M3 plastics feeds and speeds/axial and radial depths of cuts

[emac319]

Just purchased the M3 with all the upgrades. Looking for experience in plastics with this machine. Feeds/speeds successes with depths of cuts as well. Trying to get a cycle time idea of a project that I have programmed already.

Thanks!

[aforww]

Feb 26, 2017 22:05:56 GMT emac319 said:

Just purchased the M3 with all the upgrades. Looking for experience in plastics with this machine. Feeds/speeds successes with depths of cuts as well. Trying to get a cycle time idea of a project that I have programmed already.

Thanks!

Unfortunately it's not that easy lol.

1. Type of plastic?
2. Actively cooling and clearing chips via compressed air?
3. Single bit size or multiples?
4. How many flutes?
5. Upcut or straight bits?

Plastics can really be tricky due to varying melting points. Even within the same category.

[emac319]

HDPE
I would like to use compressed air to remove the chips afterwards. I haven't decided on an endmill geometry yet, however I'm thinking a two flute 1/4" end mill. When you say upcut or straight type, are you referring to helical vs straight flutes?? My initial take on cutter geometry for plastic is try to throw the chips outwards from the cutter rather then upwards which would create chip wrap around the shank.

[aforww]

HDPE
I would like to use compressed air to remove the chips afterwards. I haven't decided on an endmill geometry yet, however I'm thinking a two flute 1/4" end mill. When you say upcut or straight type, are you referring to helical vs straight flutes?? My initial take on cutter geometry for plastic is try to throw the chips outwards from the cutter rather then upwards which would create chip wrap around the shank.

It's all dependent on the type of milling you will be doing.

On using compressed air, with plastics, it's highly advisable that you use compressed air or have a good dust shoe to clear chips away from the material during the cutting operation.

Flue geometry has four basic categories. 
1. Straight
2. Up-cut
3. Compression (down-cut)
4. The combination of 2 and 3. 

With an up cut geometry, the chips are pulled away from the workpiece clearing the kerf of material and heat. Whereas the straight flute will rely on external help to clear the path, especially in deeper cuts that are the full width of the mill. 

The reason pulling the chips up and away and having compressed air or a dust shoe is important is because of "chip welding". If you don't clear the chips you run into all kinds of problems. The chips will stay in the kerf causing recutting which increases heat build-up. These chips start to "weld" themselves to each other, the bit, and the workpiece. 

Now, on the topic of flutes. I use a single flute for plastic for the same reasons above. Chip clearance. 1 flute allows a ton more room for the chips to go to meaning I can take more aggressive cuts and also worry less about chip welding. In plastics, more flutes are not better. If you are getting material wrapping around the flutes, you're taking to much material off or plunging too fast and too deep. Or, you're getting chip welding as I mentioned earlier. It also happens frequently with smaller diameter cutters simply because the smaller geometry isn't conducive to chip clearing and chip breaking. 

Speeds and feeds are all based around Chip Load. Chip load is the amount of material each flute removes per revolution. With a single flute up-cut 1/4" I shoot for anywhere from .003 - .005 inches. 

Here is a decent Speeds and Feeds Calculator www.daycounter.com/Calculators/GCode/Feed-Rate-Calculator.phtml

This is an excellent source for recommended chip loads for various materials. www.onsrud.com/xdoc/feedspeeds
    

[emac319]

Understood. I have a good amount of machining background as I am a mfg engineer in a cast iron shop. Have done lots of work with steels and aluminums as well. Have never machined plastic though. I do agree with single flute having more flute volume to remove chips. I was mainly after some ball park feeds and speeds. Thanks for the links and all the info. You seem very knowledagbe with machining. How do you like the M3? What sorts of limitations have you run into so far??

I just purchased the machine yesterday so I will be waiting three weeks to get it but I have some projects already lined up that should be able to pay for the machine pretty easily.

What types of projects have you completed with the machine??

Thanks again for all the help!

[aforww]

Feb 27, 2017 14:06:37 GMT emac319 said:

Understood. I have a good amount of machining background as I am a mfg engineer in a cast iron shop. Have done lots of work with steels and aluminums as well. Have never machined plastic though. I do agree with single flute having more flute volume to remove chips. I was mainly after some ball park feeds and speeds. Thanks for the links and all the info. You seem very knowledagbe with machining. How do you like the M3? What sorts of limitations have you run into so far??

I just purchased the machine yesterday so I will be waiting three weeks to get it but I have some projects already lined up that should be able to pay for the machine pretty easily.

What types of projects have you completed with the machine??

Thanks again for all the help!

Sorry for the layman response! We have a few folks here with machining backgrounds. I am not one of them. I only started learning all of this within the last year or so but I feel like I caught on quickly.

Hard plastics have the same characteristics as aluminum in regards to the problems they present. Plastics just have a lower heat tolerance before they start sticking. Faster is better as long as you're evacuating chips and heat.

I love this little machine. Obviously it has it's limits but it's absolutely the best bang for the buck. I haven't really pushed the boundaries of this machine yet. I've got some testing to do on that front though. I want to see just how hard and fast I can push it in aluminum. I'll try hdpe as well.

Most of my projects have been just random stuff. Parts for this or that, parts for the machine itself, stuff out of ABS, acrylic, HDPE, and aluminum.

If I remember correctly, my speeds for HDPE were:
15k RPM
40ipm
.0625" doc using a ramping approach.
This equates to somewhere near .003 of chip load.

I'm pretty confident that can be increased a fair bit. I've also read that HSS is better for plastics like HDPE than carbide but can't confirm that.

[markwisniowski]

Feb 27, 2017 1:56:11 GMT aforww said:

Feb 26, 2017 22:05:56 GMT emac319 said:

Just purchased the M3 with all the upgrades. Looking for experience in plastics with this machine. Feeds/speeds successes with depths of cuts as well. Trying to get a cycle time idea of a project that I have programmed already.

Thanks!

Unfortunately it's not that easy lol.

1. Type of plastic?
2. Actively cooling and clearing chips via compressed air?
3. Single bit size or multiples?
4. How many flutes?
5. Upcut or straight bits?

Plastics can really be tricky due to varying melting points. Even within the same category.

I'll jump on this thread since I'm messing with acrylics now

400W Spindle (0-12k rpm)

1. Type of plastic?
-- EXTRUDED ACRYLIC

2. Actively cooling and clearing chips via compressed air? 
-- No, but does focused vacuum suction qualify for anything?

3. Single bit size or multiples? 4. How many flutes? 5. Upcut or straight bits?
-- Onsurd 1/8" Single O flute Upcut solid carbide endmill
(http://www.ebay.com/itm/152275745146?_trksid=p2060353.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT)

Also, does it help to do a climb movement when roughing out and then a conventional when finishing?