Unable to make predictable cuts

[jgarrett]

I have an EMCO Maximat V10-P that I have had for several years. I really have never had a need to make precision cuts until now. In the past I have just "snuck' up on my final size.
I decided its time to learn to make predictable cuts.
I am using a Phase 2 QCTP with a indexable bit on 6061 aluminum.
I make a truing cut and measure (reads .726") with a quality B&S mike. I feed in .005" and take another cut. I should be reading .716",but it reads .713". So I use a DTI to make sure I am going in .005" and make another cut and now I read .708" I am locking the x-slide so it can't creep but after many tries I cannot make a predictable cut. Everything is tight and I can measure no play with a DTI.
I have no idea what I, or the machine is doing wrong.
Any advise would be greatly appreciated.
Cheers,
Julian

 

[dnalot]

Hi

Divide the amount you want to remove by 2. Material will be removed from "both" sides of the material. Then account for any backlash your machine may have.

Mark T

 

[compressor man]

Is it possible that your machine is flexing and not able to remove the amount of metal that you set it for in one pass?
Chris

 

[BaronJ]

Hi Julian,

What sort of tooling are you using ?

 

[XD351]

I would be checking the carriage adjustments to make sure it s not floating around on the bed and also check the compound / cross slide gibs .
Try a lighter cut but .005 though is not heavy so any machine should be able to do that .

 

[jgarrett]

Baron,
I am using an carbide indexable bit in a Phase 2 QCTP but I have tried others

XD351, I am locking the cross slide and I have put a DTI on the carriage and tried moving it around and see no deviation.

This is a pretty hefty machine,,surely it can take .010" in aluminum with out flexing!!!
Thanks,
Julian

 

[xpylonracer]

Hi Julian

You don't say which grade of insert you are using but for a fine cut on 6061 you really need a Ground insert, they have a better angle for cutting al., you may be better off using HSS ground with plenty of rake and clearance for fine cuts.

xpylonracer

 

[10K Pete]

Baron,
I am using an carbide indexable bit in a Phase 2 QCTP but I have tried others

XD351, I am locking the cross slide and I have put a DTI on the carriage and tried moving it around and see no deviation.

This is a pretty hefty machine,,surely it can take .010" in aluminum with out flexing!!!
Thanks,
Julian

Doomed to failure. Carbides won't cut that fine. Use HSS. Or just maybe, maybe, a super-fine grade of carbide lapped super sharp. Maybe.

Carbides want to CUT!!!

Pete

 

[jgarrett]

Dang! you guys are good!!!
I switched to a HSS bit and made one test cut and it was within .001"
I will try some more tomorrow,,,
Thanks,
Julian

 

[stragenmitsuko]

I agree inserts seem to need a minimum amount of material to remove otherwise they'll rub .
Try a heavier cut and see if that is predictable .

If you need to sneek up on a dimension , try a vertical sheer tool .
That tool is capable of accuratly and repeatable cuts of 0.01mm on the diameter .
I use it all the time when machining bearing press fits .
Do a youtube search for a video by mrpete222 .
He demonstrates and explaines how to grind this tool .

Pat

 

[redhunter350]

HI Julian, Not necessary to lock the cross slide indeed it will be counter productive in most cases, however I would advise you to not just try to move the dial from the set position to the new position you want, always back off and then come up to the new position. If you overshoot then back off again and come back to the new position for your cut. Due to friction if you try to move only a few thou the cross slide will often not respond as you want/need.
Hope this helps John

 

[BaronJ]

Baron,
I am using an carbide indexable bit in a Phase 2 QCTP but I have tried others

XD351, I am locking the cross slide and I have put a DTI on the carriage and tried moving it around and see no deviation.

This is a pretty hefty machine,,surely it can take .010" in aluminum with out flexing!!!
Thanks,
Julian

Hi Julian,
It seems that you have the answer to your problem. Carbide requires a fair bit of power to cut well, most small lathes simply don't have the umph. I do have some carbide tooling, but I reserve that for cast iron.

The shear tool was mentioned. This is a brilliant tool for very fine cuts. It cannot take a cut of more than two or three thou, but you will get a very good surface finish and acurate size.

Thank you for your nice words, most here have gone through the same learning experience as you are going through.

 

[bazmak]

Baron is right.I use RCT a lot but for taking light cuts with great accuracy
it has to be Sharp HSS.I have used the diamond tool and it works well

 

[goldstar31]

Baron is right.I use RCT a lot but for taking light cuts with great accuracy
it has to be Sharp HSS.I have used the diamond tool and it works well

What is RCT please? Probably, I'm NBG

Regards

N

 

[bazmak]

Replaceable Carbide Tips Norm.Called wimmet tips in the old days
They have come a long way since then

 

[goldstar31]

Thanks Barry! I'm probably having a VERY senior moment. As you know I'm not into carbides for lightweight machines-- Wot I have!

I recall Dad brazing up a tip- probably during WW2 and I did the development work for cutting spun rock wool acoustic stuff sometime after. I've got a 1" diameter thingy on my mill drill and the usual clap trap of masonry drills- but heigh ho, I'm a Dodo.

However, I've impressed the kids by buying an Apple Mac and a geriatric - as the Germans call it, a 'handy'. I don't know how to use it but one never knows.

Hope your Aussie world cools down somewhat. I'm still trying to get my head around annoying the Kiwis in November.

Take Care

Norm

 

[machinejack]

I myself am old school more like a dinosaur. I will use a good tool steel cutter over carbide any day. Less power is required, better finish, and yes it's slower. I read a book on the aspects of cutting tools. There was a photo of a tool cutting steel the cutting edge actually is not in contact but a ways back from the edge. Envision an axe splitting wood, after the initial hit the wood splits in front of the edge. Same thing happens in metal. That is where carbide comes in it's harder and more heat tolerant that tool steel. The cutting edge starts then cleaves off a shaving. Do you find it hard to take a .0005 cut with carbide to get that finish cut. In industry the final cuts are achieved with a heaver cut and will do it all day long. I've seen carbide inserts without a chip breaker with a divot worn behind the edge and still hold tolorance.

 

[bazmak]

As has been said many,many times,every tool has its use.Try taking the skin/scale off cast iron or hrst and see how long HSS lasts and as this post
started try taking light accurate cuts with carbide.Both are no go,s
Would not be able to work without either

 

[wherediditgo]

Not sure if this has been mentioned but have you ever adjusted the backlash on the the lathe spindle? When I first got my V10-P up and running I had the same problem until I got the backlash properly adjusted.

 

[jgarrett]

Thanks,,,a simple change of bits cured it!!!!