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  #1  
Old Mon 29 October 2012, 18:45
Hardouin
Just call me: Hardouin
 
Douarnenez
France
Removable Base Table

Hi all !


I begin building a MechMate. The useful area will be 1600 x 3100mm. I will use it mainly for woodworking.

I could procure steel profiles for free I'd use. They are of 2 types:

- U 60 x 140 mm
- Round 42 mm diameter

I would use U to achieve the two main longitudinal beams that will 3700mm long each. Sections recommended are 180 x 70 mm. To compensate for the loss of rigidity considering getting a frame resting on six legs instead of four. I also need to make a removable frame. To this end I intend to make some connections by bolting to obtain pieces of acceptable size and weight for handling by two people.

I set the colors green and orange welded integral parts:




Do you think this Base Table design is relevant in terms of stiffness?

About bolting should better consider tapping holes that host the bolts or nuts just anti vibration sufficient?

Thank you in advance for your feedback.

Hardouin
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  #2  
Old Tue 30 October 2012, 11:07
Allegheny
Just call me: Brian
 
Massachusetts
United States of America
Hi Hardouin,

Welcome to the forum.

I'm no structural engineer - but there are several on here including Gerald that I'm sure will chime in soon enough - but it looks good to me.

One of the problems with bolted together assemblies, no matter how the bolts are attached, is that there is always a little bit of play at the joints. This can be difficult if not impossible to overcome when reassembling and attempting to get everything true and square again.

The easiest way to overcome this is to use dowel pins. Once you have assembled the table and gotten everything squared up, drill at least two holes through each bolted connection and drive in a hardened dowel pin. Just make sure you drill completely through so you can drive the pin back out! Removing a blind dowel pin usually results in the creation of never before heard profanities - DAMHIK. When it comes time to reassemble your table, loosely bolt it together, then drive the pins back in and then torque the bolts down. And don't reuse pins, always use new ones for every reassembly.

Cheers,

Brian
Taxachusetts
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  #3  
Old Thu 01 November 2012, 13:57
marko cro
Just call me: Marko #107
 
Dakovo
Croatia
Hi again Hardouin,

I am not sure about the setup of the table, it looks pretty big and for sure it will be heavy on the top.
If you put some more metal on the lower table, you could reduce the vibration more.
I also put squared tubes for the entire table, so I can filled it with foam and reduce vibrations even more.
Can you make a calculation in this program about the weight of the whole MM ? I calculated mine and it's over 600 kg, and this was light what I wanted.
I planned to get 5 mm thickness of the tubes, but my friend persuaded me to go with 3 mm. (would be over 1000 kg)

And forgot, welcome to the forum.
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  #4  
Old Fri 02 November 2012, 05:30
Hardouin
Just call me: Hardouin
 
Douarnenez
France
Hello Allegheny !

Thank you for your suggestions.

I will very rarely disassemble the machine, only if I move from my home, may be one or two time in the machine life. (It is necessary to make the MM removable because the door is not wide enough.)
Then, I think it will be less work to redo the fine settings when reassembling rather than place and remove many dowel pins.


Hi Marko !

Unfortunately I can't make calculation of the weight in my 3D software (sketchup) because I didn't draw the internal surface of round section tubes.

But my two 140 x 60 mm U profiles are quite heavy build :


and I think the fact to had 2 more feet under the middle of the two main lateral structures is a good way to greately reduce vibration. In fact, the two center feet, are suported by a very stable, very cheap, and very stong structure : THE GROUND !

Also the 9 horizontal supports will be in 6kg/m steel.

Hardouin

Last edited by Hardouin; Fri 02 November 2012 at 05:57..
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  #5  
Old Fri 02 November 2012, 06:37
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Quote:
Originally Posted by Hardouin View Post
. . . . I think the fact to had 2 more feet under the middle of the two main lateral structures is a good way to greately reduce vibration. In fact, the two center feet, are suported by a very stable, very cheap, and very stong structure : THE GROUND !

Also the 9 horizontal supports will be in 6kg/m steel.. . . . .
We have no problems with vibrations in the vertical direction, the extra legs will make no difference.

We see most vibrations are horizontal. For this we use mass, and diagonal connections to the ground.
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  #6  
Old Fri 02 November 2012, 06:51
Hardouin
Just call me: Hardouin
 
Douarnenez
France
Hello Gerald !

Thank you for giving your point of view.

What do you think of the removable base table design as a whole and the choice of using profiles of 140 x 60 mm I got for free ?

Hardouin
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  #7  
Old Fri 02 November 2012, 07:04
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
It is okay
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  #8  
Old Fri 02 November 2012, 09:25
Allegheny
Just call me: Brian
 
Massachusetts
United States of America
Quote:
Originally Posted by Hardouin View Post
Hello Allegheny !

I think it will be less work to redo the fine settings when reassembling rather than place and remove many dowel pins.


Hardouin
Hi Hardouin,

Trust me, as long as you drill the holes for the dowel pins completely through both parts to be joined, inserting and removing dowel pins is very easy and takes little time. I bet removing or inserting 60 pins will take less than an hour - FAR less time than resquaring the table without them would require. I've used this method for quite a few multi-part jigs that I've built over the years for both my milling machines and my jig borer/jig grinders. Those jigs are dead on when reassembled, even those that are 20 years old.

Brian
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  #9  
Old Fri 02 November 2012, 10:10
Hardouin
Just call me: Hardouin
 
Douarnenez
France
What type and what brand of drill do you advise me?
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  #10  
Old Sat 23 February 2013, 09:29
Fox
Just call me: Fox
 
Amsterdam
Netherlands
I drilled mine by hand ( magnetic drill could not reach these spots ) with a 4 mm HSS drill bit ( 12 x through 15 mm of steel ), with a common drill ( mind you; not battery powered - the one with a cord ).
It took me about about an hour to do all of them. You need a bit of muscle/weight to keep the force on the drill, so it makes chips instead of burning itself up.
A drill of which you can regulated speed by the turn of a knob instead of the amount you press the button is helpful.
Drilling steel is not so difficult, just use a bit of common sense, and have a go.

Last edited by Fox; Sat 23 February 2013 at 09:34..
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  #11  
Old Sat 23 February 2013, 10:58
darren salyer
Just call me: Darren #101
 
Wentzville mo
United States of America
I have a very large table, with a lot of substructure, and still can feel the machine shake when making rapid direction changes of the gantry.
I thought it was overkill at the time, now I realize it is just enough.
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