[guru_florida]

I want to calculate the required linear axis bearings for my Z-axis. It will cut aluminum. I am looking at Moment ratings of linear bearings for *good* operating conditions maintaing constant smooth linear motion.

Lets say, the linear rail is parallel to X axis, and Y axis is perpendicular to X, and we are calculating the moment about the Y axis. In my example here, lets say I have a 32Nm bearing, or 170Nm with two in close quarters for this axis, (an example from a datasheet).

If I calculate a rough guess that my entire Z axis from the the axis of the linear bearing will have a center of gravity 10.0cm from the moment axis of rotation, does this mean my limit of force would be 32Nm * 0.10 = 320 newtons? And 170 * 0.10 for the two?

If I convert 320N weight to mass, I get 32Kg. A single block could support 32Kg safely. This doesnt include cutting force of course.

For two rails with two blocks each: I take the 170Nm rating, calculate my newton force. Convert my Z axis head assembly to weight, figure out my max cutting force in newtons, add the two forces, divide by two (2 rails) and compare to the rating? Then repeat for each axis moment.

Anyone know approximate max/typical forces for cutting aluminum?

If I am offbase anyone have links?

I tried google searching here and online, and wiki but I am still not 100% confident.

Thanks,
Colin

[ricardosantos]

Dear Guru

I am sending you a PDF file with a brief summary, had no time to translate into English.

I hope I have helped

[guru_florida]

Im afraid that doesnt help me my friend. I cant understant spanish...maybe a little french or polish, but even then probably not scientific.

It's hard enough reading math in my native language...and I am math literate.

C

[ricardosantos]

Ok my friend, I will translate for you.
Sorry the grammatical errors

[garfieldsimons]

Hmm. Seems to me your cutting forces should be deciding factor. Maximum end mill size and driving hp. A 1/4" em clogged with aluminum can add a few newtons.

[Desmid]

Could you work backwards by calculating the volume of metal cut per minute and a knowledge of the amount of energy required to machine away a cubic mm of material (I believe this is called the specific power consumption)? I am sure I have seen tables of work done removing specific volumes of different metals. Knowing the amount of work being done you could calculate the the force at the cutting tip of the mill if you knew the diameter of the end mill and the speed of revolution.

Bob

[wmyerscnc]

just a suggestion: Make it strong enough that it won't break when you crash it....

[guru_florida]

Ok my friend, I will translate for you.
Sorry the grammatical errors

Hi Ricardo,

That was a couple page document. You don't have to go to the trouble of translating it. I will find my answers in time. I am in no rush and I am resourceful. I was always good at physics, however this is my first machine design. Thanks for the offer though.

Desmid: I would like to work backwards as you say. However, I don't have any practical experience working as a machinist! I have a pretty solid table assembly now. I am playing around with a temporary Z-axis and using a rotozip tool so I can start getting a feel for feed rates in materials, cutting tools, and all the caveats. I am learning a lot having this practical experience and learning my software toolchain. (But this grasshoper still has much to learn. ) However, I am ready for my real z-axis and spindle.

My toughest cutting will be aluminum. mostly 3/8" plates of soft aluminum.

I like your suggestion though. I will put some more thought into the kinds of cutting I will do, gather some data and put it together. Time for some spreadsheets and macros!


Thanks,
C