Egg Shape bore

[ATG]

Ok the egg shaped bore question. It seems that when ever I mill bore a hole using master cam and a fadal 6535 and also 1620 I get an egg shaped bore. I understand that this is pretty standard but I would think that .0005 should be the worst that it gets. For me that is not the case. I'm getting .001 to almost .002 sometimes. I'm leaving about .007 for my finish cutter and I’m making 2 passes @ zero. Is there a trick to holding better numbers than what I’m getting......

 

 

Thanks

 

Seth

[Hardmill]

Yeah ditch the Fadal.

You can have a ballbar test done and they can

tighten it up if its not a ballscrew issue.

 

 

PEACE

[ToolMan184]

Could be your ball screws that are out. when was the last time you had them checked?

[chris m]

Dude, Fadals suck. That being said, egg-shaped circles are typically caused by one ballscrew that is sloppier than the other or one axis accelerating faster than the other; I'd run a ballbar test on the machine and see what she says.

 

In the meantime I'd slow the feedrate waaaay down and see if that helps. You may wish to post 90 degree arcs and turn the exact stop on to see if that helps, too.

[Guest]

Couple of things you might try.

 

If you're using R's try switching to IJK's

 

Slow your feedrate down.

 

Sometimes on small bores that the tool is fairly close to size, if you go too fast the ball screws do not have the time or space to make the necessary corrections.

 

A ball bar test will certainly tell you the best your machine will be able to do and perhaps allow for some maintenance to make things better if it is a machine issue.

 

and if push comes to shove.

 

Using a boring head or reamer if size allows

[ATG]

Well never........It’s less than a year old....at least the 6535 is..... I guess I should have mentioned that. I've heard that breaking the circle up into points is suppose to work better, but no luck with that one. Is there a tolerance somewhere that I could tighten up a bit........

[ATG]

I'm using a 3/4 4flute endmill with a .002 chip load per tooth and 200 surf. Does this sound about right.

[bet338]

whats the dia.,material and doc?

[ATG]

material 1018 depths anywhere from 1.0 to 1.750.

doc .1 past material thickness......

 

the dia 2.5 to 5.0

[gcode]

quote:

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It’s less than a year old

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Then call Fadal up and tell them to come out and fix it.

[Mike S @ S4A]

We had a VMC15XT at Specialized Machine that started doin that...the service tech came out & replaced the inverter ($$$$$$) two weeks later it started doing the same thing...I got pissed, opened the rear cabinet to check the techs work and SURPRISE!!! the wiring harness connector made a loose connection. We powered down, locked out, made the connector engage more snugly.

No more egg shapes..the original inverter was fine, but compumachine woudln't take back the replacement part...worth a look, eh?

[ATG]

That sounds like a great place to start

[Craig Madsen from CM3D]

Could be:

 

Ball Screw - Backlash in the screw

Thrust Bearing - Backlash / loose

Bearing holder - Not bolted down tight -

Motor Coupler - Loose

Following error - Servo tuning incorrect -

Gibs - Too Tight on one axis vs another - or too loose

Lack of oil to ways? Check for oil film on ways.

Incompatible oil vs coolant - disolves oil on ways - causing 'sticking' and wear.

 

Start at the basics - use a indicator and start 1st by checking backlash in each axis, at multiple locations along travel - if it is consistent, check adjustment of thrust bearings, if it varies, check the ballscrew.

 

Work from there.

[Thad]

If the required finish will allow, climb cut it, then conventional cut it.

 

Thad

[Rick Henrickson 65]

you need to have the machine looked at for sure

Ball bar and pitch error comp

 

if you are at 200sfm (1018 rpm)

and .002 chip load x 4fl. (8ipm)

 

this should be plenty slow even if your loopback is slow. machine needs to be fixed.

 

look at daewoo next time for a replcament in that price range

[ATG]

Thanks for all the help I will run them down one at a time. Dont you just love to inherit machinery......

[mgsanchez]

quote:

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Well never........It’s less than a year old....

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You might check that the machine is level (a quick and easy check). With lighter machines I have found that when they get out of level that they tend to twist and cause problems simular to what you are experiencing.

 

 

,

[Tim Johnson]

quote:

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Well never........It’s less than a year old....at least the 6535 is..... I guess I should have mentioned that. I've heard that breaking the circle up into points is suppose to work better, but no luck with that one. Is there a tolerance somewhere that I could tighten up a bit........

---

We have three Fadals less than a year old and one about three. They all had to have the gibs readjusted often. Our maintainance guy said the old ones were the same way. He checks/adjusts the new ones right now about every two months and as they get older he'll be able to stretch that out to about six months. But even when they're correct trying to hold roundness on a small hole is a challenge. If your gibs are adjusted you can play with your gain but if it gets set too high you'll start seeing the vertical "nervous" lines.

[Thad]

6535 is part of the "high performance" line, IIRC.

 

Thad

[SIG]

Now I don't feel as bad. I complained about a Doosan with 7tenths.The service guy came out with a ball bar, servo tuning and two 4 hr days of messing with it. 4 tenths max TIR at F30.

[Matt Berube at Ferron Mold]

quote:

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If you're using R's try switching to IJK's

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This would be the very first thing I'd try. We had an egg-shape issue of more than .015 on a very large round core insert back when we were using R's... Never again...

 

That was an expensive part to have to make twice...

[Thad]

quote:

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We had an egg-shape issue of more than .015 on a very large round core insert back when we were using R's... Never again...

---

That's a bit far out of the realm of the R vs IJK argument, isn't it?

 

Thad

[mold100]

"You might check that the machine is level (a quick and easy check). With lighter machines I have found that when they get out of level that they tend to twist and cause problems simular to what you are experiencing."

 

+1 if you sat the machine down ran it for a year maybe good to check and see if it settled at all. The concrete its on maybe thin, and all though a japanese machine half the size out weighs it theres alot of weight there.

 

Also just curious 2D contour, whats your tolerance in Mcam?

 

I would go with the backlash errors and the fact it is a FADAL, not to knock them to hard because one of the Big Mz with that much travel would set you back a new building, a shop truck, and health insurance for a couple years.

[heavychevy2155]

A 6535 is 32000 pounds, so its not a feather weight machine.

 

+1 on the leveling of machine.

 

Does it have the 18I control or the Fadal control?

[GoetzInd]

Perhaps try a helix bore.

 

Mike