My design example

Design of structural and load bearing framework.
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DonJohn
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Joined: Sun Dec 12, 2010 6:53 pm

My design example

Postby DonJohn » Sun Mar 13, 2011 6:37 pm

I made a plan for machine with chain drive(poorman BlackFoot) and would like to hear what do you think about that. Some elements i allready presented earlier in this thread.

Things i kept in mind while designing this thing were
a) have to use rollerskate bearings
b) most cuts made with sheet material should be parallel cuts (simpler to cut well than corners)
c) corners in machine have to be adjustable
d) bearings on rails have to have some kind of tensioning system
e) no drive systems under table

freesi mudel v4 1.jpg


freesi mudel v4 2.jpg


freesi mudel v4 3.jpg


freesi mudel v4 4.jpg

UPPER PICTURE: plate with bearings would be permanently fixed to the middle plate, and those two would be attatched to gantry with bolts. Upper bearings should be aligned and bolted to gantry way that the Y is perpendicular to table and then the lower bearings can be tignthend to upper bearings with threaded rods (golden on picture) and then bolted to gantry. (one benefit of this system is i find that you dont have to make perfect bearing rails, you can adjust bearings angle on gantry)

LOWER PICTURE: same principle with rails as upper picture. One pair of plates with bearings, one on X and one on Y axis should be aligned perpendiculary to each other and bolted to the X-Y connecting plate. And then opposite bearing plates can be tightened on rails.


freesi mudel v4 5.jpg


freesi mudel v4 6.jpg



This is not a finished machine, this is just a presentation of an idea, all measurements can be changed and gantry and linkages beefed up.
I'm not a native English speaker so please beer with me

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Awesomeness
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Re: My design example

Postby Awesomeness » Sun Mar 13, 2011 10:15 pm

I like where the design is heading. There are a few things that I would change.

- Instead of having the bearings ride on a ledge sticking out from the bottom of the table, I'd move it to the top surface. You'll just collect a lot of sawdust and junk down in those troughs.
- I wouldn't use the bearing trucks like that, if that's what you're doing. First, it uses 16 bearings per axis, which is a lot, and a bit of a waste. Second, it would be much simpler to use Beermkr's design over square edges. Your way would probably be a little more "self-cleaning" though.
- The gantry sides probably need to be braced, or something.

I like the idea of using the stacked MDF blocks, instead of square tubing like we had talked about (e.g. Beermkr's design). I hadn't really considered that. I think it would be good to take a few minutes and see which one is cheaper (probably the MDF), by how much, and what advantages / disadvantages each have. I suspect that the square steel tubing costs a little more, like $10-15, but you shouldn't need more than like 8' of it, and it will be very strong and easy to deal with. MDF is very weak through the edge, which would have to happen if you tried to use Beermkr's design with MDF blocks.

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DonJohn
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Joined: Sun Dec 12, 2010 6:53 pm

Re: My design example

Postby DonJohn » Sun Mar 13, 2011 11:20 pm

I dont know much about MDF because we have here available mostly "coarse MDF" (particle board? not very strong) and plywood, hence i mostly think in plywood. But i also was conserned about the strength of the edge, because i cant imagine (i dont have CNCmachine yet) and dont know how to calculate the forces that are applied on the edges when machine is working. Could it work in plywood?

I think You are right about ledges sticking out from the bottom, these make a very good trenches between table and rails for allkind of dust and debris.

But i dont agree about the number of bearings. If You meant square tubing design with U-iron as rail, then it would take the whole machine 36 bearings on rails but this design presented here uses all together 32 bearings on rails (X 16, Y 8, Z 8), so 4 less. But if You meant L-iron with bearing inside the L, then yes L-iron is much more economic in that part. But when comparing with v-bearing then this design uses 3x more bearings but bearings costs 10x less (considering prices from buildyourcnc.com), but you have to do atleast 3x more work :) to make it run.
I'm not a native English speaker so please beer with me

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Awesomeness
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Re: My design example

Postby Awesomeness » Sun Mar 13, 2011 11:57 pm



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