The Home Machinist!

I've been curious about how CNC machines maintain "Tenths" when it comes to tolerances when the oil film on a way could vary by more than that?

I've been following some of the HAAS videos and I see some of their machines do not have square ways and they say their motion glides don't wear as much as a square way. The there are statements from Manufacturers like ATRUMP who have auto oiling systems and call them "just enough" oiling systems.

Can some of you shed some light on this subject. It also comes up in our discussions regarding manual machines as well.

Dave C.

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I learn something new every day! Problems is I forget two.

Dave

First let’s talk about the difference between box way machines and linear way machines. Each has their positives and negatives. Linear way machines (what you call motion glides) typically can have faster rapids, the bearings in the ways are preloaded so they have theoretically no clearance and are more cost effective to manufacture their down fall is load capability and vibration dampening. Box way machines have much better vibration damping and load capabilities typically have slower rapids and are more expensive to manufacture. The reason box way machines can hold as tight of tolerances as they can is due to the fact of the pressure it takes to move or squeeze out the oil film from between the sliding surfaces is tremendous, way more than the cutting pressure of the end mill or other tool. I would have to go back and do a little research on bearing design to give some examples(its been 30 years since I have done anything like that) We have a 30 year old Miyano lathe with box ways and it still will hold tenths. Think about your cars crankshaft with only 40 psi of oil pressure on a relative small surface of the round crank journals compared to the flat ways of a machine with much thinner viscosity oil than we use in our machines and look at the pressures that it handles. I think what ATRUMP is trying to convey about the "just enough oiling system is more about limiting tramp oil in the coolant system, in other words they are not over oiling the machine. Hope that helps what it really boils down to is that in a small clearance like that of a machine way the oil film that exist between the two surfaces is very thin and very strong. Hope this sheds some light on your questions.

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Rick

“We make a living by what we get, but we make a life by what we give." Sir Winston Leonard Spencer Churchill (1874-1965)
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Rick,

Thanks for the explanation. That all makes sense!

Dave C.

_________________
I learn something new every day! Problems is I forget two.

I would guess that you really haven't seen some of the machines that will repeat to a micron....

no box ways - and no ball screws either

Bill,

No, I have not seen any such machines! Wish I could...

I haven't had the opportunity to be around hardly any CNC machinery. I have a real interest in how they achieve the accuracy that you speak of and that was sort of what I was asking in the first place. The oil film issue makes sense so can you offer any thing as to how a machine can hold a micron?

I was aware that it could be done and I was sure nothing I had seen was doing it. LOL

Dave C.

_________________
I learn something new every day! Problems is I forget two.

google

bumotec

a swiss company

I have developed a software interface to their machine S-191

no ball screws - all done with linear motors.

For Bumotec S191 see video:



Best regards.
hudson

Thanks hudson for the video. Is there anything that machine can't do?

Jack.

all depends on how big the part is and how much $$$ you have.