Dimensional Accuracy - Aluminum vs. Titanium

[CNCMaryland]

I'm looking for some help/discussion about something I recently noticed. I will try to give all info that I think might be relevant.

Hobby CNC Machine, 1605 Ballscrew, Linear Rails, ATC Spindle.

Test performed in aluminum reveal dimension accuracy of +/- .02mm. (.0008") - Performed with a 1/4" bit.

Test performed in titanium reveal dimensional accuracy of +/-.12mm. (.005") - Performed with a 1/8" bit.

In both cases stock to leave was left, and a finishing contour pass was made.

I wanted to get some general thoughts on this. Am I seeing backlash, tool deflection, etc?

I am going to try to do the finishing pass in titanium with a larger bit in order to reduce deflection at some point soon, but wanted to ask. Many of the guys I speak to on the regular only work in Aluminum.

Thank you in advance !

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[joeavaerage]

Hi,
titanium is many MANY times tougher than aluminum, my guess is that the machine is flexing under cutting forces, its not just
tool deflection its the whole machine.

Try the same cut in steel. Steel is tougher than aluminum too but less so than titanium so I would expect an intermediate result.

Craig

[CNCMaryland]

Thanks for the response. Ironically I was cutting steel last night and experienced the same issue. That's what got me thinking.

So tonight, I roughed out a hole with a 1/8" bit in the steel, and then followed up with a 3/16" finishing pass. The results were spot on.

Now I read about end mills not measuring out to what they are expected to be, and even more, the wear they take, often will leave them a few .01mm's smaller.

I'm wondering if since I'm not flood cooling, that the tools are wearing down fast, furthered by their small diameter deflecting, all adding up to some variance.

[the_gentlegiant]

Hmmm... let me try to shed a little light.

It's basically futile to talk about hobby machines and working in tenths or a lone thousandth in the same sentence, or even the same page for that matter. If you let the idea of working in that realm go, you're going to enjoy yourself a lot more with your machine and your machining endeavors. Mainly because you wont always be chasing your tail so to speak. Even measuring in tenths with certainty takes the tools, skills and environment to back it up.

On another note... you don't typically machine to a dimension by counting on a "size" of cutter cutting "to size." You either use cutter compensation, or make changes to your cutter path after a test cut. Because of their inherent lack of rigidity, with a hobby machine that becomes even more prevalent. I can hardly remember ever measuring a cutter diameter in my many years of machining, even with real machine tools. It's just not the way it's done. Especially if your reaching for tenths or that lone thousandth. Again, which you of course aren't doing because you're trying to enjoy yourself. :-)

Of course, have at it and try to extract everything you can out of your machine, but try to keep your head on about what you're dealing with.

Have fun.

[CNCMaryland]

Hmmm... let me try to shed a little light.

It's basically futile to talk about hobby machines and working in tenths or a lone thousandth in the same sentence, or even the same page for that matter. If you let the idea of working in that realm go, you're going to enjoy yourself a lot more with your machine and your machining endeavors. Mainly because you wont always be chasing your tail so to speak. Even measuring in tenths with certainty takes the tools, skills and environment to back it up.

On another note... you don't typically machine to a dimension by counting on a "size" of cutter cutting "to size." You either use cutter compensation, or make changes to your cutter path after a test cut. Because of their inherent lack of rigidity, with a hobby machine that becomes even more prevalent. I can hardly remember ever measuring a cutter diameter in my many years of machining, even with real machine tools. It's just not the way it's done. Especially if your reaching for tenths or that lone thousandth. Again, which you of course aren't doing because you're trying to enjoy yourself. :-)

Of course, have at it and try to extract everything you can out of your machine, but try to keep your head on about what you're dealing with.

Have fun.

I do agree with you, I don't measure my tools diameter but was just discussing some points.

Here is my issue and hopefully you will see why I have been wondering about this.

The part that I cut needs to have the backside chamfered, which I will do in soft jaws. Since my part is slightly larger than spec, cutting the chamfer is going to off, as the toolpath will be based on the expected size of the part versus the actual size of the part.

I'm of the mindset that proper machining techniques of materials will help to achieve the best results possible.

[the_gentlegiant]

The part that I cut needs to have the backside chamfered, which I will do in soft jaws. Since my part is slightly larger than spec, cutting the chamfer is going to off, as the toolpath will be based on the expected size of the part versus the actual size of the part.

I'm of the mindset that proper machining techniques of materials will help to achieve the best results possible.

Maryland eh? My mother was from Oceanside. :-)

Your parts will almost never be on size. Never. Exactly that is. And unless you're working off a drawing that is specifically tolerancing chamfers down to the enth degree, you're wasting your time. And possibly your customers' money as well. On any basic drawing you likely got plus or minus five, maybe ten on chamfers. Plus it's likely the error in the chamfer due to oversize stock is only 0.707 of the oversize to begin with.

The best way to deal with size of any part or part feature, is become completely skilled at using cutter compensation. Then you can dial in sizes or modify tool paths easily to suit less then perfect dimensions you're working with. All done right at the control. And you will always be working with less then perfect dimensions. Especially at the hobby machine level. (Does your machine even have cutter compensation? G40/G41/G42)

Again I'm not trying to stop you from doing the best you can, but being anal and a perfectionist is going to ruin your day in the long run. And perfectionism has nothing to do with proper machining techniques.

I was a perfectionist back in the day when I first started machining. It took machining of all things to break me of that. Sounds crazy but true. I even lost a great job opportunity years ago doing work for MIlltronics. The owner thought I exhibited perfectionist tendencies because of what he saw in the things I had shown him about what I'd done with machine tools. And he wanted nothing of my perfectionism, because he knew what it could likely cost him in wasted time.

To boil it down. On any given part, few dimensions actually matter. Most things are either esthetic or trying to keep material out of the way for something else that sits next to it. And chamfers are the least of that worry. Chamfers are mainly about personal protection. You don't want anyone getting cut on your parts, Especially your customer. Even if that customer is you.

Perfectionism takes time, which to your customer means money. I can assure you that unless they're asking for it and understand the costs involved, they do not want to pay for your perfectionism. If they're after starving college kid mall art and you give them a Rembrandt, they're not going to be happy. Especially if you then ask them to pay for it.

My apologies. I'm really not trying to get on your case and I'm slightly off subject. But I'm hearing in your voice things that I would hope to persuade you away from being a concern. Especially at the hobby level.

I'll shut up now. Do your best. Just don't over due it. :-)

[CNCMaryland]

Maryland eh? My mother was from Oceanside. :-)

Your parts will almost never be on size. Never. Exactly that is. And unless you're working off a drawing that is specifically tolerancing chamfers down to the enth degree, you're wasting your time. And possibly your customers' money as well. On any basic drawing you likely got plus or minus five, maybe ten on chamfers. Plus it's likely the error in the chamfer due to oversize stock is only 0.707 of the oversize to begin with.

The best way to deal with size of any part or part feature, is become completely skilled at using cutter compensation. Then you can dial in sizes or modify tool paths easily to suit less then perfect dimensions you're working with. All done right at the control. And you will always be working with less then perfect dimensions. Especially at the hobby machine level. (Does your machine even have cutter compensation? G40/G41/G42)

Again I'm not trying to stop you from doing the best you can, but being anal and a perfectionist is going to ruin your day in the long run. And perfectionism has nothing to do with proper machining techniques.

I was a perfectionist back in the day when I first started machining. It took machining of all things to break me of that. Sounds crazy but true. I even lost a great job opportunity years ago doing work for MIlltronics. The owner thought I exhibited perfectionist tendencies because of what he saw in the things I had shown him about what I'd done with machine tools. And he wanted nothing of my perfectionism, because he knew what it could likely cost him in wasted time.

To boil it down. On any given part, few dimensions actually matter. Most things are either esthetic or trying to keep material out of the way for something else that sits next to it. And chamfers are the least of that worry. Chamfers are mainly about personal protection. You don't want anyone getting cut on your parts, Especially your customer. Even if that customer is you.

Perfectionism takes time, which to your customer means money. I can assure you that unless they're asking for it and understand the costs involved, they do not want to pay for your perfectionism. If they're after starving college kid mall art and you give them a Rembrandt, they're not going to be happy. Especially if you then ask them to pay for it.

My apologies. I'm really not trying to get on your case and I'm slightly off subject. But I'm hearing in your voice things that I would hope to persuade you away from being a concern. Especially at the hobby level.

I'll shut up now. Do your best. Just don't over due it. :-)

I'm not really sure what to say honestly. Appreciate the response but it doesn't provide much insight as to actual machining. I'm using fusion as my cad/cam program.

While not striving for perfection as I will agree that's a fools game, the point is in aluminium I'm close enough to tolerance that any variances is unnoticeable.

Parts need to be within tolerance otherwise they are unacceptable.

I'm not using cutter comp. I'll just have to settle for mediocre results.

[routalot]

If you start chasing tenths,you really need to be working in a controlled environment.A hobbyist isn't anywhere needing this sort of stuff and needs to find a level where he can make stuff that works.If you want to be able to brag about the level of accuracy you can work to it might get expensive-and for what exactly? Is the objective to make things or to trade claims of accuracy with other hobbyists?

[CNCMaryland]

Really sorry I came here for help. I don't give a **** about bragging to anyone, I'm trying to make parts that fall in a tolerance that another person can use. Right now on this part I'm out .005" I really don't think reducing that variance is all that difficult.

I'll go make things that don't fit and be happy doing it.

[the_gentlegiant]

- - -

[vmax549]

Thanks for the response. Ironically I was cutting steel last night and experienced the same issue.
So tonight, I roughed out a hole with a 1/8" bit in the steel, and then followed up with a 3/16" finishing pass. The results were spot on.

.

That should have told you everything you needed to know. The 1/8 inch bit showed deflection and teh 3/16 bit did not. Alway use teh largest tool you can use and still make teh cut.

Just a thought, (;-) TP

[CNCMaryland]

That should have told you everything you needed to know. The 1/8 inch bit showed deflection and teh 3/16 bit did not. Alway use teh largest tool you can use and still make teh cut.

Just a thought, (;-) TP

You sir are correct. It did tell me everything. I just didn't have time to run the full parts until tonight. I tried to engage with the champions on this forum only to be told nonsense.

Tonight instead of running the finishing pass with the 1/8" bit I have been using, I ran the 3/16" bit. The part should measure 19.05mm, results were 19.06 consistent on each part. Other features spec'd out as well, so now I am very happy.

The advice that should have been given was tool deflection in small diameter tools is very real, and as vmax said, a good rule of thumb is to run the largest cutter you can on the finish pass for rigidity in the cut.

[the_gentlegiant]

You sir are correct. It did tell me everything. I just didn't have time to run the full parts until tonight. I tried to engage with the champions on this forum only to be told nonsense.

The advice that should have been given was tool deflection in small diameter tools is very real, and as vmax said, a good rule of thumb is to run the largest cutter you can on the finish pass for rigidity in the cut.

Some day you won't consider cutter comp as nonsense. And a good rule of thumb is to run the largest cutter possible that the part, machine and setup will allow on any and every pass, not just finishing ones.

Anyway... sorry for getting so far off in the responses offered. After a person has been doing this for a long while, you forget that there are still those that as yet know almost nothing about machining, and ask questions about things that are so basic to machining knowledge that the subject matter no longer takes part in the thoughts used to machine something. It's like you know it and act on it without thinking about it. For you it is still something to be learned through experimentation, or something to be shared by others who aren't yet blinded by the simplicity of the question at hand. Crazy to think back that far, but we all started somewhere. I'll leave you alone to your learning. Still got my own learning to do.

[CNCMaryland]

I don't think cutter comp is nonsense. But in the realm of the question I asked and the facts I provided, I received nonsense answers basically saying that a hobby machine can't be accurate, and that accuracy of parts don't matter. Now you're saying that I'm one of those who knows almost nothing about machining. Thanks, you seem like a real nice guy. You have plenty to learn.

[pippin88]

I think the_gentlegiant's response was fairly insightful.

If you hadn't worked out why a 1/8in tool in a hard material deflected more than a 1/4in tool in a soft material, then it's reasonable to think you don't know a lot about machining. Knowing that a larger tool will deflect less is very basic.

Use the largest diameter tool, with the shortest flute length and the shortest stick out that you can.

[the_gentlegiant]

I think the_gentlegiant's response was fairly insightful.

If you hadn't worked out why a 1/8in tool in a hard material deflected more than a 1/4in tool in a soft material, then it's reasonable to think you don't know a lot about machining. Knowing that a larger tool will deflect less is very basic.

Use the largest diameter tool, with the shortest flute length and the shortest stick out that you can.

I rest my case.

I was nothing but kind to you Mr. MS. Mrs. Maryland, and only tried to help. It's obvious your reading comprehension is off and that you're taking this much too personally. Which likely skewed that comprehension.

Like pippn88 said, your question and the discoveries following it speak greatly to the idea that you have very limited experience. Tool deflection is day two or three stuff in Machining 101 class. And get this straight, relevant or not, nobody holds that against you. Why would we? It only worked to steer the responses, at least from me. A newb needing help. Why not? I will admit that I got off track by offering more then asked for.
I tried to cleaned up my earlier mess so you won't have to suffer through that anymore.

You got it right - hobby machines suffer rigidity issues that lead to poor accuracy. Especially if they're run outside their designed work envelope, which isn't hard to do.

You're right again, many dimensions on many parts have little consequence. Especially beyond what you find in the average drawing legend where it states tolerances if not specified. On modern CNC equipment, the tolerances assigned to three decimal place dimensions are typically hit without much problem or extra thought at all. That's not as easy on a hobby machine. Let alone surface finish and form.

And this is a better version of what I said. Thanks pippen88 for fixing that up.

Use the largest diameter tool, with the shortest flute length and the shortest stick out that you can. (I only add) ...that the machine and setup will allow.

[routalot]

The OP may or may not be at a point where he is able to discern what course of action would be best.I think he has had sufficient advice to do it.If he does or doesn't he has attempted to get the truth out of us-Good For You.