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Balancing Turning Fixtures.

Balancing Turning Fixtures.

Balancing Turning Fixtures.

(OP)
Hi everyone, working on a turning fixture which I need to balance. Now in basic terms I've done some calculations to the counter weights I need to put on the fixture. However my question is has anyone

A) Got any easy way to weigh a block in NX 7.5. At the moment I'm modelling a block weighing it, changing the size slightly weighing it again etc, is there any quicker way of achieving a known weight?

B) Balanced a fixture. Has anyone got any information to what accuracy I need to balance it too? By this I mean my calculations tell me the block needs to be 3.1776kgs. Now if I'm modelling a block and tweaking the sizes, I dare say I'll be at it forever to try and achieve that size. So how accurate can it be? Could it just be 3.1kgs? If so how would I know what affect the other .0776kgs would have on the fixture?

Hope this makes sense.

Thanks in advance

RE: Balancing Turning Fixtures.

I can't answer your second question, but the first can be done using an optimization routine. There are two approaches that you can take, either you can use our add-on NX Optimization Wizard, or you can do this using the built-in Modeling Spreadsheet. If you don't have the Optimization Wizard I'll try to create a simple example showing how you can use the Spreadsheet optimization tools to do what you want. BTW, how many variables (expressions) do you need to edit as you try to get some pre-defined final weight? Are you changing a single expression or several at once?

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
Siemens PLM:
UG/NX Museum:

To an Engineer, the glass is twice as big as it needs to be.

RE: Balancing Turning Fixtures.

(OP)
What it is, its a welded fab which is holding hydraulics. I've had to make a large cut out in the fab to hold a hydraulic control unit. So i was going to simply add 3 blocks to the welded fab at a certain weight. Would you do this using an expression? And how? There is a function to use expressions but never really played with it. Is this what you mean?

Cheers

RE: Balancing Turning Fixtures.

Actually what you're starting to describe sounds like it's going to be going beyond what can be done driving expressions using a Spreadsheet 'Goal Seek' run. This something that you could probably do with the Optimization Wizard, but I suspect that you will be needed some direct face-to-face help from someone. May I suggest that you contact either Siemens PLM or whomever you get support from and have them help you since this sounds like it's way past what can be done from a on-line help forum.

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
Siemens PLM:
UG/NX Museum:

To an Engineer, the glass is twice as big as it needs to be.

RE: Balancing Turning Fixtures.

(OP)
Just as an example, how would you use expressions to control things? Are they like the catia v5 thing called parameters? Where its a calculation say you increase a diameter then length goes at a % of that diameter?

RE: Balancing Turning Fixtures.

Well yes, that's the simple stuff. Features are created with expressions which drive their size. For example, a 'Hole' has a Diameter and Depth Expressions, a 'Blend' a Radius, a 'Block' expressions for the X, Y and Z values.

That being said, if you're asking questions about something as basic as Expressions, it would seem that you could really benefit from taking a class in basic modeling. I say this because if you have not gotten any formal training, message boards are not the place to get it. You either need to take some real classes or find a mentor who can provide you some face-to-face help.

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
Siemens PLM:
UG/NX Museum:

To an Engineer, the glass is twice as big as it needs to be.

RE: Balancing Turning Fixtures.

(OP)
Well thats a kick in the Bollocks, thanks John.

RE: Balancing Turning Fixtures.

Hey, I was just reacting to the fact that you're attempting to perform what sounds like it would be a non-trivial task for even an experienced NX user and yet you claim to be unfamiliar with Expressions or how they can be used to create formulas which relate the sizes and shapes of different features which makes-up a solid model. I was just being honest with you, that's all.

My advice, get some personal help from someone who is familiar with NX or sign-up for a class somewhere. BTW, where are you located? And how long has your company been using NX? If they've been using it for awhile, perhaps you might someone in the office that could help you get started in the right direction.

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
Siemens PLM:
UG/NX Museum:

To an Engineer, the glass is twice as big as it needs to be.

RE: Balancing Turning Fixtures.

(OP)
I thought you meant I could use them to perform something other than what I said I was doing in the first place? Only I wasn't using a formula to control it.

If you look at my original post, it asks is there an easier way other than modelling it, weighing it then adjusting it. If using the expression (formula) to control the different sizes of a block is the way forward, then may be we should be discussing the sizes of the block length and width, and which formula to use to control the height.

For example the block is 40 x 40 x 20 and I increase the width by .1, and length by .2, this then adds x amount to the weight of the block? But on top of that, does this matter when balancing a fixture (my second point) how accurate do I need to be to balance a fixture. They both roll into each other, because depending on the second question, depends on how the formula looks for the first point........

This is what I'm asking. I'm not asking for a turtorial on how to use NX. Having said that isn't this forum here so people can ask questions on how to do things? I'm confused?!

RE: Balancing Turning Fixtures.

Quote (UGMENTALCASE)

For example the block is 40 x 40 x 20 and I increase the width by .1, and length by .2, this then adds x amount to the weight of the block?

Mass = Volume * Density

Assuming the material has a uniform density and you are dealing with a rectangular block (no holes, pockets, bosses, etc), it is pretty easy to calculate mass. It is also possible to assert 2 dimensions of your block, choose the desired weight, then calculate the 3rd dimension of your block that will yield the desired weight.

Balancing a piece of rotating machinery is a non-trivial task. Beyond getting the center of mass on the axis of rotation, what you really want is to get the principle axis of the rotating mass to align with the axis of rotation. How accurate does your balance need to be? It depends on multiple factors such as speed of rotation, mass of rotation, desired life of the bearings, safety, etc etc.

Here is a pdf that gives some idea of how much balance you need (it appears to pull from ISO 1940). The table of interest is in section 3, balancing standards (pg 132).

Here are some other links you may find of interest:
http://en.wikipedia.org/wiki/Rotating_unbalance
http://www.balancetechnology.com/pdf/balancing_bas...
http://www.google.com/url?sa=t&rct=j&q=&am...

I used Google with the search terms: "single axis balancing vibration"; I would encourage you to look through the first few links then pick out some new search terms to hone in on what you need.

www.nxjournaling.com

RE: Balancing Turning Fixtures.

Another quick way would be to check the weight, then use "Scale Body", and for "Scale Factor" use "desired weight/known weight".

RE: Balancing Turning Fixtures.

Wait, just realized that doesn't work. I think it needs the cube root of the weights. Ignore these two posts. I need more coffee.

RE: Balancing Turning Fixtures.

It is the cube root.

Scale Factor = (dw^(1/3))/(kw^(1/3))

where dw = desired weight
kw = known weight

RE: Balancing Turning Fixtures.

Hello friends, this is not that hard if we focus on the initial question, -How to calculate the length to find the desired weight. The balancing question i pass, that is complex.
As Cowski noted Mass = volume * density
or if we use the provided example m = 40*40*20* 7.8
If we change 2 variables at the same time it's more or less impossible to solve(?) but if we only seek say the width for a given length and a given height it's simple.
Steel density ~7.8 kg/ liter
1 liter = 100mm^3
and if i assume that "40" is [mm] then 40mm > 0.4 decimeter ( 1 decimeter = 100 mm)
mass = 0.4*0.4*0.2*7.8 = 0.2496 Kg
Then if the original "20"[the width] is the value to modify and the desired weight = 0.5kg

0.5 [weight]
-------------------------------------- = [width] = 0.4006 decimeter = 40.06 mm
0.4[height]*0.4[depth]* 7.8[density]

regards,
Tomas

RE: Balancing Turning Fixtures.

(OP)
Thanks for the response guys this has really helped me out.

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