Let's talk about CAM

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25 May 2014 22:59 #47310 by yoshimitsuspeed
Thanks for the info. I'm really glad you posted about this.

what do you mean about avoiding sharp corners?

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26 May 2014 00:34 #47316 by DaBit
Replied by DaBit on topic Let's talk about CAM
Let's say you are peeling away metal in 'vertical slices' of one millimeter at a time to make a square pocket. The endmill humms along nicely;a tooth enters the cut and some 40-60 degrees later it exits the cut again.

Now it enters a corner.Suddenly the endmill has to take away a millimeter from both sides of the corner, and load doubles almost instantly. This is a situation that carbide endmills don't like, Especially not in a not-ultra-stiff-homebuild-machine with a spindle that is operating close to it's low maximum torque already.

The same with plunging in the metal; standard endmills are not so good in doing that, and all drilling operations require a lot of torque. A gentle helical or ramped entry into the cut is much easier on the endmill.

Deep cuts peeling away small layers at a time work best with highspeed spindles in metal. It is not cutting speed by itself that dulls endmills, it is the combination of pressure and heat that dulls endmills. By taking small (vertical) layers away you get to the situation that the flutes are in the cut only 15% of the entire revolution and spend 85% of the time in air/coolant. In that small portion of time there is not much heat buildup in the cutting edge and not so much pressure either. This allows you to increase cutting speed, and therefore feed, a LOT. To do this with acceptable removal rates you increase the depth of the cut, which also provides the benefit of using not only the bottom few mm of your endmill but a much larger portion of the cutting length. More chips for the same money.

With an 8mm 4-flute TiAlN coated carbide endmill you can take cuts in regular construction steel of 12mm deep in one pass, 1mm wide, at 9000rpm while feeding at 2100mm/minute using only mist cooling (I use an alcohol mist; that results in completely dry chips. But mind you, while milling steel there is a potential danger since alcohol is flammable and milling steel might produce sparks). After a bucket full of chips the endmill still looks almost new.

Officially this is the territory of CAM-software that can produce constant engagement toolpaths. Unfortunately software like HSMWorks, OneCNC, SolidCAM, etc. is completely unaffordable for us hobbyists. But with some thinking and clever programming it is not hard to force CamBam to do well enough. Split a square pocket in a pocket with severely rounded corners (corner radius much larger than endmill radius) and a few operations to clear the remaining metal, for example.

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26 May 2014 04:06 #47322 by yoshimitsuspeed
Great info.
What are your recommendations for something like a pocket that requires a plunge?

What are your recommendations for something like an exhaust manifold flange where your fastest option is a single cutter width pass?
I have been running a lot of numbers this morning to figure out the limits of the machine. If I was cutting a stainless steel flange I would definitely be pushing the machine and with a 1/4" cutter may just barely be able to get it above 3000 RPM and with full radial width and small cuts like a couple mm in depth may be able to get power requirements down to .2kw. It looks like it will all be pretty near the limits.
Or would I be better stepping down to a 3/16 cutter where I can get the RPMs up a good bit more. Upsides are more power and less resistance but the downside is a smaller, weaker and more flexible cutter.
What are your thoughts for a situation like this?
Otherwise for things like pockets instead of taking a full width cut you could just do a plunge then spiral out with something like 20% of the cutter width or something like that. This still has me wondering on best techniques where you will need to plunge.

Most of my work comes from manual machining and in my experience with steel with the right feeds and speeds no lubricant or cooling should be needed. What are others thoughts on this?
It's interesting to hear you are using alcohol. Once concern I have often heard is that of water or coolant actually shocking the cutter and shortening life. At my last job even most of the CNC machining we did on steel we did dry and had very good luck with cutter life and finish. Of course this also greatly depended on the cutters as well. I know there were some brand new carbide cutters I'd throw on the mill and it would cut horribly, get hot and smoke it's self. Throw a good cutter in there and triple the feeds and speeds and it would happily cut dry all day long for weeks.

This topic has gone pretty far off topic but I would love to continue the convo.
Any way a mod can move this part into a new thread more on topic?
Not sure what the topic would be called though.

How to get by when your equipment is too small?
Using small tools in big pockets?

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26 May 2014 05:51 #47326 by DaBit
Replied by DaBit on topic Let's talk about CAM
A word of caution upfront: I am just a hobbyist with a Chinese (BF20/G0704) mill who managed to find a set of cutting parameters that the machine likes. I am in no way an expert.

yoshimitsuspeed wrote: Great info.
What are your recommendations for something like a pocket that requires a plunge?


Helical entry with a 2 degrees angle or a ramp-in over almost the entire pocket outer edge if the pocket is large enough.

What are your recommendations for something like an exhaust manifold flange where your fastest option is a single cutter width pass?


I consider the mill as just another tool, not as the 'one solution to solve all problems'. Thus, If I need only one or a few, I would drill the flange bolt circle holes using the mill so you have a reference, use the bandsaw or angle grinder to roughly shape the flange contour, then clean up on the mill using the previously drilled holes to hold the workpiece and align the mill. Cutting off chunks of metal is a lot faster than converting them into chips on the mill anyway and I can prepare flange #2 while #1 is cutting on the mill.
The large inner hole is something I would mill away completely, starting from a hole I drilled before and spiralling outwards. My drill press with it's 3/4hp motor makes a 16mm hole in steel sheet metal a lot quicker than my Chinese 24k rpm spindle does.

Using the bolt circle holes to screw down the flange makes it possible to clamp down the work tightly so it won't vibrate, and you don't need holding tabs.

If I cannot do that (or if am too lazy) and the contour cut is deep, I take small depth steps and mill a contour ~1.4x as wide as the cutter diameter so chips can get away.

But maybe your machine can handle deep slots with endmill diameter just fine. All those machines seem to be happy with different cutting parameters.
My Chinese mill definitely doesn't like plunging and slotting in steel, so I work around it.

I have been running a lot of numbers this morning to figure out the limits of the machine. If I was cutting a stainless steel flange I would definitely be pushing the machine and with a 1/4" cutter may just barely be able to get it above 3000 RPM and with full radial width and small cuts like a couple mm in depth may be able to get power requirements down to .2kw. It looks like it will all be pretty near the limits.


Stainless is one of the materials I am not very happy with. I did a motorcycle brake caliper adapter in 316 stainless for a friend using a 6mm 4-flute TiAlN coated endmill, but it was slow and it did cost me an endmill.

Or would I be better stepping down to a 3/16 cutter where I can get the RPMs up a good bit more. Upsides are more power and less resistance but the downside is a smaller, weaker and more flexible cutter.
What are your thoughts for a situation like this?


I would use the smaller cutter; 3000rpm is borderline on those spindles. They really are made for 6000+ rpm and although they can do lower RPM's (the watercooled ones at least) it is not their strength.
Maybe with a better VFD this changes, I don't know.

Otherwise for things like pockets instead of taking a full width cut you could just do a plunge then spiral out with something like 20% of the cutter width or something like that. This still has me wondering on best techniques where you will need to plunge.


Just spiral in too. CamBam gives you that option in the 'lead in/out' section of the machining operation parameters.
Spiralling out is a good thing. Use 1/10th to 1/6th of the cutter diameter, go full depth, forget the cutting speed you got from that 1950's era book. As a guideline, use 60-70% of the cutting speed the manufacturer provides for low angle of engagement cuts (they are often very agressive, great in production, not so great if you have to pay for the cutters yourself), and increase RPM and feed. Modern coated carbide endmills are definitely way ahead of HSS endmills (although I do like the toughness of HSS/HSSCo8 cutters)

Most of my work comes from manual machining and in my experience with steel with the right feeds and speeds no lubricant or cooling should be needed. What are others thoughts on this?


I do mill steel without cooling or lubrication if I can keep the feedrate up.

It's interesting to hear you are using alcohol. Once concern I have often heard is that of water or coolant actually shocking the cutter and shortening life. At my last job even most of the CNC machining we did on steel we did dry and had very good luck with cutter life and finish. Of course this also greatly depended on the cutters as well.


Alcohol has the tendency to flow into tight spaces much better and quicker than water does, the droplets in the mist are very small, and I like a blast of compressed air to get rid of the chips in the cutting zone anyway so adding a little alcohol is easy.
I do mill steel dry, but the finish pass is often close to 'rubbing away the metal' due to the limited stiffness of my machine. And if you cannot make chips that are thick enough to carry away the heat, you need something else.

I know there were some brand new carbide cutters I'd throw on the mill and it would cut horribly, get hot and smoke it's self. Throw a good cutter in there and triple the feeds and speeds and it would happily cut dry all day long for weeks.


I am done with Ebayed Chinese carbide cutters too. What they use for PCB production is good value for money, but the rest?
They cost only 20% of a decent one, but you need 10 of them to do the same amount of work.

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27 May 2014 07:02 #47373 by allenwg2005
Replied by allenwg2005 on topic Let's talk about CAM
It's been a long time since I visited this thread, and a while since anyone posted anything.

It's a little late to suggest a system but I thought in the event you looked here again it may be helpful to share a
CAD/CAM program that may help.
Go to webersys.com and check out Synergy.

I have enjoyed working with it\ and it's well priced.

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29 May 2014 11:59 #47501 by yoshimitsuspeed
Can you give a rough idea of price. I really hate it when companies make you contact them for pricing. I believe I found them at one point and I am pretty sure that's why I ignored them.

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05 Jun 2014 00:12 #47683 by yoshimitsuspeed
DaBit
I will be setting up my HY spindle and VFD today.
If you have any input I would love to hear it.
www.linuxcnc.org/index.php/english/forum...tions?start=20#47682

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05 Jun 2014 19:44 #47717 by DaBit
Replied by DaBit on topic Let's talk about CAM
Basically you have to make sure the inverter is set up for a 220V/400Hz motor. If you set it up for a 50/60Hz motor things will go wrong. But since you are able to already run the inverter, this is already done by the manufacturer.

What the manufacturers don't do is optimize the settings, so at low RPM you probably do not get any performance at all. For this you need to modify the V/f curve. Page 28 in the inverter manual is useful; it shows some graphs and description of the parameters.

Basically you want to load the motor, and change the intermediate frequency (PD006) and intermediate voltage (PD008) so you can have the motor draw maximum current (which equals maximum torque) when loaded heavily at 2500-3000rpm. Next test at other RPMs that no strange things happen. See the first few pages of the manual on how to change the display to 'display output current'.

Usually you have to increase both the intermediate frequency and voltage a bit.

Make sure the coolant flow is OK when doing this; these motors use the absolute bare minimum of copper and will produce quite a bit of heat when loaded heavily at low RPM. No large flow is needed, but you do need an uninterrupted flow of coolant.

Also: run your spindle bearings in before you do anything else. Half an hour 5000rpm, half an hour 10000rpm, half an hour 15000rpm.

Given my experience with Chinese stuff it would even be best to disassemble the spindle, inspect everything, clean and regrease the bearings with highspeed grease, and put it back together before even attempting to run it.
I did not do this, and sooner or later I will regret that given the insufficient or missing amount of low-quality-anyway grease and high amount of dirt and debris in Chinese bearings/ball nuts/etc.

(Japanese/Germany import bearings, yeah, right.. P4 rating, yeah, right...
Two sets of those bearings costs 3 times as much as the entire spindle+VFD package. Consider 'German import' as 'we shipped a box of round things that appears to resemble a ball bearing to Germany first, and had it shipped back immediately').

Also measure runout on the spindle taper. Some of these spindles are good and do comply to the <0,005mm TIR given, some of them are really bad doing worse than 0,1mm TIR. There is no pattern; either you are lucky or you are not.
The sellers usually accept complaints about that and solve it (a little pressure may be needed but luckily they are very allergic to bad reviews on Ebay), but not if you complain two months after buying and using it.

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18 Jun 2014 14:02 - 18 Jun 2014 14:06 #48049 by yoshimitsuspeed

DaBit wrote: Basically you have to make sure the inverter is set up for a 220V/400Hz motor. If you set it up for a 50/60Hz motor things will go wrong. But since you are able to already run the inverter, this is already done by the manufacturer.

What the manufacturers don't do is optimize the settings, so at low RPM you probably do not get any performance at all. For this you need to modify the V/f curve. Page 28 in the inverter manual is useful; it shows some graphs and description of the parameters.

Basically you want to load the motor, and change the intermediate frequency (PD006) and intermediate voltage (PD008) so you can have the motor draw maximum current (which equals maximum torque) when loaded heavily at 2500-3000rpm. Next test at other RPMs that no strange things happen. See the first few pages of the manual on how to change the display to 'display output current'.

Usually you have to increase both the intermediate frequency and voltage a bit.

Make sure the coolant flow is OK when doing this; these motors use the absolute bare minimum of copper and will produce quite a bit of heat when loaded heavily at low RPM. No large flow is needed, but you do need an uninterrupted flow of coolant.

Also: run your spindle bearings in before you do anything else. Half an hour 5000rpm, half an hour 10000rpm, half an hour 15000rpm.

Given my experience with Chinese stuff it would even be best to disassemble the spindle, inspect everything, clean and regrease the bearings with highspeed grease, and put it back together before even attempting to run it.
I did not do this, and sooner or later I will regret that given the insufficient or missing amount of low-quality-anyway grease and high amount of dirt and debris in Chinese bearings/ball nuts/etc.

(Japanese/Germany import bearings, yeah, right.. P4 rating, yeah, right...
Two sets of those bearings costs 3 times as much as the entire spindle+VFD package. Consider 'German import' as 'we shipped a box of round things that appears to resemble a ball bearing to Germany first, and had it shipped back immediately').

Also measure runout on the spindle taper. Some of these spindles are good and do comply to the <0,005mm TIR given, some of them are really bad doing worse than 0,1mm TIR. There is no pattern; either you are lucky or you are not.
The sellers usually accept complaints about that and solve it (a little pressure may be needed but luckily they are very allergic to bad reviews on Ebay), but not if you complain two months after buying and using it.


Thanks
I wish I had seen this sooner. I didn't see anything about running in the bearings and started cutting after getting it dialed in. It was very light duty work so hopefully that counts for something.
One thing I have noticed is the spindle has a lot of axial movement. I have been thinking about taking it apart to see if I can tighten it up.
I don't think I have come across any info or manuals on taking the motor apart. I also haven't looked into it too much. I assume I need to take off the collar at the base and then unthread the piece on the spindle with the two holes in it.
It sounds like you have taken these apart. Is that a standard size spanner to take that off? What did you use?
Do you know if/how to take up that axial play?
What grease do you recommend?
Last edit: 18 Jun 2014 14:06 by yoshimitsuspeed.

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18 Jun 2014 14:39 #48050 by DaBit
Replied by DaBit on topic Let's talk about CAM

yoshimitsuspeed wrote: Thanks
I wish I had seen this sooner. I didn't see anything about running in the bearings and started cutting after getting it dialed in. It was very light duty work so hopefully that counts for something.
One thing I have noticed is the spindle has a lot of axial movement.


It should not have any.

It sounds like you have taken these apart. Is that a standard size spanner to take that off? What did you use?
Do you know if/how to take up that axial play?


I did not take mine apart, although I think I should have done so when I received the spindle.
If you google around there are some reports about taking apart these spindles. This one for example (but there are more): www.cnczone.com/forums/spindles-vfd/1294...dle-disassembly.html

What grease do you recommend?


Some highspeed spindel bearing grease like SKF LGLT2 , Klueber Isoflex Super Tel , etc. I have no experience with either of these greases, but that is what was recommended to me.

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