Concentricity is Out of Specification

Hie all

I'm a newly graduated CNC machinist.Lately I've been give a simple part to b bore on a Mazak turning.1st hole id is 112 mm.and another is 40 id mm on the same piece.The problem occur when i received report from the QC dept saying that the concentricity is out by 0.3 mm.Ive tried changing the boring bar.Reworked on the jig.but the results are still the same.can any1 tell me why is this possible.or any other way of controlling the concentricity as wanted.Any help would b useful.Thx


JT

newbie2 said:

Hie all

I'm a newly graduated CNC machinist.Lately I've been give a simple part to b bore on a Mazak turning.1st hole id is 112 mm.and another is 40 id mm on the same piece.The problem occur when i received report from the QC dept saying that the concentricity is out by 0.3 mm.Ive tried changing the boring bar.Reworked on the jig.but the results are still the same.can any1 tell me why is this possible.or any other way of controlling the concentricity as wanted.Any help would b useful.Thx


JT

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Hello newbie2 Welcome to the Cove

Could you show us the drawing of the component?

Concentricity is out means the compared bores are not aligned. The outness of 0.3mm is too high, how much is permissible on your drawing? You will have to thoroughly check the machine, axis of the boring tool slide and the Jig etcetra to find out the fault.

Umang

Hello Umang

Im afraid i cant post the drawing here since i dont have a scanner here.

The tolerance is 0.030mm.i have a strong feeling the fault is on the jig.but as i consulted the jig maker,he told me that it still cud b controlled thru settings of the machines.so im trying to do wat i can to prove that nothing is wrong with the settings.ive tried setting it on 2 diff machines.and the results are still the same.I tried changing the boring bars.Even used a new one.So am preety sure there is nothing wrong with the boring bars.I used a DTi and checked the circularity of the hole.And adjusted the offset value on tool settings too.Did i go wrong here?plz advice.and is there anything else i can do?thx for u advice

Machining parts are received after casting.Can it go wrong thre?

newbie2 said:

Hie all

I'm a newly graduated CNC machinist.Lately I've been give a simple part to b bore on a Mazak turning.1st hole id is 112 mm.and another is 40 id mm on the same piece.The problem occur when i received report from the QC dept saying that the concentricity is out by 0.3 mm.Ive tried changing the boring bar.Reworked on the jig.but the results are still the same.can any1 tell me why is this possible.or any other way of controlling the concentricity as wanted.Any help would b useful.Thx


JT

Click to expand...

Some tips from my side:
How about the overhang of the boring bar or of the Part ? If overhang is more Concentricity may not be controlled.
How about the wall thickness of the part ? Is your clamping pressure appropriate to the wall thickness?
One doubt, are you boring both the diameters in the same setting or different ? If it is different, clamping diameter is influential.

Hie chennaiite


The overhang of the boring bar is around 30mm . Is that a lot? Overall boring length is 60mm.Pls advice.

Wall thickness is both 15 mm and 10 mm .Parts are mounted into a jig.And yes.ive checked the pressure.Its at the appropriate level.

Both of the boring are done with the same tool.And the same settings.Nothing is changed.

Am i doing everyting rite?pls advice.thank you.

Gud day

newbie2 said:

Hie chennaiite


The overhang of the boring bar is around 30mm . Is that a lot? Overall boring length is 60mm.Pls advice.

Wall thickness is both 15 mm and 10 mm .Parts are mounted into a jig.And yes.ive checked the pressure.Its at the appropriate level.

Both of the boring are done with the same tool.And the same settings.Nothing is changed.

Am i doing everyting rite?pls advice.thank you.

Gud day

Click to expand...

I feel Overhang is OK.
For the influence of Wall thickness, just try dialling both the bore diameters in the clamped condition using dial indicators after complete machining. You may get some idea.
One more point, I believe you use multiple pass for boring, try to reduce the stock in the Finish boring, if it appears more.

Hello newbie and welcome to the Cove

newbie2 said:

i have a strong feeling the fault is on the jig.but as i consulted the jig maker,he told me that it still cud b controlled thru settings of the machines.so im trying to do wat i can to prove that nothing is wrong with the settings.ive tried setting it on 2 diff machines.and the results are still the same.

Click to expand...

I agree with what Umang & Chennaiite have said so far.

Just one thing: Since you have this strong feeling that there may be some problem with the jig, maybe you could ask QC to have a look at it? If they check the jig both separately and in combination with the product they ought to be able to tell you if you are on the right track. If everything checks out, you can cross out one possible culprit.

Other questions:

Unless this is a new product, when did the problem first occur?
Has there been similar problems before, with this or comparable products?
Is every part affected?
Any variation in the concentricity result?

/Claes

Hie Claes Gefvenberg,


This is not a new part.It has been running for quite sum time.But the problem is the former machining executive resigned.And since I am his assistant , I have to solve this problem by my self.No else to guide me.I find this forum quite helpful.I haven't done dialing yet. Will do it soon and post the results here.hopefully it helps.Yes.i cud send it to the qc.but i have 2 make sure there is no problem from my side as well.

Gud day

Yes..every part is effected..

newbie2 said:

This is not a new part.It has been running for quite sum time.

Click to expand...

Ah... That is important, because presumably it has been made acc. to spec before. If so, the trick is to find out what changed, and this is why it is so important to pinpoint exactly when the problem first occured.

newbie2 said:

But the problem is the former machining executive resigned.And since I am his assistant , I have to solve this problem by my self.

Click to expand...

I see what you mean, having been in the same situation more than once. If there was no problem before he left the company, we can assume that he knew something that has not been conveyed to you. It would not surprise me if it turns out to be a way to overcome some problem with the jig, but that is just an example and remains to be seen.

newbie2 said:

I find this forum quite helpful.I haven't done dialing yet. Will do it soon and post the results here.hopefully it helps.Yes.i cud send it to the qc.but i have 2 make sure there is no problem from my side as well.

Click to expand...

I'm glad you like the Cove. I have had tremendous help from here myself over the years.

As for the cause of the problem: Never mind where it originated: The main focus must always be to find it, get rid of it, and learn something in the process: This is why I suggested enlisting help from QC.

I am looking forward to hearing your tale when you have figured it out: That way we can all learn something.

/Claes