Statics Help Needed - Fixture Design
Statics Help Needed - Fixture Design
(OP)
Good afternoon all,
I have been fighting with a statics problem and am hoping someone can help me figure it out. The problem is shown in the attached picture.
I am trying to determine the length of the base plate required to prevent the entire assembly from tipping over due to the cantilever of the milling head assembly. This dimension is listed as X in the attached picture. I have shown the center of mass for the trunnion and milling head assembly along with their weights. This entire assembly will sit on a table and will not be bolted down.
http: //files.en gineering. com/getfil e.aspx?fol der=8f46c4 5e-629c-4c 1f-a61d-d3 52d861259a &file= Fixture_as sembly.jpg
Please help me find the X dimension required and how you arrived at your solution. I have tried doing a force and moment analysis about the centroid of the trunnion without success.
Thanks for any help you can provide.
I have been fighting with a statics problem and am hoping someone can help me figure it out. The problem is shown in the attached picture.
I am trying to determine the length of the base plate required to prevent the entire assembly from tipping over due to the cantilever of the milling head assembly. This dimension is listed as X in the attached picture. I have shown the center of mass for the trunnion and milling head assembly along with their weights. This entire assembly will sit on a table and will not be bolted down.
http:
Please help me find the X dimension required and how you arrived at your solution. I have tried doing a force and moment analysis about the centroid of the trunnion without success.
Thanks for any help you can provide.





RE: Statics Help Needed - Fixture Design
If you made the baseplate just barely long enough to prevent tipping, that would not prevent collisions between the cutters and the next trunnion in line.
Mike Halloran
Pembroke Pines, FL, USA
RE: Statics Help Needed - Fixture Design
I just calculated the length of the baseplate needed and I came up with 6.6" to reach equilibrium. The total length from the back edge of the trunnion to the front of the milling head is ~14.5". My calculation of 6.6" seems a bit short. Any thoughts?
RE: Statics Help Needed - Fixture Design
To what does one attach the indicator base?
How does one clamp the fixture to the table if desired?
If the fixture slides on the (oily) table, what hits the adjacent fixture, or wall, first?
Your calculation sounds credible, but the point I'm making is that the fixture base should not be sized on the basis of 'just barely not tipping over'.
Mike Halloran
Pembroke Pines, FL, USA
RE: Statics Help Needed - Fixture Design
Valid point. I wanted to find the equilibrium point and from there add a safety factor due to the elements you've described. One reason I wanted to do the calculation was simply to practice something I learned in college and haven't used in awhile. Referring to textbooks was essentially worthless for the purpose of finding a comparable problem.
We have dial indicators on their own base. These will be placed on a granite block.
The fixture will have mounting holes in the base plate if the shop would like to attach the assembly to a table.
Thanks for your input!
RE: Statics Help Needed - Fixture Design
Let Lcg be the distance between cg's. Let a be the distance of the trunnion cg from the balance point between the cg's.
16.66*a = 30.87*(Lcg-a), and neglecting the weight of the plate.
Solve for a in terms of Lcg.
Make your plate at least long enough to be beyond the balance point between the cg's.
Ted
RE: Statics Help Needed - Fixture Design
I ended up increasing the length so the end of the place is planar with the end of the cutter head. Thanks for the feedback!
RE: Statics Help Needed - Fixture Design
Ted
RE: Statics Help Needed - Fixture Design
Ditto what Mike said about a shop technician tipping the thing over if it gets leaned on. It WILL happen, spend the extra $5 on material and carry the base out past the cutter :>)
It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.