and feed rates.
http://www.precisebits.com/tutorials/calibrating_feeds_n_speeds.htm

Take care

Dave

[Wendy]

Hello,

Best way to determine the correct settings is by testing, that is how I did it. But for the ones who wants to calculate things... here is a piece of text.

Regards, Wendy

Speed – Surface Feet Per Minute (SFM) is the actual speed at which the cutting edge of the tool is striking the material. It is used to determine spindle revolutions per minute (RPM). There are two formulas that relate these two values and take into consideration the tool bit diameter.
SFM = .262 x Diameter (inches) x RPM RPM = 3.82 x SFM / Diameter (inches) For most operations the RPM commonly runs between 10,000 to 20,000. Depending on bit diameter, the speed can be as low as 300 SFM and may run as high as 2400 SFM although it more commonly runs from 500 to 1500 SFM. This will change based on the demand for material removal and edge finish requirement. This is the first of three factors that will affect material finish.
Chip load - Inches Per Tooth (IPT) corresponds to the amount of material removed by each tooth of the cutter every time it contacts and passes the material. Sufficient chip load will create stability between the cutter and the work piece. The optimum chip load for acrylic
sheet is .004" to .015"/tooth.

Feed Rate – Inches per Minute (IPM) is the distance that the cutting tool travels along the edge or surface of the material being processed in one minute. The proper range for feed rate can be determined by considering the chip load. Operating in the lower part of the recommended range for chip load will tend to provide a better finish but at the expense of throughput. Operating at the
high end of the recommended range for chip load will result in a rough finish on the part but higher part throughputs. Typical feed rate parameters for ACRYLITE FF sheet range from 100 to 300 IPM. To establish the feed rate knowing the desired chip load, the number of cutting edges on the bit and the RPM use the following formula:
IPM = IPT x No. Teeth x RPM