[cobrakai]

Anyone have insight as to what causes this? The ripples I am referring to are on the flat side of the part. But now that I look at it, the chamfer has a ripple as well.

I roughed with a 1/2" 3Fl carbide 5000 RPM .25" DOC .1" WOC and left .005" for finishing pass. Finished with a 3/8" 3Fl, .375" DOC, .005" WOC, and I used GWizard to calculate the feed for a .001" chip thickness. I think it was something like 5000RPM and 38IPM.

My first thought is I need to go slower. But after some searching, people say this is rubbing and I actually need to go faster and aim for a thicker chip.

My understanding is that a finishing pass chip should have have a .001 for smooth finish. Roughing is .003 to .005 for our machines. Is this sounding right?

[popspipes]

Attachment 253522

I have the same marks in mine, I just ran these this evening, it depends how the light shines on them for looks, they feel smooth to the touch. I think its related to the steppers as the mark spacings vary as to the feedrate.
These profiles are done with a .25 carbide 4 flute ball mill .005 woc 20 ipm finish pass.

Personally I think your part looks good.

I am using a 1 flute .125 engraver for the chamfer and it looks a bit rough as I dont have enough rpm for them at 20 ipm.

[CadRhino]

Neat
What are those parts for

Attachment 253522

I have the same marks in mine, I just ran these this evening, it depends how the light shines on them for looks, they feel smooth to the touch. I think its related to the steppers as the mark spacings vary as to the feedrate.
These profiles are done with a .25 carbide 4 flute ball mill .005 woc 20 ipm finish pass.

Personally I think your part looks good.

I am using a 1 flute .125 engraver for the chamfer and it looks a bit rough as I dont have enough rpm for them at 20 ipm.

[popspipes]

Neat
What are those parts for

They are Zenoah carb to cylinder adapter blocks.

[cobrakai]

Attachment 253522

I have the same marks in mine, I just ran these this evening, it depends how the light shines on them for looks, they feel smooth to the touch. I think its related to the steppers as the mark spacings vary as to the feedrate.
These profiles are done with a .25 carbide 4 flute ball mill .005 woc 20 ipm finish pass.

Personally I think your part looks good.

I am using a 1 flute .125 engraver for the chamfer and it looks a bit rough as I dont have enough rpm for them at 20 ipm.

Those do look cool.

Hmm... I have dreams of a perfectly smooth finish on the side. Do you have a Series 1, 2, or 3? I have a series 2 and after watching videos online, the series 3 motors are significantly smoother and faster.

[popspipes]

Mine is a series 3, I balanced the spindle and drive parts soon after I got the machine, the main problem was the motor fan impeller which they have now corrected, that put a herring bone type wave in the finish at times.

Steppers start and stop, they are not a smooth rotation, and I think that may be what causes it or at least part of it.

My parts are small so I take the finish pass full depth less than .500 that blends in the rough passes.

[cobrakai]

Mine is a series 3, I balanced the spindle and drive parts soon after I got the machine, the main problem was the motor fan impeller which they have now corrected, that put a herring bone type wave in the finish at times.

Steppers start and stop, they are not a smooth rotation, and I think that may be what causes it or at least part of it.

My parts are small so I take the finish pass full depth less than .500 that blends in the rough passes.

Funny you mention that cause I work with steppers in my career quite often. I use microstepping drives with a resolution of 51,200 steps per revolution. Tuned properly, I can eliminate any perception of steps entirely. They are as smooth as servos and a lot cheaper. I wonder why Tormach didn't do that.

[popspipes]

Probably cost I would imagine. I would like to see them offer a dedicated machine controller, the personal computer and Mach 3 are not as problem free as I would like. I really dont trust it to let it run unattended.

Its a good machine for the price though, I am happy with mine. Mine is a retirement thing, I always wanted to learn cnc machining, so I bought it to mainly learn the trade and make a few parts, I must say I havent regretted it at all........

[cobrakai]

Oh for sure, it's a good value. It's a lot better than I can do with a hand file and cordless drill!

I too learned on the machine. Crashed it once or twice and the worst that happened was a chipped tool or gouged part. It's slow and weak enough not to really hurt itself like a pro level machine.

[mountaindew]

Mine is a series 3, I balanced the spindle and drive parts soon after I got the machine, the main problem was the motor fan impeller which they have now corrected, that put a herring bone type wave in the finish at times.

.

I have never come across this information other then the 770 spindles are balanced for high speed.
Please provide more detail on how this is measured and done. I like to keep my mill tuned and in top running order and this sounds like something to schedule and look at .
Thanks in advance for any information or tricks.
md

[Don Clement]

More information is really needed to find the cause of the periodic ripples. I would suggest using a dynamic analyzer during the machining process or a static FFT analysis of the periodic ripples so as to compare the periodic contributions from various rotating machine parts i.e. stepper motors, ball bearing races, spindle motor imbalances,cutter flexure, etc.

Don Clement

[G59]

I would suggest using a dynamic analyzer during the machining process or a static FFT analysis of the periodic ripples so as to compare the periodic contributions from various rotating machine parts i.e. stepper motors, ball bearing races, spindle motor imbalances,cutter flexure, etc.

Dynamic analyzers? LOL. And who can afford that as part of their regular maintenance programs?

Personally I don't know what causes it, but I've seen this ripple effect on servo driven mills.

[Don Clement]

Dynamic analyzers? LOL. And who can afford that as part of their regular maintenance programs?

Personally I don't know what causes it, but I've seen this ripple effect on servo driven mills.

Nowadays with the power of the PC one doesn't have to spend much to get the performance of the high priced dynamic analyzers from the last century. There are even FFT and vibration analyzer apps for cell phones: https://play.google.com/store/apps/d...id=com.app_fft and Vibrations Analysis App for Android

Don Clement

[jid2]

A major factor in surface finish is rigidity. What i see looks pretty typical for these sized machines.

I always roughed leaving .020, then a semi finish of .015 and a final finish of .005.

[TurboStep]

Anyone have insight as to what causes this?

This looks like a fairly bad case of what was discussed in this thread:
http://www.cnczone.com/forums/tormac...ml#post1140470
At the end of this post I described a simple calculation that should help you determine whether my assumption is indeed correct. If you can't follow my description simply post your feed rate and spindle speed and I'll calculate the number of "ripples" per inch that expect you're seeing.
Step

Edit:
This the kind of finish that you can (sometimes) get after balancing:
Attachment 253564

[tmarks11]

Personally I don't know what causes it, but I've seen this ripple effect on servo driven mills.

And I have got the same results on a Bridgeport when hand cranking the Y axis while side cutting with an end mill. Combination of side loading of the end mill, flex/chatter, each individual blade as it cuts, and some run-out or imbalance in your spindle. That is normal.

I don't think it is related to your steppers, or micro-stepping. The steppers are set at 2400 steps per revolution, and are directly coupled to a lead screw with 0.1" pitch. That means the pulsing of your steppers would be leaving an imperfection in your finish every 0.100"/2400 = 0.000045" (0.045 tenths of a thousandth). That would not be visible without a microscope.

If that regular repeating pattern were due to runout, the spacing of the lines would be 0.0076" apart. Spacing= FR/RPM. In the absence of any frame of reference for your picture, I am sure that what you are showing is probably more like 0.050" spacing. So probably not runout.

Funny you mention that cause I work with steppers in my career quite often. I use microstepping drives with a resolution of 51,200 steps per revolution. Tuned properly, I can eliminate any perception of steps entirely. They are as smooth as servos and a lot cheaper. I wonder why Tormach didn't do that.

Tormach does. But they are limited on control frequency because of using the parallel port as the pulse generator, so have conservatively chosen a micro stepping rate that makes the maximum pulse rate 16kHz at 110 ipm. The Lead shine drivers they use allow micro stepping to 25600 steps per revolution, but Tormach settles for 2400. That means each mi

Mach 3 documentation says don't try to get faster than 35 kHz, so there is a little room for modification before you hit that limit. Increasing micro step rate isn't going to give you a better finish, and I doubt it will give you better precision in moving the axis, since the error induced by micro stepping is already on the order of backlash and slop in the assemblies.

This looks like a fairly bad case of what was discussed in this thread:
http://www.cnczone.com/forums/tormac...ml#post1140470

mmm...Interference patterns due to two rotational frequencies.... nice, I forgot that thread.

OP, take a pair of calipers, a magnifying glass, and tell us what the spacing of your marks are.

[Don Clement]

I don't think it is related to your steppers, or micro-stepping. The steppers are set at 2400 steps per revolution, and are directly coupled to a lead screw with 0.1" pitch. That means the pulsing of your steppers would be leaving an imperfection in your finish every 0.100"/2400 = 0.000045" (0.045 tenths of a thousandth). That would not be visible without a microscope.

If that regular repeating pattern were due to runout, the spacing of the lines would be 0.0076" apart. Spacing= FR/RPM. In the absence of any frame of reference for your picture, I am sure that what you are showing is probably more like 0.050" spacing. So probably not runout.


Tormach does. But they are limited on control frequency because of using the parallel port as the pulse generator, so have conservatively chosen a micro stepping rate that makes the maximum pulse rate 16kHz at 110 ipm. The Lead shine drivers they use allow micro stepping to 25600 steps per revolution, but Tormach settles for 2400. That means each mi

Mach 3 documentation says don't try to get faster than 35 kHz, so there is a little room for modification before you hit that limit. Increasing micro step rate isn't going to give you a better finish, and I doubt it will give you better precision in moving the axis, since the error induced by micro stepping is already on the order of backlash and slop in the assemblies.


mmm...Interference patterns due to two rotational frequencies.... nice, I forgot that thread.

OP, take a pair of calipers, a magnifying glass, and tell us what the spacing of your marks are.

Or by direct measurement using an eddy current sensor Eddy-Current Sensors Overview - National Instruments on the spindle with output fed into an A/D (e.g PC. sound card or National Instruments A/D card) and then FFT would give more useful frequency info that could then be related back to what rotating components could be a contributor of the ripples.

Don Clement

[TurboStep]

If that regular repeating pattern were due to runout, the spacing of the lines would be 0.0076" apart. Spacing= FR/RPM.

Reading you post I was wondering where you got your values from. Then I returned to cobrakai's original post... oops! (chair) staying away from the workshop today appears to have been a very wise decision!
So, according to my calculations using the value of 5.4 as explained in the other thread, this would give 5000RPM / 5.4 / 38ipm => 24.4 "ripples per inch" or about 0.040", which is fairly close to the value you estimated.

Here's a quote for Don: Make things as simple as possible, but not simpler.

Step

[Don Clement]

Here's a quote for Don: Make things as simple as possible, but not simpler.

Step

I also believe in Minimum Effective Action. Having worked in both the frequency domain and in the time domain when given a choice the frequency domain will yield much more info.The O'scope time domain display can only show so much info. The FFT transform into the frequency domain of the same signal will give one so much more insight.

Don Clement

[zephyr9900]

You are onto something, Don. I think I'd low-pass filter the part by rubbing it with a resiliantly-mounted (i.e. rubber sanding block) piece of abrasive paper. This would tend to remove the higher-frequency components of the surface without disturbing the basic shape.

Randy