Surface Finish Issues Re-visited

[1ctoolfool]

I was reading this post about surface finish

Surface finish issues on VF3-SS-YT

and I am very curious about this because I have been wondering about what really separates Haas from other machines.

If you read thru the post on page 3 and 4 there are some pictures and a sample tool path. I ran this toolpath on my 2008 VF-2YT and my 2006 minimill and I got identical results to what Mr. Flat in the post is complaining about. There are .0001" circular marks on the floor of the finished surface that cannot be removed with scrubbing with a scotch-brite pad. In the photos he claims the identical path run on a Mori that the machining marks can easily be removed with a scratch pad. The marks were referred to as "coining" marks that coincide with zero speed changes in direction in x and y. This is not a tool deflection issue or a coolant issue (same results with and without coolant, and with larger diameter endmills running the same program). And if another machine can do it as Mr. Flat claims then it is not a programming issue. The only change I made to the toolpath was to cut .005" deep instead of .055". I measured the "surface finish" with a Federal MasterTest .03" diameter stylus and I think the .0001" measurement is fairy accurate although I admit the test is crude.

What I want to understand is if this is normal for a machine in the same price range. I am willing to accept this if you have to spend double or even 25-50% more to get this .0001" scratch to go away. However if a Hurco, or Milltronics, or Fadal or other similar machines can pass this test then there is something amiss. The construction of all these machines is nearly identical and they probably even use the same suppliers for the motion components so I want to know what's up.

I love my machines and this has never been a problem for me, but now that it has been brought to my attention I would like to understand what is normal and acceptable under these conditions. I don't have access to another machine to test, but I know some people who do and I plan on investigating further.

1ctf

[Donkey Hotey]

Man, 1/10th is not much. I am also surprised to see those photos since I just spec'd a VF-3YT for work (and now I'm rethinking it).

I'm sure the issue is due to rigidity. I can remember thinking when I bought my Acra knee-mill, I thought it was a massive piece of unbendable iron. Then, while playing with a height presetter, I discovered that I could turn the LED on and off with just finger pressure on the top of the casting. No matter how rigid we think these machines are, deflection in the tooling, the workholding and the casting are real.

At under 0.0005, I'd bet that it's nothing more than the mass of the machine changing directions, that is causing flex. I'd guess that Haas might need to work on their acceleration/deceleration parameters to reduce that, in the YT machines.

[1ctoolfool]

Not an extended Y issue. Same results on a VF2-YT and a mini mill, which is a pretty compact machine. I'm also going the measure the difference in spindle overhang between a VF2 and a VF2-YT

Remember we're talking about a 3/16" endmill cutting .005" deep in aluminum.
not a rigidity issue here, except as it pertains to overhang and vibration.

Tomorrow I'm going to run on a regular Vf2 and a horizontal.
I'm looking for a result as shown in the Haas vs. Okuma photo in the post mentioned above.
I'm guessing there is at least a 50% price difference in the two machines.

I'm most interested in the result of the same program run on a similarly priced vertical. I want to be sure this problem boils down to price. If it does, I'm ok with that.

1ctf

[kojack]

I have a VM-3 with the extended Y axis 26 inches

I faced a 6 inch wide 13 inch long alum plate with a 1inch inset end mill

I couldnt feel the step over lines not even with a fingernail

rubbed some scotch brite on it and all the line went away ...


When doing fast pocketing and .050 step downs with 100 percent tool step over

I need to run spring passes ...

[Donkey Hotey]

Have you tried breaking the sharp corner on your endmills (with a stone)? A very talented friend of mine swore that if you bought Hanita endmills and just stoned the sharp point off of the tips of the endmill, it would give a beautiful finish (he gained this experience in a Haas shop).

As he told me, the tips are what create the scoring. I haven't tried his theory but it seems reasonable; take off the tips and the rest of the cutting edge turns into a wiper.

Yes, I regularly experience the same thing on my VF-2, even though it wasn't nearly as bad as those photos of the 3-YT. I also (sometimes) get tiny ridges side-to-side in pockets where the passes overlap.

The biggest thing affecting finish for me has been the brand of endmills. I'll admit I haven't gone back and read the threads but have different brand endmills been tried? I was buying Putnams from Enco and MSC but noticed a much nicer surface finish out of similar sized Accupro endmills (also from MSC). One of these days, I'm going to give Hanita a try.

My VF-2 is loaded with 1/4 and 1/2 Accupro endmills right now. I did some pocketing with them and the finish was noticeably better. For reference, they are both Accupro 2-flute, AlTiN (TiAIN) coated. I bought them to do some stainless but they also worked much better in the aluminum. They're my new darling.

My problem is that I don't do enough volume through the machine to wear out the cutters and need to try different brands. I'm sharing my limited experience and hoping to learn something from others.

[dertsap]

looks like a deflection issue to me
the tool is recutting over a finished surface , if you look at the photo's the swirls are where the cutter has already removed material and the tool pressure is not constant , but when it gets back into a constant tool pressure the path becomes more consistent ,

[ktm666]

the machine just cant change directions that fast and is less than perfectly rigid. the cutter has time to dwell in one spot and the machine moves a little with it.

the best you can do is try to change directions off the part whenever possible, and use a nice fluid radius when you cannot. your cam software should have that option.

[ckirchen]

On my Mini Mill, I mounted a tenth indicator to the table and zeroed it on the bottom of the spindle (the black cylinder). When I push against the front of the spindle cover (i.e. parallel to the CL of the tool release button), it doesn't take much effort to move it .001".

Chris Kirchen

[1ctoolfool]

Ok, I know why this is happening more or less, so I'm reading that this is normal and any vertical in this price range is going to have the same result?
How much more does a machine cost that can pass this test?

[Geof]

Originally Posted by 1ctoolfool Ok, I know why this is happening more or less, so I'm reading that this is normal and any vertical in this price range is going to have the same result? How much more does a machine cost that can pass this test?

About another $28,000

I commented somewhere, I cannot remember which thread, we run the same program and part on a VF2 with a 10,000rpm spindle and a SuperMiniMill with the extended Z axis and 10,000rpm spindle. There are noticeable differences in the surface appearance in the facing of the top surface; the swirls on the SuperMini extend for more than twice the distance than the VF2 and are more pronounced.

I have seen pictures from a fancy double column machine compared with a standard design and it was completely free of 'swirls'.

Put this phrase into Google; machining at the center of gravity and start going through the links.

I suspect the cost to get one of the machines described in these links is going to be two or three times a VF2.

[easyvalk]

I have a new (5 months old) Haas VF3YT-50 and I promise you this oher than a couple of quirks like not being able to peck tap, I absolutely love this machine and it runs the same parts with the same surface finishes as my three year old Mazak Nexus 410A. So go ahead and get the Haas they are great machines for the money.
Thanks Everett

[Donkey Hotey]

Quick hijack: yes, you can peck tap. Do a search for it. There are a number of threads on here that address it.